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Bark River Closing Down

American company Bark River Knives is shutting down. There is a pretty good write-up of the situation in this Outdoor Life article. One thing the article doesn’t discuss is the large number of people coming out now who say that Bark River or Mike Stewart owes them money for past services or products. Since the company is going away, I thought this was a good opportunity to discuss the mistakes it made in design and manufacturing that others can learn from. This includes other knife manufacturers and custom knifemakers. And for knife buyers, you can look for signs that indicate issues with a knife before purchasing it.

Mislabeling of Steel

One of the biggest controversies of the Bark River situation is the owner, Mike Stewart, admitting that they were purchasing China-produced blanks, reworking them, and stamping CPM-154 and “Made in USA” on them. He also defended this practice saying in their testing the steel was almost as good as CPM-154 and that since they performed “5 operations” on each knife that counted as Made in USA. Testing a steel and saying it is “almost the same” does not mean you can mislabel it. I think that much is basic. You can’t buy a car manufactured in China and decide it works just as well as a Dodge Charger and slap the logo on it. This would be illegal for infringing a trademark, both for the Dodge Charger and for the CPM-154. Also, Mike Stewart seems to have a very poor understanding of what “Made in USA” entails. Even if he had started with raw barstock from China and manufactured the knife from start to finish it would still not be legal to mark it as “Made in USA.” He would have to have a qualified label like “Made in USA from imported materials” or something along those lines. But even that label would of course not qualify when starting with a finished knife blank from China. But as a steel metallurgist, the most upsetting part to me is the misrepresentation of what the steel is. It’s obvious they just don’t care what the steel is as long as they can justify putting a label on it they think would sell better.

Broken Bark River Scout Knife

In 2022 there was a video from Dutch Bushcraft Knives (DBK) where they tested a knife in MagnaCut from Bark River Scout and it broke at the jimping while they were batoning (autocorrect does not like either of those words).

  

They talked to Bark River and were told the fault was with the steel and they pointed out some discoloration in the fracture surface, claiming this indicated an inclusion in the steel. An inclusion is a non-metallic compound in steel like an oxide or sulfide. Inclusions are present in every piece of steel, the question is about how many and how big. Inclusions that are so large you can see them with the naked eye are rare, and the discoloration they pointed out in the video does not look consistent with an inclusion.

Another Broken Bark River Scout

Bark River broke a knife of the same model in MagnaCut during manufacturing and sent it to Niagara Specialty Metals requesting an investigation into the steel. Bob Shabala of Niagara sent the blade to an independent third-party metallurgist named Gary Maddock. He evaluated the broken blade and sent a report to Niagara and Bark River.

Stress Concentrations

So this is a completely different knife of the same model that broke in the same exact place. And not even from using the knife but just while manufacturing it. So we must start discussing what a “stress concentration” is (also called a “stress riser”). I wrote a whole article about stress concentrations back in 2019. As the name implies, a stress concentration is any region of a part where the stress is concentrated. One simple way of concentrating stress is by having a reduced area in a portion of a part. As a metallurgist we often perform “tensile tests” where the standard is to have a reduced cross-section in the region to be tested. This ensures (almost 100%) that the fracture will occur in that reduced area:

Stress is just load divided by area, so if the width in that region is half of the rest of the flat piece, the stress would be twice as much in that region. However, stress concentrations can be much more extreme than this. The most common example of a bad stress riser is a sharp corner. This leads to very high stress in a small region of a part, such as is shown in this simulation:

The red region shows a much higher stress than the rest of the part being pulled apart. So we can predict with some high level of certainty that this part would break right at those sharp corners. This is all relevant, of course, because the jimping on that knife led to a stress concentration when the knife is being flexed.

So how could Bark River have avoided the stress concentration of the jimping? One method is to remove the jimping altogether, of course. There has been debate in the knife community for decades as to whether jimping is beneficial. Another way would be to round out the design of the jimping to reduce the stress concentration. Making it shallower and more rounded would be beneficial. An example would be this FreeReign knife from Demko:

Surface Roughness

Another important factor in this knife breaking is that the method used to cut the blank led to a very rough surface, and that surface was not cleaned up within the jimping.

So Gary Maddock noted that the rough surface in that jimping may have accentuated the stress riser. The rough surface has many discontinuities in it; basically areas that already look like a crack. It makes crack initiation easier because a crack is already half formed. The other thing he noted is that there was “No evidence of thermal damage” and “Microstructure appears normal under the surface.” He noted this because laser cutting can lead to a “heat affect zone” (HAZ) where the microstructure can be different than the rest of the steel. Laser cutting essentially means the steel is being locally melted, so when steel has been melted and resolidified this leads to a cast structure which is likely to be more brittle than the rest. Even away from the melted region the steel can be rehardened and thus be harder and more brittle than the bulk steel. So for both the possibility of HAZ with laser cutting and for high surface roughness with laser or waterjet it is best to refinish the perimeter of blades after they are cut out.

Bark River MagnaCut Corrosion Resistance

Some Bark River Knives were reported to easily stain or rust in MagnaCut. Mike Stewart claimed that was because MagnaCut is not a stainless steel. He claimed “i would never have listed this as a True Stainless – Crucible does but I disagree with them.”

It is silly that he was claiming to have knowledge of what classifies a steel as stainless better than the steel manufacturer itself. The most basic definition of what a stainless steel is is that it has at least 10.5% Cr, which MagnaCut has. However, this definition is overly simplistic, as there are some steels like D2 tool steel which are famously not stainless despite having enough chromium to meet that definition. The high carbon (and lack of most other elements) in D2 means that about half of its chromium is tied up in carbides and thus cannot contribute to corrosion resistance. The stain resistance from chromium comes from the element forming a chromium oxide layer at the surface. If the chromium has already formed a compound with the carbon it is not able to form a compound with oxygen. This available chromium is known as chromium “in solution” in the iron. As I have covered in the article about MagnaCut development, it was designed to not have any chromium carbide in the microstructure after heat treatment. As another side note, while the bulk chromium of MagnaCut is 10.7%, because the steel is about 8% vanadium/niobium carbide (leaving 92% steel matrix), the chromium in solution is actually higher than 10.7%, closer to 11%. This is because very little chromium is present in the vanadium and niobium carbides. In other words, if there was no chromium in those carbides the chromium in solution would be 10.7 divided by the volume of the steel matrix, 0.92 = 11.63%. And the true test of corrosion resistance is in actual corrosion testing, where MagnaCut does very well compared with other stainless knife steels.

Heat Treatment

I talked to people with some knowledge of Bark River heat treating and I did not uncover any practices that would lead to poor corrosion resistance on that side. As far as I know Bark River only sends knives to outside heat treating companies, and what information I could obtain indicated they did not request any modifications to the heat treatment.

Belt Contamination?

Another theory I have seen commonly is that Bark River is using the same belts on MagnaCut that they used on non-stainless steels, leading to easily rustable particles on the steel. Bark River vehemently denies this, claiming that they do not mix the belts. This could be true but particles left of the steel could still pose an issue. For example, they might not be thinking of certain polishing steps they are performing where it is unlikely they are swapping anything out – such as buffing wheels. However, one thing to note is that particles left on steel, even stainless steel particles left on itself, can still promote corrosion. These particles are very small and very high surface area, and they act as sites for corrosion to initiate. There is a standard industry practice called acid passivation where stainless steel is treated with a weak acid, typically nitric or citric acid, which is for the purpose of removing free iron from the surface. These practices are not that common in the knife industry as far as I have seen but it is still a good example of how the condition of the surface is very important for future corrosion resistance. There are many other factors that a corrosion expert would want to discuss such as surface finish (finer is better), whether the steel is in contact with any other metals such as pins or bolts, etc.

Do We Know Why?

I cannot say definitively why Bark River knives have had reports of poor corrosion resistance with MagnaCut. The above is only laying out some of the possibilities.

Did Bark River Actually Use MagnaCut?

There is a video from Gravy Train Outdoors where he claims to have XRF tests that show Bark River MagnaCut knives were not actually made with MagnaCut. XRF testing is common for confirming the composition of steel when someone is concerned it has been mixed up. These testers are often called “Positive Metal Identification” (PMI) testers. However, I reviewed this video and found many problems with this testing:

1. He says in the video that this is a soil XRF tester, not one designed for distinguishing metals.
2. He reports a composition in an AI readout he used to interpret the results, but also shows the readout from the tester at the end. They do not look even remotely similar to each other. For example, he makes a big deal of a significant amount of tungsten (1.3%), which is not an intentional addition to MagnaCut. However, at the end when he shows the tester its screen reports that tungsten was not detected. I don’t know if the data file he got to feed into the AI was not from his tests, or if the AI misread the file or hallucinated its own values.
3. The composition he reports in the video, and those visible on the tester at the end – do not look like any known steel. I actually have no idea how to read the results of the tester since it says 160% iron. Perhaps that has something to do with it being a soil tester.
4. He showed in the video another MagnaCut Buck knife but it was not tested with the soil tester. He would likely have seen that its results also do not make sense with the soil tester.

The report from Gary Maddock did not include a composition measurement but the microstructure does look like MagnaCut. Niagara Specialty Metals reported that they checked it with XRF before sending it to Maddock but did not formally record the result.

KnivesShipFree has had some independent XRF testing performed and not found any knives to be mislabeled in their inventory apart from the Chinese mislabeled CPM-154.

DLT has shipped knives to Niagara Specialty Metals to check their knives with XRF.

While I can’t rule out the possibility of there being mislabeled MagnaCut knives from Bark River, I have not seen any evidence to suggest that there are.

Conclusions

Stress concentrations are quite common in knives, both production and custom. It seems to be an element that is rarely considered by designers and makers. If you want a high-performing knife that won’t break, they need to be considered in the design process and when purchasing a knife. For knife manufacturers and knifemakers it also helps to test a knife in ways that are at the extremes of their intended use case. This type of testing would have quickly shown Bark River that their knife was not ready to handle any task with small flexing forces.

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Video

There is also a video version of the following article:

Metallurgists and Knifemakers

Back in 2022, I did a YouTube video called “Do Knifemakers Know How to Heat Treat?” I found video clips where knifemakers explained how to heat treat and how it works, and then I pointed out the misconceptions and misunderstandings they had about metallurgy and heat treating. It worked well because responding to how the knifemakers explained things let me address commonly repeated, untrue claims. Because when I cover my own material, I’m typically just teaching, rather than correcting misunderstandings. However, a handful of comments on the video said I was being unfair or unkind to the knifemakers.

I was a bit surprised by those comments because I thought, “Of course I know more about how steel works because I am a professional PhD metallurgist, so no one should be offended about teaching my discipline.” However, we can always debate the proper tone for such things. But I also think some people misinterpreted my mindset in the video as criticizing, or even parodying, the knifemakers’ understanding of metallurgy. There are also some knife buyers (and even fellow knifemakers) who will lionize the heat-treating prowess of certain knifemakers and believe that they know more than they do. The level of metallurgical understanding of knifemakers varies widely, from knowing almost nothing to having a professional level of knowledge. Many knifemakers are curious about metallurgy because they want to make the best possible products.

Blade Cutlery Hall of Fame Dad and Me

This is largely why I became a metallurgist. My dad, in his knifemaking and Damascus-making, loved learning about metallurgy, and I wanted to learn about it as well. (You can watch an interview with him here). Growing up, my father and I were always excited about the prospect of speaking with metallurgists, such as employees at Crucible Steel or Professors like John Verhoeven. Hoping to gain some secret knowledge from these professionals who had dedicated decades to studying steel. Even now that I am a metallurgist, there is still much to learn. I often learn new things from blacksmiths, bladesmiths, and knifemakers. They may have practical experience that contributes to my understanding of steel. So this article is dedicated to the times when craftsmen taught metallurgists things.

“Damned Good Stuff” and Impact Testing

Harry Brearley invented stainless steel in the early 20th century (1912-1914ish), and he developed the common 420 stainless steel, which remains widely used in knives. I wrote a whole chapter in my book, The Story of Knife Steel, about him and what led to the discovery of stainless steel. I pulled a lot of quotes from him because I thought he was funny and interesting.

Brearley credited cutlery manager Ernest Stuart of Mosley Cutlery Company with the success of stainless steel [1]: “It is due to him to say that, from the very first trials, he had confidence in the possibilities of the steel. He made unremitting efforts to adapt the process of knife-making to the unusual qualities of the steel and, so far as the initial use of stainless steel for cutlery is concerned, the credit is due to him and his firm.” Stuart was also the one who named it “stainless” steel, giving it the name it still has today.

The reason I bring up Brearley is because of things he wrote about working with practical craftsmen (such as Ernest Stuart) and their contributions to the understanding of metallurgy. His father was a steelworker and had no scientific training. Brearley said that he was “in appreciation of men, typified by my father, who have exerted a greater favourable influence on the practice of steel-making than they are given credit for.”[1] “The value of scientific control, with its measurings and weighings, is undeniable, but it is sadly blemished by a strutting vanity and snobbish intellectual pride which smothers with confusions aspects of a subject it does not understand.”[1]

Brearley also said that his brother was a more hands-on person than he was [1]: “He is a better workman, a better observer and more resourceful experimentalist than I am; but he has stuck to the furnaces, mills and forges and done things whilst I have read about them, and looked at things other people were doing, and taken some trouble to describe them in the language learned from books.”

Caption from Brearley: “My brother (sees) more with the naked eye than most people see in them using laboratory equipment. On the other hand, I spent about 20 years in a laboratory, mainly occupied in measuring things. The picture is intended to be symbolic: My brother on the right-hand side is looking at a fractured surface of a piece of an ingot, and I on the left-hand side am pretending to be doing something with a pair of calipers.”

To illustrate the fact that ordinary workers often have methods that are superior to the scientist, Brearley described the history of toughness testing [1]:

For a century or two the blacksmith has been in the habit of ending a bar of iron or steel after first nicking it with a slate. When the bar is broken, as intended, through the nick, the effort required to break it, appreciated by the smith’s muscles, is registered in his mind – his extremes of judgement are “rotten” and “damned good stuff.” There is not the slightest doubt in the smith’s mind that the material he intends to make something from is all the worse for being “rotten” and all the better for being “D.G.S.” Many years ago, thirty maybe, a young man in Rugby, named Izod, was called upon to explain why of two pieces of steel one failed hopelessly and the other did its job very well. Both chemical analysis and every conventional form of mechanical testing showed that the two pieces were identical; but this young man knew they were not. Bethinking himself of the blacksmith, he notched both pieces, and found the one was “rotten” and the other “D.G.S.” In order to state the difference, which was the only difference he could find, quantitatively, he made a pendulum hammer very much like the existing Izod testing machine, and then went to South Africa, blissfully unconscious that his Rugby adventure was the lead to a new kind of official testing.

This is a good example of a time when blacksmiths had a simple test for telling whether a piece of steel was processed correctly, and the methods used by the metallurgists would not reveal these most basic properties. The common test used back then by metallurgists, which continues to this day, is the tensile test. The tensile test involves pulling a piece of steel (tension/tensile) until it breaks. The load capacity of the steel is measured during this test along with how much the steel has elongated while it is tested. This generates a “tensile curve” that shows the yield strength, ultimate strength, and ductility (amount of elongation) of the steel. So there is a lot of information that is gained in one simple test.

You’ll see the different regions of a tensile test above. The “elastic deformation” region is where if you remove the load the piece of steel returns to its original dimensions. This is like bending a paper clip and letting go, it returns to the original shape. You will notice that the “curve” is in fact a straight line in the elastic region; as you load the steel it gets longer, and if you let go it returns to its original length. However, if the “yield point” is exceeded, the steel will remain permanently elongated. Just like if you bend a paper clip too far it will remain bent. The “ultimate strength” is the maximum stress the steel can take (stress is load divided by cross-section). The stress actually drops after that until the steel breaks while the steel “necks,” the steel reduces its cross-section before fracture.

In Edwin Izod’s recounting of his learning about impact testing he said [2]:

For some considerable time, however, owing probably to the greater facilities now available, tensile tests … seem to have displaced almost every other test, and in many present-day specifications for steel no other test is prescribed. In special cases, however … it is usual to include a falling-weight test. … [O]bviously a steel that possesses inability to withstand shock would be immediately detected by this method, and it is highly probable that many cases of peculiar breakage would have been avoided had a standard brittleness test been specified, as well as a tensile test; in fact, fractures have occurred in steel which are inexplicable by known chemical or standard physical tests; and some experiments … show that a ductile steel, as evidenced by the usual tensile tests, may be exceedingly brittle.

So he found that a rapid impact test behaved differently a tensile test. This became known as the Izod impact test, which is similar to the Charpy impact test. The difference between an impact test and a tensile test is in the “strain rate” of the test. Tensile tests are done with a relatively slow increase in load being applied. If you take a knife edge and flex it, or take a whole knife and bend it, you are performing an operation relatively similar to a tensile test (or a bend test), where the load/stress is applied fairly slowly. However, if the steel is rapidly impacted the behavior is somewhat different. This is like chopping something hard with a knife, or dropping a knife tip-first into the ground. The knife may have been fine with cutting hard materials, but when dropped the tip broke off. The rapid rate of an impact test can induce brittle behavior in otherwise ductile materials. Blacksmiths had already known this from their experience with breaking pieces of steel, but it took metallurgists longer to figure that out.

Schematic diagram of Charpy impact test

Tensile tests also reveal brittle materials (see below), which shows up with a low ductility result. In fact the majority of knife steels are very high in hardness and contain brittle carbides, so most of them do not have much ductility in a tensile test. Bending tests tend to do better with tool steels because the tested volume is smaller. However, there are certain types of embrittlement that do not show up in a tensile or bending test and are better revealed through impact testing because of the strain rate difference.

Example tensile curves from here

Frank J. Richtig

I previously wrote about Richtig in an article about his knives. I also covered his history in The Story of Knife Steel book. Richtig began as a blacksmith apprentice at 19 years old in 1906. In 1908 he and a friend set up their own blacksmithing shop until 1923, when he sold his share. In about 1916, he began experimenting with a heat treating process for knives. In July 1925, he leased a shop and began producing knives. Despite his previous experience as a blacksmith, his knives were made by stock removal. His typical knives had a cast aluminum handle though some rare knives had leather washer handles. He primarily produced kitchen and butcher knives though also produced some fighting knives for soldiers.

A Richtig butcher knife that I own

In the early 1930s, Richtig and his wife began traveling to the state fair to demonstrate the superiority of his knives. They would take old pieces of steel like railroad spikes, axles, or horseshoes, and he would hammer the knife through the steel and then slice through newspaper afterward. In 1936 his knives were featured in Ripley’s Believe It or Not!, which was published in newspapers across the country. Richtig advertised that his knives could pass these tests due to superior heat treating [3] : “We have discovered and developed a special new process in tempering knives. This method of tempering assures you of a better and more lasting quality of cutlery.”

Richtig in Ripley’s Believe it or Not

Richtig did, however, say that hammering his knives through iron or steel would void the warranty, and that the knives were ground somewhat thicker for the demonstrations [4]:

If knife proves to be defective in any way within six months after purchase, return same to us and we will gladly replace it. However, if the knife blade back shows it has been hammered upon or shows abuse in anyway, the guarantee is void and the knife will not be replaced… These knives are made of high-grade steel and are suitable for all ordinary uses in the home or place of business. They will do all we claim for them. In reference to the cutting of cold chisels, axles and many other steel articles, I wish to say that in my steel and iron-cutting demonstrations, I use the same steel and temper you will find in my regular stock knives. The size and thickness of the blade is the same, the only difference you will find is in the grinding of the cutting edge. I do not sell my knives for the purpose of cutting steel and iron. The purpose of my steel-cutting demonstrations is to show the toughness and temper in my knives. Many thousands of people have seen my steel-cutting demonstration and were greatly amused by them. Striking a knife with a heavy hammer in cutting steel requires special skill and experience, both of which I have learned and mastered during the thirty years I have been making and improving these knives. My knives are made for general all-around use where good, substantial knives are required.

Richtig’s impressive feats have led many to try to find his heat treatment process. Measurements of Richtig’s knives revealed that the steel composition was nothing special, a simple high-carbon steel like 1095 or W1 [5] . Richtig used steel from the Ryerson Steel Company in Chicago, branded as Ryolite [6] .

When Glen Lambert asked him about his heat treating process, Richtig answered [7], “A man is entitled to some secrets, and that’s mine.” He told Lambert [7] “he had found no one worthy of being told or taught his knifemaking, and until he did, nobody was going to get his ‘secret.’ During his declining years no one came forward, and when he passed away … so did the tempering process.”  Of course, this didn’t stop people from trying to recreate his heat treatment. His legend only grew in recent decades as two research papers were published in 2000 [5] and 2015 [8]. The 2000 paper proposed that Richtig had been using an “austempering” process for a bainite microstructure, a type of heat treatment that wasn’t discovered until after Richtig was already famous for his knives’ superior heat treatment. Read about austempering and bainite in this article. In the research reported in 2015, they heat treated 1095 steel using an austempering process and could not match the superior properties reported in the 2000 research paper!

However, there are problems with this conclusion. One is that the hardness of Richtig’s knives varied widely; the knife the researchers attempted to mimic was only 39 Rc, while another knife they tested averaged 50 Rc. The butcher knife I purchased measures 57 Rc. Harlan “Sid” Suedmeier has also tested several Richtig knives and found them to vary in hardness. While Richtig owned a Paragon electric furnace for heat treating, Suedmeier is not sure when he obtained it, which could explain some of the variability. Paragon furnaces did not start until 1948, though perhaps he had another furnace before then.

The two knives analyzed in the 2000 paper

The very low-hardness knife from the research paper is thicker than many of his other blades, and the microstructure shows evidence that the knife wasn’t fully hardened. This “intermediate” microstructure is challenging to mimic with a typical oil quench and temper, or even austempering treatment. The soft phases are very ductile and give the overall steel greater ductility. So the blade that was used for the tensile testing was likely softer than the majority of Richtig knives and was not representative of the typical properties.

The large knife was only 39 Rc and was not fully hardened as can be seen by the remaining pearlite and ferrite

The small knife was fully hardened

Another issue in the 2015 paper where they tried to mimic the 39 Rc knife was that they used a test specimen size that was much larger than what was used when generating the strength-ductility values in the original 2000 paper. The use of a larger test specimen leads to the same strength value but a significantly lower ductility value. One of the researchers from the 2015 paper, Dr. Jared Teague, has since commented that he believes the specimen size is likely the cause of the lower ductility values in that study.

Comparison of tensile curves from a small tensile specimen (red) and a standard tensile specimen (blue). The small tensile specimen had the same strength but measured much greater ductility.

When comparing the tensile properties of the soft Richtig knife to quenched and tempered 52100 in the 2000 paper, they found that the soft steel had better ductility (strain) for a given level of strength (blue dots). Another evidence of the underhardened nature of the soft Richtig knife is comparing the yield strength (red dots) where you can see that the Richtig knife yielded at a much lower stress.

And while the researchers from the two papers were impressed by the properties of the underhardened steel from Richtig’s large knife, in their testing they even found that 52100 austempered at 300°C (570°F) had superior strength (blue dots) and ductility (green dots). However, the 400°C austempered condition was similar to the Richtig knife for strength and ductility. However, the yield strength was higher for the researchers 400°C austempered condition. This shows that it is unlikely that Richtig was using austempering for bainite.

So how did Richtig accomplish his steel-cutting feats? He gave us the clues in the information he had previously provided: he left the edge thicker, and he had 30 years of experience cutting iron and steel with them. Sid Suedmeier, an expert on Richtig knives, shared similar thoughts. I asked him what Richtig’s secret was, and he gave me a one-word answer: “Practice” [9]. The steel and heat treating that Richtig used were not necessarily extraordinary, but he made good knives and was not afraid to test them. His showmanship in demonstrating his knives gave the buying public an irresistible hook, and he became famous for it. But I think Richtig’s most impressive feat might be bamboozling metallurgists several decades later into believing he was using a super heat treatment.

Questek Ferrium M60S Steel

M60S was a brand new steel designed specifically for knives and cutlery that was announced back in 2003. I have written about this steel previously in this article, where I more thoroughly described its history and the design behind it. Here is the first page of the datasheet which advertises what was supposed to make it better:

Questek is a company that designs new materials using “Integrated Computational Materials Engineering” (ICME). In other words, they use computer simulations to design new materials. This sounded especially forward-thinking and advanced in 2003. A new knife steel designed by computer-aided metallurgists? Wow! However, this steel never came to market. I contacted the inventors of this steel about why it didn’t come to market and Professor Greg Olson told me by email: “I recall denting of cutting edges due to early yielding from retained austenite.” I had remembered this result. Knifemaker Jerry Hossom reported edges that deformed easily from a sample of the grade he had been provided, heat treated to 60 HRC [10]. Hossom also reported that a knife in S30V had very little damage [11].

Jerry Hossom test of chopping an 8d nail. 61 HRC 154CM (top) and 60 HRC M60S (bottom).

What led to the easy deformation? It wasn’t hardness, 60 HRC was roughly the same as the 61 HRC of the 154CM blade. The difference was in the yield strength of the material. Typically yield strength and hardness are highly correlated, but there are some cases where they deviate. If you look at the M60S datasheet you will see that it says at 60 HRC the yield strength was 250 ksi and the ultimate strength was 350 ksi. This is a relatively low “yield ratio,” or the ratio of yield strength to ultimate strength, YS/UTS. This means that in terms of yielding behavior, the stress required to deform this steel would be lower than other steels heat treated to 60 HRC. I have seen some people speculate that this lower yield strength comes from the strength of this steel being achieved with carbide precipitation rather than strictly higher carbon martensite. However, when comparing the yield strength of Ferrium-series steels [12] to AerMet-series steels [13-16], a non-stainless precipitation strengthened steel, the Ferrium yield strength is significantly lower (M60S is the orange dot):

You can see that as the ultimate strength increases, the yield strength of the two sets of materials diverges more and more. This is somewhat clearer if we plot vs yield ratio instead:

You can see that for the AerMet grades the yield ratio was flat with increasing ultimate strength (and hardness), but for the Ferrium grades like M60S the yield ratio decreased. So while a lower hardness/strength Ferrium grade has been commercialized as Ferrium S53, the yield strength issue became more relevant after pushing the hardness up to 60+ HRC for knives. As Professor Olson noted, this was due to excessive retained austenite in the higher strength Ferrium grade M60S. When steel is quenched from high temperature it transforms from the austenite phase to the hard martensite phase. With certain compositions and temperatures, the austenite does not fully convert, leading to “retained” austenite. Retained austenite can lead to reduced yield strength even while at the same hardness:

Caldie data from [17]

Data from [18]

The Ferrium grades may be more prone to having excess retained austenite than AerMet due to the high chromium content required for being a stainless. It might be possible to modify the alloy design to overcome this limitation but it probably wasn’t worth the time and expense required for doing so. But this is yet another case where a practical test by a craftsman revealed an issue that metallurgists did not predict beforehand. In Professor Olson’s email to me he had also noted that Al Pendray had made a knife in the steel, which I have included a picture of below.

Al Pendray knife in Ferrium M60S

Metallurgists and Knifemakers Working Together

Of course for many of the examples above, the knifemakers/craftsmen and metallurgists were not antagonistic towards each other. Some of the best breakthroughs happen when they work together on a common goal. One of my favorite examples is bladesmith Al Pendray and metallurgist John Verhoeven.

Al Pendray was a bladesmith trying to develop a consistent process for making Wootz. Verhoeven is an emeritus metallurgy professor. Both men reported that they needed the other to solve the question of how Wootz Damascus was made. I won’t recount the entire history here. Verhoeven has a book about the history which I reviewed here. And I also have a chapter about it in The Story of Knife Steel. There are also a couple of videos on YouTube (Video 1 and Video 2). But I will include a couple of my favorite quotes about what the two thought of each other.

Pendray Wootz knife

Verhoeven said about Pendray [19]: “He could have gone to college and gotten a Ph.D. just like that. I never worked with anybody that could learn faster. And he is extremely patient. I think Al is an amazing man. It’s been a pleasure for me to know him.” Verhoeven also reported that Pendray said that it was another famous metallurgist who encouraged him to pursue the mysteries of Wootz [20]: “Al often spoke in a sort of reverent tone of ‘Dr. Cyril Stanley’ and how Dr. Smith had taken him aside at the meeting, encouraged him in his work, saying that it was his opinion that the mystery of how to make these blades would probably be solved by a working smith.”

My Own Experiences

I did a really big study on pattern-welded Damascus a few years ago. My father was a major supporting person in this study as he produced quite a bit of the Damascus for the study. One of the combinations he wanted to look at was 1095 and nickel. The nickel is very soft while the 1095 was heat treated to high hardness like normal for a knife. He felt this might be a good combination to determine if the “Damascus cutting effect” could happen, an old claim that a combination of hard and soft metals could lead to a saw-tooth or serration effect leading to higher slicing edge retention. I told him we shouldn’t waste our time because it wouldn’t work but he insisted. When we tested it we found – it out-cut plain 1095 by a significant margin, out-cutting every other low alloy steel combination, even ApexUltra/L6. In other words, we proved the Damascus cutting effect. And while we didn’t find that effect for several other combinations, it took my knifemaker father to convince me to look at it in the first place.

I hope you enjoyed being tricked into learning about tensile tests in these stories of metallurgists and craftsmen.

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[1] Brearley, Harry. Steel-Makers and Knotted String. Maney Pub, 1995.

[2] https://archive.org/details/sim_engineering_july-december-1903_76/page/431/mode/1up

[3] https://history.nebraska.gov/blog/stronger-steel

[4] Suedmeier, Harlan. “More About Richtig Knives.” Knives ’88. 1987.

[5] Wadsworth, Jeffrey, and Donald R. Lesuer. “The knives of Frank J. Richtig as featured in Ripley’s Believe It or Not!®.” Materials characterization 45, no. 4-5, 2000: 315-326.

[6] Suedmeier, Harlan. Phone conversation, 2022.

[7] Lambert, Glen. “F.J. Richtig: Believe It or Not Cutler.” Knives ’84. 1983.

[8] Teague, J., R. LeMaster, J. Rinksc, A. Winkelmannd, and L. Bartlett. “Attempted Replication of Frank Richtig’s Forgotten Steel Heat Treatments.”

[9] Suedmeier, Harlan. Phone Interview, 2019.

[10] https://www.bladeforums.com/threads/3v-why-arent-more-companies-using-it.407739/post-3800523

[11] https://www.bladeforums.com/threads/s30v.485714/page-2#post-4754204

[12] Kuehmann, Charles J., Gregory B. Olson, and Herng-Jeng Jou. “Nanocarbide precipitation strengthened ultrahigh-strength, corrosion resistant, structural steels.” U.S. Patent 7,967,927, issued June 28, 2011.

13] https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/AerMet%20340.pdf

[14] https://www.carpentertechnology.com/hubfs/Data%20Sheets/AerMet100.pdf

[15] https://www.carpentertechnology.com/hubfs/Data%20Sheets/AerMet_360_Datasheet.pdf

[16] https://www.carpentertechnology.com/hubfs/Data%20Sheets/AerMet%20310.pdf

[17] Rehan, Muhammad Arbab, Anna Medvedeva, Berne Högman, Lars‐Erik Svensson, and Leif Karlsson. “Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel.” steel research international 87, no. 12 (2016): 1609-1618.

[18] Park, W., M. R. Hilton, A. R. Leveille, and P. C. Ward. “Microstructure, fatigue life and load capacity of PM tool steel REX20 for bearing applications.” Tribology & Lubrication Technology 55, no. 6 (1999): 20.

[19] Oppenhemier, Todd. Alfred Pendray, Wootz Hunter – An Homage to a Remarkable Craftsman. YouTube video, 2018.

[20] Verhoeven, J.D. Damascus Steel Swords: Solving the Mystery of How to Make Them. 2018.

The post 3 Times Knifemakers Proved Metallurgists Wrong appeared first on Knife Steel Nerds.

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Video

Here is the video version of the following information:

Can You Even Tell the Difference?

I have seen a common comment on knife forums and on my YouTube videos. It seems to be one of those statements that different people unintentionally copy from someone else. Everyone seems to think they thought of it on their own. It has a lot of variations but boils down to one statement: “People can’t tell the difference between knife steels anyway.”

The reason why the variations matter is because people are making different points when saying it. I believe that these kinds of statements started out as a criticism of certain knife buyers: “You never use your knives so you wouldn’t know what knife steel was even used.”

Another variation is to say that “premium” knife steels are all good and the differences between them are so small that nitpicking about which one is used is unimportant.

But I have seen people take this statement to the extreme and claim that there actually is no real difference between steels at all.

Edge Retention

This discussion can go a lot of different ways so let’s start with one of knife enthusiasts favorite topics – edge retention. If we look at the CATRA chart for different steels, for example:

Those tests were all done with identical edge geometry. You can also see the approximate effect of hardness by looking at the dashed diagonal lines (some steels were also tested at multiple hardness levels). You will notice that there are steels that tested under 300 mm of cardstock cut, all the way up to 1150 mm. That is a huge range. If we compared 8670 and Rex 121 in virtually any side by side slicing test with identical edge geometry I find it hard to believe that someone wouldn’t see the difference.

The Car Analogy – Commuter vs Soccer Parent

But most knife users are not doing side by side tests to compare steels. And that’s fine. When we cut random things, a random amount per day (or week, or month) it is very difficult to know how much cutting one knife did vs another. It’s like if I was comparing the gas mileage of two cars. If I was a commuter making the same drive to and from work five days a week and not driving my car at any other time, the comparison would be obvious. I may not even need to run any numbers to know if one car had only 20% better gas mileage, much less 100% better. However, if it is a family car, being driven around for different kids activities, sometimes going to the store, sometimes sitting for two days, etc. it would be very difficult to be able to tell if one car had 20% better gas mileage than another. The usage would be too variable. That doesn’t mean that I’m not actually getting better gas mileage out of one of the cars. It just means that I would have to look at some numbers to find out. (Where this analogy partially falls down is that our cars do show us the average MPG where the knife does not have a record of how much it cuts in between resharpening).

The point I am making is that just because someone couldn’t tell that there was a difference doesn’t mean that there wasn’t a difference. A knife can be cutting longer even if you didn’t notice. That also doesn’t mean that you have to buy a new knife any time there is a new knife steel. Just like you don’t need to buy a new Honda Accord just because they redesigned it for 2026. Engineers make improvements to products, and progress will continue.

Differences within Category

However, I can also agree that there is a level of nitpicking that can be unproductive among knife enthusiasts. This is especially true when people are arguing about minute differences between steels within the same “category.” For example, comparing the edge retention of S30V and M390. The differences are going to be small. There would be little difference to select one knife over another if the main goal was to achieve a small percentage increase in edge retention by selecting M390. That is partially ignoring other tradeoffs between them, of course. But they are both powder metallurgy stainless steels with 4% vanadium with similar edge retention. They are in the same “category.” Sometimes there are improvements with new steels within a given category, or at least a different set of tradeoffs that could be more desirable for different applications. But usually we are not talking about massive differences.

If, however, we are talking about 8670 vs S125V, yes, these steels are massively different. Simple low alloy steels used by forging bladesmiths vs a high wear resistance stainless steel by a stock removal maker would not be the same. These are totally different categories and will behave very differently in many ways. Calling these differences indecipherable would be nonsensical.

Edge Geometry

Steel is only one part of the equation. Every knife buyer knows that different knives can perform very differently even in the same steel. Even if they had identical heat treatments. Because edge geometry is the most important factor for knife performance.

When pure cutting performance is desired, thin, acute edges are king. It makes an even bigger difference than the steel or heat treatment. You can see that the “cheap” AUS-6 with low wear resistance can cut just as long as the high wear resistance S110V. That is if the AUS-6 is at 12.5 dps (25 total degrees) and the S110V is over 20 dps.

So this is another case where knife buyers may be confused about what the real effect of steel is. They might have one knife in a “super” steel that doesn’t cut very well and doesn’t cut very long all because the knife has a thick edge. Then another knife in a common steel that cuts great and keeps cutting. They conclude that the steel type must be nothing but hype.

Toughness

Big chopping knives and axes generally require thicker, more obtuse edges to handle abuse. Below I have images of AEB-L knives that I tested with controlled impacts at 15 dps vs 25 dps. With the 15 dps edge it only took 0.31 ft-lbs to generate a good size chip, and 1.36 ft-lbs to completely blow out the edge. With 25 dps with the same 1.36 ft-lbs there was just a minor ripple.

So just like with edge retention, the edge geometry is going to be most important, before steel type or heat treatment. However, there are real differences in toughness between different steels. Some are more prone to chipping and breaking than others:

I have definitely seen more broken Spyderco knives in high hardness Maxamet and Rex 121 than I have in higher toughness steels. That is the tradeoff. Engineering is all about tradeoffs. If you want the ultimate in wear resistance you will no longer have the ultimate in toughness. Some steels will have a higher wear resistance for a given level of toughness, but there will never be a magic steel that is perfect in every category. This is another of the many reasons why you can’t just say that there is no difference between steels. The right steel should be chosen for the right knife and the right buyer/user.

Toughness is one of those properties where you have enough of it until you didn’t. Either the toughness was sufficient for the task and there was no chipping or breaking, or the knife failed. So there can always be a debate as to whether how much toughness is enough. Because that will change based on the edge geometry and how the knife is being used.

Hardness

Hardness is less a reflection of steel type than it is of heat treatment, but there are still ranges. Some steels can’t go any higher than 60 Rc or even lower. Some steels like the “super” high speed steels can go all the way up to 70 Rc. Hardness is another of the places where I see people misinterpret steel properties, especially when it comes to relatively soft steel. Knives with soft steel will almost always deform rather than chip. This is sometimes misinterpreted as the steel having high “toughness.” If a knife edge deformed it failed due to insufficient strength, not because it was high in toughness. For example, knifemaker Shawn Houston compared an ESEE in relatively soft 1095 and compared it with a MagnaCut knife with similar edge geometry but higher hardness. In the nail chop test the 1095 failed due to deformation while the MagnaCut did not. This was due to hardness, not toughness.

Corrosion Resistance

Stain resistance is one of the more obvious categories, I think, and is less debated. Stainless steels rust less than non-stainless steels. And there are some stainless steels that are better than others. For some buyers it is acceptable to keep their knives oiled and the environment and use isn’t a problem for corrosion. But in either case I think we can all agree that some steels (when heat treated properly) show better resistance to corrosion.

Sharpening

Another area where people generally tend to notice steel difference is in sharpening. However, even in this case it isn’t as simple as some people perceive. Edge geometry is also important for sharpening. Thin edges require very little material to be removed, so even high wear resistance steels aren’t much more work to sharpen. It also matters what abrasives are being used. I used very hard CBN abrasive in my CATRA knives when resharpening and there wasn’t much difference between 8670 and Rex 121 in terms of how much strokes were required to raise a burr. The mechanical removal of material was more the limiting factor. It also matters to what level of polish you are taking it to. Those CATRA knives were only being sharpened to 400 grit. Polishing to high grit levels, especially with softer abrasives, can take much longer with high wear resistance steels with hard vanadium carbides. Heat treatment is also a factor. I found that deburring and getting a crisp edge was challenging with steels that had high retained austenite. I don’t have the space to write about what retained austenite is here, but you can have high retained austenite in virtually any steel if it is heat treated improperly.

Summary

So there was my little rant about whether steels are all the same and no one can tell the difference. They are different. And even if you didn’t notice that doesn’t mean they weren’t different. There are a lot of factors that can control whether someone notices when one knife is outperforming another, with steel being only one of them. And the bigger factor might just be commenters trying to win points with their spicy opinions about steel choices.

The post Knife Steel – Can You Tell the Difference? appeared first on Knife Steel Nerds.

Background

MagnaMax has been in development for a long time. When I first proposed the idea for MagnaCut to Crucible and Niagara in June 2019 I also proposed a high wear resistance version I was calling “stainless 10V.” This version was intended to match the combination of toughness and wear resistance in the non-stainless grades K390, Vanadis 8, and CPM-10V. K390 has developed some popularity in recent years from Spyderco using it in many knives. This steel hits a real sweet spot for having good toughness with very high wear resistance. That high wear resistance gives it excellent edge retention. MagnaMax achieves that same level of toughness and edge retention but with the same excellent corrosion resistance of MagnaCut. MagnaMax achieves these properties by using the same general approach to composition as MagnaCut while increasing carbon, niobium, and vanadium for wear resistance. We are still waiting for the ok from our patent lawyer before releasing the composition, but that will hopefully come soon. The first commercial “heat” of MagnaMax has been delivered to a few knife companies, so it is time to talk about the steel, even if we can’t reveal every detail yet.

With MagnaCut I tried to preach the benefits of “balance” for properties. Not going too extreme for any one property. I promoted the benefits of thinner edges using its excellent toughness, while still having very good wear resistance and edge retention. However, I knew that for some knives they would still benefit from higher edge retention, and that many knife enthusiasts would want a higher edge retention version of MagnaCut. So here it is. I tried to increase the edge retention by a large margin while still maintaining the goal of good balance, and I think the new steel is very successful at achieving that.

Video

There is a video version of the following information:

Edge Retention

The biggest change from MagnaCut is of course the increase in edge retention. MagnaMax matches the edge retention of K390 and Vanadis 8, as was intended:

This also puts it in the same range as steels like CPM-10V and CPM-S110V. It puts it above several notable steels like M390, ZDP-189, S60V, S30V, and CPM-M4. This is a sizeable increase in edge retention over MagnaCut.

Toughness

My stainless toughness chart has gotten pretty busy. MagnaMax is just above Vanax, S35VN, CPM-154, and XHP. These four steels were the toughest powder metallurgy stainless steels available prior to MagnaCut. So MagnaMax matching or exceeding the toughness of these grades is exciting. You will notice that MagnaCut is on the chart twice, once as “MagnaCut” and once as “Erasteel MagnaCut.” You can read about the switch to Erasteel for MagnaCut in this article.

Comparing against its benchmark grades, MagnaMax is the same as Vanadis 8 and K390, a small step above CPM-10V. So even though it is a stainless it still matched the toughness of the non-stainless powder metallurgy steels. So those that have been happy with the toughness of their K390 knives will also be happy with MagnaMax.

Edge Retention-Toughness Balance

Comparing the edge retention and toughness at the same time, MagnaMax also looks excellent on the chart:

With similar edge retention to S110V but substantially higher toughness, the property balance is much better than previous stainless PM steels. This datapoint is for 62 Rc, it could be a bit higher for edge retention at the cost of some toughness at higher hardness. You will notice that in the past, if you wanted higher edge retention than MagnaCut or S35VN, there was a steep drop off in toughness, and the toughness was relatively flat with higher levels of edge retention from there. MagnaMax has similar toughness to S35VN but with much greater edge retention, also highlighting its well-balanced properties. Comparing with the popular M390, MagnaMax is a significant improvement in both toughness and edge retention. Previously this combination of toughness and edge retention was only available in non-stainless powder metallurgy steels.

Microstructure

MagnaMax gets those excellent properties by achieving a very fine carbide structure made up of hard vanadium and niobium carbides. It has a similar amount of carbide to K390, with a somewhat finer carbide size:

MagnaMax

K390

MagnaMax has about 16% carbide volume, which is roughly double MagnaCut. This is why MagnaMax has so much greater wear resistance and slicing edge retention:

MagnaCut

MagnaMax has so much greater toughness than previous high edge retention stainless PM steels because its carbide volume is much lower and the carbides are much smaller. Chromium carbides are relatively large in powder metallurgy steels, so eliminating them from the microstructure gives much better toughness. Notice how big the carbides are in M390:

M390

S90V

S110V

Corrosion Resistance

One of the things that made MagnaCut popular was that its corrosion resistance was surprisingly excellent, better than most other stainless knife steels. I compared its corrosion resistance to other high edge retention stainless steels with my standard 1% saltwater test:

M390 and S110V actually have pretty good corrosion resistance, I had previously given both a “9” in my knife steel ratings. So it isn’t surprising that both of those grades had only a few small rust spots in this test. S90V has worse corrosion resistance and had significant rusting. MagnaMax, however, showed no rust spots in this test.

The Long, Long Development

MagnaMax has been a long time coming. As I said in the intro section, I first proposed it in 2019. We made the first heat with Crucible Steel in 2023. Crucible made a second heat right before their bankruptcy. The first heat was used by a few knifemakers and knife companies but did not have a name yet. So the companies called it different things like MagnaX, ProjectX, etc. That second heat did not provide as much information for dialing in the composition as I had hoped as they overshot the carbon target but a sizeable margin. This heat was primarily sold to Spyderco for their mule series of knives. These knives are a good representation of the steel’s properties, though the high carbon means that the corrosion resistance is lower for that prototype steel than the final versions. It’s still very good corrosion resistance, but not as good as it could have been. Once we have more representations of the final material for testing I will be doing further work like developing final datasheets and ensuring that all of the element targets yield consistent properties even when they are on the lower end or upper end of their allowable ranges. There are a lot more heat treatment combinations I need to test to optimize recommendations so that the material has its best possible combinations of hardness, edge retention, toughness, and corrosion resistance.

Wide Release Date

As I explained above, it is a bit difficult to say what the release date of MagnaMax is/was. In some ways it has already been released. However, the steel has not been given a final, wide release when it can be regularly purchased. There are many pounds of MagnaMax ingots being delivered over the next few months, from our dual powder steel suppliers of Erasteel and Carpenter. The official release date will be some time in Q2 of this year (2026).

Summary

MagnaMax maintains the excellent corrosion resistance and hardness of MagnaCut, while significantly improving its wear resistance and edge retention. This means it took a small cut in toughness, of course. MagnaMax matches the toughness-edge retention balance of K390, which has been popular in Spyderco folders recently. I think this is a sweet spot for performance for a wide range of knives that benefit from high edge retention. I’m excited to see what kinds of knives MagnaMax ends up in.

The post MagnaMax Is Here: The Next Evolution in Knife Steel appeared first on Knife Steel Nerds.

Crucible, Niagara, Erasteel, and MagnaCut

In case you haven’t been following steel news, Crucible Steel went through a bankruptcy and no longer exists. I interviewed Bob Shabala of Niagara Specialty Metals about this transition several months ago. Niagara is the company that purchased ingots from Crucible and would hot roll, anneal, and distribute them to knife companies and steel suppliers. They have also recently started a new online store to better sell directly to individual knifemakers. Niagara has managed to keep production going for a wide range of Crucible (and other) knife steels, including:

MagnaCut, CPM154, S30V, S35VN, S45VN, S90V, 3V, 4V, CruWear (NSM Wear), 154CM, 20CV, M4, CPM D2, D2, 440C ESR, 416SS, 6-4 Titanium. MagnaMax should be available in early 2026.

Erasteel purchased the rights to Crucible Steel trademarks. Erasteel is headquartered in France, but its powder metallurgy production is in Sweden. Niagara worked with Erasteel to retain the exclusive rights to purchase MagnaCut ingots and sell the steel to knifemakers and knife companies. Erasteel produces very high-quality powder metallurgy steel. Bob Skibitski was the head of the powder metallurgy steel production at Crucible Steel for 20 years and was hired by Erasteel. He reports that Erasteel production yields higher-quality, “cleaner” steel. You can read his thoughts in an article on Niagara’s website.

Video

There is a video version of this article:

Previous Testing of European Powder Metallurgy Steels

I have published two studies before comparing manufacturing from different powder metallurgy companies. One compared M390, 20CV, and 204P (with the somewhat different Elmax thrown in). The other compared Z-Wear (same as CPM-CruWear) between Crucible and European production. With the M390/20CV/204P study I found the biggest difference between manufacturers was the oxygen content. Oxygen is an impurity and it leads to oxide inclusions that are detrimental to properties. This is something advertised by companies like Bohler-Uddeholm, that their process is “cleaner” and leads to fewer oxides. However, the toughness of the grades was identical, perhaps in part because the carbide content is quite high and carbide size of M390/20CV/204P are basically the same. Even though Bohler advertises a finer powder size, the carbide size is mostly a result of carbide “coarsening” during high-temperature processing after the powder is made, rather than differences in powder size.

M390

20CV

So the carbide volume, carbide size, and resulting toughness are primarily controlled by the composition and method of manufacture (powder metallurgy) rather than the quality of the production. If the oxides are smaller and in a lower volume than the carbides, then the limiting factor for toughness is the carbide, and so oxide inclusion content doesn’t much come into play.

In the Z-Wear study I thought there might be more of an effect of oxide inclusions than the M390 because it has significantly lower amount of carbide. However, the two steels tested relatively similarly in terms of toughness:

In this case the European-produced version of Z-Wear had slightly higher toughness but it was also at a lower hardness, giving it a slightly worse hardness-toughness balance. In general I called them equivalent in the article. I actually suspect that Zapp had accidentally mixed up the labels of the steels because the oxygen content was lower in the steel that was labeled as “USA” once it was delivered to me. That would mean the European steel had a slightly better hardness-toughness balance, rather than the USA Crucible version.

USA vs European Z-Wear that might have been mislabeled before they were sent to me

Dialing in the Composition for Erasteel MagnaCut

With switching over to Erasteel for MagnaCut production we had several things we needed to figure out. One that might be surprising to people is that steel composition testing is highly dependent on calibration of the instrument and which technique is used. For example, there were significant differences in composition measured between grades in the M390/20CV/204P study and the Z-Wear study. This is not always clear because there is some distribution of composition in manufacturing. If the target is 10% chromium, there is some acceptable range by the manufacturer like 9.5-10.5% Cr. So you can’t measure just one example from different manufacturers and know what the offsets are. So we took pieces of MagnaCut from multiple Crucible “heats” and sent them to Erasteel so that they could have appropriate offsets to match the Crucible material. We will continue to monitor the performance of the new MagnaCut material because of the distributions. If heats on the low end or high end of certain elements are not performing well in one performance category or another we could shift the target or tighten the acceptable ranges. This is the side of development and quality control that is often not seen by the end customer and is probably not very exciting.

Erasteel vs Crucible MagnaCut

One very important part of MagnaCut is its high corrosion resistance. So I tested with my standard 1% saltwater spray test. Most stainless knife steels will see some rust spots with this test. In this case neither the Crucible or Erasteel material showed any rust spots:

I also tested the hardening response. For a given heat treatment the hardness was very similar, perhaps the Erasteel material was slightly higher:

Surprisingly (based on the Z-Wear and M390 results), the toughness of Erasteel MagnaCut was significantly higher:

You can see that the Erasteel MagnaCut was significantly higher, matching AEB-L at ~62 Rc, and exceeding it at ~64 Rc. I wouldn’t necessarily extrapolate that up to AEB-L levels at 60-61 Rc but in that hardness range it was very good. Comparing with non-stainless steels this also makes Erasteel MagnaCut look more competitive:

While Crucible MagnaCut was a bit below the best results of CPM-CruWear and Z-Wear, the Erasteel version matches or exceeds it. In my knife steel ratings I had given MagnaCut a “7” for toughness and CPM-CruWear an “8,” so this is exciting. MagnaCut has a similar carbide volume to CPM-CruWear but has even smaller carbides so it was always a bit disappointing that the measured toughness wasn’t matching it. Perhaps this was a case where oxide inclusions were reducing toughness slightly in the Crucible version. Erasteel MagnaCut even roughly matched the new Bohler K888 steel, advertised for its high toughness, and tested better than steels like Vanadis 4 Extra. One thing to note is that toughness differences are basically on a “log scale,” meaning that differences at small values are bigger than those at large values. So the difference between 5 and 10 ft-lbs is about the same as between 10 and 20 ft-lbs.

One difference I noted in toughness testing is that using an austenitizing temperature of 2150°F (1175°C) and then tempering to desired hardness led to better toughness than lower austenitizing temperatures. With Crucible MagnaCut the optimum property balance was with 2050°F (1120°C).

You can see that for a constant toughness of ~20 ft-lbs that the hardness can be higher for that same toughness with a higher austenitizing temperature, about a 2.5 Rc increase.

Summary and Conclusions

The MagnaCut now being produced by Erasteel matches or exceeds the properties of the previous Crucible version. Specifically the toughness showed an improvement. We will continue to monitor the properties of the new material to ensure the performance meets expectations with the new manufacturing partner.

The post Testing Erasteel MagnaCut (vs Crucible Original) appeared first on Knife Steel Nerds.

Bill Moran and Bob Loveless are the most influential knifemakers in the modern era. They were two key figures in the rise of custom knifemaking, which began in 1970 with the formation of the Knifemakers Guild. Both predated the Guild and had fully formed philosophies on knifemaking before its formation. There are an impressive number of dichotomies between Loveless and Moran. For two men who were influential in a similar time period for making the same product – knives – they had surprisingly different philosophies. Both men served as president of the Knifemakers Guild in the early years: Moran from 1972-1973, and Loveless from 1971-1972 and again from 1973-1974. B.R. Hughes wrote about the two knifemakers in 1986 [1]:

Future knife historians should be aware that Loveless and Moran had little in common. Loveless was an advocate of the stock removal method of making knives using stain-resistant steels, while Moran was a champion of the traditional forged blade. There were other, deeper differences. Loveless felt that quality should not be a condition of membership and that requirements should be as loose as possible to encourage new members. Moran was of the opinion that the Guild should have moderately strict guidelines and that members should be responsible to the Guild for unethical behavior… Be that as it may, the two, not friends by any means, ‘buried the hatchet,’ at least publicly, for the welfare of the Guild.

But looking at Moran and Loveless and how they viewed knifemaking is not only of historical interest. The arguments they were making decades ago are similar to those you can still find between some forging bladesmiths and stock removal knifemakers. And while they weren’t the only knifemakers making those arguments back then, they were two of the most influential voices. So it is valuable to examine the origins of these arguments to understand why some knifemakers still can’t agree.

Moran and Studying the Ancients

Moran was splitting time between a dairy farm and knifemaking from the 1940s. Moran found the book Bowie Knife, published by Raymond Thorp in 1948. Moran recalled [2]: “I must have read that book at least fifty times, and it certainly had a tremendous impact on me. It was during this same period that I began to attend gun shows in the Baltimore area. I was the only knifemaker who exhibited at these shows… People would stop at my table at a gun show back in the 50s and they would like my work, but when they discovered that I wanted $15 or so for a knife, they’d almost run away!” He sold the farm in 1960 and built a new shop, going full time as a knifemaker. Moran emphasized in his 1960 catalog how the study of ancient blades was key to his methods [2]:

I am the only maker of classical ancient blades… I do not make any wild claims that these knives can be used for cutting bolts or metal as a test of the knife’s quality. Moran Knives have long been acclaimed by many leading authorities as being the finest made today. They are probably the most expensive knives made because of the painstaking craftsmanship that goes into them. However, this results in a superior quality that one is unable to obtain in any other way. These knives will be collector items of future years… To my knowledge these knives are the only ones made today that are completely hand forged, hand tempered, and handmade in every respect… An immense amount of research and study of blades and forging techniques from ancient times until today has been required… The tempering process alone can only be learned by many years’ experience. This technique is the same as that used by the blade smiths of the seventeenth century. It was this tempering that enabled those blades to withstand such severe strain in combat.

Moran believed that ancient blades were better than modern knives, which is why he attempted to learn from them, as he said in his 1975 catalog [2]:

We must remember that the finest blades which have ever been made were developed at a time when one’s life depended on his blade. Anyone who does not believe this is true should make a study of ancient blades. It soon would be apparent to them that these were the finest ever made. I have tried to follow the methods and techniques used by the ancient smiths. These methods have worked out quite well for me. In all the years I have been making knives I have never had one returned with a broken blade.

Early Moran Knives. Weyer photo.

Moran Steel Choices

When it came to steel choices, Moran also believed that simpler was better, as he said in 1975 [2]:

Today, we hear a great deal about new and super steels. In over 30 years that I have been engaged in knife making, I have of course tried most all of the steels available in search of a superior steel. It is true that the corrosion resistant steels of today are far superior to the old stainless steels, but, what most people do not realize is that these steels were designed to hold their hardness at a high degree of heat. This of course, is unnecessary in a knife. Most of the high alloy steels have 12 to 18 percent chrome. This is a very definite drawback to good edge-holding qualities. It is true that this steel does have some advantages, such as being corrosion resistant, and this can be important to some people who do not have the time to wipe and oil their blade… Any steel manufacturer will tell you not to use the complex high alloy steels unless you need tools that allow you to cut under high heat, etc. For most tools and especially knife blades, one should stick to the high grade carbon steels. I myself, have found after 30 years of experimentation that the steel with the best all around qualities for a blade is in the straight carbon range. The high alloy steels have far more drawbacks than they have advantages.

Moran’s Differential Heat Treatments

Moran would heat treat his blades to have a hard edge but a “spring” tempered spine and soft tang. In 1960 he said [2] that this gave the blades “a combination of strength and edge holding quality that is unattainable from production made blades.” Again he made an appeal to ancient techniques [3]: “Of course this was a method used hundreds of years ago – especially in Europe – to make a better blade.”

Moran and Forging

Of course Bill Moran was famous for promoting forged blades. He believed that this was an important part of the ancient process, and claimed that it led to improved performance. In 1950 he said [2]: “The bar of steel is heated in a specially designed field stone forge … and forged by hand on the anvil. Every blade is heated and reheated, then forged dozens of times before the forging operation is finished. This hand forging greatly improves the quality of the blade.”

Moran believed that the performance improvement was due in part to the (now discredited) technique of “packing” as he said in 1975 [2]: “I use a technique known as hammer hardening or packing. This is an important step that unfortunately is understood by only a few smith’s. After the blade is forged almost to the finished shape, the blade is then hammered at a rather low heat with rapid, light blows. This causes the grain to be better aligned and the steel to be far more compact. This should only be attempted by a smith with a great deal of experience.” While “packing of molecules” is rarely claimed by bladesmiths anymore (iron atoms cannot be forced closer together), there are some that still perform cold or warm forging techniques for other purposes, so this could just be a case where Moran did not understand the metallurgy though there can be small benefits to the technique anyway.

Moran bowie. Weyer photo.

Moran and the Reintroduction of Pattern-Welded Damascus

Moran popularized pattern-welded Damascus in the early 1970s. This was due to his studies of ancient blades [4]: “Ever since I can remember, I, like all who love fine blades, have been fascinated with the beautiful Damascus blade. Many legends abound throughout history pertaining to the wonderful quality of these remarkable blades. After years of study and research, I felt I would like to try making them.” Moran would claim that Damascus blades had better properties [5]:

No one was more surprised than I, when I found this steel did have most unusual qualities. I found these blades could be left as-quenched and still have good flexibility, they also would hold a very good edge. Indeed I am now convinced that many of the old legends concerning these blades are true. These blades were far superior to any other blade because of the hundreds of alternating layers of iron and steel. The principle is the same as plywood or the laminated bow. I am now convinced that Damascus blades stopped being made so long ago for the same reason the wonderful composite bows of the Turks died out; that reason being they were so terribly difficult to make and after the fall of the Saracen empire, man went back to the self-bow which was made from a single piece of wood. The same being true for the Damascus blade; it was so much easier to make a blade from a single piece of steel.

Moran presented his first Damascus blades at the 1973 Knifemakers’ Guild Show in Kansas City. Knifemakers and collectors alike were very impressed. Butch Winter wrote [6]: “In those days the Guild Show crowds weren’t that big. There were a few people looking at Moran’s knives but they more or less were agog and didn’t understand what he’d done. The other makers were saying, ‘I wish I could do that,’ or ‘How’d he do that?'” Moran said that pattern-welded Damascus was key to bringing back forging and making his business sustainable [7]:

[T]he first year I showed my Damascus blades in Kansas City, I took in the most money I had ever made at any one show. For the first time, it occurred to me that it just might be possible to earn a decent living making knives. However, making Damascus cut my production by about two-thirds, and as I get older, it seems that I can’t make knives as quickly as I once did, and I was never a very fast bladesmith.”

Early 1970s Moran Damascus dagger. Weyer photo.

Loveless and Knife Design

Bob Loveless first attempted making knives after reading an article about Randall knives in 1953. He tried to buy one from Abercrombie & Fitch (then a sporting goods store) but the salesperson was rude and said it would be many months to be able to purchase one. Loveless made his own knife and returned to Abercrombie to show the rude sales clerk. He found instead that the clerk had been fired, but the floor manager was impressed with his knife and began ordering dozens of them.

Loveless is perhaps best known for his unique design sense. However, early on his knives looked a lot like Randall’s [8]:

[My first knives] looked a lot like knives that Bo Randall produced. The knives all had narrow tangs, single guards, leather washer handles with finger grooves and an aluminum pommel. Looking back, there is really no comparison between what we produce now and those early knives. They might have been good, solid edged tools, but they were lacking in aesthetics. Thankfully, over the years I’ve been able to break out of that early mold and create knives that not only are functional, but also look good.

Early Loveless knives. Weyer photos.

Loveless felt that first the knife must look good, and then when the customer picks it up it has to feel good [9]:

Eye appeal is the very first thing – it has a bearing on whether or not the knife will be accepted… If it is not appealing to the eye, then the prospect won‘t pick it up. If he doesn’t pick it up – you’re lost. But for the intelligent outdoorsman, you have got to get him to pick up the knife.

A knife must feel good in a man’s hand. Whether we realize it or not, our sense of touch is very critical to us. We get a lot of our input from our fingertips … it has to feel good … since we are directing our effort to the user’s hand primarily … it’s important to the knifemaker to understand the function of the hand… The knife designer, if he’s good, realizes that the human hand defines everything from the guard on back, in his work.

Loveless believed that having real experience was important to designing his knives [10]:

Unless you’ve had field experience, you can’t make hunting knives. I see knives with cutting edges that are too thick. With blades that are too long… With awkward and ill-shaped handles. Too many knife makers don’t understand their own hand. Their knives are not user friendly. You can’t teach a guy to make a good hunting knife if he’s never been in the woods, shot a deer, and been up to his elbows in deer guts. It’s like giving a typewriter to a man who is illiterate.

Loveless’s more developed style. Weyer photo.

Loveless and Steel

Loveless saw his process as iterating and improving to develop a knife that was better than any before it [10]:

Knife making can be thought of as an endless chase after perfection in design and execution – an ongoing pursuit of better steels and materials, and, of course, of working hard enough and being lucky enough to realize the measure of success that will give us a decent living. Some of us keep at it, often working long hours into the night after the demands of a regular day job. Sometimes, it becomes too much and we drop out. Yet it keeps calling us back – perhaps later when we can afford a better shop – to try again.

Loveless did not believe in forging of blades, and performed stock removal instead [8]:

I had no idea that flat stock in the steel of my choice (Jessop 139B) was available. When I ran out of steel, I contacted the manufacturer. The woman who answered the telephone suggested that I try their flat stock. I realized right then and there that I’d forged my last knife. Her suggestion was what you might call “a light bulb moment.” When that light came on in my head, I realized that there was no point in beating a piece of round steel stock flat, when you can buy it flat already. No matter what the forging community believes, you can’t improve a piece of steel by heating and beating on it.

While Moran used very simple steels, Loveless was looking for a modern alloy that would enhance performance. Loveless had started with a high nickel steel, Jessop 139B, relatively similar to 15N20 with 2.5% nickel. He liked the steel for its high toughness and found the nickel to improve the corrosion resistance. Next he tried the high silicon shock resisting steel S5 because it had a very high toughness rating according to the steel information he managed to find. The S5 made good knives with excellent toughness and good edge holding but he had issues with sudden fractures in the knives because of the fast brine quenching specified by the datasheet [11]:

S5 has almost 2% Si and 1% Mn, and when everything went just right, we got some very fine working knives out of it. Very high toughness of course, but also very good edge holding. But it was a Brine-quenching steel, and with S5 two problems were never licked: sudden, brittle fracture during testing, and rusting that seemed to pop out of the blade before my eyes. The brittle fracture just shouldn’t have happened, and two out of three times it didn’t. But the third time, I would put knife after knife in the vise for a simple bending test, and watch the damned things bust with very small bends. I hollered at metallurgists, kicked the dog, my kids wouldn’t bring me their report cards, my internist was pulling his hair, and my Old Lady was making me eat out in the shop.

Loveless even managed to request a “special modified melt of slightly different Silico-Manganese Shock steel” [11]. But he still had issues with the knives fracturing because of the severe brine quenching [6]:

I’d end up mumbling to myself, watching the moon go down and the sun come up trying to figure out what was going wrong. Never did, either. So I have a bad taste in my mouth over this kind of steel, which has been recognized for years as the best stuff to make chisels out of…the properties of the Shock steels intrigued me, and still do. But there was the rusting, and I got tired of having to hone my knife everytime I started out hunting, so I began wondering about things like that.

Loveless made a wish list of his ideal steel and eventually found it in 154CM stainless steel, as he wrote in his 1972 catalog:

So all during those years I was building in my mind a picture of what the perfect Loveless Knife steel would be, and what it would offer: working hardness exceeding Rc 62, working ductility and toughness at that hardness, and finally rust-resistance equal to the usual Knifemaker’s 440C, which I had tried but rejected due to poor edge-holding. During the summer of 1971, I learned of a steel made by a leading Tool Steel producer in the East (Crucible). They had developed it for service in the high-temperature regions of the fan-jet engines on the 747 aircraft, and it was alloyed to hold strength at 700 deg. F. My examination of the alloying, and a study of the heat-treating procedures suggested by the maker, led me to think it might be a candidate for fine hunting knives.

I ordered a quantity of 500-lbs, which was delivered in August. Test knives were made immediately, and placed in the hands of friends here in the West and in Canada, and I began hearing from these men, all critical knife users, within two weeks, with their comments. Previously knife buyers had to make a choice when they ordered a knife. The knifemakers, this one included, could offer edge-holding, or rust-resistance, but not both qualities, in the same knife. Typically, those of us who valued field performance preferred to make our knives from one of the better medium or high-carbon Tool Steels, in the judgment that edge-holding was the main reason for the existence of the benchmade knife. But two things were immediately apparent, in the letters commenting on the new knives. First, they did hold their edge, better than did my previous alloy. And second, they didn’t rust, in normal service, even if not cleaned up right away. We had to unlearn some things, and learn some new things, in the way of Shop practice, in making these new knives. But it was soon quite apparent that we had found a new kind of steel, and that this new steel was yielding the results I had been looking for. Knives made from Grade 154CM are indeed fine working knives… Exposure to blood acids in big game stains the blade slightly, if anything, but badly-pitted blades just don’t happen, and even the staining is rare. And the cutting edge holds up better than did the older Silico-Manganese Alloy knives. Blades are put in service at a working hardness of Rc 62-64, and are quite ductile and tough at that hardness… All Loveless Knives made since September of 1971 are of this fine new steel. We have almost 300 knives in the field now, and the results have exceeded my early hopes. The 154CM Alloy has brought new and better quality to Loveless Knives, and it’s the kind of steel I had hoped to find for years.

Weyer photo.

154CM and the Japanese version ATS-34 would become a standard for stock removal makers for decades (and is still used by companies like Emerson). Knifemakers also continue to use CPM-154 and RWL-34 (The RWL stands for Robert W. Loveless). Loveless enjoyed learning about steel and metallurgy. He wrote [11] that his copy of Tool Steels by Roberts, Hamaker, and Johnson was “well-thumbed and beloved.” Loveless wrote an article about metallurgy in 1975 which wasn’t too bad (according to this PhD metallurgist) [11]:

Eight thousand words or so ago, I set out to tell you something about steel, and knifemaking. Whether I succeeded or not is up to you, and how hard you want to work at knowing the world of fine knives. You won’t learn it all from an article, and may never learn it all in one lifetime for all I can see. But that’s what makes it interesting, even challenging, and yes … fun. There’s a little more to it than you thought there was. Right?

Loveless did not believe in “secret” heat treatments, in his article about heat treating he described his process and said sarcastically [11]: “[I]f you’ve ever wondered what goes on behind closed doors at the dark of the moon get ready!” He used modern heat treating methods rather than a forge or torch. He laid out his heat treatment steps for 154CM including a furnace, a cold treatment, and multiple tempers. He summarized the process afterward [11]: “If there’s any ‘secret’ to making knives like this, I’ve given it above, and I encourage you to try for the same results.”

Tradition vs Modernism Continues to This Day

Loveless and Moran seemed to disagree in almost every possible way. However, their fundamental philosophical differences seem to come down to tradition vs modernism. Moran found inspiration in ancient blades and thought that the secrets to superior blades was in the study of those blades. Loveless felt that through iterative design improvements and the use of new steels developed by modern science that superior performance could be obtained. Of course, this is somewhat simplistic. Moran developed new techniques and designs himself, and Loveless said that his tapered tangs could be found on blades from the 1800s.

Moran would take his love for the forged blade and found the American Bladesmith Society in 1976 along with Don Hastings, Bill Bagwell, and B.R. Hughes. This organization continues to this day and has continued to have a strong influence on those that forge blades. It remains relatively uncommon for bladesmiths to forge stainless and high alloy tool steels. While it is true that those steels are more difficult to forge, this is not the only reason why they remain uncommon. After all, it is also more difficult to use these steels with stock removal techniques but they are used much more frequently by those makers. The ABS founders did not believe that new steels were better, as Bill Bagwell said [12]:

Frequently, I note in some bit of literature that so-and-so is using a fantastic jet-age steel for his blades. Frankly, just because a given steel is great when used for the turbines of jet aircraft engines doesn’t necessarily mean that it is the ultimate cutlery steel. A blade that is forged, however, is made from steel that the smith has in effect manufactured expressly for a knife, and this makes possible the toughest, strongest, most effective cutting edge possible, but at the same time this blade will be relatively easy to sharpen once it gets dull.

The ABS bylaws specified (and continue to specify) that a JS or MS stamp cannot be used on a stainless blade, even if forged [13]. They justified this rule by claiming that stainless steels are inferior [13]:

[T]he Society discourages the continuous use of stainless steel for forging blades unless and until forged stainless steel blades have been proven, to the satisfaction of the Board, capable of being forged into quality blades that will consistently pass the standard ABS cutting and bending tests.

The ABS cutting and bending tests are much easier to pass with simple carbon steels since they require a differential heat treatment, which is difficult to perform with a stainless steel because of its high “hardenability” (air cooling leads to full hardness). It isn’t even possible to pass the Journeyman Smith cutting tests with a stainless steel, as the JS cutting test says that “Only forged blades of homogenous carbon steel are allowed.” I think that san-mai and other laminated type construction are ideal for the ABS bending tests, which would work very well with stainless steels. This would also demonstrate forging skill rather than only heat treating skill. The differential heat treatment can be performed with low alloy steels that have not been forged, so they are not an indicator of forged blade performance but only heat treatment. Stainless san-mai has become much more common over the past 10-15 years (though more commonly it is stainless “sides” with a carbon steel core).

The ABS board also claimed that stainless steels do not benefit from forging like carbon steels do. I have continued to hear this claim from many bladesmiths. B.R. Hughes wrote in 1977 [14]:

440C, D2, and 154CM are all … stain resistant steels, and all three will take and retain an edge for long periods of time even under heavy usage. It was not, incidentally, feasible to attempt to forge such sophisticated steels as those mentioned in the last two paragraphs, and the [common] view that many modern cutlers take of forging may in large measure be due to the fact that a few misguided souls even tried to forge 440C and even D2 by guess and by gosh, and the results were mostly awful.

Of course there have been a few brave bladesmiths who have used stainless steel despite the heavy social pressure of the ABS to avoid it, but they have remained a small number. For those who are brave, I have an article on how to effectively heat treat stainless steels that have been forged.

Nick Rossi knives in forged AEB-L

Another big difference between now and then is that the most common stock removal steels were 440C, D2, and 154CM, as Hughes mentioned. Those steels were very different than simple carbon steels. They have much higher carbide volume and thus higher wear resistance, but toughness is limited from those carbide structures. The chromium carbides were also relatively large which also limited toughness. So these steel choices led to very different properties, on the one end were low wear resistance simple steels with good toughness and ease in sharpening, used primarily by forging bladesmiths. On the other end were steels with high wear resistance and relatively low toughness (and some complained about sharpenability), used primarily by stock removal makers. Things have changed since then, such as the rise in popularity of AEB-L. Ironically, that steel dates back to the late 1960s, before the formation of the Knifemakers Guild, but did not become common in USA custom knives until the 2010s. AEB-L was designed for razors, and it has a much finer microstructure and much higher toughness than grades like 440C, D2, and 154CM. It has a much more similar performance profile to a low alloy steel favored by forging bladesmiths. And of course there are now a wide array of powder metallurgy high alloy and stainless steels available with a wide range of properties at different levels of wear resistance, toughness, and corrosion resistance.

I do think that claims from bladesmiths about the superiority of forged blades have slowed down. It was still relatively common in the 1990s and early 2000s but I don’t see it as much anymore. From my perspective the divide between forging bladesmiths and stock removal makers is smaller than ever. I do not see as much arguing about superiority as happened decades ago. It is most common for knifemakers to choose the method that is most appealing to them without making judgments about superiority (or inferiority) of the other method. So I think that improvement should be celebrated.

More History of Knives and Steel

Did you enjoy learning some history of knifemakers and the steels that they used? Then you will love my book The Story of Knife Steel. It is full of stories direct from the mouths of knifemakers, knife company owners, and metallurgists. Learn the development of steels, how they were introduced to knives, and the development of Damascus patterns and techniques. It is available in PDF, paperback, or hardcover. It is also available as a PDF bundle along with Knife Engineering 2nd edition.

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[1] Hughes, B.R. “The Knifemakers Guild: Beginnings.” Blade Magazine. August 1986.

[2] Hughes, B.R. and C. Houston Price. Master of the Forge, William F. Moran, Jr. and His Classic Blades. 1996.

[3] McEvoy, Harry K. “A living legend in modern cutlery William F. Moran, Jr.” Knife World. February 1979.

[4] Material handed out at the 1973 Knifemakers Guild Show written by Bill Moran.

[5] Moran Knives brochure 1973.

[6] Hughes, B.R. “Happy 25th, Damascus!” Blade Magazine. November 1998.

[7] Hughes, B.R. “William F. Moran Knifemaker Profile.” American Blade Magazine. April 1979.

[8] Hollis, Durwood. Knifemaking with Bob Loveless. 2010.

[9] Spangenberger, Phil. “R.W. Loveless: Leader in the Field.” Guns & Ammo Guidebook to Knives & Edged Weapons. 1974.

[10] Williams, Al and Jim Weyer. Living on the Edge: Logos of the Loveless Legend. 1992.

[11] Loveless, R.W. “Steel and Knives: A Bladesmith’s Bible.” Knife Digest. 1975.

[12] Hughes, B.R. “Interview: Bill Bagwell.” Knife World. February 1978.

[13] https://www.americanbladesmith.org/wp-content/uploads/2021/03/ABS-ByLaws-2-7-2013-Signed.pdf

[14] Hughes, B.R. “Steel.” Knife World. December 1977.

The post Moran vs Loveless – Knife Steel Edition appeared first on Knife Steel Nerds.

Video

There is a video version of the following information:

What is Buderus?

Buderus is a steel mill in Germany. They have several of their own knife steel products, including Nitro-V, Nitro-B, and Nitro-X7. They have also produced a wide range of standard grades, including 1095, 80CrV2, 15N20, and W2.

Buderus was purchased by Bohler-Uddeholm in 2005, which was then purchased by voestalpine in 2007, meaning Buderus was then owned by voestalpine (voestalpine is not supposed to be capitalized) [1]. Buderus was sold by voestlpine at the end of 2024 [2], and that process was completed in February 2025 by Mutares SE &Co. [2]. The previous owner, voestalpine, stated that they were selling Buderus because they were “concentrating its product portfolio on the technologically demanding high performance materials segment, while simultaneously reducing its share of standardized tool steel and high-grade engineering steel production, the price of which is coming under increasing pressure due to greater competition from outside Europe” [3].

At the time of the sale, Buderus had 1,100 employees and units capable of making steel from beginning to end, including melting, casting, forging, hot rolling, and cold rolling [4]. Mutares is a soulless private equity company, so of course, they did not hold on to Buderus for long. They began the process of selling the hot rolling mill and heat treat facility to GMH Gruppe in August 2025 [5]. Mutares also sold the drop forging unit to a subsidiary of itself, FerrAl United Group (no, corporate business doesn’t make sense). Mutares said this would secure 670 jobs for Buderus, and GMH Gruppe said their two units would account for 300 of those 670 employees [6].

What happened to the other ~450 employees? Those were let go because the steelworks was shut down by Mutares [7], meaning no more melting and casting of steel for Buderus. Electric steelmaking was apparently difficult to make profitable in Germany due to high energy costs [8]. We were also told that the cold rolling mill would shut down. Cold rolling allows steel to be rolled down even thinner than a hot rolling mill, and also gives a better surface finish and tolerances.

GMH Gruppe is also a steel company, so they announced [6] that the acquisition of the Buderus hot mill “closes an existing production gap … expanding product range to dimensions of up to 300 mm square. This enables access to new markets – including those beyond the traditional passenger-car combustion-engine segment.” With the steelworks shut down Buderus can continue to make steel but they will be sourcing ingots from other facilities within GMH Gruppe – these include Georgsmarienhütte GmbH, Stahlwerk Bous, Schmiedewerke Gröditz, and Pleissner Guss [6].

Will Buderus Cease Production of Knife Steel?

I contacted Buderus and asked if they would continue to offer knife steel with these changes. Christian Simon, the head of sales responded, confirming that they would continue to source ingots from the sources within GHM Gruppe listed above, also mentioning Energietechnik Essen GmbH, the company that makes Cronidur 30 (sold as LC200N by Zapp). He then added information specifically about knife steels:

“Based on our billet and strip rolling mills, we can now offer you hot strip from Wetzlar in an even broader range of materials. You can, of course, continue to obtain our popular NITRO grades from us as hot strip. And whether ingot casting, continuous casting, or ESU grades – our modern electric arc furnaces are already producing Green Steel for a sustainable future.

For the time being, Buderus Edelstahl operates under the name GMH Precision Machining GmbH. We will soon provide further information about the new Buderus Edelstahl brand within the GMH Group.”

Sven Kunzer, Managing Director, added in a separate email:

“[N]ow the things are getting clearer. We are offering our knife grades like Nitro-V, Nitro-X7 and Nitro-B as hot rolled strip.”

In other words, no longer available as cold rolled strip, but hot rolled steel will be available. Buderus metallurgist Clemens Trinks sent me a document about their new production route which confirmed that they will be offering steel as thin as 2 mm (0.079″) which is likely thin enough for the majority of applications. Though Clemens also mentioned potential limits for width depending on the grade and that is likely even more so for the very thinnest sizes. The annealing available has also changed due the restructuring, and they have now moved to open air annealing box furnaces. To remove scale they are using shot blasting.

How Are People in the Knife Industry Responding?

There is confusion in the knife industry about what exactly is happening with Buderus. New Jersey Steel Baron has been selling Buderus steel to knifemakers for many years now. Their official communication [9] about Buderus said only that Buderus is permanently closing and says that these steels will not be returning. I believe that New Jersey Steel Baron did not know that Buderus is continuing and will continue to offer knife steel. Or perhaps they were ready to move on from Buderus. NJSB is correct that Buderus has been an important supplier of knife steel in recent years. Several difficult to obtain steels like W2 were regularly available in good sizes and prices due to Buderus. Other knife steel suppliers should pick up the slack from NJSB if they decide to no longer purchase these grades from Buderus.

There is also a recent Blade Magazine article [10] that interviewed a few people in the knife industry. They seem to all be under the impression that Buderus is closing for good. So we should get the word out that Buderus is still making knife steel.

Summary and Conclusions

There were some troubling reports about Buderus going away but those were premature. The recent statements I got from Buderus employees about continuing to produce knife steels in hot rolled strip are very positive. They should be able to continue making it through the new group’s steelworks to provide ingots and slabs for hot rolling. I don’t think it should be understated just how many different knife steel grades have been produced by Buderus in recent years, and hopefully for many years in the future.

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[1] https://www.voestalpine.com/specialtymetals/en/about-us/history/

[2] https://mutares.com/en/mutares-has-completed-the-acquisition-of-the-business-of-buderus-edelstahl-gmbh-from-the-voestalpine-ag/

[3] https://www.voestalpine.com/group/en/media/press-releases/2024-10-23-voestalpine-sells-buderus-edelstahl-to-mutares/

[4] https://www.buderus-steel.com/en/company/about-us/

[5] https://mutares.com/en/mutares-portfolio-company-buderus-edelstahl-has-signed-an-agreement-to-sell-two-business-units-to-gmh-gruppe/

[6] https://www.gmh-gruppe.de/en/news/acquisition-of-buderus-edelstahl-gmbh-business-units-legally-completed/

[7] https://www.marketscreener.com/news/buderus-edelstahl-to-be-broken-up-after-mutares-takeover-hundreds-of-jobs-affected-ce7c50dedd8af725

[8] https://www.ffh.de/nachrichten/hessen/mittelhessen/442556-buderus-edelstahl-in-wetzlar-das-wars.html

[9] https://newjerseysteelbaron.com/steel-signals-1-on-the-closures-of-crucible-and-buderus/

[10] https://blademag.com/knife-news/buderus-mill-closure-threatens-10xx-carbon-steel-supply-for-knifemakers

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Patreon

Research like this is made possible by Patreon supporters. That allowed me to purchase the carbide straightening hammers and perform the experiments below. Join at Patreon.com/KnifeSteelNerds if you would like to support further research.

Video

There is also a video version of the following information:

Knife Engineering 2nd Edition

The following study was included in my new book Knife Engineering 2nd Edition. Those that bought the book have already seen some of this information. There are several other studies in the book that have not been published on my website. Go buy the book to see them!

Peening

Using a carbide hammer on a piece of steel is a type of “peening.” Peening is a general term for working the surface of a material, usually by cold work. I have an older article about cold work such as cold rolling and cold forging. And a somewhat newer article where we tested the properties of 52100 after cold working. Cold work strengthens/hardens a metal or material. If you cold work an entire piece such as through cold rolling you get an increase in hardness depending on the percentage of cold work, such as we measured with 52100:

Of course if you cold work too much eventually you will introduce cracks, just like if you continue forging a piece of steel when it has gotten too cold. Peening is a form of cold work that is only applied to the surface. Perhaps the most common and best known form of peening is “shot peening” where steel shot is sprayed against the metal to cold work the surface. This is sometimes done to give a matte finish to metals but generally it is performed to enhance performance of certain parts. The cold work applied to the surface creates an “residual compressive stress.”

Image from [1]

Image from [2]

When knifemakers hear “residual stresses” they sometimes worry but these compressive stresses are not a bad thing. Residual stresses are those stresses that remain when the original force is removed, the stress remains, i.e.. “residual.” Shot peening creates a “compressive” residual stress, as opposed to tensile stress. When the surface is in compression that creates an environment where crack growth is suppressed. You can think of the compressive stress as “pushing” cracks back together rather than pulling the cracks open. So shot peening is often performed on parts that fail to “high cycle fatigue,” or cyclic loading. These are parts like crankshafts, gears, etc. that see millions of cycles and fail due to slow crack growth. Shot peened parts last through many more cycles than those that are not peened. Knives do not generally fail due to high cycle fatigue so this wouldn’t necessarily lead to improvements in knife performance. But we would not expect it to negatively affect performance either.

Image from [2]

However, there can be dangers to peening. Just as a metal can be cold worked so much that it cracks, a part can also be “overpeened” leading to surface cracks, as seen below in 1045 steel:

Image from [1]

Peen Straightening

Straightening pieces by peening has been around for over 100 years. For example, here is one illustration of how to do it from 1910:

Image from [3]

The peening is performed on the opposite side from typical forging. The peening “stretches” the worked surface which returns the piece flat. This can be done with most peening methods including shot peening. However, hammer peening has become common for knifemakers over the past decade or two. This can be performed with a carbide ball or with a chisel.

Image of carbide ball hammer and chisel from Kyle Daily

The chisel and carbide ball lead to somewhat different behavior when it comes to stretching the material. The chisel leads to more “vertical” stretching while the ball leads to even stretching around each impact:

Schematic illustration of the movement of material around a carbide ball impact on the knife. Image from Kyle Daily.

Schematic illustration of the movement of material around a chisel impact on the knife. Image from Kyle Daily.

The chisel is preferential in some ways because generally for straightening you only want material moving in the direction of the curve you are trying to straighten. However, the stress from a chisel can be more dangerous because of how concentrated it is, potentially leading to overpeening. Kyle Daily recommends using a carbide ball hammer (which he makes and sells) and he uses a method where he makes vertical lines of the carbide ball impacts to create the directionality instead.

Image of straightening a knife from Kyle Daily.

Kyle has a YouTube video where he shows his method:

Tests with Peening

I have gotten many questions from knifemakers the past few years asking if straightening by peening is leading to microcracks that are embrittling the steel. As described above, peening, does not mean cracks are forming. It is a cold work process, and as long as the steel is not overly cold-worked there are no negative effects on properties. To test this, I used a carbide ball straightening hammer on some toughness coupons of heat treated MagnaCut. For one condition, I hit the pieces in many places before grinding and finishing both sides (the peened surface was removed). On the other coupon I ground and finished the coupons first and then I hit it many times with the straightening hammer after. With these three different conditions (with three samples of each condition) I measured the impact toughness. This test measures the energy required for breaking the steel. So if there were any pre-existing cracks we would expect to see a reduction in the measured impact toughness. The results in comparison with samples that saw no carbide hammer blows are shown below:

All of the specimens performed very similarly to each other. The one that was straightened after finishing did have slightly higher toughness. I am not sure if this is due to improvement from the peening or if it is just from statistical variability from testing. It isn’t impossible that the surface peening did help a little bit but the improvement was small in either case.

Dangers of Peen Straightening

While my tests showed no negative effect of hammer peening, there are still dangers to the practice. A knifemaker previously sent me a knife that had a crack in the handle. When the handle scales were removed it was found that the crack had initiated within the peening dimples:

It is a bit hard to tell in the pictures but these were relatively deep peening marks. It appears that this steel was “over peened” and thus cracks were formed in the surface of the steel and grew from there.

Summary

Peening is a surface cold working process to create a residual compressive stress in the surface. A compressive residual stress can be beneficial, especially in parts that fail to high cycle fatigue (knives do not generally fail in this way). Peening is an effective way to straighten thin curved pieces of metal, such as warped steel knives. Peening does not negatively affect steel when done properly. However, cracks can be formed if the steel is “over peened.”

---

[1] Maleki, Erfan, Okan Unal, and Auezhan Amanov. “Novel experimental methods for the determination of the boundaries between conventional, severe and over shot peening processes.” Surfaces and Interfaces 13 (2018): 233-254.

[2] https://www.amtechinternational.com/shot-peening-benefits-gears/

[3] Smith, Robert Henry. Text-book of advanced machine work: prepared for students in technical, manual training, and trade schools, and for the apprentice and the machinist in the shop. Industrial education book Company, 1910.

The post Is Straightening with a Carbide Hammer Dangerous? appeared first on Knife Steel Nerds.

New video with Q&A! If you want to ask questions for Q&A videos come join us at Patreon.com/KnifeSteelNerds

The post Knife Broke with CPM-3V! Isn’t it a Tough Steel? (Q&A Video) appeared first on Knife Steel Nerds.

11/18/2025: I added that the book is now available in South Africa from SD Knives & Supplies.

Links to buy are at the bottom of the article!

Video

Knife Engineering

In recent years, I have been mostly known as the “MagnaCut man,” but before MagnaCut, my biggest success was probably with Knife Engineering. When I started my website, Knife Steel Nerds, I hadn’t thought about writing a book because I thought I was doing a website instead. But I soon realized that a website works better for individual articles than it does for introducing an entire subject. So that led me to writing the book Knife Engineering: Steel, Heat Treating, and Geometry. That allowed people to learn the subject in order with all of the appropriate introductory material. The book has been a big success with many copies sold and many rave reviews from knifemakers and knife buyers alike. I tried very hard to make the subject as easy to understand as possible, and so it has been gratifying to hear people say that the book was exactly that.

The Second Edition

So why a second edition? There are a lot of reasons:

1. Since the first edition, I have tried to do as many experiments as possible in areas that I only had prior scientific journal articles to reference for those subjects. These included studies I performed on thermal cycling of both carbon and stainless steels, comparing different types of quench oils, and the performance of Damascus steels. There is an extra chapter in the second edition from one of these studies, all about forge heat treating. I always learn new things by conducting experiments for myself, and of course, I can test knife steels that are currently popular among knifemakers and knife companies. This significantly improved those sections of the book as the data was more directly applicable, and I could compare different types of heat treatments to give better recommendations.

2. One thing that surprised me a bit was that many knifemakers bought Knife Engineering just to see the heat treatment recommendations in the book. So I improved that section by including recommended forging, normalizing, and annealing temperatures for each. Before, those temperatures were only found for select steels in other parts of the book. I also updated each recommendation with whatever new testing I had done since the first edition. The new recommendations section also has its own table of contents with all of the steels listed.

3. New formats and wider availability – since the first edition was published I now have the option of printing the book in hardcover. I have seen some very tattered looking paperbacks of Knife Engineering! I also am publishing a PDF digital copy to Payhip. So the book will be available in paperback, hardcover, and PDF. The PDF edition also means that the book is available anywhere in the world. Before if you were in a country where print on demand was not available the book could be costly to import.

4. There are also many miscellaneous figures and experiments sprinkled throughout the book that make it significantly better when it comes to supporting information. It would be a bit tedious to list them all, but several of them haven’t even appeared on my website. In the first edition I restricted my own heat treating experiments primarily to a later chapter called “Practical Aspects of Heat Treating.” I moved most of those into the relevant chapters including many new experiments – annealing, austenitizing, tempering, etc. That way the new stuff is incorporated into the book and also the reader can learn about it within the chapter rather than a disconnected place later in the book. Overall the text is about 15% longer in terms of word count.

5. An index – the most requested missing thing from the first edition was an index. This was surprisingly painful to make. I had to double-check each page number, and it took forever. I think this is like smoking a pack of cigarettes, where each one removes 28 minutes off the end of your life. That definitely happened when I double-checked the index.

6. Improved formatting – I learned a lot about formatting books while working on my other book, The Story of Knife Steel: Innovators Behind Modern Damascus and Super Steels. There is a lot of extra white space in the first edition, and I wanted to make it look more professional. There are a bunch of charts and figures that look washed out, and so I redid them all to give them more contrast.

7. References – the first edition has the references I used at the end, but I did not include reference numbers within the text. This was a decision I made to improve the flow of the book and so as to not scare away general readers. But I regretted it almost immediately. Readers wouldn’t know which references are backing up which points, so figuring out which to read would be very difficult. I also knew that adding them back in would be way more work than including them in the first place. The references are small “superscript” numbers and I don’t think they have affected the flow of the book at all.

How to Buy

I spent 18 months working on the second edition. I thought it would take me a few weeks and get it knocked out. But it turns out making a new edition of a book is nearly as much work as writing a whole new one. Sometimes it felt like more! So I am excited for people to read it and hear what they think about the new and improved book.

Here are links to buy:

Worldwide

PDF: https://payhip.com/b/98jgz

There is also an available PDF bundle for $10 off if you get both Knife Engineering and The Story of Knife Steel: https://payhip.com/b/XFyLU

I have not put any DRM or anything on the PDF. There is a tiny watermark at the top of the page that gives an order and name so that if the PDF is distributed we know who did it. Please don’t steal the book.

United States

Paperback: https://www.amazon.com/dp/B0FYWBPFWF

Hardcover: https://www.amazon.com/dp/B0FYW8DRGX/

If you don’t see your country below I recommend the PDF.

South Africa: Paperback

United Kingdom: Paperback, Hardcover

Germany: Paperback, Hardcover

France: Paperback, Hardcover

Spain: Paperback, Hardcover

Italy: Paperback, Hardcover

Netherlands: Paperback, Hardcover

Poland: Paperback, Hardcover

Sweden: Paperback, Hardcover

Belgium: Paperback, Hardcover

Ireland: Paperback, Hardcover

Japan: Paperback

Canada: Paperback, Hardcover

Australia: Paperback

Comparisons

The hardcover is definitely my favorite version. I’m glad that is an option now. The PDF is great if you have an iPad or can’t get the book in your country.

If you never got a copy of The Story of Knife Steel make sure you get one of those as well!

The post Knife Engineering 2nd Edition – Expanded and Updated appeared first on Knife Steel Nerds.

We traveled to Nevada to visit my dad, Devin Thomas, and make some Damascus with Pop’s ProCut. Along the way we saw some sites around my hometown and my wife tries to prove that her town is better.

The post Making ProCut Damascus with Devin Thomas appeared first on Knife Steel Nerds.

The post Q&A Video: New Steels and Special Heat Treatments appeared first on Knife Steel Nerds.

Patreon

Thank you Patreon supporters! Through Patreon support I was able to pay for metallography and for the consumables for making coupons and running the CATRA experiment. If you want to support more knife steel research please join us at Patreon.com/KnifeSteelNerds

Video

Here is the video version of the following information:

What is Tamahagane?

Tamahagane is the name used in Japan for steel made with their centuries-old process. There are several videos available online to see the process such as this one. It starts with “iron sand” which is a naturally occurring form of iron mostly composed of magnetite, Fe₃O₄, though can also contain some hematite (Fe₂O₃) and other constituents like quartz and titanium dioxide [1]. One nice thing about magnetite (as the name suggests) is that it is magnetic, so it can be relatively easily separated from other minerals with magnets. The iron sand is then “smelted,” which is the process of reducing the oxide ore to the base metal, in this case, iron. The smelting is performed in a traditional furnace called a tatara. A clay tub is used which is layered with charcoal and the iron sand [2]. The charcoal acts as a reducing agent to turn the magnetite into iron, and also is a carbon source to turn the iron into steel (steel is iron plus carbon). The charcoal reduces the steel because carbon monoxide and carbon dioxide forms when it burns in air. The carbon monoxide (CO) reduces the magnetite to iron [3]. At the end the clay vessel is broken and the tamahagane is removed, which is in the form of rough and porous sponge-like pieces that also contains slag (large undesirable inclusions). The swordsmith separates pieces by “grade” which corresponds to the approximate content [4]. The grade is determined by color and also the fracture appearance [4]. The swordsmith then forges the pieces gently, and then folds and forge-welds them multiple times to eliminate porosity, remove some slag, even out the carbon content, and break up inclusions and impurities.

The “sponge-like” pieces of tamahagane after smelting. Picture from Wikipedia.

Soo all of that describes the manufacturing process. Ultimately tamahagane is a simple carbon steel. It is even simpler than a typical carbon steel like 1095 or White #1, because it is lacking intentional additions to those steels of manganese and silicon. So the steel has carbon of some content (described next) and then only trace amounts of other elements.

While there are a few individual swordsmiths that make their own tamahagane, most of the tamahagane produced in Japan comes from Nittoho tatara in Shiname Prefecture, the last of its kind. All tamahagane production had ceased by World War II. But this facility was restarted in 1977 and continues to produce the traditional steel for Japanese swordsmiths.

Published Tests of Tamahagane

Carbon Content and Composition

The cutting edge of Japanese swords has typically been found to be around 0.5-0.8% carbon [2, 5-9]. However, there are different types of construction used in Japanese swords, such as the “kobuse” method that uses a low carbon core and a higher carbon sides and cutting edge. Thus, the low-carbon pieces of tamahagane can be used in these low-carbon portions, giving the blades greater ductility and reducing the chance of catastrophic breakage. Measurements of the core carbon content have returned values between 0.01% [7-8] and 0.2% [2]. Sometimes steel with a carbon content in between these two extremes is used on the sides [2,7-8].

Schematic of “kobuse” construction from [3]

However, the carbon content is not always perfectly distributed throughout. Analysis of a modern kogatana knife (utility knife) produced by Sadanao Mikami had a range of carbon from 0.6% on one end to 2.0% on the other [5-6]. The uneven carbon content can come from distributions within the original pieces, mixing of low carbon and high carbon pieces (often done intentionally), and performing an insufficient number of forge-folding operations to even out the carbon. They reported that the average carbon content was 1.03% for the entire knife [5]. There were also small amounts of other elements:

Composition of modern kogatana by Sadanao Mikami [5]

Microstructure and Hardness

Japanese swords are produced to have a “hamon,” a visible line that distinguishes between a soft spine and the hard cutting edge. Thick clay is applied to the blades at the spine to slow the quench rate so that it does not harden. The hard phase at the edge is martensite, and the soft phase is pearlite. At the hamon transition, there is a combination of martensite and pearlite. The low carbon core contains large amounts of soft ferrite. The pearlite content of the core is determined by the carbon content, more carbon means more pearlite.

Images of microstructure from a “modern” sword (1945) and an “old” sword (~600 years old) at different locations [9]

Micrographs of a ~600 year old sword [7]

Studies on the hardness of Japanese swords correspond to these differences in microstructure and carbon content. Typically, the hardness at the edge is between 600-900 HV [2,3, 5,7, 9] and the spine is between 100-300 HV [2, 3, 7, 9]. This corresponds to about 55-67 Rc at the edge and 0-30 Rc at the spine (Note: Rockwell C hardness only reliably goes down to 20).

Microhardness values of ~600 year old sword [7]

Microhardness of a “Koto” style Japanese blade (before 1596 AD) [3]

Microhardness from the 1945 and 600 year old swords [9].

Impurities, Inclusions, Forge Welding, and Folding

A study was performed along with swordsmith Sadanao Mikami on the effect of forging and folding on impurities and inclusions in tamahagane [10]. The process is shown in the figure below:

The forge welding and folding process used in Ref. [10]

The swordsmith started by hammering chunks of tamahagane into sheets, then cutting those sheets into chips. The chips are sorted by carbon content by hitting them with a hammer. High carbon chips break and low carbon chips don’t. The low carbon chips were stacked together and forged together into a bar, then cut and restacked six times (A1-A6); this was repeated with the high carbon chips (B1-B6). Then the low and high carbon bars were stacked together and forge welded together, followed by cutting, restacking, and forge welding six more times (C1-C6). The microstructure became more evenly distributed through the forge welding process as the carbon content became more equalized, as shown in the following images:

Microstructure evolution of tamahagane after forge-folding operations [10]

One common claim of folding and forge welding is the elimination of inclusions, oxides and slag that are present in the original tamahagane pieces. The researchers found that while bands of FeO were present in A1 and B1 from oxides present in the original pieces, they were not found in A6 or B6. In other words, the FeO bands were eliminated by further forging and forge welding. They were originally present in bands from forge welding flat pieces together. They also found silica (SiO₂) and Fayalite (Fe₂SiO₄) inclusions in the steel. The silica particles were less than 1 micron and the Fayalite inclusions were 16-20 microns in length in the A1 and B1 samples. The thickness of the Fayalite bands was significantly smaller than the FeO, about two microns.

Iron oxide bands forge welded into tamahagane during initial forge welding

The Fayalite was reduced from 16-20 microns long in the A1/B1 specimens to 14-15 microns in the A6/B6 specimens. These were further reduced to 13.1 microns in the C1 specimens and down to only 8.2 microns in the C6 specimens. So while forge welding and folding did not significantly reduce the volume fraction of Fayalite inclusions, they were reduced in size, more isotropic (round), and more evenly distributed after that process.

Inclusions in tamahagane steel in the C1 condition (one forge weld of low and high carbon steel), left, and after six folding and forge welding operations, right [10]

In a study on a kogatana knife produced by Sadanao Mikami had relatively homogenous oxide inclusions in the size range of 5-10 microns [5]. They reported a volume of 4-7% inclusions.

Oxide inclusions in modern tamahagane knife [5]

Analysis of a ~600 year old sword [7] found an inclusion content of 0.8-1.9%, which they found to be much higher than the content in a modern production steel (labeled “ordinary steel”).

Volume percent of inclusions in ancient sword vs modern steel [7]

Micrographs of inclusions in ancient sword [7]

Analysis of another ancient sword found an inclusion volume of 1.1% [3]. The authors claimed that this inclusion content is low enough to avoid a “significant reduction in its toughness.”

Inclusions in pre-1596 AD sword (cross-hair scratch added intentionally) [3]

Strength and Toughness

Tensile tests of a sword by swordsmith T. Takaichi were performed and compared with a conventional carbon steel with similar carbon content of 0.55% C [2]. They found that in testing of the steel before heat treating that the conventional steel (S55C) had greater utility than the tamahagane sword steel (S1). When observing the fracture surfaces, they found oxides in the tamahagane and they speculated that it was these oxides that led to the lower ductility.

Stress-strain curves and fracture appearance of tamahagane sword steel (S1) and conventional steel (S55C) [2]

In tests of a ~600 year old sword and a 1945 sword, they measured the strength and ductility of the swords with a 4-point bending test [8-9].

4-point bend test of tamahagane swords [9]

They found the ancient sword to form a crack at around 0.88 ton-force, but the blade did not fully break and continued bending until final fracture. The 1945 sword broke at 2.62 ton-force and did not have the load drop from cracking that the ancient sword had. They calculated the bending strength of the swords as 2552 MPa for the ancient sword and 4645 MPa for the 1945 sword. They claimed that these results are “in a range of performance tool steel” [8]. The hardness of the cutting edges were similar in the two swords. Instead, they said the difference in measured strength was because the 1945 sword had a 5 mm hardened area while the ancient sword had only 1 mm of hardened area (see earlier microhardness charts).

I didn’t find much other toughness testing of tamahagane so comparisons between this traditional steel and modern carbon steels are in short supply. I found one study of miniature charpy specimens taken from a Japanese sword [11], but they did not compare with similar tool steels. Furthermore, the values at the edge of the knife where we would probably be more interested were essentially zero:

Image taken from [11]

Effect of Carbon Content on Final Properties

While there seems to be a consensus that the cutting edges of tamahagane Japanese swords are in the range of 0.5-0.8% carbon or so, I am not sure if the carbon content was and is that consistent. There was the one study on the tamahagane knife where they found carbon values as high as 2% within the same knife that read 0.6% in other locations [6]. I also found a study on different iron sand use at the Nittoho tatara (the last major facility remaining), and found that they had moved to a different source of sand that resulted in higher carbon and lower impurities [4]. So I think there is reason to believe that carbon content of tamahagane has gone up in recent decades.

The carbon content is very important to steel properties. One of the best known is the effect of carbon on the resulting as-quenched hardness. The higher the carbon content, the higher the hardness, though it levels out around 0.6% carbon:

Image from [12]

Carbon has an equally strong effect on impact toughness, even when tested at the same hardness for different low alloy tool steels:

Higher carbon also gives steel more iron carbide (cementite) which gives it greater wear resistance. This can give knives greater edge retention because edge wear is slowed. However, for a sword this wear resistance is not really beneficial, and toughness is a much more important property. So the 0.5-0.7% range of carbon would be about optimal for a sword, given the high combination of hardness/strength and toughness that you get from this microstructure. But for smaller knives, kitchen knives, etc made with tamahagane higher carbon could be beneficial for wear resistance.

1.25%C steel with significant carbide content (white particles)

0.6%C steel with almost no visible carbide

My Tamahagane for Testing

I recently went to Japan and took a class from Yuya Nakanishi, also called Masahiro. You can watch a video of our trip to Japan and making the “kogatana” (a utility knife). We took home our two knives that we made with him. However, I also wanted to test the steel for toughness which would be difficult with just the knife, as the standard toughness test uses rectangles. So I asked him if I could have a piece for toughness testing and he let me have one. This piece had already been through the forge welding and folding process. I also asked him what temperatures to use for heat treating and he told me 780°C for austenitizing and 180°C for tempering. I normalized and annealed the piece first, and followed his recommendations by austenitizing for 10 minutes, quenching in water, and tempering twice for one hour at each time.

Image from https://morinokyoto.jp/masahiro_en/

Carbon Content

I measured the broken toughness specimen with LECO combustion for carbon and sulfur content and got 1.06% carbon and 0.001% sulfur. This carbon content puts it into a range similar to White #2 (1.05-1.15%C). This is a good range for a utility knife, though as explained above would be on the high side for a sword. I am not sure if this is because Masahiro intentionally used higher carbon tamahagane for these smaller knives, or if it is due to carbon fluctuations, or higher carbon tamahagane being made at the Nittoho tatara. If I hear back from Masahiro I will update the article. This is very close to the carbon content in the kogatana by Mikami of 1.03% [5], which perhaps provides evidence that the carbon content of tamahagane has increased from older blades. I wasn’t able to measure other elements because of the size of the steel that I had.

Micrographs

The carbide structure looks consistent with the measured carbon content of 1.05%. It has a significant amount of small and evenly distributed carbides, but a smaller volume than the higher carbon 26C3. It looks closer to O1 and 52100, though the carbides are even finer in the tamahagane.

Micrograph of the heat treated tamahagane

O1 steel

52100 steel

Looking at a lower magnification micrograph, the carbide structure appears relatively consistent throughout. There are no visible layers from the forge-folding process. There is a “bright spot” in the upper left portion of the image. Higher magnification reveals that this is not carbide clusters but either an etching artifact or retained austenite.

Lower magnification of tamahagane

Impurities and Inclusions

The inclusion content of the tamahagane provided to me is very low, lower than reported inclusion contents in the journal articles that I cited. Using threshold measurements I estimate the inclusion content to be around 0.1%. I am not sure why this steel is so much “cleaner” than those analyzed in the other studies.

Polished (unetched) surface of tamahagane. Black particles are inclusions.

There is a small amount of orange, square/rectangular particles in the steel. These are likely titanium nitride (TiN) as these particles are typically yellow/orange and angular [13]. Iron sand typically has TiO₂ in it [1], and the Mikami blade had 0.03% Ti in it [5], so the presence of TiN is not entirely unexpected. Titanium and nitrogen have a strong affinity for each other, and these particles are often found in steels with small titanium additions.

Titanium nitride particles (TiN)

Hardness

The hardness of my toughness coupon was 64.6 Rc. This is relatively high in hardness, maybe even a bit high for a utility knife. However, it is within a reasonable range, and would provide very good cutting and edge retention. This lines up closely with tempering of other simple high carbon steels, such as 1.25% carbon steel 26C3, shown below. The 26C3 is somewhat lower in hardness, though this steel was tempered in another oven. My furnace is very good at maintaining a consistent temperature during tempering, so “overshooting” is less common.

I am not able to measure the hardness of the edge of the knife that I made at Masahiro Tantojo, as it is only hardened at the edge. It would require cutting it apart and using microhardness measurements to see. Since the knife was tempered by eye by the swordsmith it could be significantly different in hardness. The tempering was performed for a very short period, until it reached a temperature where water would sizzle when he touched the blade. My guess is that it is higher in hardness, somewhere between 65-67 Rc. However, if the carbon content is significantly lower in the blade it is possible that it would also be lower in hardness.

Toughness

Given the relatively high hardness of 64.6 Rc, the toughness was not chart topping. I measured 5.8 ft-lbs. However, this is a relatively high value for that level of hardness, as you can see when compared against other low alloy steels here:

As you can see the toughness falls right on the same line as 26C3 (green line in the upper image). So the tamahagane appears to be behaving similarly to conventionally produced low alloy high carbon steels. Overall I think this is a good result considering that some studies I cited before showed a potential reduction in toughness from oxides.

Edge Retention

Comparing the edge retention is a bit tricky since the kogatana design is different than the standard test knife that I use for CATRA testing. This knife is thinner behind the edge, about 0.010″ (0.25 mm) after sharpening, while our test knives are around 0.015″. This gives the thinner knife an advantage for a given edge angle, as shown in this earlier study on 154CM steel:

There is also the complication that I do not know the hardness of the kogatana knife, my guess is it is in the range of 65-67 Rc. When I tested it with CATRA I got 370 mm, which would also lend credence to the hypothesis that it is on the upper end of hardness.

There aren’t many low-alloy steels I have tested that would be in that hardness range. The light grey dotted lines show the approximate relationship between hardness and edge retention. So you will notice that the tamahagane is on the same line as most of the other low alloy steels, especially after accounting for the knife being thinner behind the edge. This is not too surprising given that most of the low alloy and carbon steels have tested in a similar range after accounting for hardness.

Tim Zowada Information

Tim is a bladesmith who makes his own bloomery steel using iron sand from Lake Superior. He was an author on one of the cited papers above along with Dr. John Verhoeven. He had the following comments after reading my report:

Here are a couple things that might be helpful. In general:

1. The final carbon content is determined by the average initial carbon content and the number of folds. More folds decrease the carbon content. The outside of the billet will decarburize during forging. That decarb layer is folded in with each weld, decreasing the average carbon content. Plus, the oxidation of the billet (scale) will decrease the overall size of the billet during all the folding and welding. For high quality steel, the typical number of of folds will be between 10 and 15. It ends up being a balancing act based on experience. Yoshindo Yoshihara prefers about 0.7% carbon for his swords. His brother prefers 0.6%. Maybe I have that backwards. The Art of the Japanese Sword (Yoshihara) is an excellent book that you should own. I’m not sure why the carbon content varied so much in your blade. My best guess is a low number of folds. A quick nital or ferric chloride etch would tell. You would be able to see lighter and darker bands of varying carbon content. Typically, the carbon content is pretty much homogeneous through the bar by about eight folds.

2. High hardness and low abrasion resistance is an advantage for my straight razor work. At 65 HRC, the blades hold up very well against whiskers. But, with the low abrasion resistance, a clean leather strop will remove enough metal to keep them sharp. They don’t need to go to the stones very often.

3. Like many things, the final carbon content and quality of the steel will vary from smith to smith, and batch to batch. I think what you got was a good representation of high carbon (1.0%) tamahagane.

Summary and Conclusions

Reviewing the prior studies on tamahagane, researchers of this material have been pretty realistic about its properties. At its best, tamahagane performs like other simple carbon steels. The potential for higher oxide inclusion content potentially limits its toughness, though in my own experiments it was roughly in line with the toughness you would expect for a steel made with modern methods. It is very interesting to learn about traditional methods for making steel and how they compare to the more advanced methods that we have developed since.

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[1] Tanii, Hiroshi, Tadahiro Inazumi, and Keiichi Terashima. “Mineralogical study of iron sand with different metallurgical characteristic to smelting with use of Japanese classic iron-making furnace “Tatara”.” ISIJ international 54, no. 5 (2014): 1044-1050.

[2] Okayasu, Mitsuhiro, H. Sakai, and T. Tanaka. “Mechanical Properties of Samurai Swords (Carbon Steel) Made Using a Traditional Steelmaking Technology (tatara).” Journal of Material Sciences & Engineering 4, no. 2 (2015): 1-6.

[3] Verhoeven, J. D., and Tim Zowada. “Comparison of Two Swords of Antiquity: The Japanese Sword and the Muslim Crucible Damascus Sword.” Metallography, Microstructure, and Analysis 12, no. 6 (2023): 934-943.

[4] SUZUKI, Takuo, and Kazuhiro NAGATA. “Effect of the charge of” Komori” iron sand on the properties of” Tamahagane” steel produced by” Tatara” operation.” Tetsu-to-hagané 85, no. 12 (1999): 911-916.

[5] Das, Ananda Kumar, Takuya Ohba, Shigekazu Morito, and Muneo Yaso. “Evidence of Lath Martensite in High-C Japanese Sword Produced from Tamahagane Steel by Tatara Process.” In Materials Science Forum, vol. 654, pp. 138-141. Trans Tech Publications Ltd, 2010.

[6] Matsumoto, Chihiro, Ananda Kumar Das, Takuya Ohba, Shigekazu Morito, Taisuke Hayashi, and Go Takami. “Characteristics of Japanese sword produced from tatara steel.” Journal of Alloys and Compounds 577 (2013): S673-S677.

[7] Yaso, Muneo, Toshifumi Takaiwa, Yoshihiro Minagi, Kunichika Kubota, Shigekazu Morito, Takuya Ohba, and A. K. Das. “Study of microstructures on cross section of JAPANESE SWORD.” In European Symposium on Martensitic Transformations, p. 07018. EDP Sciences, 2009.

[8] Yaso, Muneo, Yoshihiro Minagi, Toshifumi Takaiwa, Kunichika Kubota, Tsuyoshi Kanaizumi, Takuya Ohba, Shigekazu Morito, and Taisuke Hayashi. “Study of Metallurgy and Mechanical Property on Japanese Sword.” In Materials Science Forum, vol. 738, pp. 222-227. Trans Tech Publications Ltd, 2013.

[9] Yaso, Muneo, Toshifumi Takaiwa, Yoshihiro Minagi, Tsuyoshi Kanaizumi, Kunichika Kubota, Taisuke Hayashi, Shigekazu Morito, and Takuya Ohba. “Study of Japanese sword from a viewpoint of steel strength.” Journal of Alloys and Compounds 577 (2013): S690-S694.

[10] Takami, Go, Takuya Ohba, Shigekazu Morito, and Ananda Kumar Das. “Microstructural observation on materials of the japanese sword under fold-forging process.” In Materials Science Forum, vol. 654, pp. 134-137. Trans Tech Publications Ltd, 2010.

[11] Misawa, Toshihei, and Shin-Ichi Komazaki. “Ductile-brittel transition evaluation of Japanese sword and weld metals using miniaturized impact specimens.” In European Structural Integrity Society, vol. 30, pp. 119-125. Elsevier, 2002.

[12] Krauss, George. “Martensitic transformation, structure and properties in hardenable steels.” Metallurgical Society AIME,(1978): 229-248.

[13] Descotes, Vincent, Thibault Quatravaux, Jean-Pierre Bellot, Sylvain Witzke, and Alain Jardy. “Titanium nitride (TiN) germination and growth during vacuum arc remelting of a maraging steel.” Metals 10, no. 4 (2020): 541.

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Video

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Misunderstandings about Hardness and Corrosion Resistance of MagnaCut

I have been seeing a disturbing number of comments around the internet saying something like the following: “Larrin says that 60 Rc MagnaCut has better corrosion resistance than 64 Rc MagnaCut, so there are different hardness levels for different applications.” I have never said such a thing. It is true that there are different levels of hardness for various applications, but hardness does not dictate corrosion resistance; therefore, it is not one of the parameters by which they would make this decision. I have a video where I have talked about the pros and cons of higher and lower hardness. How you heat treat a given steel can affect its corrosion resistance but a whole range of hardness values can be achieved with both good or bad heat treatments. I will give a variety of examples for this. A separate but related topic is about how hard different steels can be heat treated to when related to their corrosion resistance. For example, the very corrosion resistant Vanax and LC200N top out around 59-61 Rc. I will explain why they don’t get any harder and why this is partially due to those steels having very high corrosion resistance.

Chromium and Corrosion Resistance

When iron is in a corrosive environment it forms rust – an iron oxide. If you add chromium to iron, the corrosion resistance is increased the more chromium you add. The chromium forms with oxygen to make a passive film at the surface which prevents rust from forming:

The following chart shows an old classic study [1] of corrosion rate of steel in high humidity environments. You will see that the corrosion rate went down with increasing chromium until about 12% Cr. Sometimes the cutoff for a steel being “stainless” is given as 10.5, 11, or 12% chromium. There isn’t any real agreement as far as I can tell. But corrosion resistance will increase with even greater amounts of chromium; it isn’t an on/off after some arbitrary cutoff.

Data adapted from [1]

Heat Treating and Corrosion Resistance

In the annealed (soft) state stainless steel is not yet stainless. When a knifemaker or manufacturer receives steel it is in this annealed condition so it is easy to drill, grind, machine, etc. Most of the chromium is in the form of carbides in the steel. When the chromium is tied up with carbon as a carbide it cannot form the chromium oxide layer at the surface.

There are three major steps to heat treating: austenitizing, quenching, and tempering.

Austenitizing

During austenitizing the steel is heated up to a high temperature and then held, allowing the chromium carbides to be dissolved (or partially dissolved) to put more chromium in solution so that the chromium oxide passive layer can be formed. Below shows the increase in chromium vs austenitizing temperature for Elmax and Vanax:

So one of the key variables for corrosion resistance is the austenitizing temperature because heating it hotter means more chromium in solution. However, the amount of chromium in solution is also controlled in part by the composition. The chromium in solution for Elmax at a very high temperature of 2200°F (the datasheet recommends no higher than 2010°F) is still below Vanax when it is austenitized at 1800°F (well below what the datasheet recommends). Austenitizing at a higher temperature also leads to increased hardness, so in that way higher hardness can sometimes mean improved corrosion resistance.

Quenching

During quenching the steel is rapidly cooled to form the hard phase of steel, martensite. Martensite formation is controlled by temperature rather than time. There is a “martensite start” temperature and a “martensite finish” temperature. In some cases martensite finish can be below room temperature and in that case the steel does not fully transform, meaning some austenite remains in the steel. This is called “retained” austenite. If there is too much retained austenite the hardness is reduced in the steel, and also the edge performance is bad and the knife would be very difficult to sharpen. One of the major factors for martensite start (Ms) and martensite finish (Mf) temperatures is the carbon content, as shown in the chart below.

With higher austenitizing temperatures and more carbide being dissolved, this does not only put more chromium in solution but also more carbon, as seen in this chart of Vanax and Elmax. Or in the case of Vanax, I included the carbon and nitrogen, since nitrogen also contributes to hardness in a similar fashion to carbon.

All of the above happens as long as the quench is sufficiently fast to avoid other competing transformations that will occur with slow cooling. Carbides can precipitate during slow cooling which would also reduce corrosion resistance. This can happen with the relatively common gas quenches that are used in large vacuum furnaces by many knife manufacturers. I covered this in a previous article/video about custom vs production heat treating.

Cryo and Cold Processing

You will notice that the Vanax hardness dropped at 2025°F while the Elmax hardness increased all the way up to 2150°F. These heat treatments included a cryo step in liquid nitrogen after the quench. If cryo had not been used the Vanax would have seen a drop below 2025°F and the maximum hardness would not have been as high. The Elmax likely also would have seen a hardness drop in this tested range. As an example, the following chart shows AEB-L steel when quenched to room temperature vs placed in a freezer or in liquid nitrogen:

AEB-L steel vs austenitizing temperature

The AEB-L achieved its peak hardness around 1975-2000°F just like the Vanax and then dropped in hardness with further increases in austenitizing temperature. It reached a max hardness of around 64 Rc, though when no cold treatment was used it maxed out around 62 Rc. The reason for the drop in hardness above a certain temperature is because of retained austenite. In other words, the martensite finish temperature was below room temperature. Using liquid nitrogen after the quench means cooling the steel to a lower temperature getting closer to martensite finish. However, some retained austenite will stabilize and not be transformed even with the very low temperatures of liquid nitrogen, which is why the hardness still drops with an austenitizing temperature that is too high.

So the use of cryo can allow both higher hardness and corrosion resistance if the austenitizing temperature is increased. For a fixed austenitizing temperature, typically there is a 1-2 Rc increase but the corrosion resistance would not be affected.

Tempering

After quenching, steel is tempered to improve its toughness. The tradeoff is that hardness is also reduced through tempering. Below shows a tempering chart for MagnaCut with different austenitizing temperatures.

Different austenitizing-tempering combinations can be used to achieve the same level of hardness. For example, to achieve ~60 Rc, you could use 1950°F and 300°F, 2000°F and 400°F, or 2100°F and 500°F. Because the higher austenitizing temperature potentially means more chromium in solution we would expect the 2100°F and 500°F combination to achieve the best corrosion resistance for that hardness. A unique aspect of MagnaCut is that all of its chromium carbide is dissolved around 2050°F, as shown in the chart below. So if instead we were heat treating to ~63 Rc, 2050°F and 300°F, 2150°F and 400°F, and 2200°F and 450°F would all have approximately equal corrosion resistance. So austenitizing above 2050°F still leads to an increase in hardness for a fixed tempering temperature but the corrosion resistance would be unaffected.

There is an important aspect to tempering and corrosion when it comes to a different regime of tempering, however. Stainless steels and other high alloy steels see a bump in hardness by tempering above about 750°F, as shown in the following chart for Elmax:

You can see that the hardness sees a peak with tempering around 500°C (930°F). This increase in hardness comes from precipitation of small chromium, molybdenum, tungsten, and vanadium carbides. Because chromium is coming out of solution as a chromium carbide this “secondary hardening” also leads to a decrease in corrosion resistance. Below shows Vanax steel that I tested with a 1% saltwater spray test for 24 hours where one was tempered at 400°F and the other was tempered at 1000°F. The 400°F temper Vanax showed no corrosion while the 1000°F temper led to significant rusting.

Vanax tempered at 400°F (left) or 1000°F (right) before a 1% saltwater spray test

It is relatively common for knifemakers and knife manufacturers to temper at 950-1000°F. They do this for several reasons, though the main one is that the higher tempering temperature means the steel is less sensitive to overheating. This allows them to apply certain coatings to steel (that require higher temperatures to apply than a typical “low” temper of 400°F). It also means they don’t have to be as careful with grinding because the steel can be heated up much higher before approaching the tempering temperature (where the steel would soften).

The high tempering temperature can be used with many stainless steels to achieve similar levels of hardness as the low tempering temperature. In other words, you can have two knives at 60 Rc, 62 Rc, etc. with very different corrosion resistance depending on whether they tempered in the low range or the high range.

Hardness vs Corrosion Resistance for Different Steels

So after all of that we can return to our discussion of what makes one steel more corrosion resistant than another. Below shows Vanax and Elmax after a 1% saltwater spray test for 72 hours:

The Elmax rusted while the Vanax did not. Both were austenitized at 1975°F which is the recommended temperature for both steels according to their datasheets, and both were given a temper in the low range (400°F). As shown in the earlier chart, the difference in corrosion behavior is primarily due to higher chromium in solution for Vanax, which would roughly be 11.5% for Elmax and 14.5% for Vanax. As seen in the hardness chart, Vanax would actually be a bit harder than Elmax for this identical heat treatment. However, Elmax can be austenitized at higher temperature and achieve significantly higher hardness than Vanax which reaches its maximum around 61 Rc. The reason is because chromium also reduces martensite start and finish temperatures. Vanax has more chromium in solution for a given carbon/nitrogen in solution:

This means that for a given austenitizing temperature, Ms and Mf are lower in Vanax than in Elmax. So as seen below with an austenitizing temperature of 2025°F, the Ms was about 150°C. The Mf is sufficiently low that even with liquid nitrogen not all of the austenite is transforming to martensite, and thus hardness was lower with 2025 than 2000°F. Elmax, however, still has a predicted Ms above 150°C all the way to 2200°F, which is why its hardness increased all the way to 2150°F (the highest temperature I tried).

Thus an approximate relationship is created when comparing different steels to each other for their maximum hardness vs their corrosion resistance:

This trendline is usually correlated with chromium in solution. For example, Vanax and LC200N have >14% chromium in solution, which gives them a very high corrosion rating but also limits their potential hardness. On the other end of the spectrum is ZDP-189, which achieves very high hardness and is advertised as a stainless steel, but I discovered a few years ago that it is not, in fact, stainless. I measured only 8.6% chromium in solution with ZDP-189, which is quite low. D2, for example, I measured at 7.7% with a relatively conventional heat treatment, which is famously called a “semi-stainless” steel.

There are other complicating parts to this trendline, however. It does not always perfectly correlate with chromium in solution. Molybdenum, for example, is an element known to improve pitting resistance and to strengthen the chromium oxide passive film. In tests I did with 1% saltwater there was an improvement in corrosion resistance for a given chromium in solution if the Mo was increased:

CPM-154 with its high molybdenum content (4%) had acceptable corrosion resistance even with only 9.5% chromium in solution. (Note: the “corrosion ratings” in this chart are a rating of how much the samples rusted and not the same as the “corrosion rating” in the hardness trend plot which are from my knife steel ratings).

You may have also noticed that S90V, S125V, M390, and S110V are all above the hardness-corrosion resistance trendline. In other words, they have unexpectedly high maximum hardness for their corrosion rating. These steels all have a very high volume of carbide (>20%). Carbides are very hard particles and when the volume of them is reaching these high levels it can affect the bulk hardness that is measured. You can see that for the following two charts comparing non-stainless tool steels with different amounts of carbide (Vanadis 4 Extra, 10V, and 15V):

So while M390 and 14C28N both have similar Cr in solution (depending on austenitizing temperature), the M390 reaches higher hardness because it has so much more carbide:

M390 has a lot of carbide

14C28N not much carbide

The other steel above the trendline for hardness-corrosion resistance is MagnaCut. It does not have particularly high carbide volume, about the same as Vanadis 4 Extra:

MagnaCut also does not have particularly high chromium in solution, around 11%. Instead, MagnaCut has superior corrosion resistance to those other steels because all of its chromium carbides are dissolved in heat treatment. With typical stainless steels they have many chromium carbides, and the chromium in solution is lower around each carbide:

Thus the chromium carbides act as corrosion initiation sites. This is somewhat similar to the phenomena called “sensitization” in low carbon stainless steels that are cooled too slowly.

Image from [2]

Instead, all of the carbides in MagnaCut are vanadium or niobium carbides (after heat treating). Therefore those corrosion initiation sites are missing and so it has superior corrosion resistance for a given level of chromium in solution.

Comparing Steels vs Comparing Heat Treatments

Perhaps it is the above discussion that confuses some people, and they mix the low potential hardness of Vanax and LC200N with heat treating of other steels and assume that lower hardness means better corrosion resistance. However, as I have discussed, hardness and corrosion resistance don’t really correlate for an individual steel. If anything, higher hardness sometimes correlates with higher corrosion resistance. If you use higher austenitizing temperatures in combination with a fast quench and cryo, and temper at a low temperature, you get maximum corrosion resistance. That is also a recipe for high hardness (as long as the austenitizing temperature isn’t too high). However, tempering can be increased without detriment to corrosion resistance to heat treat to lower hardness levels (as long as the >750°F range is avoided).

Summary and Conclusions

Austenitizing temperature, quench rate, and tempering can all affect corrosion resistance. Austenitizing higher leads to both higher hardness and better corrosion resistance. Beyond a certain temperature cryo is necessary to get higher hardness, and even then there is a temperature beyond which hardness decreases. Quenching too slowly, as happens often in industry, can lead to a reduction in corrosion resistance. Tempering in the high temperature range (>750°F), also relatively common, significantly reduces corrosion resistance. Combinations of heat treating variables can be used to achieve a range of hardness values while maintaining high corrosion resistance. In other words, hardness does not correlate with corrosion resistance for a given steel. However, when comparing different steels to each other, there is a trend where more corrosion resistant steels typically have a lower maximum hardness. Molybdenum alloying, avoiding chromium carbides (such as in MagnaCut), and having a high volume of carbide all lead to higher potential hardness for a given level of corrosion resistance when comparing different steels to each other.

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[1] Binder, W. O., and C. M. Brown. “Atmospheric Corrosion Tests on High-Chromium Steels.” In Proceedings of ASTM, vol. 46, pp. 593-606. 1946.

[2] https://newzelindustries.com/what-is-sensitization-in-austenitic-stainless-steel/

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Video

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Development

In March 2024 Joey Berry of Pop’s Knife Supply called me and said he wanted to develop a new steel. He said that their most popular steel was 80CrV2 and so he wanted to make “80CrV3.” “You mean 80CrV2 but with a little more vanadium?” He said no but some kind of “sequel” to 80CrV2 that would be more exciting. I told him that doesn’t give me much to go off of but I would think about whether I had any good ideas along those lines. I thought about gaps in the market in the area of low alloy knife steels (“Carbon steel”) that would also be usable by the knifemaker that is buying 80CrV2. It occurred to me that our selection of high nickel steels is very limited; 15N20, L6, and 8670 are pretty much it. These steels are high in toughness and offer good hardness to go with it, but have no real wear resistance to speak of. 80CrV2 is in a similar position just without the nickel. I thought if we added some tungsten and vanadium to a high nickel steel we could make the steel more balanced; give it some wear resistance along with the high toughness. Those carbide pinning elements would mean that the steels are more beginner friendly for forge heat treating. 15N20, for example, already sees grain growth around 1500°F (815°C) and so its toughness drops very rapidly even when only slightly overheated. If the tungsten and vanadium were kept in check the forgeability, grindability, and polishability would remain high. This would also offer an alternative to other tungsten/vanadium steels like Blue #1, V-Toku2, Wolfram Special, 1.2519, and others. Those steels don’t have much toughness to speak of, so we could combine the best of the nickel steels with the best of the tungsten/vanadium steels. Another exciting element with the high nickel is the possibility to use the steel in pattern-welded Damascus as a “bright” layer. This gives an option for a higher wear resistance steel with better edge retention for that component of the Damascus. I told Joey about my idea and we decided to move forward with it.

We took the composition I came up with to a steel mill in Europe and they agreed to make it. I spent a bunch of time working on optimal annealing for the somewhat similar 15N20 based on the limitations of their production annealing process. Based on that we generated an annealing procedure to make the steel respond well to forge heat treating.

Composition and Tungsten/Vanadium Carbides

Here is the composition of Pop’s ProCut compared with other grades in its category. The far right column says “MC (%)” which is a calculation of how much total vanadium and tungsten carbide each steel contains after heat treating. One thing you will notice is that since tungsten is a heavy element it does not contribute as much to the MC as you might expect. For example, CruForgeV with 0.75% vanadium has more MC than Wolfram Special which has ~2.25% tungsten. ProCut uses a combination of vanadium and tungsten in a similar fashion to O7 and 1.2519 steels. So it has similar MC to steels like Blue #1, 1.2519/O7, and Wolfram Special, and more MC than Blue #2 and O1. The other nickel nickel steels (15N20, L6, and 8670) of course do not have any MC. These very hard carbides give the steel wear resistance.

Austenitizing, Tempering, and Hardness

A major goal for this grade was to be “easy” to heat treat with a forge. This requires a wide range of austenitizing temperature where full hardness is achieved while avoiding a toughness drop with higher temperatures. 80CrV2 steel varies a lot with starting microstructure, and two of the mills that make the steel lead to very different heat treating response:

So we wanted to avoid this issue that 80CrV2 sees. We did this by keeping the chromium low and also working with the manufacturer to dial in the annealing procedure so that carbides aren’t too coarse (making them difficult to dissolve). I also compared the austenitizing response with my recommended anneal (described later):

You can see that the hardness reaches its maximum around 1475°F and then does not change above that temperature. If using the anneal I recommend the microstructure is a bit finer and so this can be dropped even further to 1375°F. Thus for heat treating in a forge you can heat the steel to “a shade brighter” after reaching nonmagnetic and the steel will fully harden. If you forge and follow the recommending normalizing and annealing procedure you can even quench from nonmagnetic if you wish.

If the steel is austenitized in that range (1475°F or higher) the tempering is roughly the same regardless of the austenitizing temperature. Here are datapoints for both 1550°F and 1625°F:

You can see that the hardness is relatively high, still 64 Rc after tempering at 300°F, which is generally as low as I recommend for tempering most any steel. With a 450°F temper the steel is still above 60 Rc.

Toughness

Austenitizing

In our heat treating and toughness experiments we found three different regions of toughness behavior:

Below 1500°F, the steel shows an increase in toughness with increasing temperature. From 1500-1575°F the toughness is roughly flat. 1625°F and above shows a big jump in toughness where it is flat again up to at least 1675°F. The reason for this behavior we figured out by looking at the microstructure. These images were taken by knifemaker Shawn Houston of Triple B Knives:

1425°F, 400°F temper

1475°F, 400°F temper

1600°F, 400°F temper

You can see that the carbide content is significantly reduced by austenitizing at 1475°F as opposed to 1425°F. This significant change in cementite (iron carbide) raised toughness. Then when the temperature is further increased to 1600°F and above, virtually all of the cementite is gone and all that remains is the small volume of hard vanadium and tungsten carbides. The presence of these small carbides is what prevents grain growth even at high temperatures. The carbides “pin” the grain boundaries.

15N20 and L6, in contrast, show a drop in toughness at much lower temperatures because they do not have those carbides to pin grains. The steel 1.2519 does have the W/V carbides but it sees a drop in toughness above 1500°F because it gets excess carbon in solution, leading to plate martensite. The carbon content in ProCut is controlled so that the matrix carbon does not reach excessive levels even at high temperature. This gives ProCut a very wide austenitizing range.

Tempering and Toughness

Like many other knife steels, ProCut sees a peak in toughness with a tempering temperature of around 450°F (230°C). Above that the toughness drops due to a phenomena called “tempered martensite embrittlement” which happens in all steels. There is lower toughness with tempering at lower temperatures as well, of course, corresponding with the higher hardness. The behavior of toughness with tempering temperature is roughly similar whether using the higher or lower austenitizing temperature range.

Hardness vs Toughness

This creates two different heat treating ranges, where the steel can be austenitized high (1625-1675°F) to max out toughness with some cost to wear resistance and edge retention, or austenitizing lower (1475-1575°F) to retain more carbide for wear resistance. The steel still maintains a toughness advantage vs previous tungsten/vanadium steels due to the nickel addition and controlled carbon content with the lower austenitizing range. However, with the high austenitizing range it achieves levels of toughness similar to 8670, 15N20, and L6 but with enhanced wear resistance due to the small tungsten and vanadium carbides.

To compare with other steels you can look at the following chart:

Grinding and Polishing

I don’t have a quantitative test for grindability. Reports from knifemakers so far say that grinding and polishing is very easy with the steel. Some low alloy steels developed for higher wear resistance like CruForgeV are more difficult to polish due to relatively large vanadium carbides that are found relatively frequently. This steel we controlled the W/V content to try to avoid large carbides. Because of the limitations of standard steelmaking (as opposed to powder metallurgy) there are still very occasional larger carbides but they are much rarer than a steel like CruForgeV. So far those few carbides don’t appear to be affecting polishing and finishing.

A lower magnification image of ProCut showing that large carbides aren’t observed most of the time

One of the rare large carbides in ProCut

A micrograph of CruForgeV showing large carbides. Notice there is a magnfication difference vs the ProCut images.

Quenching, Oil Selection, and Hamon

The “hardenability” of ProCut is relatively high, which I also found in testing of 15N20. The high nickel content gives it this hardenability. Air cooling from 1600°F with 1/8″ steel resulted in 60.7 Rc, though from lower temperatures like 1350°F the hardenability is lower (I measured 35.3 Rc). This means that ProCut can be quenched in virtually any quenching oil, even canola, and with relatively thick cross-sections.

This high hardenability means that ProCut is not well suited for developing a hamon. The best choices for a hamon are low hardenability steels like 1095, W2, and 26C3. I won’t say it is impossible to develop a hamon but there are better choices. It is likely still fine for other differential methods like an edge quench.

Forging, Thermal Cycling

Maximum forging temperatures are most greatly affected by the carbon content. High carbon steels are easier to overheat, leading to crumbling while forging. The carbon content of ProCut is limited to ~0.87% so this is not a huge factor with ProCut. For safety I put in the datasheet to limit forging to 2200°F (1200°C). Some knifemakers, especially Damascus makers, push the boundaries of forging temperatures and this can be dangerous. Like with other steels, if you continue to forge when the steel gets too cold this is also a danger in terms of cracking. I haven’t heard a lot of feedback in this area so let me know how the steel behaves for you. The high hardenability means that the steel can sometimes harden in air while cooling from the forging temperature. This can lead to cracking if there are stress risers in the blade.

The “thermal cycling” procedure for ProCut is relatively simple. Like with other steels I prefer to do a single normalize and anneal, so only two steps. I have written about this procedure in past articles. The normalizing step is for dissolving any undesirable carbides and other structures. For this steel it would be in the range of 1600-1650°F where the cementite is dissolved. With a furnace you can hold at this temperature for 10-15 minutes before air cooling. With a forge by eye you just need to heat somewhere into that range or a bit higher.

The annealing procedure is then done by heating to nonmagnetic and slow cooling. I recommend faster cooling rates than is typical for datasheets and this type of anneal is called a “Fast DET” anneal. For simple heat treatments you can slow cool either in a furnace or in an insulating media like vermiculite (available in the garden section of home improvement stores). I tried a range of cooling rates in my furnace. I held the steel for 30 minutes at 1350°F and slow cooled at different rates to measure the annealed hardness. At 50°F/hr cooling the resulting hardness was 23.9 Rc. After 500°F/hr the hardness was 24.5 Rc. I also tried setting the furnace to 1000°F/hr but it only maintained that cooling rate until about 1250°F and slowed from there, the average rate of cooling was about 680°F/hr. That resulted in 26.2 Rc, which is plenty soft enough. Shawn Houston did an anneal with 250°F/hr and he measured 21.2 Rc. Here is the microstructure after normalizing and annealing at 1350°F for 30 minutes, and cooling at 250°F/hr:

Normalized and “Fast DET” annealed microstructure of ProCut (21.2 Rc)

“As-received” annealed microstructure of ProCut (12 Rc)

You can see that the faster annealing procedure results in a finer microstructure which is why the austenitizing response was different (see the prior as-quenched hardness chart). The toughness was still relatively similar despite the very different starting microstructure (see the toughness vs austenitizing temperature chart). Those datapoints were generated using a 100°F/hr anneal which is what I recommended in the datasheet. Somewhat faster and slower cooling rates would have a similar result.

Use in Damascus

The high nickel content means that ProCut is a good replacement for 15N20 or L6 as a bright layer in pattern-welded Damascus. This gives an option for providing higher edge retention whereas 15N20 and L6 have almost no wear resistance apart from their hardness. An initial forging experiment with 1084 and ProCut resulted in excellent contrast:

Edge Retention

Pop’s ProCut did surprisingly well in the CATRA test. The heat treatments performed were 1650°F with a 450°F temper (61.2 Rc), and 1500°F with a 300°F temper (64 Rc). As I have written about before, CATRA is not the best for low alloy steels because the sand particles in the test media are harder than cementite (iron carbides). Even with different media they wouldn’t be at the top of the chart but they would be a bit better. It could be that the relatively low amount of cementite in ProCut helped for the CATRA test. But even if that were the case if we compare with another steel with low cementite content like 8670 or 1095, there was a significant boost to edge retention through the tungsten and vanadium additions. Perhaps with the lower carbon compared with other W/V steels meant that there was less of tungsten and vanadium found in the cementite, allowing them to form more of the hard WC and VC carbides.

Toughness-Edge Retention Balance

With the high toughness plus the unexpectedly good CATRA numbers the ProCut looks very good compared with other low alloy steel options:

Corrosion Resistance

This is a non-stainless steel and should not be expected to be stainless. People say that the 2% nickel in 15N20 gives it somewhat better corrosion resistance than carbon steels but I have not developed a test for comparing corrosion resistance of low alloy steels.

Cryo

There is a certain lore out there with knifemakers claiming that some steels “need” cryo and other steels “don’t benefit” from cryo. Part of this lore is that low alloy and carbon steels are in the “don’t benefit” category. Simple carbon steels and low alloy steels still see an increase in hardness with cryo, typically 0.5-2 Rc depending on the steel and the heat treatment. There is a small cost to toughness because of the increase in hardness. ProCut is the same. As an example of another low alloy steel we experimented with see 52100. I did experiments from 1500°F and 1650°F and found, as expected, that hardness increased. The higher temperature led to a bigger bump from cyro which is also typical. None of the edge retention or toughness tests I showed in the article so far used cryo in any of the heat treatments. But if you want even higher hardness for edge retention and strength you can add a cryo step after quenching.

Comparisons to Other Steels

1084 and 15N20

These steels are relatively “easy” to heat treat in that you can heat them up and quench them and get full hardness. However, they are very easy to overheat leading to grain growth and a drop in toughness. They also have almost no carbide thus having very little wear resistance.

80CrV2

This steel is also lacking in wear resistance though overheating is not much of an issue because of the vanadium addition. It also varies a lot between manufacturers and needs more temperature prior to quenching making it more difficult to perform a forge heat treatment.

52100

In the lower austenitizing range (for higher wear resistance), ProCut compares favorably with 52100 in terms of properties. 52100 has a very good combination of toughness and wear resistance. ProCut is easier to heat treat for an amateur knifemaker and also has the option of the high toughness heat treatment.

O1 and 1095

These are old standard steels. O1 has the benefit of being “oil hardening” so it is easier to quench. I have found both to be very sensitive to overheating because of excess carbon in solution. See my article on O1.

5160, 8670, and L6

These steels have significant chromium additions so they are more difficult to heat treat in a forge. They also don’t have any carbide left over after heat treating and thus their wear resistance is very low.

Blue #2, Wolfram Special, 1.2519

These steels have similar wear resistance for edge retention but significantly lower toughness and do not have the benefits of being beginner friendly.

ApexUltra

This is another low alloy steel I helped develop. It has significantly higher wear resistance and attainable hardness than ProCut, which also means lower toughness. I would recommend ApexUltra for those looking for maximum performance in the “carbon steel” category. Though I wouldn’t call it a difficult steel, it is best for makers that have a bit of experience first.

Heat Treatment Recommendations

In a Forge

Heat to “one shade brighter” after reaching nonmagnetic, quench in oil (most types are fine), and temper twice for one hour each time at 300-450°F (150-230°C) to desired hardness.

In a Furnace

Maximum toughness: 1650°F (900°C) for 10-15 minutes.

Higher edge retention: 1500°F (815°C) for 10-15 minutes

Quench in oil (most types are fine), and temper twice for one hour each time at 300-450°F (150-230°C) to desired hardness.

Thermal Cycling after Forging

1625-1675°F for 10-15 minutes, air cool. Without a controlled furnace, heat into that rough range and establish an even temperature distribution prior to cooling.

1350°F for 30 minutes, cool at 100°F/hr to 1100°F. After that it can be cooled more rapidly. Without a controlled furnace, heat to nonmagnetic and slow cool such as in vermiculite.

Summary and Conclusions

I am happy with how Pop’s ProCut turned out. It offers good balanced performance when compared with other low alloy non-stainless steels. Better edge retention than 1095, O1, 80CrV2, L6, 15N20, etc. And depending on the heat treatment its toughness approaches 8670, 15N20, and 5160. And on top of this it is beginner friendly, being easy to heat treat, grind, and finish.

The post Pop’s ProCut – A New Carbon Steel for Knives appeared first on Knife Steel Nerds.

Thanks to my Patreon supporters for supporting knife steel research. Patreon supporters saw this interview a couple of days ago. You can see the latest results of my testing early if you join at Patreon.com/KnifeSteelNerds

Video Interview

Transcript

I made some tiny edits for clarity and removed a lot of “um”s and “you know”s and repeated words but otherwise I left the interview alone.

Larrin Thomas:

I’m Larrin. This is Knife Steel Nerds. I have with me Bob Shabala of Niagara Specialty Metals. And we have a lot to talk about in the wake of the Crucible bankruptcy, and a lot of things that are happening right now. So, Bob, could you start out by telling us your position at Niagara and some of the history of Niagara Specialty Metals?

Bob Shabala:

Sure. Yeah, thanks for having me on. I’m the president and CEO of Niagara Specialty Metals. I’ve been here for 31 years. Niagara Specialty Metals started in 1982 by two gentlemen, Barry Hemphill and Lou Valery, primarily as a mill to service the tool steel industry. They bought slabs of steel and hot rolled it into sheet or plate. Quickly, it grew into more of a service company where people would send them material to roll and ship back to them. Then over time, we expanded capabilities to be able to process stainless steels, aerospace alloys, titanium, maraging, and the cutlery grades that are of interest here today.

In 2009, Crucible was our biggest customer. They went bankrupt the first time, and we came to an agreement where they would supply us with all the CPM alloys, and we could market them and sell them to whoever we want.

So from 2009 until present day, they were our sole supplier of PM alloys. They were great to work with, they were very responsive. But we could see the writing on the wall starting last year that things weren’t going well and that they were in trouble. So that’s when we started reaching out to other suppliers to, uh, to get us the steel we need for, for this market.

In addition to that, we have 40 employees. In 2004, Barry Hemphill was the remaining sole owner of the company. He essentially gave it to the employees. He turned it into a 100% ESOP (Employee Stock Ownership Plan). So everybody working here is an owner of the company. So when they retire, we buy the shares back from them, and it’s worked out very well for all the employees that are here. So when it comes time to fill positions, it’s not easy, but it’s easier than most places. And typically, once we get somebody in here working and they understand the value of the ESOP and working for a small employee-owned company, they tend to stay for a long time, which is great. We have very minimal turnover, so we can take our time training somebody because it takes three to five years to train somebody on all the jobs we have here. So the model has worked out very well for us.

Larrin:

So you mentioned PM alloys. That refers to powder metallurgy alloys, or specifically (in this case) steels for the knife industry. And Crucible invented that technology back in the late 60s, early 70s. And so they had a great legacy of making those steels. You know you had other suppliers for regular conventional steels, which are ingot cast, right? And so, powder metallurgy, a lot of the best knife steels are made with powder metallurgy. So anything with a CPM in front of it was powder metallurgy. So many of the best steels like S30V, S35VN, MagnaCut, you know, those are all powder metallurgy. So, Crucible going away is kind of a blow.

Another thing I want to hear about a little bit is the unique capabilities of Niagara. There’s really not any competitors in the USA for what you’re doing, right? What makes it so challenging to hot roll steel for knives?

Bob:

So for our initial rolling operation, we would just call it the plate mill. It’s in a fairly small area compared to most big mills. So we have the unique ability to reheat. So, take a grade like Rex 121 or Rex 76, we might have to reheat those plates every two or three passes. So we’re able to do that, whereas some mills, once you take it out of the furnace, they can only roll it so far and then that’s it. It’s also a hand mill, so we can take anything from 100 pounds up to 3,000 pounds and roll that into a different dimension. When we buy slabs, they start out anywhere from three to six inches thick. So if we’re rolling down to anything less than a half inch, what we do is roll it to an intermediate size. Then we anneal it to soften it back up. We’ll de-scale it to clean the surface, send it down to our sheet mill where we then reheat it again, finish roll it to size, anneal it, flatten, and ship.

I guess people don’t do what we do because the quantities are relatively small. We take on anything from one piece to a truckload, and our ability to deliver on time and relatively quickly is hard to beat. So that’s why we have this small segment of the market kind of, not to ourselves, but, why we’re doing well with this kind of product.

Larrin:

So I know for the steel that I developed, MagnaCut, a major reason why I was able to make it happen is because I got your buy-in early on. Crucible was a bit skeptical of trying a grade that I designed since I had not designed any tool steels or stainless steels before. So I know you guys have had a big commitment to the knife industry. Getting steels from other companies is often challenging because a lot of times, they’re sitting around in several-inch-thick pieces. So I think that’s awesome that Niagara has been so good. And the reason why we have a lot of these awesome grades is because Niagara is able to roll them and deliver them, at a good pace, like you said.

So Crucible, you hear, they’re maybe not doing well. So, what was your approach next? What did you start doing to make sure that we weren’t losing out on everything?

Bob:

Sure. Yeah. So last January, January 24, we started increasing our inventory with Crucible. So we started ordering more than we needed to, to kind of boost the inventory. And then, last fall, just in discussions with Crucible, we knew they were for sale. They had announced that. And I asked the president of the company in my position, should I start looking for other places to buy steel? And he said, yes. So I give him a lot of credit that he didn’t try to hide the fact that they were in a desperate time.

So we already had relationships with Carpenter Technology. We’ve processed millions of pounds for Carpenter and Erasteel for other industrial customers. So we, we reached out to both mills, explained our situation, and they were happy to help. So they both right away started looking into the ability to make MagnaCut. Because that’s our most popular grade right now. Erasteel already makes a version of CPM 154. So we ordered test heat of those grades from both mills. And they’ve been fantastic. You know they basically have delivered when they said they were going to deliver. We know the quality is good. It’s just a matter of ensuring that chemistries from different mills, you know, certs are, they don’t read right or they don’t read exactly the same. There might be some offset between mills. So, before we start releasing anything to the public, we want to make sure that it performs like it should. And we really should have everything ready to go here in the next next quarter or so.

Larrin:

So what you’re talking about is that different mills have different equipment for measuring the composition of the heats. And those pieces of equipment can be calibrated somewhat differently. And so one mill might measure 14% chromium and another might read 14.5% chromium for the same thing. And so if you’re then trying to transition grades over between companies, it might behave slightly differently if they have the same composition target. So we’re trying to work on any offset that might be necessary. Not that there would be a problem with a grade with a slightly different composition, but if all of your customers are used to heat treating at specific temperatures, and then it starts heat treating as if you’re 25 or 50 degrees hotter, you know that could be an issue for them if all the steel’s coming out different.

But the quality is high from Erasteel and Carpenter. They have a good reputation for making powder metallurgy steel.

Bob:

Yeah. Yeah. For years, Carpenter would send us their cutlery alloys in addition to aerospace and tool steel. So I think all of the XHP that’s ever been processed and sold to the market has been rolled here in Niagara Specialty, and we’re now stocking it. They felt that they would have better success or move more XHP if they would just sell us the steel and let us sell it to whoever we want. So that’s starting to take off. We also have their version of S90V, 10V, M4. So, yeah, it rolls really nice. There’s really no issues with it at all.

Larrin:

Well, I know XHP, which is a powder metallurgy stainless steel used in knives, that it has had a reputation for being difficult to obtain or having inconsistent availability. And I do think that’s one thing that Niagara has maybe been the best at is just having steel in the sizes that you want available to buy. When you call up these steel companies and they say, yeah, we can get you XHP, just you need to order many tons of it, and then you need to wait a year, it’s not very enticing. And if you’re a small custom knife maker, then obviously it’s just a total no-go. It’s impossible.

So what about our ability to make new alloys? We’re trying to make a new steel with the same concept of MagnaCut, but with improved wear resistance called MagnaMax. Are we going to be able to make that happen now that Crucible is gone?

Bob:

Yeah. So that’s a grade that, thanks to you, we had a prototype heat or an initial two heats made at Crucible, and the feedback’s been great. So, we patented it with you. We also trademarked it. So that gives us the ability to buy from both mills. And they both are getting ready to make it. So by, I think, the fourth quarter this year, we should have heats from both mills ready to go. As far as future alloys go, it’s something we’ll have to discuss with them. You know, our primary concern right now is getting the grades that we’ve always sold and making sure they test out and we get them locked in. And then we can have discussions with them about making new grades as you develop them.

Larrin:

So I guess we haven’t said explicitly that Erasteel bought the IP of Crucible CPM alloys, so all their powder metallurgy alloys. So that includes trademarks and also patents. Though there’s not very many patents remaining because all of the patents date back to before Crucible’s first bankruptcy in 2009. Is there any chance that Crucible will come back, or are they just Erasteel now?

Bob:

I think they’re just Erasteel. I don’t know all of the particulars of what’s going on inside the Crucible facility, but I just don’t see that getting started back up. In fact, I don’t see any domestic companies getting ready to atomize iron-based alloys that would be used in cutlery. There’s atomizing for nickel alloys and maybe titanium, but, um, iron base, I think, is just such a small portion of the overall steel industry. Nobody’s going to put the kind of money into it that they would be required to, and to bring that back on shore.

Larrin:

Well, that would be very disappointing. Nickel and titanium alloys, they have higher profit margins, which might explain why they prefer to make those, even if they have atomization equipment.

So, are we going to continue to make all these grades? I mean, Crucible had… a ton of grades, S30V, S35VN, S45VN, S90V, (etc.) there are so many. Are we going to be able to keep all of those, or are we going to need to simplify the portfolio?

Bob:

We could, in theory, buy them all. Except for 15V, I think that the atomizing temperature on that is higher than what Carpenter or Erasteel can do in their atomizing furnace. They both have said that they can’t make 15V. So until we come up with an alternative there, I think that grade’s going away. But yeah, everything else we could buy. I mean, I think that once MagnaMax comes out, we will take a look at the existing grades in our portfolio and decide if some should be obsoleted. You know, we tried to bring S6 V back a few years ago. We bought a small heat and half of that heat is still here. That didn’t work out. Sales of 20CV have slowed down. So that might be a potential candidate to not buy anymore. But we still sell a lot of CPM-154, S30V, S35VN, S45VN. So I don’t see any of the major grades going anywhere anytime soon. And they’re all on order. We have all those grades on order with Erasteel at this point.

Larrin:

So, how is branding going to work going forward? Are you going to use the same names, or are some grades going to have different names?

Bob:

Yeah, so anything we buy exclusively from Erasteel will retain the CPM grade name. We’re not going to enforce (the prefix) CPM. So if people want to buy S30V, I think we’ll just be calling it S30V. And that satisfies everybody. CPM CruWear, because of an existing agreement they have with another company, we’re going to have to rebrand that. You know, that’s still a big moving grade for us. They currently make that same composition. They have been making it for years. So we’re going to buy that, and it would just be rebranded NSMWear, unless somebody can give me a better name. S90V is not a real big grade for us. And we have a lot of that in stock from Carpenter that we bought during COVID as a way to let Crucible focus on cutlery grades. We had placed orders for industrial grades with Carpenter. So their name for that is CTS 420CW MOD.

Larrin:

And that is not a good name.

Bob:

And I don’t see anybody putting that on a knife blade. So I think we’re going to rebrand that as NSM90 and just try to make sure everybody understands it’s the exact same composition, or virtually the same exact composition, as CPM S90V. So those two grades we’re going to rebrand and see how it goes. And that gives us the ability then to buy from both mills and be single source like we were with Crucible.

Larrin:

So we’re going to have continued availability. Niagara, they’re a great American company specialized in rolling these difficult grades to thin sizes that we need for knives. Everything is in motion to continue. Is there a chance that there is a gap in availability, or is it going to be a smooth transition?

Bob:

Yeah, there’s going to be some disruptions, almost certainly. I think once people found out that Crucible is going out of business, there’s some panic buying. So hopefully everybody has what they need for the next five or six months, but everything except for a CPM-154, MagnaCut, we still have plenty of stock to get us through for the next several months. It’s just a matter of getting in these initial heats, getting them approved. And once that happens, it’s full speed ahead. So I think that the next quarter or so, there are going to be disruptions almost certainly. But once approved, I think that Erasteel and Carpenter both are really looking forward to participating in this in a meaningful way. And they’re here to support us and the whole knife community.

Larrin:

Well, that’s great. I am biased, but I think Niagara is an awesome company and a major reason why we have so many knife steels available in a good range of sizes.

Bob:

Thank you.

Larrin:

So I’m happy things are continuing. I’ve gotten messages from a bunch of knife companies that are freaking out, worried that stuff isn’t going to be available anymore. I keep telling them that Niagara is going to keep stuff going and not to worry.

So hopefully we can quell some of those fears. Supply is going to continue. I think people didn’t always realize that, yes, like Crucible was making the powder and sending slabs to Niagara, but Niagara is the company processing all this steel and selling it all. So hopefully we can get the word out that Niagara is a great company that is delivering all these steels, and Niagara is still here and Niagara is doing well and continuing to make these steels.

Bob:

Yeah, we’re financially very sound. You know, the people we have working here, they’re awesome. I mean, they really make it happen. You know when we have something important, like a new heat of MagnaCut coming in from Erasteel and we need to get it approved, they’re right on it. Literally unloading it from the truck and putting it on the saw and cutting it into blocks to get it rolled the next day. So they really are invested in (the) success of the company and the industry as a whole. So yeah, we’re here for the long haul.

Larrin:

And Niagara’s made some upgrades in recent years, right?

Bob:

Yeah. We did our biggest project ever last year. It’s still in process, but for us it was big. I mean, it is about a $7 million investment. So we added about 15,000 square feet to our sheet mill building. And then we had six small electric box furnaces that they did the job for several years, but the heat in them could be uneven. The elements were delicate and expensive to replace. And it was a bottleneck. The guys could work faster than the furnaces. So lots of times they’re just waiting for the steel to heat up. So once we got the building built, we put in a continuous gas furnace. So now the sheets are in the furnace for 25 to 35 minutes instead of three hours. And the temperature on the blanks is really uniform from front to back and side to side. So the gauge coming off our mill is much more even and easier to control. The surface is a lot cleaner. There’s no scale because it’s not in the furnace as long.

And then the last step of the process is going to be a new housing for the rolling mill itself. So the housing is essentially the structure that holds the rolls and the rolls are, rotating and feeding; that’s where the steel goes through to get reduced. The new housings are complete, but we’re not ready to put them in here yet. We need another month to get all the wiring in place and control panels. So around Labor Day, we’re going to install that. So there we’re going to increase our separating force. There’s going to be some machine learning on it so we can put in recipes. Right now, we just turn the dial and get it to where we think it needs to be, and then we have to check the gauge. So in the end, once that comes in, with the much stronger housing, it should be higher throughput, even more uniform gauge from piece to piece.

So that was a real big investment for us. In addition, we’re getting ready to put on another, I think about 12,000 square foot building for our grinding operation. We have a Blanchard grinder for grinding our sheets to size that’s starting to get a bit of a bottleneck. So we already bought another Blanchard grinder, 84 inch diameter that’s in storage until the building gets built.

We have a fiber optic laser that we can cut up to about 3/8 of an inch and we use high-pressure nitrogen in that. So we cut a lot of knife blanks for the industry now. And that’s starting to get busier. So we cut for small shops that give us a DXF file, we can cut their blanks for them. And (that) saves them shipping whole sheets to a laser shop and then taking the blanks to their place. So kind of a one-stop shop here. So with that filling up, we want to get another laser to put in the new area. And then outside of the cutlery industry, we do a lot of bandsaw cutting. So we roll a lot of big heavy plate, or people send us their plates, and we saw cut it into either small rectangular shapes or strips or full-size plate. So over the past couple years, we’ve spent two to three million dollars in in bandsaws just upgrading our cutting capabilities.

Larrin Thomas

Wow, on bandsaws.

Bob

Yeah. There we have two of them now, they’ll cut in two directions. So all of our bandsaws to date either just cut along the length of a plate or across the end. These two axis ones, we can cut the ends first, then the head goes back, and then it’ll just strip it out. So just put the plate on there one time and you’re done, essentially let the machine do the work. So it just makes it easier to get accurate cuts. The guys like it cause it’s safer, a lot less handling moving plates around. So, yeah, that’s been a big part of our business.

Larrin

Well, thanks, Bob. Hopefully, we answered people’s questions and didn’t just add to the confusion. So we’ll have to bring you back on if we get a lot more questions based on the interview. But thanks for joining me and talking about Niagara and the whole plan for keeping knife steel going.

Bob

All right, anytime. Thanks, Larrin. I appreciate it.

The post The Future of Knife Steel with Bob Shabala of Niagara Specialty Metals appeared first on Knife Steel Nerds.

Still working on getting an update to everyone about the status of knife steel after Crucible’s bankruptcy and the sale of many of the assets to Erasteel. Still more i’s to dot and t’s to cross.

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Video

Here is the video version of the following information:

History of CPM-3V

The thing most don’t know about CPM-3V is that it is a powder metallurgy version of an older conventional steel called Vasco Die. Vasco Die was patented by Harry Johnstin of VASCO in 1964 [1]. This was the first popular “8% Cr die steel” which created a new category. The most popular cold work die steels were (and are) A2 and D2. D2 is used for higher wear resistance and A2 is used for higher toughness. The 8% Cr is right in the middle between D2 (12%) and A2 (5%). And with the 2.5% vanadium for wear resistance and the relatively low carbon of 0.8% it has an interesting combination of properties, better overall than either A2 or D2. The steel was advertised as twice as tough as D2 while have ten times the wear resistance of A2. This created a new category of cold work die steel which is still seen today in steels like DC53 and Sleipner. You can read more about the history of Vasco Die and all of the developments that led up to it in my book The Story of Knife Steel. Vasco Die was never really used in knives, though the higher carbon version, Vasco Wear, did get used by some knifemakers, and by Gerber in some production knives. And of course CPM CruWear, the PM version of Vasco Wear, has also developed some popularity in recent years.

In the mid-1990s, Kenneth Pinnow and William Stasko of Crucible were looking to make a high toughness powder metallurgy tool steel. Up until that point, powder metallurgy steels had focused on high hardness high speed steels and creating new steels with higher wear resistance than was possible with conventional steelmaking like CPM-10V. Crucible’s highest toughness PM steel was CPM-M4 and that was basically an accident. Uddeholm had released Vanadis 4 in the late 1980’s to be a more balanced steel and its toughness didn’t even match CPM-M4. Uddeholm would later redesign this steel and call it Vanadis 4 Extra. Pinnow and Stasko realized they needed a steel with lower carbide volume. Powder metallurgy leads to higher toughness because it keeps the carbide size small, but to achieve the highest levels of toughness they needed to have less overall carbide. They experimented with a few compositions and found that a PM version of Vasco Die had excellent toughness and wear resistance.

It is somewhat surprising to me that they managed to patent this steel in 1997 [2] since Vasco Die had already previously been patented (though the patent had expired). It seems their claim was that the powder metallurgy process significantly changed the steel, and in more ways than just making the carbides smaller. With conventional casting of steel there is significant segregation of elements, and this led to relatively large chromium carbides which couldn’t be dissolved in Vasco Die. With powder metallurgy, the heat treated microstructure is free from chromium carbide and has only vanadium carbide instead.

Images from 3V patent showing CPM-3V (Fig. 1) and Vasco Die (Fig. 2). The larger carbides labeled “C” are chromium carbides. 3V is only small vanadium carbides.

CPM-3V became Crucible’s go-to steel for applications requiring high toughness; they released it around 1999. Surprisingly this steel didn’t really take off in knives. And I would argue it never really has. Jerry Hossom was the first custom knifemaker I noticed using it regularly. In more recent years perhaps the best known user of the steel is Nathan Carothers with his “Delta” heat treatment. I don’t mean to suggest no one is using 3V, I see currently available knives from a range of manufacturers including Bark River, ESEE, Cold Steel, and others, but it never seems like there are as many 3V knives as there could be. I think it being non-stainless has held it back as knife manufacturers tend to stick with stainless steels.

Heat Treating and Hardness

I did a new set of heat treating coupons for CPM-3V as I wanted to go a bit higher on austenitizing temperature than coupons I had done for the book Knife Engineering. The hold time at 1850°F was 45 minutes, 1950°F was 30 minutes, 2050°F was 20 minutes, and 2150°F was 10 minutes. While CPM-3V is typically heat treated in the 58-62 Rc range because of its excellent toughness, it can be heat treated to higher hardness if desired. This is significantly higher than the 61 Rc the datasheet shows the steel maxing out at. This is because I used the low temper range (300-500°F), rather than the datasheet recommended high temper range (1000-1050°F).

Microstructure

CPM-3V has about 5% vanadium carbide, and is free of chromium carbide despite the relatively high chromium content. This is in contrast to Z-Tuff which has about 3% chromium carbide and only 1% vanadium carbide. CPM-1V also has about 1% vanadium carbide but about 2% M6C (molybdenum/tungsten carbides found in high speed steels). So 3V has only a bit higher carbide volume than those two steels but it is all the hard vanadium carbide type which should mean more balanced properties.

3V (1925°F) – 5% carbide volume

Z-Tuff (1925°F) = 4% carbide volume

CPM-1V (2050°F) – 3% carbide volume

Toughness

One mystery about CPM-3V toughness comes from a patented Crucible steel that was never released commercially, a modified version of 3V. The steel was patented in 2006 by Alojz Kajinin and Andrzej Wojciesczynski. I actually wrote about this modified steel in my very first article on Knife Steel Nerds in February 2018. I didn’t even advertise the article because it was a test before I wrote a series on austenitizing that I did promote with the announcement of the website. The modified 3V was designed by partially replacing vanadium with niobium, which made the carbides smaller. They showed experiments in the patent that the longitudinal toughness of 3V was much higher than the transverse toughness. With transverse toughness the crack grows along the rolling direction, and carbides and impurities are aligned along the rolling direction giving easier paths for crack growth. However, with the modified 3V they found the transverse toughness to be roughly equal to the longitudinal toughness.

So for a new experiment on CPM-3V I decided to test both the longitudinal and transverse toughness and see if the transverse toughness was really as bad as it was shown in the 3V mod patent. I used an austenitizing temperature of 2000°F, plate quench, cryo, and a temper at 400°F. This resulted in about 61.5 Rc, which is significantly higher in hardness than our original 3V toughness tests. Those coupons were heat treated by Warren Krywko who heat treated a whole bunch of toughness coupons that I tested early on. I think maybe the cooling rate in quenching he was performing was somewhat slower than what I did, maybe because he was doing many specimens at the same time in the plate quench. That is significant because a slower cooling rate leads to both lower hardness and lower toughness, as I wrote about in last month’s article. All of the coupons we heat treated were tempered at 400°F rather than the 1000°F temper the datasheet recommends, because of our earlier findings with CPM-CruWear/Z-Wear.

Comparing the hardness-toughness to the previous CPM-3V tests I found significantly better properties. The transverse toughness I measured was only ~7% worse than the longitudinal, which is quite impressive. The transverse toughness reported in the 3V mod patent looks like an anomaly, I have never seen such a large difference between longitudinal and transverse toughness. Though I have to say, the very small drop between longitudinal and transverse toughness I measured here is quite impressive.

With the improved toughness measurements 3V nearly rivals the results of Z-Tuff and CPM-1V which both have lower carbon and vanadium. This actually does make some sense, as the carbide volume is similar between the three steels. To me the composition designs of Z-Tuff and CPM-1V are not totally optimal because they have a significant amount of non-vanadium carbides. The best toughness-wear resistance balance is generally achieved by having all vanadium carbides. Perhaps in the future we could explore higher hardness heat treatments like in the 62-64 Rc range.

Wear Resistance and Edge Retention

I tested the CATRA edge retention of 3V way back in my giant CATRA study. It did exceptionally well for its level of toughness at 463 mm cardstock cut, significantly higher than CPM-1V and CD1/Z-Tuff. Looking back I do think the heat treatment used was cheating a bit, as the tempering temperature was only 300°F. If the tempering temperature was a more appropriate 400°F, the austenitizing temperature for the same hardness would be higher and thus there would be a bit less carbide in the steel. However, this would only marginally affect the final result.

Edge Retention-Toughness Balance

The combination of wear resistance and toughness of 3V is quite impressive. I added a new datapoint for 3V with its newly higher toughness test. I had to adjust up the CATRA edge retention based on the predicted change with hardness for the chart since the CATRA knife was 1.4 Rc lower than the toughness coupon. CPM-3V is really in a class of its own for the level of toughness it has for the level of edge retention. Of course it doesn’t do anything too crazy when it comes to edge retention, but it is sufficient for many knives and has excellent toughness to go with it.

Corrosion Resistance

I have never tested the corrosion resistance of CPM-3V. With its 7.5% Cr and no chromium carbide its corrosion resistance can be quite good for a non-stainless. Some people talk about “semi-stainless” steels and if any steel were to fit in this category it would be 3V. It actually has more chromium in solution than D2, which is perhaps the best known “semi-stainless” steel. Z-Tuff and CD#1 also have a similar chromium content but because they have some chromium carbide in the heat treated condition we would expect 3V to have somewhat better corrosion resistance. In a corrosion test performed by Scott Larimore and Kelly W., CPM-3V was found to survive “in the elements” without rust. However, this was only the case with the low temper condition (<750°F) but not the high temper condition (>750°F). This is expected, though the stark difference never fails to surprise me. The low temper condition is labeled “3VL” and the high temper condition is labeled “3VH.”

Corrosion test by Scott Larimore and Kelly W.

Summary and Conclusions

I think CPM-3V has an excellent set of properties with very high toughness and decent wear resistance and edge retention for that level of toughness. With the 7.5% Cr and lack of chromium carbides its level of corrosion resistance is also quite good for a non-stainless steel. I don’t see anyone out there criticizing the steel, but somehow it seems to never quite get the recognition and popularity it probably deserves.

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[1] Johnstin, Harry G. “Alloy steels and articles thereof.” U.S. Patent 3,219,442, issued November 23, 1965.

[2] Pinnow, Kenneth E., and William Stasko. “Wear resistant, powder metallurgy cold work tool steel articles having high impact toughness and a method for producing the same.” U.S. Patent 5,830,287, issued November 3, 1998.

The post CPM-3V – Still the Best High Toughness Steel appeared first on Knife Steel Nerds.

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Video

Here is the video version of the following information:

Heat Treating Steps and Equipment Types

There are three major steps of heat treating performed by a custom knifemaker or a factory, and an optional fourth:

1. Austenitizing – heating the steel up hot and soaking
2. Quenching – Rapidly cooling the steel
3. Tempering – reheating the steel to a lower temperature such as 400°F (200°C) for 1-2 hours. This is typically performed 2-3 times (cooled to room temperature in between).
4. Cryogenic or cold processing is an optional step that can be performed after the quench or in between tempering steps. It involves cooling the steel to as low a temperature as possible.

Fundamentally these steps can be performed with a wide range of equipment, and that equipment can have an effect on the results. Below I have written about some of the basic equipment setups.

Austenitizing

The austenitizing step is performed somewhere between 1450 and 2250°F (785-1230°C), so this is not happening in a kitchen oven. The biggest difference between small batch heat treating done by an individual knifemaker and a factory is the size of the furnace. Knifemakers will use a benchtop unit such as those made by EvenHeat or Paragon. Therefore the number of knives that are in the furnace at once is much greater in a factory furnace. There are pros and cons to both situations apart from just the number of knives that are heat treated at once. A furnace is not perfectly evenly heated, it is going to be slightly colder at the door, for example, and there will be some thermal “gradient” and relatively hot and cold spots. Typically there is a “control” thermocouple that measures the temperature and the furnace is constantly adjusting to hit the target temperature. If you are heat treating one knife at a time that is directly next to the thermocouple you can be sure the temperature the knife sees is very close to what the thermocouple is measuring. With a loaded up furnace there will be some variation in temperature. That could be only a few degrees or in extreme situations there could be a 20-30°F+ difference between blades in the center of a furnace vs the “corners.”

Custom knifemakers do not always use furnaces. It is relatively common for knifemakers to use a forge which is relatively uncontrolled and the goal is to pull the blade after it is heated into the right range. Some knifemakers will try to hold a specific temperature within the forge or improve the uniformity of the forge by using a “baffle,” also called a “muffle.” This can be as simple as a large piece of pipe. And less common, though still done by some, is to use a torch to heat the edge or the entire blade. Again, this is relatively uncontrolled compared with a furnace.

Quenching

Quenching also varies quite a bit. Steels are rated by “hardenability” in terms of how fast they need to be quenched. The general categories are “air hardening,” “oil hardening,” and “water hardening.” An air hardening steel can be quenched with pressurized gas or even just in still air. Oil hardening knives are quenched in oil, and water hardening steels are quenched in water. Factory knives tend to use air hardening steels, in part because they are better suited to large batch heat treating, and in part because all stainless steels are air hardening. With custom knives, “plate quenching” has become popular in the past couple decades. Plate quenching involves placing the steel between two plates (usually aluminum) and the plates draw heat out of the blade. This is faster than sitting in air and also helps maintain flatness during quenching. The most common quenching method for factories is a pressurized nitrogen gas quench. The pressure of the gas is typically rated in “bars” where a “1 bar” quench would be atmospheric pressure, and 2 bars would be double atmospheric pressure. The higher the pressure, the faster the quench. However, this is not the only factor that matters. How “loaded up” the furnace is will also dictate the quench rate. If many blades are stacked with each other, that increases the volume of each and thus it takes longer to cool it down. You can easily imagine how a 4 inch thick block of steel takes longer to cool than a 1/8″ thick blade. And if a relatively small number of blades are in the furnace, and they are well separated, that will mean a faster quench rate even with the same pressure quench. The heat treaters usually want to load up the furnace as much as possible for efficiency. Here is a random YouTube video that shows vacuum furnaces:

Slower quenching means that hardness and toughness is reduced. Below shows a published study [1] on M2 high speed steel tested with 2 bar, 6 bar, and 9 bar quenching in a vacuum furnace. They tested the hardness and also toughness with a bend fracture test. With higher quench pressure, both properties were improved. With slow cooling, carbides are precipitated at the grain boundaries. This depletes carbon from the matrix, reducing hardness. And those precipitated carbides are brittle and reduce toughness, especially since they are present on grain boundaries.

Data adapted from [1]

In a study on Uddeholm Dievar tool steel [2] they compared toughness between air cooling and oil quenching. They found the same 48 Rc hardness with both conditions but the oil quenched steel had 25% better toughness. They took micrographs of both conditions, and you can see the grain boundaries in the air cooled steel. The dark grain boundaries are visible because of the carbides formed along those boundaries.

Image from [2]

Vacuum furnaces are not the only method used by production knife facilities but are by far the most common. One counterexample is Paul Bos heat treating, which is located at Buck Knives and also performs all of the heat treating for Buck. See the video below. They use a conveyer belt furnace and the steel comes out the other side and cools in air. This type of cooling is generally faster than a pressure quench in a vacuum furnace because of how much time it takes to cool down a fully loaded vacuum furnace.

Tempering

Tempering has similarities to austenitizing in that we are heating to some temperature and holding there. The main difference is that tempering is from a much lower temperature, typically in the range of 300-1050°F (150-565°C). This means that it can be performed in less specialized equipment. Many custom knifemakers will use a kitchen oven or toaster oven.

Cold or Cryogenic Processing

Cryo processing generally involves the use of liquid nitrogen. This can be simple, like dipping a knife into a liquid nitrogen Dewar, to fancier setups that spray liquid nitrogen, or cool down a refrigeration unit with liquid nitrogen. There are also refrigeration units that can get very cold without liquid nitrogen, though are generally at a somewhat higher temperature. Liquid nitrogen is about -320°F (-196°C). Dry ice is also relatively common for subzero temperatures, it is about -109°F (-78°C). I have also tested the use of household freezers, which are in the range of 10°F to -15°F (-12 to -25°C). This is not as effective since it isn’t as cold, though it can still effect the transformation of steel.

Measured Properties Comparing Commercial and Custom Heat Treating

Below I have collected several examples of measured properties between commercial heat treating and small shop heat treatments. This type of data is not widely available so hopefully it is enlightening.

Hardness

The final hardness of the steel comes from several factors. Austenitizing from a hotter temperature, or tempering from a lower temperature, usually means higher hardness. Cold or cryo processing can increase the hardness another 0.5-3 Rc depending on different factors. However, even with the same austenitizing, tempering, and cryo setup, the quench rate will affect the final hardness. This is one of the biggest differences between typical factory and typical custom heat treating.

For the MagnaCut datasheet I measured hardness for a whole range of austenitizing and tempering combinations with “plate quenching” with no cryo, a household freezer, and liquid nitrogen. We also sent steel to Peters Heat Treating, which has typical factory vacuum furnaces that use a pressurized gas quench. They tested with a “2 bar” nitrogen gas quench. You can see that the hardness after the pressurized gas quench by Peters (bottom) is typically 0.5-1 Rc lower than when I plate quenched individual pieces.

Different steels can be more or less sensitive to these differences. MagnaCut has 2% Mo in it which increases its hardenability (thus it is less sensitive to quench rate). However, AEB-L has no Mo and thus it can benefit more from a fast quench. Of course an oil hardening steel would be very soft even with a high pressure quench in a vacuum furnace. For air hardening steels I have heard reports of up to 2 Rc difference between a plate quench and a 2-bar gas quench in a vacuum furnace.

Of course with oil hardening steels they require an oil quench. This is more difficult to do in large batches than air hardening steels. However, factories that are setup for oil quenching will have a relatively similar quench rate to a custom knifemaker. Both are quenching in oil so there isn’t much difference.

Toughness 

I have toughness data for vacuum furnace heat treating of MagnaCut from three different heat treaters that use vacuum furnaces, which I have compared against my own experiments with plate quenching.

The “2-bar” and “Unknown pressure” heat treaters were targeting the same hardness with the same temperatures. I am not sure the reason for the discrepancy in hardness. For toughness, both are a similar offset below the “Plate Quench” numbers because of the slower quench speed. Presumably they had a similar quench rate. The slower quench rate led to a reduction in toughness for a given hardness. The faster 10-bar quench also used a higher austenitizing temperature and a higher target hardness, so the faster quench is not the only reason for higher hardness. However, for a given hardness this heat treatment was closer in toughness to the “custom” heat treatment using a relatively rapid plate quench.

Carbon and Low Alloy Steels

Below are results from heat treating of 52100 with a heat treatment performed by knifemaker Warren Krywko and also two heat treatment facilities that can do oil quenched blades:

The austenitizing temperatures and quench rate were similar in the case of 52100 since all were quenching in oil. Therefore the hardness and toughness was similar whether it was done in a small shop or by a commercial heat treatment company.

Forging and Thermal Cycling by Custom Knifemakers

One way that custom knifemakers will try to make their heat treatments better than factory knives is in forging and thermal cycling of their blades prior to the steps we outlined above (austenitizing, quenching, and tempering). While knifemakers typically will claim that forging, and especially thermal cycling, is for the purpose of refining the grain size, instead the biggest differences are from affecting the carbide structure prior to austenitizing. The steel manufacturers typically want the steel to be as soft as possible for easy machining and grinding by the end customer. The very soft steel is achieved by having a relatively coarse annealed microstructure. If instead the carbides are smaller and the steel is a bit harder in the annealed condition, then the hardness-toughness balance can be improved somewhat. By modifying the normalizing and annealing process (called “thermal cycling” by knifemakers) you can achieve these results. Click here for an article about normalizing and annealing. This thermal cycling could likely be replicated to some extent even in a factory setting, but typically the time, logistics, and cost make this less feasible when hundreds or thousands of blades are being produced. Below I have the same 52100 chart as before but this time I added in results from 52100 that was forged and thermal cycled by my father Devin Thomas. To be clear, it was the modification to the carbide structure through a different normalizing and annealing process that led to the change in properties, not the forging. You can read about the process that was followed in this article on 52100.

Some steel manufacturers will have a coarser starting structure than others, leading to differences in how the steel responds to heat treatment. In my study on 80CrV2, I found that one steel manufacturer’s steel needed significantly higher temperatures than the others to achieve the same hardness. Notice how the “Buderus” material is softer than the steel labeled “Jantz” or “AKS” which were also heat treated as-received from the manufacturer. The “KSN cycling” used my own recommended normalizing and annealing. The cycling procedure I performed did not start with forged steel, showing that the improved microstructure can be achieved without forging.

We found that this result lined up with the starting microstructure:

Buderus-annealed 80CrV2

Jantz-Supplied 80CrV2

80CrV2 with “KSN cycling”

The smaller carbide size also led to improved toughness for a given hardness with 80CrV2. Notice that toughness was similar for each condition but at higher hardness when the starting carbide size was smaller:

Forging and Annealing Stainless Steels

While “thermal cycling” is much, much more common with simple carbon and low alloy steels, there are improvements to be had even with stainless steels by refining the carbide structure. Below are results for AEB-L and MagnaCut:

You can see that in both cases we had relatively small improvements to the hardness-toughness balance by improving the annealing process that was used for those two stainless steels. You can read about how those were optimized in this article on forging and annealing stainless steels.

When Custom Heat Treatments are Worse

In many cases the difference is pretty small between a “basic” heat treatment and one with more involved thermal cycling. Usually with more complex and “dialed-in” heat treatments the potential improvements are small, on the order of 10-20%. When I refer to a “dialed-in” heat treatment I am also referring to other aspects like optimizing austenitizing and tempering temperatures. I have many articles on my website for various steels, such as when I found that CPM-CruWear has better toughness with a low temperature temper of 400°F/200°C despite the fact that the datasheet recommends the high temperature range (~1000°F/540°C) instead. However, these types of temperature optimizations can be (and sometimes are) done by either factories or by individual custom knifemakers.

When using complex or “fancy” heat treatments, the chance of making the steel worse is usually greater than the chances of making it better. I think every buyer should be skeptical of knifemakers that are claiming their heat treatments are significantly better; without quantitative, controlled testing methods the knifemaker is unlikely to know whether an improvement has been achieved. I have heard many knifemakers claim improvements based on changes they made that basically have no chance of improving anything. And some of those modifications are actually making it worse. For Knife Steel Nerds I have tested heat treatment changes I was sure would improve the steel, but instead found worse properties. For example, I did a rapid triple quench heat treatment of 1084 using salt pots. The hardness ended up the same, but I was shocked to see that the toughness had been significantly reduced, especially since the grain size was small in all three tested conditions. The normal furnace heat treatment is labeled “Furnace in air,” the short salt pot heat treatment is labeled “Salt pot, 3 mins,” and the triple quench is the same label with “(x3)” added. In this case the best result was with the basic and boring heat treatment.

But the above examples I have given on improved (or worsened) custom heat treatments all assume furnace heat treating with well controlled temperatures. There is a much more common and pernicious form of custom heat treating which is largely accepted in custom knifemaker circles: forge heat treating. The biggest problem with forge heat treating is that the temperatures are not well controlled. Typically the knifemaker does not even know for sure what the temperature is. There are some methods, like using a magnet, that are used to try to be more consistent, but none are as good as using a furnace with well controlled temperatures. Some steels are more sensitive than others, and some methods are better at being consistent, but none are perfect. Knifemaker/metallurgist Juha Pertulla did an experiment with forge heat treating of 1075 steel where he found that holding the steel for only one second beyond reaching nonmagnetic had already led to increased grain size and reduced toughness. Using 80CrV2 with its vanadium addition made the steel less sensitive to overheating. In my own experiments with forge heat treating I also found 1084 steel (similar to 1075) to be sensitive to overheating:

I have had multiple knifemakers argue with me that I am wrong about the unreliability of forge heat treating. Three of them have sent me steel they heat treated to show me how their forge heat treatments are consistently high in performance. Every case I have tested so far has resulted in poor toughness from overheating. Here is one example:

When Custom and Factory Heat Treating is the Same

Many custom knifemakers do not perform their own heat treating and instead send to commercial heat treaters. This can be for a variety of reasons, but three common scenarios are: 1) the knifemaker doesn’t have the cash for investing in heat treating equipment, 2) the knifemaker doesn’t trust himself to learn how to properly heat treat and/or trusts the commercial heat treater more, or 3) the knifemaker works at a high enough volume that a commercial heat treater makes more sense. In these cases there is unlikely to be much difference between the heat treatment performed on the knives for an individual knifemaker and those performed on “factory” knives. Of course, the lines are sometimes blurred between “custom” and “factory” knives where knifemakers may outsource many steps beyond heat treating. There isn’t anything inherently wrong with this it just means we can’t always neatly categorize things.

Edge Retention

Many years ago I analyzed a set of CATRA edge retention data from a major knife manufacturer and wrote two articles about it: Part 1 and Part 2. Later I obtained my own CATRA tester and did a large set of tests on a wide range of steels. I have had some knife enthusiasts argue that because I was performing my own custom heat treatments that my tests should not be accepted out of hand. Usually this is because they think a steel over- or under-performed relative to where they had already decided this steel should be on the chart. To study this I compared a range of steels that I had tested to the knife manufacturer’s dataset:

The relative position of each steel was basically the same whether it was my tests with “custom” heat treatments or the knife manufacturer with “factory” heat treatments. However, you will notice that my results were consistently somewhat higher than the knife manufacturer, averaging about 17% better. This is not because my heat treating was superior, but rather due to differences in the design of the blades, the edge geometry, and how the blades were sharpened. The “behind the edge” thickness was greater with the production-made test knives. Also, the knives that I tested were sharpened with an Edge Pro which keeps the edges very “triangular” without rounding. The factory sharpened knife edges instead have a more convex shape, which makes them behave more like an edge sharpened to a more obtuse angle. The factory knives were given a polishing step at the end of sharpening. My knives were sharpened to 400 grit, relatively coarse, which gives the steels enhanced slicing edge retention. I have tested the effect of edge finish on CATRA edge retention in the past:

Another clue is seen when we plot the percent difference between my “custom” knives and their factory knives vs the total CATRA edge retention:

If we ignore Maxamet, the percent difference is greater with lower edge retention steels. I promise I do not have secret heat treatments that can make 55 Rc 420 steel cut 50% longer. Instead it was because of the differences in sharpening and edge geometry. With the low wear resistance of 420, how much cardstock it cut was largely controlled by its cutting ability (sharpness and edge geometry) rather than its wear resistance.

To illustrate just how important the edge geometry is, here is a chart showing the effect of total edge angle vs CATRA edge retention:

You can see that AUS-6 with a 27 degree edge (13.5 degrees per side) cut about 400 mm of cardstock. This matched the performance of the significantly more wear resistant CPM-154 with a 34 degree edge, which is only 3.5 degrees per side greater. And that same 400 mm is measured with the very wear resistant S110V with an edge angle of about 41 degrees. If CPM-154 is given a 27 degree edge instead, it matches Maxamet with a 41 degree edge! So small differences in sharpening can make a big difference in the result of an edge retention test.

Custom knives are often given thinner edges than factory-made knives. In general, when superior edge retention performance is measured with custom knives, it is due to better edge geometry rather than any kind of super, unmatchable heat treatment. When a custom heat treatment does perform better with identical edge geometry and steel it can usually be attributed to higher hardness. In my own CATRA experiments, the effect of hardness is greater than other changes to the heat treatment. This is in contrast with toughness measurements where I often find significant differences when changing heat treatment variables.

Seattle Ultrasonics Kitchen Knife CATRA Study

For one more dataset that shows the importance of edge geometry I can show the “Quantified Knife Project” of Seattle Ultrasonics. I performed the CATRA tests for this project. We measured the cutting performance of a range of low- to high-end factory knives and one custom made knife. For the initial cutting ability (how much cardstock cut in the first back and forth strokes), the only difference in performance was edge geometry and sharpening. In this case the correlation with edge angle is very strong as we would expect:

However, even when we plot edge angle vs CATRA edge retention, we find overall the trend with edge angle is still very strong:

For the majority of the knives, the strong effect of edge geometry completely washes out any potential analysis for the effect of steel type and heat treatment. This is despite the fact that there is a wide range of steel from 56 Rc low wear resistance stainless steels (1.4116) in many of the European knives to ~60 Rc VG10 in many of the Japanese knives. The main exception to the trend are those values at ~820 and ~1050 mm. Those are for the steel advertised as “FC61” steel which is a proprietary name. I have seen speculation that the FC61 is similar to AEB-L or 13C26 (relatively low wear resistance), but this very high performance would seem to point towards it being something more wear resistant. However, not many of the knives were below 20 degrees so there aren’t many other comparisons.

Another specific knife I want to point out is the custom Moritaka knife, the only custom knife that we tested. It was one of the best performers at ~650 mm. This was in Blue Super steel which in my testing with a 30 degree angle was only at 338 mm. So the superior results for this custom knife were not from a super heat treatment or magical forging but instead from a smaller edge angle. Of course it should be noted that the very low edge angle also makes this edge more delicate; it is more likely to chip in use. Everything is a tradeoff.

Sharpenability, Edge Stability, and “Mushy Edges”

In my prior CATRA studies which have included over 50 steels, I have only had significant issues with sharpening a small handful of them. This is in part due to the use of CBN abrasives which makes sharpening even high vanadium steels very easy. Instead, the difficult to sharpen knives were from heat treating, not steel. Those difficult-to-sharpen knives had high retained austenite, which meant that deburring would leave behind a ragged edge which wasn’t very sharp. High retained austenite comes from austenitizing at too high of a temperature, especially in combination with slow quench speeds and when cryo isn’t performed. You can learn more about retained austenite in this article on cryogenic processing.

Both small batch and commercial heat treaters can have issues with retained austenite. But there are a couple areas where commercial heat treaters are at a disadvantage. One is the slower cooling rate we have been discussing throughout this article. Slower cooling stabilizes the retained austenite which makes less of it transform during cold and cryo treatments. The other is that commercial heat treaters often like to perform cryogenic steps in between the two tempering cycles, where cryo is less effective. The first tempering step also helps stabilize austenite just like slow cooling does. They prefer to do it between tempering steps because the cryo processing is less likely to lead to distortion, warping, or cracking. But it is less likely to do so in part because the cryo processing isn’t doing as much. To be clear, some knifemakers doing their own heat treating will also do cryo in between tempering, and some commercial heat treaters will perform cryo directly after the quench when it is more effective.

High retained austenite also makes steel behave as if it is softer than it is. Two knives with the same hardness will behave differently if one has significantly more retained austenite than the other. One area is in sharpening as already mentioned, but the high RA knife will have edges that deform more easily.

With proper selection of austenitizing temperatures and cryo processing, retained austenite can be limited to levels where it doesn’t affect the performance of the knife. Some steels have more issues than others. For example, I found that the datasheet-recommended austenitizing temperature for CPM-S110V was quite high. Steels like Vanax and LC200N are difficult to heat treat beyond 58-60 Rc so the heat treaters are forced to austenitize at the very peak of the curve where it is easy to “overshoot.” For example, here is a comparison between Vanax and Elmax steel with a range of austenitizing temperatures, using cryo and a 300°F (150°C) temper:

You can see that while you can use a pretty wide range of austenitizing temperatures with Elmax and achieve 61+ Rc (and then temper down to target hardness), the range for Vanax is much narrower. The peak hardness is around 1975-2000°F but already at 2025°F the hardness has dropped. When there is a hardness drop from austenitizing too high this is the point where there is too much retained austenite, and in some cases the very peak can also be questionable. So Vanax is difficult to heat treat for 60+ Rc while also avoiding excess retained austenite. When the composition of the steel is slightly different from batch to batch, the austenitizing temperature where peak hardness is reached will vary slightly. This in combination with variation in temperature within a furnace, and between furnace batches, which means that it is usually better to be a bit conservative with the temperature and go a bit lower than the absolute peak.

Corrosion Resistance

The carbides precipitated during a slow quench are also detrimental to corrosion resistance. Of course, other heat treating variables also matter. A higher austenitizing temperature means more chromium carbide is dissolved, putting more chromium in solution for better corrosion resistance. And it is relatively common in industry to use the high tempering range of 950-1050°F (510-565°C) which reduces corrosion resistance. This can make the very high corrosion resistance Vanax behave more like a “normal” stainless steel. I have an article on my corrosion resistance testing here. This high temperature tempering range can be used by both custom knifemakers and commercial heat treaters but I see it somewhat more often with commercial heat treating.

Vanax tempered at 400°F on left and 1000°F on right. Sprayed with 1% saltwater for 24 hours.

Who Knows More About Heat Treating?

In many cases the knowledge of the person performing the heat treatment is more important than the equipment being used. A heat treatment without any issues gives you 90-95% of the potential performance. It is when there is some problem with the heat treatment where the performance is noticeable to the end user. I have written about this in an old article called “What a Good Heat Treatment Can and Cannot Do.”

When a knifemaker or knife company outsources their heat treatment to a commercial heat treater, they typically ask for a target hardness and leave it up to the heat treater. The commercial heat treater presumably has significant experience with heat treating, especially with obtaining consistent results, avoiding catastrophic issues, and with troubleshooting common problems. However, many heat treatment facilities lack metallurgists, and when it comes to measuring properties, the hardness test is by far the most common. As I have shown multiple times in this article, hitting the target hardness is only one tiny piece of the puzzle. Some heat treatment facilities are better than others.

When it comes to custom knifemakers doing their own heat treating, the level of knowledge varies widely. Of course it goes without saying that the average knifemaker is not a metallurgist. In general, I would say that the average knifemaker has knowledge of the basic steps of heat treating, but their knowledge of the mechanisms behind each step is relatively poor. I reacted to knifemaker explanations of heat treatment in this video. If the knifemaker knows how to heat treat correctly and how to follow a datasheet they are usually fine. It is when they are trying to diagnose issues or to modify the heat treatment that they get in trouble without knowing how things “work” in the steel. I have an article and video about the basic steps of heat treating and how to follow a datasheet. For those that want to learn more about what is happening in the steel and how to modify heat treatments for different purposes I have many articles on my website as well as my book Knife Engineering. There are a few knifemakers that have put in the time required to understand heat treating and gained hands-on experience to become well-informed, excellent heat treaters.

Differential Hardening and Hamon

This article is already too long but I did want to mention specialized heat treatment techniques that are almost exclusively performed by custom knifemakers. One is developing a hamon, which is often for artistic purposes rather than strictly performance. Various types of other “differential hardening” techniques are used for specific performance goals like edge quenching or tempering back the spine with a torch. These are famously done to pass the 90 degree bend test required for Journeyman or Master Smith performance testing.

Summary and Conclusions

We went over a lot in this article so I will try to sum up. One of the biggest differences between commercial and custom heat treating is the quench rate. The slower quench rate in many vacuum furnaces used by knife production facilities and large custom knife makers can often lead to a reduction in hardness and toughness. A faster quench that can be accomplished with other equipment gives better properties. The degree to which this matters can be debated, but there is a potential for small batch heat treating to be superior. The potential for improving edge retention with heat treatment is somewhat overhyped. Hardness is the main area where edge retention can be improved, and this can generally be achieved with commercial heat treating. The biggest differences between “good” and “bad” heat treatments come when there is a problem in the heat treatment. It is the heat treaters who can avoid these problems (and diagnose them when they come up) that perform the best heat treatments.

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[1] Gonçalves, Cristiane, André Slaviero, Rafael Mesquita, André Tschiptschin, and Paulo Haddad. “Effect of cooling rate during quenching on the toughness of high speed steels.” Journal of ASTM International 8, no. 4 (2011): JAI103483.

[2] Taljat, B., J. Tušek, D. Klobcar, P. Boscarol, and Giorgio Scavino. “Heat and surface treatment of hot-work tool steel for optimum in-service performance.” In The Use of Tool Steels: Experience and Research: Proceedings of the 6th International Tooling Conference, vol. 1, pp. 67-80. 2002.

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Atlantic 33 Steel

There are a few places to purchase this Atlantic 33 “non-tempering” steel so I have been getting questions about it over the past couple years. The information is pretty scant and the descriptions are mysterious and confusing to anyone who knows steel [1]. In the advertising it says things like: “Drawing of temper to suit different requirements is unnecessary and completely eliminated.” Also there is no composition listed and the heat treating instructions are very barebones. “Suitable hardness is obtained by merely heating the tool and quenching it in water.” And, “May be heated to almost a melting heat without danger of distortion.” It basically just says to heat treat it however you feel like and skip the tempering. If it’s true that it doesn’t matter how you heat treat that is great, but otherwise it would be nice to know how to best heat treat the steel.

What is a Non-Tempering Steel?

While the advertising online calls Atlantic 33 “a new departure alloy steel” it is in fact not new, it has been around since the mid 1930s [2]. Here is an ad for the steel from 1937:

1937 ad for Atlantic 33

However, “non-tempering” steels actually go back even further than Atlantic 33. The earliest I found was the steel “ABC” made by Darwin and Milner starting in 1909 [3][4]. This steel company was run by Paul Kuehnrich who developed several tool steels including D3 and D5 (later slightly modified to be the common D2 in 1928). He was an early pioneer in tool steel who I wrote about in my book The Story of Knife Steel.

Another early non-tempering steel I found was called Simplex which in 1915 had some advertising which uses a lot of language similar to what we still see for Atlantic 33:

Composition  of Atlantic 33 and Other Non-Tempering Steels

There were several other non-tempering steels that would be released over the following years though they never gained much prominence. Here are several that were available in 1954 [5]:

You can see that all are medium carbon, roughly 0.3-0.4%. Each has a chromium addition and either W or Mo (including the original ABC). There is also a Cu addition in some of them. The reason for the copper addition is somewhat of a mystery. Copper additions are not unheard of but are relatively uncommon in low alloy steels, especially back in the 1930s. Copper can help with grain size control from copper precipitates but I have no insight into the 1930s thought process by Atlantic Steel. In any case there were several non-tempering steels without any copper so it does not seem to have been necessary.

What Makes Them “Non Tempering”?

Even in the 1915 ad for Simplex they do not claim that nothing happens during tempering of these steels. It says that “No tempering is necessary except in the case of very small tools, such as punches, when it may be drawn to a straw color with advantage.” In other words, the steels benefit from tempering just like any other steel. However, they selected the carbon content to be in the range of 0.3-0.4% so that they would obtain sufficient hardness for the intended tools while not being brittle. Lower carbon steel is tougher and more ductile than high carbon steel, so you can achieve similar toughness by tempering less with a lower carbon steel. It is kind of an odd idea to recommend skipping tempering altogether. Heating to 300-500°F degrees doesn’t seem all that onerous even in these supposed simple shops they are talking about. So it seems to be a case of marketing more than anything else. Other 0.3-0.4% carbon steels could be used in a similar way. The Ryerson Non Tempering steel could even fit within the 4135 steel specification though the chromium content is borderline for 4135 (0.8-1.1% Cr).

What Happened to Non Tempering Steels?

So Non-Tempering steels saw some use in the industry, though were never particularly popular. Seemingly they were the most useful in shops that have very simple (in other words, bad) heat treating facilities. Those shops that wanted to make quick blacksmith tools, punches, shear blades, and other tools that are subjected to impact at room temperature. The steels fell out of favor by the 1960s and were largely replaced by silicon (S2, S4, S5, S6) or tungsten shock-resisting steels (S1) [6].

What is a Flutagon?

Initially the Atlantic 33 steel was advertised on its own. However, now you often see the steel called “Flutagon Atlantic 33” or “Atlantic 33 Flutagon” and even some people calling it only “Flutagon.” Flutagon was a trademark term by Atlantic steel in 1940 [7] for a new shape of the steel bars they were using that they claimed was more convenient, etc. Because the new shape was advertised for Atlantic 33 the two names became somewhat conflated. However, I think it is better to call the steel “Atlantic 33” and use Flutagon to refer to the shape of the bars instead. After all, the steel is also available in hex bars. Here is a 1941 ad for the new Flutagon shape for Atlantic 33:

1941 ad for flutagon shape

Datasheet for Similar Steel

I did not find a datasheet for Atlantic 33 but I did find heat treating information for Bethlehem’s similar “Non-Tempering” steel from 1958 [8].

Forging and Annealing

The forging temperature range recommendation is pretty standard, 2100-2150°F (1150-1175°C) and finish at 1700°F (925°C).

The datasheet says annealing is recommended if machining will be performed after forging. It says to start at 1400°F (760°C) and cool at a very slow rate of 20°F/hr (11°C/hr) to 900°F (480°C). It is pretty standard for datasheets to recommend such low cooling rates.

It is somewhat strange they recommend such a specific procedure for annealing given the intention of the steel is simple heat treating setups. The steel could be annealed by heating to nonmagnetic and putting in slow cool media like vermiculite.

Normalizing?

There is no mention of normalizing in the Bethlehem datasheet. Perhaps with the low carbon content they were less concerned about it. If you do normalize, the similar 4135 steel has a pretty typical 1600°F (870°C) normalizing temperature.

Austenitizing Temperature

One of the selling points for the steel being viable for simple heat treating setups is that it can be quenched from a range of austenitizing temperatures and still have decent properties. The extra alloy added to the steel helps it resist grain growth, thus having decent toughness even with relatively high austenitizing temperatures. However, perhaps we shouldn’t over-exaggerate this point too much. There is a small drop in toughness and ductility, and a small increase in grain size by austenitizing hotter than the optimal range, which appears to be about 1500-1600°F (815-870°C), see page 170 above. 4135 is typically austenitized at 1600°F (870°C) which is consistent with those results. The steel is relatively insensitive to overheating but if using a furnace I would stick with that range.

Quenching

This is typically an oil hardening steel. Tool Steels by Roberts [6] recommends using water if the cross-section is larger than 2-1/2 inches in diameter.

Tempering Temperature

While the steel is advertised as “non-tempering,” you can see on the page 170 chart the effects of tempering. Comparing “As-quenched” (not tempered) to 300°F (150°C) you can see that the low temper leads to the same hardness (555 Brinell or about 54 Rc), but an increase in yield strength, as well as elongation and reduction in area (measures of ductility). Increasing the tempering temperature to 400°F provides a further increase in yield strength, elongation, and reduction in area at the cost of a little hardness (~1 Rc). So unless I was in a big hurry I would probably still temper these “non-tempering” steels in the range of 300-400°F.

Summary

“Non-Tempering” steels have been around since at least 1909, while Atlantic 33 came out in the 1930s. The steel became connected to their trademark “Flutagon” shape in 1940. The main advantages of non-tempering steels are simple heat treatment where a wide range of austenitizing temperature is acceptable for good properties. While they are advertised as not requiring tempering, the properties actually are improved by tempering. However, the relatively low carbon content is what gives the steels decent properties even when skipping tempering. Other steels with 0.3-0.4% carbon would also behave similarly if tempering was skipped and there isn’t anything particularly special about non-tempering steels apart from the marketing. Austenitizing is best in the 1500-1600°F (815-870°C) range and I would temper Atlantic 33 at least at 300°F/150°C for the small improvement in properties.

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[1] https://www.canonballforge.com/about-a33

[2] https://archive.org/details/sim_industry-week_1936-04-06_98_14/page/66/mode/2up?q=%22non+tempering%22+

[3] https://books.google.com/books?id=WH8zAAAAIAAJ&pg=PR57&dq=%22non+tempering+steel%22

[4] https://babel.hathitrust.org/cgi/pt?id=wu.89074782335&seq=282&q1=3332

[5] https://archive.org/details/sim_american-machinist_mid-november-1954_98_24/page/149/mode/1up?q=%22atlantic+33%22

[6] https://babel.hathitrust.org/cgi/pt?id=uc1.b4418480&seq=426

[7] https://books.google.com/books?id=logbAQAAMAAJ&pg=PA823&dq=%22flutagon%22

[8] https://babel.hathitrust.org/cgi/pt?id=uiug.30112008811041&seq=172

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