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Video

There is a video version of the following information as well:

Properties

When it comes to knife steels there is a whole range of properties that we might want to achieve, such as:

• Hardness
• Toughness
• Wear Resistance
• Corrosion Resistance
• Cost
• Forgeability
• Grindability
• Polishability
• Sharpenability
• Availability
• Marketability

Some of these properties are desirable to the end user, but some are mostly for the manufacturer. For example, properties like hardness, toughness, wear resistance, corrosion resistance, and sharpenability are all things you want in your knife steel. Some properties are desired by both buyers and makers, such as low cost. However, the costs are different for the maker than the buyer. A large part of the cost for the manufacturer is grinding and polishing. A steel may be relatively inexpensive but difficult to grind and finish and thus end up relatively expensive to use.

A few properties are things we may not think about regularly, such as availability and marketability. It can sometimes be an advantage to use a steel no one has ever heard of, perhaps pushing the exclusivity of the steel. However, there are generally advantages to a steel that is already well known and well regarded. It takes work to have to educate customers about why their unusual or unique steel is a good choice.

Availability is another aspect of steel that knife buyers typically do not think about. There are many, many steels that have been made over the years and many of them are no longer made. Finding it in a catalog somewhere doesn’t mean that you can buy it. Even when a company is making a steel, often those steels are not available in the sizes necessary for knives. Hot rolling steel to the thin sizes needed for knives is relatively uncommon. And some steels are widely available in certain countries or to certain customers but not to others. For a long time people were requesting that I test the common Chinese knife steel 8Cr13MoV, but it is primarily sold to knife companies (not individual knifemakers) in China (where I do not live). So despite 8Cr13MoV being very common in cheap knives, it is not as easy to get a bar of it as an individual living in the USA. And there are costs to importing steel from another country, such as shipping and tariffs. If a knife company or maker wants to market their knives as “Made in USA” they will want to use USA-made steel or they will have to market it as “Made in USA with foreign materials” instead.

We would love to have a knife steel that is a 10 out of 10 for every property – the unicorn steel that has ultimate hardness, toughness, wear resistance, corrosion resistance, is easy to forge, grind, and polish, and is super cheap at the same time. Of course we know it isn’t possible. So when developing and engineering a new steel it is a question of tradeoffs and which ones we are willing to make.

The Matched Set Method

Sometimes knife buyers get caught in the budgeting and minutiae of all of the different steel choices out there. Worrying about whether to use Elmax or S30V is about two choices within the same “category.” Often it is the bigger jumps that are significant, such as whether you need a steel with high toughness to resist breaking and chipping or high wear resistance for slicing edge retention. The first time I am aware of where a steel company made this clear was Carpenter with their “Matched Set Method” which they introduced in 1935 [1], and is described in the 1937 book Tool Steel Simplified.

In the chart above I labeled each with their AISI designations (A2, D2, etc.) but otherwise it is unmodified from 1937. The categorized steels by high wear resistance (wear), high toughness (tough), and balanced properties (hard). To get high wear resistance you have to give up some toughness and vice versa. And they are also categorized by “hardenability,” which is a measure of how fast you need to quench a steel to achieve full hardness, either water, oil, and air for the quenching medium required. Water hardening steels were cheaper but required fast quench speed, were prone to distortion because of those fast quenches, and couldn’t be used for larger tools requiring through-hardness. In the knife world, water or oil hardening grades are favored by forging bladesmiths because of how easy it is to forge them.

Generational Breakthroughs

Of course I don’t mean to imply that there is never a reason to develop improved versions for different categories, or to create steels that sit in the middle between two different categories. There were generational improvements just to lead to the original Matched Set Method. For example, before the late 1800s all steels were “carbon steels” as carbon was the only element really added to them. “Water wear” F2 tool steel was developed by adding 3.5% tungsten to form hard tungsten carbides for wear resistance. Air hardening steels came by adding significant chromium additions, which also led to higher wear resistance from the formation of chromium carbides. The discovery of alloying was one of the most important transition points in steel history, which you can read more about in my book The Story of Knife Steel. The existence of high chromium steels also led to the development of stainless steels, very important to knives of course. The first stainless steel ever commercialized was intended for use as a knife steel. To understand what I mean by generational improvements and to get a feel for what is possible for future improvements I am going to discuss several prior improvements in this article.

Another important breakthrough occurred in the 1960s and 1970s with the introduction of powder metallurgy technology. With powder metallurgy they solved the issue of large carbides and inconsistent properties in steel by skipping the part where the liquid steel slowly cools down in a mold. Instead, the liquid steel comes out of a nozzle in a stream that is sprayed with gas so that it rapidly solidifies into fine grains, or “powder” steel. The powder is then placed in a steel can under high temperature and pressure, called hot isostatic pressing (HIP) to turn it into a solid ingot. Crucible Steel in New York and Pennsylvania developed this process and they found great improvements in toughness without any reduction in wear resistance by refining the microstructure with this process.

The technology wasn’t the only significant advancement, however. They also found that steels could be optimized for the PM process, as the best alloys for powder metallurgy were different than those optimized for conventional steelmaking. They first realized this when they found that M4 high speed steel went from being among the lowest toughness conventional high speed steels to the very toughest CPM high speed steel. They discovered that the high vanadium content went from being a liability to an asset. Vanadium carbides would form at high temperatures in solidification leading to large, brittle carbides. However, because powder metallurgy keeps the carbides small in solidification, it is the growth rate of the carbides that is important instead. Vanadium carbides are more stable than chromium (M₇C₃ and M₂₃C₆) and molybdenum/tungsten (M₆C) carbides and so would grow at a slower rate during high temperature processing like HIPing and hot rolling. Vanadium carbides are also among the very hardest and thus contribute more to wear resistance than chromium and molybdenum/tungsten carbides. So the combination of high hardness of vanadium carbides (wear resistance) and small size (toughness) led to high vanadium steels having excellent properties. This eventually led to the development of CPM-10V in 1978 which was a tool steel with ~10% vanadium for incredibly high wear resistance while still maintaining equal better toughness than the popular D2 tool steel.

Powder Metallurgy Stainless Steels

Crucible used their knowledge of vanadium alloying in the development of CPM-440V (now called CPM-S60V), a modification of 440C with 6% vanadium and extra carbon to go with it. This steel was released around 1983. However, this steel did not have especially excellent toughness because it still had a large amount of chromium carbide, softer and larger carbides which were detrimental to the toughness-wear resistance balance. In 1995 CPM-420V was released (now called CPM-S90V), patented by William Stasko, Kenneth Pinnow, and John Hauser. They reduced the chromium content from 17 to 14%, and increased the vanadium content from 6 to 9%. This led to an improvement in both toughness and wear resistance vs S60V. CPM-S30V, released in 2002, used the same concept as S90V but reduced the vanadium to 4% for higher toughness (and lower wear resistance). S30V also utilized increased Mo (2% rather than 1%) and partially replaced carbon with nitrogen (0.2%), both for better corrosion resistance, ideas explored in the S90V patent but not ultimately used in the commercialized version. CPM-S110V and CPM-S35VN were released around 2009-2010 and these steels used niobium to refine the microstructure. Niobium was also found to improve corrosion resistance in S110V because it does not increase the amount of chromium carbide like vanadium does. Micrographs of how much finer the microstructure is of S110V than S90V can be seen below:

CPM-S90V

CPM-S110V

MagnaCut

MagnaCut used all of the previous developments in its design as long as one more – a further reduction in chromium. The above steels had about 10-12% chromium “in solution” which is the chromium that is not tied up in carbides and thus can contribute to corrosion resistance. So these steels still had more chromium than was strictly necessary for corrosion resistance with 14% chromium. And I also knew that the properties had been greatly improved by reducing Cr from S60V to S90V. So for MagnaCut I intentionally designed the steel to have sufficient chromium for good corrosion resistance and then balanced the rest of the composition to avoid chromium carbide formation. It used a combination of niobium and vanadium for small, hard carbides for wear resistance. This gave significantly improved toughness because the carbides were much smaller than those found in high chromium stainless steels. And the corrosion resistance was also greatly improved because chromium carbides were eliminated. Those chromium carbides act as sites for corrosion to initiate, because they create locally reduced chromium content in solution around each carbide.

M390 – high chromium stainless powder metallurgy steel with relatively large carbides

MagnaCut – much smaller carbides

This improved toughness-wear resistance balance from the microstructure improvement of MagnaCut gives it properties similar to the best non-stainless PM steels:

The chart above shows orange dots for non-stainless steels and blue dots for stainless PM steels. You can see that the toughness for a given level of CATRA edge retention (edge wear) is significantly lower for the stainless steels, apart from MagnaCut which overcame this previous gulf in properties. This was the result of a series of generational improvements, a simplified version of which being 420 -> 440A -> 440C -> S60V -> S90V,S30V -> S110V,S35VN -> MagnaCut. Big improvements in steel come when we can move up and to the right at the same time, an improvement in both toughness and wear resistance. When you add another constraint such as corrosion resistance or hot hardness, that makes it more difficult to achieve the highest balance of toughness and wear resistance. I have images in The Story of Knife Steel that show the evolutionary tree of different steel types such as this one for stainless knife steels:

Not all of those grades (S60V, etc.) were an improvement in every category, but in general there was an improvement over time in terms of the balance of toughness, wear resistance, and corrosion resistance. It is difficult to improve all of these at the same time, or even two of the three at the same time, without affecting the others. But a true generational improvement comes when engineers figure out how to break through previous barriers, such as when MagnaCut managed to make it to the same toughness-wear resistance balance as the non-stainless PM steels.

MagnaMax

I chose to make MagnaCut a “balanced” steel in the realm of CPM-4V and CPM-CruWear. This meant it filled a niche that had not previously been filled. However, the alloy concept of avoiding chromium carbide and using only hard vanadium/niobium carbides could be used for other combinations of toughness and wear resistance. When I first proposed MagnaCut to Crucible and Niagara I also said that we could make a stainless version of CPM-10V with the same idea. That eventually led to MagnaMax which was recently released. MagnaMax has double the carbide of MagnaCut for significantly greater wear resistance.

Magna-Family Steels

MagnaMax was the first addition to the “Magna-Family” of grades. I call it a family despite only having two steels because there are many other options. To be clear, I am not currently announcing new additions and none are coming in the short term. But the same concept could be used for a higher toughness version of MagnaCut, for example. Essentially the opposite direction of MagnaMax. Another balancing act in steels I have not yet discussed, however, is the balance between hardness and corrosion resistance.

You can see that in general, higher hardness leads to lower corrosion resistance and vice versa. However, this is true when comparing steels, not for comparing hardness within a single steel. A steel can be heat treated to maximize hardness and corrosion resistance at the same time, as I have explained in the past. MagnaCut had improved hardness for its level of corrosion resistance because of its lack of chromium carbide. But modified versions could be made for higher hardness and reduced corrosion resistance or improved corrosion resistance at the cost of some hardness. Thus we would have a new “matched set” for the potential family of Magna-series steels:

Again, I must be clear that I don’t actually believe we will release all of these. In fact, perhaps only the center steels will ever be released, since we hit a very good balance between hardness and corrosion resistance for MagnaCut and MagnaMax. However, it could be interesting to make the other versions for specific applications, either for high hardness stainless steels or to make improved “saltwater” stainless grades.

How Small of a Niche Can We Fill?

As I said when it comes to all of the potential variations of MagnaCut, just because we can fill a niche doesn’t mean we can or should. Having too many available grades can make things confusing to customers and increase logistical complexity. Unfortunately I don’t have the power to eliminate old steels to replace with the new better ones to lead to a simpler market. With too many available grades there can also be a situation where it doesn’t make monetary sense to make certain niche products. It costs money to develop a new product and the return on investment may not be worth it if the resulting sales are not great enough. So unfortunately there are often real-world limitations to just how many steels it is possible to develop and release.

Copies and Small Modifications

When I see people complaining about “too many new knife steels” often this is partly out of confusion. They don’t realize that many of the “new” steels are several (or more) years old and were not well known for knives prior. Many “new” steels are older steels released under a new name by a different company or in a different country. And many consumers have a hard time keeping up with all of the compositions and names, and don’t know how to interpret a steel composition to know when something is the same. I have seen many knife enthusiasts on forums or social media where they misunderstood that a small difference in published silicon, or a minor element like manganese not being listed, does not mean that the steel is different. But even outside of straight copies, many new steels are only small modifications of prior products. Here is a list of new steels over the past decade (outside of steels I have developed):

• Nitro-V (2017) – minor modification of AEB-L
• S45VN (2019) – S35VN with added chromium and nitrogen
• M398 (2019) – M390 with more carbon and vanadium
• SPY27 (2020) – Spyderco-exclusive CPM stainless steel with 1.5% Co
• AR-RPM9 (2020) – China-produced sprayform version of 9Cr18MoV (440)
• XEOS (2022) – Takefu modified 440 grade with higher Mo
• H2 (2022) – replacement for Spyderco’s earlier H1 austenitic stainless
• STRIX (2023) – Takefu powder metallurgy stainless for 64-65 HRC
• K888 (2024) – CPM-1V with added cobalt
• Nitro-X7 (2024) – their earlier Nitro-B with higher carbon
• A-421 (2025) – Carpenter conventional stainless steel with small amount of TiC
• Aigami (2025) – Hitachi conventional stainless for higher hardness than GIN5 (AEB-L)

The degree of change for each of these varies, with some being very tiny to a few being relatively significant. The majority are small to medium modifications of prior grades. This list does not include any “new” grades which are simply copies. I don’t think I would characterize any of those grades as “generational improvements.” Those are difficult to achieve, of course. But when it comes to predicting the future of steel development, the majority of it is going to be products like those above, and many of the new grades will be copies and minor modifications.

Grades for Forging

The pace of change for low alloy grades for forging has been pretty slow, and the majority of grades were developed over 50 years ago. One exception was CruForgeV, released in 2009. However, that grade was released at the same time as a Crucible bankruptcy and none has been made since. Some of it is still out there but in some ways it serves as a cautionary tale. I have been able to develop two grades for forging, Pop’s ProCut and ApexUltra. I do believe that both of these grades were able to deliver “generational improvements.” Pop’s ProCut used nickel alloying plus tungsten/vanadium alloying to deliver a new combination of high toughness with wear resistance that wasn’t previously available. Past high toughness forging grades like 15N20, 8670, and 5160 have extremely low wear resistance. ProCut was able to break through this barrier. It also provided a uniquely easy to heat treat design, with an austenitizing window that is over 200°F wide. This gave it a great combination of properties while also being “beginner friendly.”

ApexUltra took a different track where the goal was to make a forging grade that maxes out cutting performance – achieving higher wear resistance and good toughness at high hardness than previous grades like Blue Super and 1.2562/F2. I had noticed that 52100 had a better toughness-edge retention balance than many other low alloy steels that are forgeable. The difference is in the 1.5% chromium content. The chromium has two major effects – 1) the iron carbides are enriched in chromium which increases their hardness and they contribute more to wear resistance. 2) the chromium decreases the amount of carbon in solution, making “plate martensite” less of an issue which makes steel brittle. So ApexUltra used the 1.5% Cr from 52100 in combination with the tungsten/vanadium additions of Blue Super to achieve edge retention greater than past low alloy steels.

More Grades for Forging?

There are different opportunities for forging grades but they might all suffer from the too-small-niche problem. Some possibilities include:

Powder metallurgy forging grade – A 2-4% vanadium PM low alloy steel would be interesting. It could offer even higher wear resistance than ApexUltra, likely with higher toughness as well. However, forging bladesmiths are historically very price conscious and they don’t like vanadium steels because of the extra difficulty in finishing. So ApexUltra is likely to be as good as it gets for now.

Hamon steels – To make a good hamon requires the steel to have very low hardenability with low Mn and no Cr or Ni additions. The standard choices are 1095, W1, and W2. Potentially hamon steels with different levels of toughness and edge retention could be made but again this application is likely too niche. Hamon steels are difficult to heat treat because of their low hardenability so outside of a hamon they are not really desirable.

Damascus – Pop’s ProCut works great in Damascus as a bright layer because of its high nickel – it can even be paired with ApexUltra for a high performance Damascus. A steel that matches the properties of ProCut generally but without nickel would be good for an easy to heat treat Damascus that offers relatively high toughness. However, the nickel-free version wouldn’t be better, it would just be good for a Damascus combo. So again the niche is likely too small.

A Modern Knife Steel Matched Set Recommendation

I first gave recommendations for knife steels in different categories in 2019. I updated these in Knife Engineering and again in the second edition. My current recommendations are as follows:

The grades in bold are those that I developed. This chart also gives us a place to discuss potential holes and areas that perhaps could be improved. Some holes that are still present:

The obvious one is the high wear resistance “extra stainless” category, which is the category I use for saltwater steels. Some knife companies have used MagnaCut in their knives designed for saltwater though I would prefer the corrosion resistance was even higher for those applications. Uddeholm used to make a Vanax 75 which had higher wear resistance than the current Vanax. A good solution for this category could potentially be a higher corrosion resistance version of MagnaMax.

Vanax and LC200N are pretty good steels. However, a higher corrosion resistance version of MagnaCut would have better toughness than Vanax.

I think it would be difficult to improve on Vanadis 8/K390/10V and CPM-CruWear. They have excellent toughness-wear resistance balances. Improving over that would require a generational improvement that we haven’t seen in the non-stainless PM space for several decades. It might require exploring unique solutions in terms of the matrix composition and carbide types.

The very high toughness non-stainless steels like Z-Tuff could use some improvements. All of those available have softer carbides such as chromium carbides or tungsten/molybdenum carbides. CPM-3V is very good and only has vanadium carbides but it could be argued it is more in the balanced properties than truly the maximum toughness category.

AEB-L/14C28N are excellent steels though we could have higher wear resistance in this category through a powder metallurgy steel with vanadium and/or niobium carbides. The high toughness Magna-family grade would fit this category.

Expanding the Envelope

My categories do not cover all possibilities. For example, there are higher wear resistance steels than those in my “high wear resistance” category. Examples would include steels like CPM-15V, Maxamet, CPM Rex 121, CPM S125V. We have been hearing that some of these may be going away like 15V and Rex 121. From what I know they never liked making S125V. The reason they may go away is that the temperatures required for making them are very high or carbides will form in the liquid, either leading to a large carbide size (not desirable with powder metallurgy of course) or even creating manufacturing issues like clogging the nozzle. The temperatures get high enough that the ceramic refractory is eroded by the liquid steel, requiring frequent relining. Not all steels are in danger of going away; I haven’t heard anything about Maxamet being in danger. But one thing that could be done would be to redesign steels around a certain temperature limit to try to make similar high wear resistance steels that do not have these manufacturing issues.

In terms of steels that have even higher toughness than my “high toughness” category I am not too interested in those. There have always been high toughness grades out there but at some point the wear resistance and/or hardness is low enough that it is not particularly useful for knives.

Steels Designed for Grinding and Finishing

Grinding and finishing are very important to knifemakers and manufacturers. High wear resistance steels and large carbide steels have low grindability. Finishing and polishing are especially sensitive to large carbides and high hardness carbides. Vanadium carbides are harder than typical abrasives like aluminum oxide. For highly finished and mirror polished knives, it is better to avoid significant vanadium and niobium additions. Since this limits us to softer carbide types the potential for generational improvements is limited. Here are my recommendations for steels that are easy to grind and polish:

There are many gaps in this table though that may not be a bad thing. Very high wear resistance steels with only soft carbides end up with very low toughness because they have so much carbide. I put ZDP-189 in the “high alloy” category rather than the “stainless” category because my corrosion testing showed very poor tests with this steel. A ZDP-189 that is actually stainless could work, especially in Japan. An “extra stainless” balanced steel – a more corrosion resistant CPM-154, may have some uses.

Cost and Conventionally Produced Steels

Many of the best steels in terms of properties are produced with powder metallurgy. However, this significantly increases the cost of producing these steels. Another factor for cost is that cost of abrasives and time in polishing can often exceed the cost of the steel. Here are my recommendations for low cost steels:

I struggled a bit with some of these categories. The high toughness S7 is somewhat limited in hardness, generally under 60 HRC. The biggest debate in my mind internally was what to put for “balanced” stainless and ended up with 8Cr13MoV. It gives up quite a bit of toughness to get a small wear resistance improvement over AEB-L and 14C28N. I think significant improvements could be possible in this category. For example, I worked on a grade called NioMax in lab-sized quantities even before working on MagnaCut. In small quantities it had similar toughness to AEB-L/14C28N but with enhanced wear resistance. As of yet it has not been released.

The limitations are much greater when not using powder metallurgy. The drop-off in toughness is a lot more rapid as wear resistance and carbon content is increased. There have been fewer generational improvements in the conventional steel space and I think there are opportunities there.

Summary and Conclusions

If you want to learn more about the past generational improvements and what led to different steels being used in knives, make sure you read my book The Story of Knife Steel: Innovators Behind Modern Damascus and Super Steels. Understanding the past gives us a better idea of what is possible in the future. As to what is possible in the future for knife steel, I laid out some possibilities above, and I can’t really be sure which will happen. I would like to make more Magna-family steels and to work  on improving conventionally produced steels, but some may be too niche to be commercially viable. But the thing I can be sure about is that more copies and minor modifications of prior steels will definitely come out.

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[1] Machinery vol 42. 1935, p. 64.

The post What Could be Next for Knife Steel? appeared first on Knife Steel Nerds.

Wide Release Date for MagnaMax for Small Knifemakers

MagnaMax will be on sale May 1st, 2026 at 9am on Niagara Specialty Metals’ online store: https://nsm-ny.com/shop/

You can create an account beforehand so that you are ready to buy once the steel goes live. We made the following commercial to get pumped for the release:

Intro

I wrote an article (and created a video) about MagnaMax properties a few months ago. So I won’t be rehashing all of the properties here. Basically, MagnaMax is designed to have enhanced wear resistance and edge retention vs MagnaCut with similar corrosion resistance and hardness potential.

You will also see in the chart above that MagnaMax offers superior toughness and edge retention to the popular M390 and 20CV. It is very difficult to improve both of these properties at the same time, so this is a big improvement. It also maintains similar toughness to grades CPM-154, S35VN, and Vanax, which were formerly the toughest PM stainless steels prior to MagnaCut. So it offers a significant edge retention improvement to those grades, which have had a reputation for good properties in the past.

That property summary article did not have specific heat treatment recommendations because I was waiting on the final material. The initial heat of steel had carbon on the low end of the specification, so it wasn’t as representative of the average material as I wanted. No change was made to the target composition or the specification, it just landed at the lower end for carbon. So now that I have received and tested material closer to the midpoint of the specification I performed a more comprehensive set of tests. Knifemaker Matthew Gregory helped to make the majority of the toughness coupons.

High Level Heat Treatment Summary

Before we get into all of the details I can give a simple summary so you don’t get lost.

With Cryo:

Austenitize 2100-2250°F (1150-1230°C). The baseline temperature for good properties is 2150°F (1175°C).

Plate quench for faster cooling and slightly higher hardness.

After cooling to approximately room temperature, place immediately in liquid nitrogen. The amount of time it sits in the liquid nitrogen doesn’t matter that much, it just needs to reach the temperature. An hour is fine. What does matter is not wasting time before putting it in the liquid nitrogen. You don’t need to check the hardness beforehand.

Temper 300-450°F (150-230°C) twice for two hours each time. 350°F (175°C) is a baseline temperature for good properties.

Without Cryo:

Use your household freezer. It is a myth that it doesn’t have any effect. There is no reason to do no cold treatment. Everybody has or can get a freezer. Dry ice is even better, but despite being about 100°F colder than a freezer often behaves closer to a freezer than to liquid nitrogen.

Austenitize 2050-2100°F (1120-1150°C). 2100°F (1150°C) is a good temperature. It might be possible to go somewhat higher but I worry about excess retained austenite.

Plate quench for faster cooling and slightly higher hardness.

After cooling to approximately room temperature, place immediately in the freezer or dry ice. The amount of time it sits in the freezer doesn’t matter that much, it just needs to reach the temperature. An hour is fine. What does matter is not wasting time before putting it in the freezer. You don’t need to check the hardness beforehand.

Temper 300-450°F (150-230°C) twice for two hours each time. 350°F (175°C) is a baseline temperature for good properties.

Austenitizing hold times:

The required hold time changes with temperature. This is the soak time required after the piece reaches the temperature. It rarely hurts to add extra minutes, it is more common to have an issue with undersoaking.

2050°F (1120°C): 20 minutes

2100°F (1150°C): 15 minutes

2150°F (1175°C): 10 minutes

2200°F (1205°C): 5 minutes

2250°F (1230°C): 5 minutes

Hardness and Cryo

I first made a series of coupons to test the hardening response, including with the addition of a freezer or liquid nitrogen treatment after quenching. I used the soak times in the section above.

You can see that with no cold treatment the peak hardness was 2050°F (1120°C) after tempering at 300°F (150°C). Hardness drops with higher temperatures from excess retained austenite. Hardness rose when using liquid nitrogen all the way to 2250°F (1230°C). It would be unlikely to keep rising much beyond this temperature and the possibility of melting grain boundaries starts to become more of a danger. The freezer also rose all the way up to 2250°F but to a lesser extent. Because the increase was small beyond 2100°F (1150°C) this is why I limited my recommendation for the freezer to that temperature. That makes me think both the retained austenite and hardness of the martensite were increasing beyond that temperature, leading to relatively flat behavior. Excess retained austenite can lead to worse sharpening behavior when deburring. Overall this hardening response is not radically different than MagnaCut.

Nothing too crazy showed up in the tempering. You can see that a cold treatment leads to less hardness loss in tempering. Compare 2050°F with and without a cold treatment, or 2100°F with liquid nitrogen vs the freezer. Note that I have a single curve for both freezer or liquid nitrogen from 2050°F, and this was because the two were sufficiently similar to have a single line. Plus don’t want to make the chart too busy.

You will also notice that the hardness reaches an initial minimum at 600°F (315°C) and then rose to a secondary peak around 900°F (480°C). This is known as “secondary hardening.” I don’t recommend tempering in that range, especially with stainless steels, because it reduces corrosion resistance. For example see two Vanax coupons below, both sprayed with 1% saltwater. The one of the left was tempered at 400°F (200°C) and the one on the right was tempered at 1000°F (540°C).

Toughness

We also tested a series of charpy toughness coupons for this heat of MagnaMax. I used my standard coupon which is quarter size (2.5 x 10 mm) and unnotched. Three coupons were tested for each condition. We used liquid nitrogen in the heat treatment of all of these coupons directly after the quench. We used austenitizing temperatures of 2000-2250°F (1095-1230°C) and tempering temperatures of 300, 350, and 450°F (150, 175, 230°C).

The hardness was slightly lower than the small hardness coupons I showed results from before:

Looking at the resulting toughness, it rose from 2000 to 2050°F (1095 to 1120°C), was relatively flat up to 2200°F (1205°C), and then dropped somewhat up to 2250°F (1230°C). This is why I recommended a baseline austenitizing temperature of 2150°F (1175°C) as this appears to be roughly the peak hardness-toughness, though an argument could also be made for 2200°F (1205°C), in part due to a couple of the 2150°F results being on the low end and a couple of the 2200°F being on the high end. This is likely due to statistical variability of testing.

You can also see that toughness increases with tempering temperature as we would expect, which also corresponds to a hardness decrease. Lower hardness generally correlates with higher toughness.

There was a greater increase in toughness between 300 and 350°F (150-175°C) than between 350 and 450°F (175-230°C), which is why I recommended 350°F (175°C) as the baseline tempering temperature.

Hardness-Toughness Balance

But what we would like to maximize is the highest toughness for a given hardness. So I plotted hardness vs toughness below.

You will notice that the maximum hardness-toughness combinations were generally 2150-2200°F (1175-1230°C) and tempering at 350-450°F (175-230°C). The exceptions include: 1) 2100°F (1150°C) with 450°F (230°C) because that combination gave the best properties for lower hardness. And 2) For maximum hardness you need 2150-2250°F (1175-1230°C) in combination with the minimum tempering temperature of 300°F (150°C). I next overlaid those best heat treatment conditions on top of the similar non-stainless steels K390, Vanadis 8, and CPM-10V:

Erasteel MM#1 is the first heat that was shown in the prior article about MagnaMax properties, and Erasteel MM#2 is the final tested material above. You can see that both have a similar hardness-toughness balance, though the new one is skewed to somewhat higher hardness, as expected from more carbon. You will also see that the toughness is very similar to K390 and Vanadis 8, an excellent result given that MagnaMax is a stainless steel with similar wear resistance. So we greatly improved corrosion resistance over those steels while maintaining their other properties. I next plotted those hardness-toughness values vs other stainless powder metallurgy steels:

You can see that MagnaMax has superior hardness-toughness than virtually all of the powder metallurgy stainless steels apart from MagnaCut. This includes steels with a good reputation for toughness including Vanax, XHP, S35VN, and CPM-154. And below I have the more complete graph of stainless steels which is a bit busy:

Corrosion Resistance

I compared the final higher carbon version of corrosion resistance to the earlier and both passed the 1% saltwater corrosion test. Showing a picture of two clean samples isn’t very interesting, so here is the earlier image of MagnaMax vs other steels:

Each of those was austenitized from 2150°F (1175°C). MagnaMax (and MagnaCut) were designed for all of the chromium carbides to be dissolved around 2050°F (1120°C). After the chromium carbides are dissolved the corrosion resistance doesn’t appreciably change with even higher temperatures. This is different than most other stainless steels which have chromium carbides all the way up to the melting temperature. But using even higher than 2050°F does provide some factor of safety, better ensuring the chromium carbides are fully dissolved.

The other main factors for corrosion resistance are quench rate and tempering temperature. I mentioned in the tempering section that tempering above about 750°F (400°C) leads to a reduction in corrosion resistance and I showed a test with Vanax to illustrate that. Quenching isn’t an issue unless it is very slow, which leads to carbides precipitating on the grain boundaries which can reduce corrosion resistance.

Edge Retention

The primary factors for edge wear resistance are carbide volume, carbide hardness (controlled by type), and steel hardness. While the carbides are very important when comparing different steels, there is less of an impact within a given steel. It is true that austenitizing higher dissolves a bit more carbide but this effect is generally drowned out by the increase in hardness. So in general, achieving a higher hardness results in greater edge retention, and there isn’t much point in worrying about the exact austenitizing and tempering temperatures that were used to get there. I have the graph below of CATRA results I tested previously to show where MagnaMax lands and the effect of hardness on the results:

Summary and Conclusions

So I have shown the majority of the heat treatment data that I generated and my reasoning for the different recommendations. I am overall happy with how the heat treatment response ended up. If you want to see the simplified heat treatment recommendations, scroll back near the top where it said “High Level Heat Treatment Summary.” Hopefully that is simple enough for everyone. If not then ask questions in the comments. MagnaMax will be on sale May 1st, 2026 at 9am on Niagara Specialty Metals’ online store: https://nsm-ny.com/shop/

The post How to Heat Treat MagnaMax Steel 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.

Patreon

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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.

The post Testing Tamahagane – Traditional Japanese Steel appeared first on Knife Steel Nerds.

My steel research is supported through Patreon. Patreon supporters saw the news on Pop’s ProCut before anyone else. There is currently an article about the upcoming MagnaMax only available on Patreon.

Video

Here is a video version of the following information:

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.

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.

Thanks to Roman Kasé for donating the K888 and Niagara Specialty Metals for donating the CPM-1V. Thanks to my Patreon supporters for funding this study, those dollars went toward metallography and CATRA blade grinding. You can support knife steel research by visiting Patreon.com/KnifeSteelNerds

Video Version

There is also a YouTube video of the following information:

History of Matrix Steels

Matrix high speed steels were developed in the 1960’s by VASCO. I previously wrote about historical and current matrix steels in this article. The original steels came out of improved techniques for measuring the composition of the “matrix” of the steel. Some of the carbon and alloying elements go toward forming carbides, what remains is in solution in the “matrix” of the steel. Carbides help with wear resistance but are detrimental to toughness, so the metallurgists decided to make high toughness steels by taking the measured matrix composition of the best high speed steels and using that composition instead. The first was a matrix version of M2 high speed steel called VASCO-MA, and they followed that up with Matrix II, a matrix version of M42 high speed steel.

Jumping ahead to the year 2002, Crucible released CPM-1V, which is a powder metallurgy version of VASCO-MA. The steel was released to offer the highest toughness of any of their available powder metallurgy steels, even CPM-3V. In 2005, Bohler released K890, advertised as a competitor to CPM-3V, it sort of looks like a cross between CPM-1V and CPM-3V, with elevated carbon, vanadium, and cobalt when compared with CPM-1V. K888 was released at the beginning of 2024, and it is essentially CPM-1V with a cobalt addition. Cobalt is added to many high speed steels for higher hardness (with a decrease in toughness). You can read more about the effects of cobalt on steel in this article.

One intriguing thing about K888 is that Bohler is advertising that it has higher toughness at 64 Rc than their prior K890 has at 62 Rc, and that K888 sees only a small drop in toughness between 62 and 64 Rc.

Bohler’s chart of toughness for K888

Toughness drops significantly with higher hardness so the claim that K888 maintains its high toughness at such a high hardness value is exciting. For example, in testing by Hitachi of their tool steels they found that above 62 Rc the toughness of their steels drop significantly:

Hitachi toughness chart for their steels

Experiments

So I was interested to compare K888 and CPM-1V to see the effect of the cobalt addition, and I had not yet tested CPM-1V so this was a good excuse. Knifemaker Roman Kasé was able to obtain a couple small pieces of K888 for me and I got CPM-1V from Niagara Specialty Metals. CPM-1V is also now available at Alpha Knife Supply. I tested the steel for hardness, toughness, and edge retention.

Microstructure

The big benefit of matrix steels is the lower volume of carbide. Carbides are brittle particles so the less carbide found in the steel the greater the toughness. Shawn Houston did the metallography for the two steels:

CPM-1V 2050°F austenitize – 3% carbide volume

K888 2050°F austenitize – 4% carbide volume

K888 has somewhat more carbide as expected, ThermoCalc predicts 1.15% MC (vanadium carbide) and 1.84% M6C (tungsten/molybdenum carbides) in K888; CPM-1V it predicts 0.87% MC and 1.34% M6C. But the big surprise is how much bigger the carbides are in the K888. We will see if this affects the measured toughness later in the article. I have some comparable grades below such as Z-Tuff and CPM-3V, two high toughness powder metallurgy steels, as well as the conventionally produced matrix steel Caldie. CPM-1V has the finest carbides of any powder metallurgy steel I have looked at so far. You can see even more micrographs here.

Z-Tuff

CPM-3V

Caldie

Hardness

Bohler shows that K888 can be heat treated as high as 64 Rc if you use the high end of the austenitizing temperature and temper within the recommended window (blue shaded region):

I made full tempering curves for both K888 and CPM-1V. I don’t typically do full tempering curves (it takes forever), but I thought it would be useful for comparing the effect of the slightly higher carbon in the K888 as well as the cobalt addition.

The hardness I measured for K888 is roughly equal to what was shown in Bohler’s datasheet. You can see that the potential hardness is higher for K888, which is due to the cobalt addition and slightly higher carbon. However, CPM-1V is still capable of relatively high hardness. To get a better feel for the two grades, I have a comparison between the two steels on one plot:

The K888 curve is for an austenitizing temperature of 2000°F and CPM-1V is 2050°F. With the lower carbon in CPM-1V it needed a higher austenitizing temperature to have equivalent as-quenched hardness, and here the CPM-1V was slightly higher as-quenched. However, K888 saw a bigger jump in hardness with a 300°F (150°C) temper than CPM-1V did. This is “precipitation strengthening” due to small carbides coming out during tempering. The same effect happens in the high temperature range around 900°F. You can read more about precipitation strengthening, also called secondary hardening, in this article on tempering. The higher hardness after tempering is then maintained across the tempering range in K888. This is a result of the cobalt addition, which is an alloy that slows the kinetics of tempering. This is what makes cobalt useful for high speed steels, which are designed to hold their hardness at high temperature.

Toughness

I used a few different combinations of austenitizing and tempering to compare CPM-1V and K888. For K888 I compared the low and high temperature tempering with 2050°F (1120°C) along with 1000°F (540°C) and 350°F (175°C). Based on the K888 tempering chart from Bohler, the 2050-1000 combination is presumably the one they used for the 64 Rc toughness datapoint, so it was an important one to test. I also tried a lower austenitizing temperature, 2000°F (1095°C) with 400°F (200°C). For CPM-1V I used all low temperature tempering with 2000-400, 2050-300, and 2050-350. The resulting hardness and toughness is below:

The first thing that sticks out is that the CPM-1V tested significantly better than the K888. The 2050-300 treatment led to 64 Rc and 22 ft-lbs, an excellent combination of hardness and toughness. 2050-350 led to 62.5 Rc with 36 ft-lbs, again an impressive combination. The 2000-400 heat treatment, however, did not lead to an improvement in toughness when compared with 2050-350 despite the lower hardness.

For K888 the 2050-1000 heat treatment, which is presumably the heat treatment used for the 64 Rc toughness datapoint in the datasheet, had the best toughness, but it was still below the result for CPM-1V at comparable hardness. The other interesting thing was that the low temperature tempering at 350-400°F did not seem to be high enough to give the steel good toughness. This may be from the cobalt addition delaying tempering.

K888 does not look particularly impressive on the chart, though it did manage to have somewhat higher toughness than CPM-CruWear at comparable hardness. The CPM-1V was again somewhat higher than K888 around 64 Rc, showing a clearer improvement in toughness at that high hardness. At 62.5 Rc, the CPM-1V continues to look impressive, having comparable toughness to high toughness steels like Caldie, CPM-3V, and A8 mod when they are at significantly lower hardness. Z-Tuff still remains alone at the top of the chart since the 2000-400 heat treatment of CPM-1V did not lead to an improvement in toughness. However, if the CPM-1V is extrapolated to lower hardness we would expect similar toughness to Z-Tuff:

It would be interesting to test other heat treatments to see if this extrapolation to lower hardness could be achieved. Such as a 2050°F austenitize with a higher tempering temperature such as 400-500 or 1000°F to see if the toughness could be further improved in the 60-62 Rc range. Because the low tempering range was not successful for K888, modified heat treatments for lower hardness would explore lower austenitizing temperatures with the same 1000°F, or increased tempering temperatures beyond 1000°F (540°C). Presumably the toughness would remain below CPM-1V due to the larger carbides. Alternatively it would also be fun to test Z-Tuff with a lower tempering temperature of 300-350°F and see what its toughness is like at higher hardness. So far I have only tested it after tempering at 400°F.

To show how good the toughness of CPM-1V is compared to low alloy steels and stainless steels I created charts with 1V overlaid on those:

Edge Retention

I tested one CATRA knife each, Shawn Houston ground the blades after I heat treated them. Each were heat treated using an austenitizing temperature of 2050°F (1120°C) and a tempering temperature of 350°F (175°C). This resulted in 63.1 Rc for CPM-1V and 63.9 Rc for K888.

As expected the two steels are near the bottom of the chart, following the approximate edge retention of AEB-L and ApexUltra. If compensating for hardness, the two steels also approximately match CD#1 (nearly identical to Z-Tuff) and A8 Mod. So I think overall the two steels did about as well as could be hoped for high toughness powder metallurgy steels with low carbide volume and only 1% vanadium.

Summary and Conclusions

These are two matrix high speed steels based on the original matrix steel VASCO-MA, though K888 has slightly higher carbon plus a cobalt addition. The cobalt addition led to somewhat lower toughness in the K888 when compared with CPM-1V. The cobalt did lead to more tempering resistance and higher hardness, though that tempering resistance also affected its toughness, especially in the low temperature tempering range (350-400°F). CPM-1V has an excellent combination of hardness and toughness in the 62-64 Rc range, though it may be possible to achieve higher toughness in the 60-62 Rc range if we try higher tempering temperatures. K888 and CPM-1V have similar edge retention, close to AEB-L, ApexUltra, and Z-Tuff/CD#1. Overall after testing these steels CPM-1V is my preference for a steel that maintains very good toughness at high hardness. I don’t know of any knife supply companies offering K888 yet, and is apparently difficult to obtain from Bohler right now, though CPM-1V is currently available at Alpha Knife Supply.

 

The post Matrix Steels K888 and CPM-1V appeared first on Knife Steel Nerds.

The following is a collaboration project between myself and Malachi Chou-Green. He obtained the Vanadis 60, did some heat treating experiments, and also did metallography including some fancy electron microscopy. He also heat treated and machined the CATRA knife that I tested. His original experiments were published some time ago on his Patreon, so if you want to see what he is up to I recommend visiting his Patreon page and becoming a supporter.

Video

The following information is also available as a video:

Background of Super High Speed Steels and Vanadis 60

High speed steels with greater than 2% vanadium for wear resistance were developed in the late 1930s  and early 1940s leading to M4 high speed steel and T15 high speed steel. I have written a short article on the history of M4 steel, and my recent book The Story of Knife Steel has a more etensive history if you are interested in reading further. Previously vanadium was found to lead to very hard carbides for very high wear resistance but when the additions exceed ~2% the steel would not harden. The breakthrough in the 1930s was that they learned that more carbon was necessary in conjunction with the vanadium, to compensate for the carbon that was being tied up in the vanadium carbides. However, vanadium was still limited to about 4-5%, otherwise the carbides would become too large and the steel would fracture during forging and/or rolling.

Another development occurred in the early 1960s when it was discovered that greater control over carbon content and cobalt addition could be used to make high speed steels that could be heat treated to 70 Rc. Several steels were patented within only a few years by different companies, with the most common being VASCO Hypercut patented in 1963, given the standard designation M42. You can read more about the history of these steels in this article. The compositions of these steels are shown in bold, and the older lower carbon versions of each are shown below each of the bold compositions in the “M40” series.

Around the same time Crucible developed powder metallurgy technology which was capable of creating finer microstructure in tool steels by avoiding the slow solidification associated with conventionally cast alloys. They began producing these steels for commercial scale in 1970. You can read more about how powder metallurgy works and its history in this article. At the beginning Crucible used this technology to improve performance of existing steels like M2 or T15, but they also began designing steels specifically for the technology. The first of these was CPM Rex 76, patented in 1972, which was a high hardness high speed steel with 3% vanadium.

Shortly after Crucible introduced their powder metallurgy technology, Stora in Sweden introduced their own version of the technology. This led to a legal battle that Crucible would eventually win, requiring Stora and Uddeholm to pay fines. Stora developed a higher vanadium 70 Rc high speed steel called ASP 60 which was introduced by 1975. It had 6.5% vanadium for higher wear resistance than Rex 76. Uddeholm purchased Stora in 1976. In 1978 Crucible published results of their experiments [1] comparing Rex 76 and ASP 60 which they claimed showed that higher than 3% vanadium did not lead to better performance in high speed tools. They also made a 6% vanadium version of Rex 76 and they demonstrated that it had no better tool life than the standard 3% vanadium version.

J.H.G. Stake of Uddeholm was not happy with these claims. He said [1], “I represent the firm that sells the steel mentioned which is available commercially, the ASP steels by the ASEA-STORA process. It is very difficult to comment on the slides shown here regarding the comparison between ASP 60, Rex 76, and Rex 76 with 6% vanadium. The main reason is that the trials have been done without any coolant and that is very unusual in commercial application in general practice. We prefer to go to the toolmaking industry and have the trials made there.”

Uddeholm would eventually begin selling ASP 60 under the name Vanadis 60 instead, and Erasteel which also had historical connections to Stora, would sell it under the name ASP 2060. Both have the same composition. Despite Crucible’s earlier claims about 3% vanadium being as much as is necessary, they would later release higher vanadium versions of Rex 76. The 9.5% vanadium version called Rex 121 was released in 1998 [2]. The 5% vanadium version is known as Rex 86 (Zapp sells it as Z-Max) which was released in 2005 [2]. Other high vanadium 70 Rc powder metallurgy high speed steels would be released by other companies, many of which are shown below:

For more exciting knife steel and tool steel history, plus a history of the modern knife industry including custom knives, high-end production knives, and Damascus, see my book The Story of Knife Steel.

Composition and Microstructure

As mentioned above ASP 2060 (Erasteel) and Vanadis 60 (Uddeholm) are identical in composition. They have molybdenum and tungsten (and to a lesser extent chromium adn vanadium) added for “hot hardness,” the ability for a steel to maintain its hardness at high temperatures. This is important for machining operations where the tools are run at “high speed” and thus heat up due to friction. Hot hardness is created through a phenomenon called “secondary hardening” where the precipitation of very tiny carbides causes the steel to further harden when tempering at high temperatures, which you can read about in this article. The vanadium content of Vanadis 60 is relatively high at 6.5% for wear resistance. Cobalt is added to further improve hot hardness by affecting how the carbides form in secondary hardening (as opposed to forming carbides such as molybdenum and tungsten). You can read more about cobalt in this article.

The toughness and wear resistance of high speed steels is largely controlled by the carbides. Where increasing carbide volumes and sizes tend to decrease toughness, increased volumes of harder carbides increase wear resistance. Each of the above mentioned steels forms some M6C carbides (tungsten/molybdenum carbides) and MC carbides (vanadium carbides). With this in mind, vanadium carbides are generally more desirable because they are harder and smaller than the tungsten/molybdenum carbides. Therefore the vanadium carbides are less detrimental for toughness while also contributing more to wear resistance.

Below I have calculated carbide contents using Thermo-Calc for Vanadis 60, Rex 86, Maxamet, and Rex 121. Importantly these are “equilibrium” calculations, meaning they assume an infinite hold time. Each is calculated for the austenitizing temperature that was used for the CATRA knife coupons I tested.

So based on total carbide volume alone we would expect Maxamet to have the highest toughness (it has the lowest carbide volume), followed by Rex 86, Vanadis 60, and finally Rex 121. Maxamet and Vanadis 60 have similar MC content but Vanadis 60 has higher M6C, so we would expect Vanadis 60 to have higher wear resistance than Rex 76, Rex 86, and Maxamet, but less than Rex 121.

Below are the micrographs for these steels to compare with Malachi’s Vanadis 60 micrograph.

Maxamet austenitized from 1975°F

Z-Max/Rex 86 austenitized from 2150°F

Rex 121 austenitized from 1925°F

Looking at the micrographs above, the carbide volume of Vanadis 60 appears to be similar to that of Maxamet, but the carbides are a bit smaller. Z-Max has a similar carbide size to Maxamet but a lower carbide volume. Rex 121 has the most carbide and the largest carbides as expected based on its composition.

We measured the carbide volumes of each steel using a simple method called “point counting” to compare with the Thermo-Calc estimates. The total carbide volume measured was significantly lower in Vanadis 60 and Rex 86/Z-Max than the equilibrium estimate. This is relatively unusual as equilibrium carbide volume estimates ten to underpredict the true carbide volume because it assumes an infinite hold time at austenitization temperature. Maxamet and Rex 121, both had carbide volume a few points above the Thermo-Calc equilibrium estimate which is more typical.

Malachi also took scanning electron microscope (SEM) micrographs of Vanadis 60 austenitized at 1900 and 2125˚F using the “backscatter” imaging technique where contrast is partially generated from composition differences within the sample. Heavier elements scatter more electrons back into the detector leading to bright areas. Thus vanadium carbides show up as grey while the tungsten/molybdenum carbides are white, due to the relative atomic weights of the carbide forming elements (V < Mo < W).

Vanadis 60 austenitized from 1900°F

Vanadis 60 austenitized from 2125°F

Using different colors he point counted the volume of M6C, and total carbides and compared them against the Thermo-Calc predictions. The measured M6C (tungsten/molybdenum) carbide volume was lower than Thermo-Calc, while the measured MC (vanadium) carbide volume was high. So it appears that Thermo-Calc is overpredicting M6C carbide and underpredicting MC carbide stability in Vanadis 60. Perhaps similar differences are leading to the overprediction of carbide volume in the Z-Max, and imply that the MC carbide volume of Z-Max may also be greater then Thermo-Calc predicts. This could partially explain why Z-Max preformed better in CATRA testing than my equation suggested it would.

Hardness and Heat Treating of Test Coupons

The ASP 2060 datasheet has a better heat treatment hardness chart than the Vanadis 60 datasheet so I have included it below:

Malachi reported that he got 70.5 Rc with 2125-1000°F (1160-540°C) and 68.8 Rc with 1900-1000 (1040-540°C). He also austenitized the CATRA coupon from 2025°F (1100°C) which I tempered at 1000°F (540°C) for a hardness of 68.4 Rc. Malachi reported to me he later measured the temperature of the furnace he was using and found it to be reading too high, (thus the furnace temperature was lower than 2025°F), which may explain why the hardness was lower than his previous 1900-1000 coupon. I also heat treated toughness coupons using 2025-1000°F and the resulting hardness was 69.0 Rc. As expected Vanadis 60 is capable of very high hardness.

Edge Retention

To test the edge retention, Malachi heat treated and machined the CATRA knife for testing. I performed the final sharpening and tested for slicing edge retention:

Somewhat surprisingly the resulting edge retention was only slightly higher than Z-Max after compensating for hardness, and was significantly below Maxamet. This was puzzling because Maxamet and Vanadis 60 have similar vanadium and carbon, while Z-Max is somewhat lower in both elements.

Based on our carbide volumes measurements, both the Maxamet and Vanadis 60 CATRA knives should have carbide volumes around 22%. However, as discussed previously Thermo-Calc seems to underpredict vanadium carbide and overpredict tungsten/molybdenum carbides in Vanadis 60 so perhaps the same thing is happening in Maxamet. This could be compounded by the difference in “tungsten equivalent” contents between the steels. Tungsten equivalent is calculated by multiplying the molybdenum content by two and adding it with the tungsten content, to account for the difference in atomic weight between the two. Since tungsten and molybdenum form M6C carbide, steels with higher tungsten equivalent contents are more prone to M6C carbide formation. The tungsten equivalent of Maxamet is 13% and Vanadis 60 is 20.5%, so perhaps the structure of Maxamet is mostly MC type carbides. We would need to do backscatter imaging with the Maxamet to confirm if there is indeed more MC carbide in the Maxamet than Thermo-Calc predicts.

Toughness

I heat treated and machined the Vanadis 60 charpy toughness coupons using the same 2025-1000°F heat treatment as the CATRA coupon, resulting in 69 Rc:

As expected by the very high hardness (69 Rc) and the relatively high carbide volume (~22%), the toughness was fairly low at 2.7 ft-lbs. Zooming in on the high hardness steels I added a trendline showing the approximate change in toughness with hardness for CPM T15, CPM Rex 45, CPM Rex 76, and Z-Max. Vanadis 60 looks like it has toughness a notch down from those steels while being more in line with Maxamet. This makes sense given that Maxamet has about the same carbide volume while those other steels have have lower carbide volumes ranging from 14-18%. Carbides are very hard particles and so they are detrimental to toughness. You can also see that as hardness goes up the difference between the highest and lowest toughness steels decreases. So at 61.5 Rc we have measured values all the way from ~4 ft-lbs to 45 ft-lbs. But at 67 Rc it only ranges from 2.6 to 5.9 ft-lbs. Thus it seems the higher the hardness the less influence the carbides have on the measured toughness.

One interesting thing to note is that the spread in toughness was particularly high for the Vanadis 60 coupons, coming out at 3.4, 2.1, and 2.6. This spread is especially apparent when we look at the 95% confidence intervals of the toughness measurements of other high hardness steels shown below. I am not sure what led to the variation, perhaps it was merely chance.

While it is hard to predict toughness trends, it seems that at the same hardness we would expect Vanadis 60 to have toughness between that of Z-Max and Maxamet, leaning more towards the Maxamet end of the spectrum. As mentioned above, the Vanadis 60 and Maxamet samples tested have similar carbide volumes but Vanadis 60 has finer carbides. Usually, we would expect finer carbides to lead to better toughness, however in this case the improvement seems somewhere between quite small and non-existent. Toughness in steels is determined by two factors, crack initiation and crack growth. In tool steels, the ductility is low enough that usually, crack initiation is the controlling factor, in these cases smaller carbides are harder for cracks to initiate on, leading to better toughness. However, crack growth is generally easier with a smaller interparticle distance (the distance between carbides). So while crack initiation is usually the controlling factor, maybe as the carbide volume increases, improvements to toughness caused by finer carbides are mitigated by their risk of increasing crack propagation.

Summary and Conclusions

Our testing of Vanadis 60 found toughness about where you would expect given its high carbide volume and very high hardness, and as expected it is capable of very high hardness and has excellent wear resistance. However, the slicing-edge retention was lower than we predicted based on the composition, testing more similarly (but still a bit higher) than Z-Max rather than the more compositionally similar Maxamet. We also explored the interesting history of Vanadis 60; while several other 5%+ vanadium 70 Rc powder metallurgy steels have come since then, Vanadis 60 was the first.

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[1] Kasak, A., and E. J. Dulis. “Powder-metallurgy tool steels.” Powder Metallurgy 21, no. 2 (1978): 114-123.

[2] https://www.crucible.com/Products.aspx?c=7

The post Testing Super High Speed Steel Vanadis 60 appeared first on Knife Steel Nerds.

New YouTube video is a Q&A from Knife Steel Nerds Patreon supporters. The following topics were covered:

Nitro-V vs 14C28N

Carbide pullout during sharpening

What is difficult about high hardness heat treating of MagnaCut

What steels are coming next after MagnaCut

Does a fine grain mean a good heat treatment?

What are good pocket sharpeners?

The post What is Next After MagnaCut? Q&A Video appeared first on Knife Steel Nerds.