S30V Steel – History and Properties

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And thanks to Dick Barber for talking to me about the development of S30V.

S30V Background

S30V is a knife steel produced by Crucible, released at the end of 2001 [1]. Crucible has been a part of the knife steel industry for many decades, such as with steels like 154CM which was developed in the late 1950’s and gained popularity in knives through Bob Loveless in the early 1970s. I wrote about the history of 154CM in this article. Crucible also famously developed powder metallurgy steels which started commercial-scale production in 1970. Powder metallurgy allowed higher alloy steels and finer microstructures because of the rapid solidification process. You can read more about how powder metallurgy works and its history in this article. Crucible developed several powder metallurgy steels including 10V, S60V (formerly 440V) and S90V (formerly 420V), but none of them really gained wide use in knives. 10V, developed in the 1970s [2][3], had very high wear resistance with good toughness but was not stainless. With poor grindability and little stain resistance it has never been used much outside of individual custom knives. S60V was released in the early 1980’s [4], perhaps the earliest PM stainless tool steel. S60V is not a bad steel and has relatively high edge retention, but its grindability and toughness are also relatively poor and its corrosion resistance is only mediocre. S90V, patent filed in 1995 [5], managed to improve on wear resistance, toughness, and corrosion resistance of S60V but its high wear resistance, and therefore poor grindability, means that it has never been a mainstream knife steel.

Dick Barber, former Crucible metallurgist who was the lead developer on S30V, asked Chris Reeve (of Chris Reeve Knives) why they were using BG42 steel rather than one of the available Crucible products [6]. Chris said that if Crucible made something better they would buy it. That conversation led to Dick, along with Ed Severson, conducting interviews with many knifemakers and knife companies about the properties they desired in a knife steel. They interviewed people like Sal Glesser, Ernest Emersion, Tony Marfione, Phil Wilson, Bill Harsey, Mike Jones, Steve Ingrim, Tom Mayo, Jerry Hossom and Paul Bos [7]. The early versions of the steel were first tested by Chris Reeve Knives making that company very significant to what the final product became. The goal was to design a steel which was superior to BG42 in terms of toughness, edge retention, and corrosion resistance. Improving all of those properties at the same time is difficult but I’m sure it helped that S30V is produced by powder metallurgy. S30V also needed to be easily heat treated with common knife heat treating equipment which was why Paul Bos was consulted.

Evolution of Steel Design Prior to S30V

154CM was designed for bearings, and was essentially a modification of 440C by reducing the chromium (Cr) by ~3% and adding 4% molybdenum (Mo). The molybdenum was added so that the bearings could be operated at high temperature, but it was discovered that partially replacing Cr with Mo led to similar corrosion resistance to 440C. S60V, however, was essentially 440C but with 5.5% vanadium added and enough carbon to maintain similar hardness potential. In the development of S90V, the Cr was reduced relative to S60V, dropping from 17% to 14% similar to the modification of 440C to make 154CM. However, the Mo was not increased to compensate. The Cr was reduced for a different reason, however. Chromium and vanadium both compete to form carbides. Carbides are hard particles in steel that add to wear resistance but detract from toughness. With a low Cr (5%) steel like 10V, basically all of the vanadium forms the very hard vanadium carbides (VC) which contribute to wear resistance and edge retention. The chromium also forms some softer chromium carbides but they are dissolved at typical heat treating temperatures. Softer chromium carbides do not contribute as much to wear resistance but they detract just as much (or more) from toughness as vanadium carbides do. Therefore, having only vanadium carbides means a better wear resistance-toughness balance. The higher the chromium content, the less vanadium carbide is formed for a given vanadium content, and more and more chromium carbide is formed. You can read more about carbide types and how elements interact to lead to different amounts in this article on carbides.

So what they did in the development of S90V was reduce the chromium content by 3% and add a corresponding amount of vanadium while maintaining a similar carbon content. This resulted in a similar amount of carbide, but much more of it is vanadium carbide, which results in higher wear resistance. Vanadium carbides also tend to be smaller (read this article) so having less chromium carbide means better toughness as well. And less chromium carbide means that even though S90V has less chromium, less is tied up in carbides so that the chromium is free in the steel to improve corrosion resistance. See this article to learn about corrosion resistance. Below is a table summarizing the resulting properties including the amount of chromium carbide (M₇C₃), vanadium carbide (MC), measured toughness (higher is better) wear resistance in a crossed-cylinder wear test (higher is better), and corrosion measured in a 10% boiling acetic acid solution (lower is better):

Design of S30V

So with all of those lessons learned, it was known that a lower chromium content would allow vanadium to go further in terms of its contribution to wear resistance. Another fact known is that a reduced carbon and vanadium content would lead to a steel that was tougher and easier to grind because of a reduction in overall carbide content. This is why 3% vanadium 3V has much better toughness and grindability than the 10% vanadium 10V, though at the cost of wear resistance. So to design a more balanced steel than S90V with improved toughness and grindability, a reduction in carbon and vanadium was necessary.

Crucible started with 154CM as their basis, replacing 2% Mo with 2% vanadium. However, in testing of that steel Chris Reeve Knives wanted more wear resistance to better differentiate from BG42, leading to an increase in vanadium up to the final 4%. The increase in Mo from 1% in S90V up to 2% in S30V provided an increase in corrosion resistance with the relatively low 14% Cr. Molybdenum improves corrosion resistance, as mentioned earlier in connection with 154CM. Another change to S30V is that an intentional nitrogen addition was made of about 0.2%, which was made to improve corrosion resistance but also means improved hardening when heat treating. You can read more about what nitrogen additions do in this article on nitrogen additions as well as this article on S45VN. As described in the S45VN article, nitrogen also decreases the chromium carbide content while increasing the vanadium carbide content, though I’m not sure that was recognized at the time that S30V was designed.

The resulting design of S30V provided an improvement over BG42 for the desired properties:

1. Toughness – improved because of a small reduction in carbide content along with using powder metallurgy for finer carbides
2. Edge retention – increased vanadium for hard vanadium carbides led to increased wear resistance and therefore slicing edge retention
3. Corrosion resistance – With the vanadium addition, less chromium carbide is formed in the S30V leading to improved corrosion resistance relative to BG42 and 154CM

Properties of S30V

Heat Treatment Response

The goal in terms of making a steel “easy to heat treat” was accomplished primarily by ensuring the steel could by austenitized (hardened) by heating to a temperature no higher than 2000°F. Some furnaces are limited to relatively low temperatures, and at the time of the release of S30V, there were many knifemakers with Paragon brand furnaces with a maximum temperature of 2000°F. Another factor with ease in heat treating is how fast the steel must be quenched from high temperature and still achieve full hardness. Molybdenum additions improve “hardenability” so that slower air quenches can be used, so the 2% Mo helped in that regard. As shown in the datasheet, S30V can reach at least 64 Rc when using cold treatments, and can easily be tempered down to the 58-61 Rc range common for many knives.

Microstructure

The carbide structure of S30V was finer than the common 154CM (BG42 is similar) because of powder metallurgy. It was also somewhat finer than the previously available S60V and S90V.

S30V

154CM

S60V

S90V

Edge Retention

Below shows the results of CATRA experiments reported by others that I have shown in other articles. The edge retention of S30V is still pretty good relative to other knife steels, better than steels like XHP, Elmax, 154CM, 440C, etc. It is a bit below steels like ZDP-189, S90V, and 20CV/M390. With my own CATRA experiments the relative position of S30V is approximately the same, but I will be talking about those experiments in a future article.

Toughness

The toughness of S30V is similar to other stainless steels in its class according to my own toughness experiments, though not record-setting, as seen in our standard toughness test utilizing unnotched 1/4 size charpy specimens:

However, I think the toughness of S30V could be further improved with better heat treating, if we use what we learned with heat treating S35VN, S45VN, and SPY27. The S30V sample I tested was austenitized at 2000°F and tempered at 500°F. Perhaps the toughness could be improved to 7-8 ft-lbs at 1-2 Rc higher hardness if using 2025-2050°F and 400°F:

Corrosion Resistance

The corrosion resistance of S30V and the similar S35VN have been found to be better than CPM-154, in a range I would call “above average.” The corrosion resistance has been improved somewhat with the new S45VN, but S30V is good enough for many knives. This was also confirmed in my own corrosion resistance testing, where a higher rating below means better resistance to corrosion. S30V and S35VN are very similar for corrosion resistance.

Legacy of S30V

S30V gained wide usage in a relatively short period of time. To this day S30V is very common in production and custom knives, to the point where it is even considered by some to be a “boring” choice because of its ubiquity. Personally, excitement over the release of S30V in 2001 was part of what led me to become a metallurgist and to eventually research and write for this website. Modifications of S30V led to the development of the also popular S35VN, and the more recent S45VN. So even as S30V is replaced to some extent, it is often by steels that owe some of their design to the older S30V. S30V continues to be the benchmark other stainless knife steels are compared to.

Summary

S30V was designed to offer a “balanced” stainless steel which could offer good grindability, toughness, corrosion resistance, and edge retention. It was designed in conjunction with knife companies, knifemakers, and heat treaters to learn the properties that they wanted in a knife steel. The lead development metallurgist was Dick Barber who used the history of stainless steels developed by Crucible to inform the designs that were tried, including important details like the amount of chromium used, how much vanadium to achieve the right balance of properties. And molybdenum and nitrogen additions were used to balance the corrosion resistance along with edge retention and toughness. Good heat treating response was achieved allowing heat treatment to be performed in a range of different furnaces. The resulting edge retention is better than steels like Elmax, S35VN, CPM-154, and BG42, though a bit worse than S90V and M390. The toughness measured was good, though could possibly be improved through more optimized heat treatments than what I used. Corrosion resistance is “above average” and has been sufficient for many knives that have been released over the almost 20 years S30V has been available.

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[1] http://www.seamountknifeworks.com/js/web/viewer.html?file=articles/pdf/S30V_update.pdf

[2] Haswell, Walter T., and August Kasak. “Powder-metallurgy steel article with high vanadium-carbide content.” U.S. Patent 4,249,945, issued February 10, 1981.

[3] “Powder metallurgy tool steel article.” British patent 1443900, issued July 28, 1976.

[4] Chilton’s iron age 226, no. 21 (1983): 53.

[5] Pinnow, Kenneth, William Stasko, and John Hauser. “Corrosion resistant, high vanadium, powder metallurgy tool steel articles with improved metal to metal wear resistance and a method for producing the same.” U.S. Patent 5,679,908, issued October 21, 1997.

[6] https://www.bladeforums.com/threads/the-true-history-of-s30v-development.1015831/

[7] https://www.bladeforums.com/threads/chris-reeve-green-beret.384825/page-5#post-3538203