The History of 3V, Cru-Wear, and Z-Tuff Steel

Thanks to Patrick Gosselin for becoming a Knife Steel Nerds Patreon supporter!

Thanks to Kenneth Pinnow for talking to me about 3V steel development, Gary Maddock for talking to me about PD#1, CD#1, PD#5, Z-Wear, and Z-Tuff, and Mark Zalesky and Clay Aalders for getting me a scan of a 1979 Knife World article about Vasco Wear.

Vasco Die

In 1964, Harry Johnstin of Vasco Metals Corporation filed for a patent on a new steel made for “hot forging dies” [1]. The steel was designed to to have good hot hardness, meaning high hardness is maintained even at high temperatures seen in forging operations. The goal of the steel was also to offer a good combination of hardness, wear resistance, toughness, grindability, and corrosion resistance [1].

An important starting point for the development was improving wear resistance with vanadium without negatively affecting “grindability.” This property was measured with the “grinding ratio” which is the amount of metal removed divided by the amount of wheel that is removed in a grinding operation. If the value is below 1.0, more wheel is removed than metal which would be very poor grindability. The higher the value is, the less wheel wear is required for a given amount of grinding. They started with a based composition of 0.85% carbon, 7.5% chromium, and 1.5% molybdenum, and tested different levels of vanadium. They also compared to a Latrobe steel with 4% vanadium:

They found that by increasing the vanadium content to 2% led to a significant improvement in grindability, while the 2.6% vanadium steel had similar grindability to 0% vanadium. The 4% vanadium steel from Latrobe had very poor grindability. Therefore they set the vanadium content in between 2% and 2.6% to have an improvement in both wear resistance and grindability. This improvement in grindability is likely due to an improved carbide structure from the vanadium addition.

They also found that toughness was good in this steel, especially when compared with the 4% vanadium steel:

Based on these good results, they released the steel as “Vasco Die,” which was advertised as having “twice the toughness of D-2 and wear resistance up to 10 times that of A-2” [2]. And in the years shortly after they made modified versions, one for higher toughness called “Vasco Tuf” [3] and another for better hardness and wear resistance called “Vasco Wear” [4]. The Vasco Tuf had reduced vanadium, presumably to keep the carbide size smaller for better toughness. The Vasco Wear had a tungsten addition, presumably for higher hardness with high temperature tempering (secondary hardening), and better hot hardness.

Compositions from [5]

Vasco Wear in Knives

Vasco Wear saw use in knives shortly after its introduction. The earliest mention I found of it related to custom knives is 1979 [6], though it was probably used even earlier. Among the earliest makers to use Vasco Wear were Ted Dowell [6] and Bernard Sparks [7]. Ted Dowell continued to use the steel regularly for decades [8]. In the 1979 article in Knife World by Butch Winter, he reviewed two Ted Dowell Vasco Wear knives, including the “Kitchen Bowie” and the “Funny Folder.” He noted that edge retention was excellent, saying, “This is the weirdest steel I’ve ever used. It cuts and cuts and cuts! It looks dull and even feels dull, but it still cuts!” He also said that the toughness was good despite the excellent edge retention, a test of chipping a half gallon of ice was unable to dull the knife. He did say that the knife stained though did not rust, and ultimately stated, “I just can’t be happy with a steel that stains. Edge holding, of course, is important to me, but I am willing to make what I like to call one of life’s essential compromises.” His wife, however, did not mind, “I’ll give up several degrees of edge holding ability for more stain resistance, but Rita is made of stronger stuff. She says she doesn’t care what color the blade turns as long as it stays sharp!”

Image from [6]

Vasco Wear was also used by Gerber in production knives by 1987 [9].

Gerber knife in Vasco Wear [9]

8%Cr Die Steels

This series of Vasco steels successfully created the category of 8% Cr die steels. In the past, cold work die steels were typically either A2 (1%C-5%Cr) or D2 (1.5% C-12%Cr). D2 was used for applications that benefited from high wear resistance, and A2 was used where higher toughness was necessary. I wrote about the history of A2 here and D2 here. The 8% Cr steels offered toughness close to A2 and wear resistance close to D2, making them very versatile. Other companies followed with their own 8% Cr steels including Daido DC53 in 1987 [10], Hitachi SLD10 in 1989 [11], and others came later including Uddeholm Sleipner in 1998 [12]. These steels had increased Mo relative to Vasco Die to improve hardness with high temperature tempering, and reduced vanadium to maintain a smaller carbide size for better toughness. The reduced vanadium means that the wear resistance was also reduced, though that is an acceptable trade-off for certain applications.

Vanadis 4, 6, and 10 Steel

Currently Uddeholm produces a powder metallurgy steel called “Vanadis 4 Extra” that was introduced in 2002. However, the reason the steel is called “Extra” is because it is an improved version of an earlier steel called simply “Vanadis 4” which they filed a patent for in 1986 [13]. The original Vanadis 4 used as its basis 8% Cr. The patent does not specifically refer to Vasco Die or other similar steels but 8Cr-1.5Mo-1Si-0.4Mn is identical to the base composition of Vasco Die. They also developed Vanadis 6 and Vanadis 10 which contained 8% Cr and those were released somewhat after. Early versions of Vanadis 6 and Vanadis 10 are shown in the Vanadis 4 patent though they were slightly modified by the time they were released. These steels are essentially Vasco Die but with increased vanadium, and a corresponding increase in carbon.

Crucible, 3V Steel, and Cru-Wear

The patent for Vasco Die expired around 1982. The patent for Vasco Die only covered carbon contents as low as 0.8% which means it did not cover Vasco Tuf, and the patent does not mention tungsten, which means it did not cover Vasco Wear. However, it would have been difficult to produce those steels without a lawsuit that they were too similar to the patent. Some time after the patent expired, there were many companies producing their own version of Vasco Wear, including Crucible with Cru-Wear, which was introduced in 1994 [14]. Other versions include SB Wear, Carpenter Micro-Melt PD#1, Latrobe Lescowear or PGK, Spectrum Metal SpectrumWear, Thyssek-Krupp TSP3W, and Zapp Z-Wear.

Crucible began looking at powder metallurgy versions of Vasco Die and Vasco Wear in the mid-1990s [15]. Crucible had success with high speed steels like CPM-M4, CPM-T15, CPM Rex 76, and CPM Rex 20. And high wear resistance cold work steels like 10V and 15V. I wrote about the start of their powder metallurgy steels in this article, where I also explained how the process works. However, they didn’t have a high toughness powder metallurgy steel. The closest was maybe CPM M4, which is more of a “medium toughness” steel. Uddeholm had released the original Vanadis 4 (non-extra). However, with internal testing Crucible researchers had determined that CPM M4 had similar toughness to Vanadis 4 but with better wear resistance. Comparing different available tool steels, it was clear that high toughness steel was not possible without reducing the carbide volume, despite using powder metallurgy technology:

To test lower carbide volume steels they looked at powder metallurgy versions of Vasco Die and Vasco Wear. These steels had significantly higher toughness than other available powder metallurgy tool steels.

The powder metallurgy versions of Vasco Die and Vasco Wear saw about twice the toughness as the original conventionally cast versions. The wear resistance was found to be similar between the PM Vasco Die and Vasco Wear (at least in the crossed-cylinder wear test), and this was found to be because Vasco Die had more vanadium carbide than Vasco Wear. The increased carbon in Vasco Wear primarily increases the chromium carbide content, and chromium carbides are not as hard as vanadium carbides. Vanadium carbide is much more effective at improving crossed cylinder wear testing:

Therefore they pursued a patent on powder metallurgy Vasco Die steel, and called it CPM 3V. It is a bit surprising to me that they successfully patented a powder metallurgy version of a previously patented conventionally produced steel from another company. I was able to interview Kenneth Pinnow, one of the two metallurgists that hold the 3V patent. He told me that the successful finding was that using powder metallurgy technology led to a change in carbides from mixed vanadium and chromium carbides (2.8% VC and 1.7% CrC) in Vasco Die to fully vanadium carbide in 3V (5.1% VC). This was a previously unknown effect. In conventional ingot casting, the cooling rate is slow leading to segregation of chromium and therefore the formation of chromium carbides. This can lead to chromium carbide formation in steels that “thermodynamically” would not form chromium carbides at those temperatures. With powder metallurgy, the cooling rate is so rapid that the segregation does not occur and all vanadium carbide formed instead. With steels with high carbon and/or chromium contents, chromium carbides will still form such as in the original Vanadis 4, CPM Cru-Wear, K190, or stainless steels.

3V and PM Vasco Wear in Knives

3V saw use in knives shortly after release, and it’s difficult to pinpoint any one person who used it first. 3V was released around the same time as it was patented, available around 1997. It saw basically immediate use in knives, though I don’t think it’s ever 100% taken off as a common knife material. I think that is probably due to it being non-stainless. However, it has seen relatively frequent use ever since its release. Powder metallurgy Vasco Wear came later, and has been building steam as a choice for good wear resistance and toughness. Carpenter PD#1 (Punching Die #1) came first in terms of commercially available powder metallurgy Vasco Wear, the earliest reference to it I have found is from 2003 [16]. Now other steels with the same composition like CPM Cru-Wear and Z-Wear are also available. 3V and CPM Cru-Wear both offer a very good combination of toughness and wear resistance and can make great knives.

Carpenter CD#1 and Zapp Z-Tuff

Another steel which used Vasco Die and Vasco Tuf as inspiration is Carpenter CD#1 (Coining Die #1). I was able to speak to one of the developers, Gary Maddock, who confirmed to me that Vasco Die and Vasco Tuf were the basis of the new steel. CD#1 used a carbon content intermediate to those two Vasco steels with a similar chromium and molybdenum content. The vanadium content was further reduced from Vasco Tuf, to the same level as Crucible’s 1V. And nickel was added to further increase toughness. You can read about how nickel affects steel toughness in this article. CD#1 was released around 2004 [17]. It is among the toughest powder metallurgy steels now available. Given its vanadium alloying, it is probably one of the most wear resistant steels in its toughness class as well, increased wear resistance would likely necessitate reduced toughness.

Later, CD#1 was brought to Zapp as Z-Tuff with a slightly modified composition, with increased molybdenum for better secondary hardening, and correspondingly decreased chromium so that the the balance of the grade is not shifted. Zapp Tool Alloys was a USA branch of a pre-existing German company which was started to sell PM tool steels after the bankruptcy of Crucible. Zapp initially sold PM M4, T15, A11LVC (9V), and A11 (10V) but added powder metallurgy Vasco Wear as Z-Wear and their modified CD#1 as Z-Tuff.

Carpenter PD#5

In 2005, Carpenter released PD#5 which is a 4% vanadium version of PD#1 (Vasco Wear) [18]. It looks very similar to Vanadis 4 except that there is also a tungsten addition for increased secondary hardening. This steel has a small decrease in toughness for a small increase in wear resistance relative to PD#1.

3V Modified with Niobium

In the first article published to this website I wrote about a modified 3V steel that was patented but never released. It replaced most of the vanadium in 3V with niobium, which resulted in finer carbides for improved toughness with the same level of wear resistance. The original 3V has much lower toughness in the transverse direction as the longitudinal direction, while the modified version has near parity between longitudinal and transverse toughness. Read about why the direction of testing matters in this article.

However, that was not the only modification, as they added tungsten to 3V at a similar level as Vasco Wear. Which is a surprising callback again to the original inspiration for 3V coming from Vasco products.

Toughness

I previously wrote an article on the toughness testing of Z-Wear and conventional Cru Wear. You can see a summary of those toughness results here:

Z-Wear (CPM Cru-Wear) showed very good toughness up to relatively high hardness. 3V achieved a high level of toughness consistent with what Crucible has reported about it. And Z-Tuff is one of the toughest steels we have tested, perhaps the toughest when hardness is considered (61.5 Rc!). It was my recommendation for best high toughness high alloy non-stainless steel. Cru-Wear (non-CPM) matches the toughness of S35VN despite being a conventionally produced ingot steel.

Edge Retention

3V and CPM Cru-Wear have decent edge retention, with CPM Cru-Wear being a bit better. In the manufacturer CATRA dataset, CPM Cru-Wear was in between 3V and Vanadis 4E, as would be expected by its carbide content. Though V4E and Cru-Wear are in a similar class so if the CPM Cru-Wear is at higher hardness it can do better for wear resistance. To me it looks like 3V did a little bit better than would be expected (in the Bohler-Uddeholm data below), I’m not sure if that is a true result or test variability. Either way, it did pretty well in edge retention for its level of toughness. I don’t have any edge retention numbers for Z-Tuff, its carbide volume is quite low (~3%) so we would not expect its edge retention to be incredibly high. However, 3V did better than expected so maybe Z-Tuff would as well.

Corrosion Resistance

Corrosion testing of these steels is not particularly common as they are not typically used in applications leading to corrosion. Those applications would necessitate a stainless steel. However, a benefit of the relatively high chromium in these steels means that they can be classified in the “semi-stainless” category. In fact, according to my estimates, the chromium in solution and therefore the corrosion resistance of Cru-Wear and 3V is higher than D2. So while these steels would not be confused with stainless grades, they should offer some stain resistance. You can read more about how I estimated corrosion resistance in this article. Using the low temperature tempering range (300-500°F) leads to better corrosion resistance than the high temperature tempering range (>750°F) used in secondary hardening.

Microstructure

Conventionally Produced Cru-Wear

CPM Cru-Wear/Z-Wear – 10% carbide volume

CPM 3V – 5% carbide volume

Z-Tuff – 3% carbide volume

The powder metallurgy process greatly reduces the carbide size of Cru-Wear, which explains why its toughness is so greatly improved. You can read about how carbides affect toughness in this article. The carbide volume numbers I determined from my micrographs are similar to those reported in the 3V patent, I found about 5% carbide volume for 3V and 10% for CPM Cru-Wear. The patent reported 5.1% and 9.3%. The patent also has a micrograph for conventional Vasco Die but patents have terrible image quality.

Summary and Conclusions

Vasco Die was a very influential steel, starting the category of 8% Cr die steels. A higher toughness version, Vasco Tuf, was used in certain applications. And a higher wear resistance version, Vasco Wear, saw some use in knives. The popularity of Vasco Die and Vasco Wear led to other modifications of the category including Daido DC53 and Vanadis 4. Eventually 3V was patented which is a powder metallurgy version of Vasco Die. Powder metallurgy versions of Vasco Wear were also released including Carpenter PD#1, Crucible CPM Cru-Wear, and Zapp Z-Wear, which have had building popularity ever since. A high toughness powder metallurgy version of these steels was also developed called Carpenter CD#1 and a slight modification by Zapp called Z-Tuff. The excellent properties of this series of steels is a testament to the good design of the original Vasco Die in 1965.

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

[2] Design News 23, no. 21-26 (1968): 125.

[3] Steel 164, no. 9-17 (1969): 10.

[4] Metal Progress 107, (1975): 4.

[5] Metal Progress 114, (1978): 77.

[6] Winter, Butch. “The Alternative, Vasco Wear.” Knife World July (1979): 7-12.

[7] Fowler, Ed. “Whatever Happened to Bernard Sparks?” Knife Talk II: The High Performance Blade (2003): 168.

[8] https://www.bladeforums.com/threads/ted-dowells-address-phone-number.188075/#post-1541006

[9] Winter, Butch. “Sharpen Up.” Popular Mechanics April (1987): 92.

[10] Matsuda, Yukinori. “Cold tool steel.” Japanese Patent 6411945, issued January 17, 1989.

[11] Kada, Yoshihiro, Atsushi Kumagai, Atsusuke Nakao, Toshio Okuno, and Takehiro Oono. “High hardness and high toughness cold tool steel.” Japanese Patent 02277745, issued November 14, 1990.

[12] Sandberg, Odd, and Boerje Johansson. “Cold Work.” Sweden Patent 511747, issued March 27, 1998.

[13] Roberts, William and Borje Johansson. “Verktygsstaal intended Foer cold working.” Sweden Patent 457356, issued December 30, 1986.

[14] Selland, K. J. “Crucible Service Center Unit Unveils Cold Work Tool Steel.” American Metal Market(USA) 102, no. 99 (1994): 4.

[15] 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.

[16] Maddock, Gary R., and Robert Carnes. “The ABC’s of Alloy Selection, Heat Treating and Maintaining Cold Work Tooling.” Metal Forming (2003).

[17] Carnes, Robert and Gary Maddock. “Tool Steel Selection.” Advanced Materials & Processes June (2004): 37-40.

[18] https://cartech.ides.com/datasheet.aspx?i=102&E=455