Knife Steels: M390, CPM 20CV, and CTS 204P

To all intents and purposes, these are all the same steel. As far as composition, they are almost exactly the same. M390 is made by BU (Bohler Uddxxx) in Europe. CPM 20CV is made by Crucible in the United States. CTS 204P is made by Carpenter in the United States.

Don't confuse 20CV with 20CP, 20CP is essentially the same as S90V and something else entirely.

All three of these are superb steels, in many ways the best balanced knife steels available today. M390 is probably the best known and has a strong following. I have found my Spyderco knives in 20CV and 204P to be superb. It is often said that few knife users would be able to find any difference between these steels. In other words, anything you hear about one can be applied to the others. With 20 percent Chromium, they are extremely corrosion resistant, maybe the most stainless of stainless knife steels.

PM process and "generation"

There is confusion about the statement that BU uses as "third generation" particle metallurgy to make M390. This really only is significant in the context of the history of BU. Comparing this to a "second generation" processes used by say Carpenter is meaningless.

In the thread above, a gentleman from Carpenter is quoted as follows. He is quite careful to emphasize that he is in no way trying to say anything negative about the product made by BU.
The first generation powder product that was originally produced in Sweden by Erasteel and Anval (now CPP AB) consisted of air induction melting in a top pouring furnace followed by pouring the molten metal into a tundish from which the molten metal is bottom poured out of the tundish and is atomized to produce a coarse powder, typically -1000 microns or -500 microns.

The second generation powder product as practiced by Erasteel, CPP AB, and Böhler, consists of the first generation air induction melting process followed by pouring the molten metal into a heated, refining tundish called an ESH tundish (Electro-Slag Heated tundish), where the molten metal is heated with graphite electrodes (Erasteel and Böhler process) or a plasma torch (CPP AB). The refining tundish permits the molten metal to be purified (reduce the amount of inclusions). After refining, the molten metal is poured out of the bottom of the tundish and is atomized to produce a coarse powder, typically -1000 microns or -500 microns (the same powder size as the first generation process).

Böhlers third generation powder product consists of the second generation process followed by a modified atomization process that produces a finer powder, typically 250 microns. Böhler claims the finer powder reduces the presence of coarse carbides compared to the first and second generation, coarser powder.

As noted above, CPP AB uses the second generation powder process. CPP BVL (BVL is our facility in the US and our source for CTS 204P) uses both air induction melting and vacuum induction melting coupled with the use of reticulated refractory filters in its tundish to produce 150 micron powder (finer than Böhlers powder) for P/M tool steel millform products. CPP BVLs powder manufacturing process does not directly compare to the European classification system of first, second and third generation powder processing. BVLs vacuum induction melting + filtration process plus the use of -150 micron powder is cleaner than the third generation process. The air induction melting process + filtration process plus the use of -150 micron powder is equivalent to the second generation process with a finer powder than the second generation process.

Effectively, from a dimensional perspective, our 2nd generation process produces a finer, 150 micron powder than their 3rd generation process which is 250 microns. And I don't believe they would argue that their 250 micron material would have finer carbides than our 150 micron material.

So there you have it in detail. The key point is that CTS 204P is made from a 150 micron powder, whereas M390 is made from a 250 micron powder, which is even finer than the 3rd generation product from BU.
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Tom's Knife Info / tom@mmto.org