Working with Crucible Materials CPM 3V Steel

by Spencer Hochstetler, Philip Smith and Bill Tindall

The following information is a summary of what we were either told by the supplier and/or heat-treater, or what we found from our experience. We welcome additional suggestions, tips, disagreements, cookies (real ones).

See knives@crucibleservice.com for ordering information. There was a $75 minimum when we ordered and the cost was $15 per pound. The steel will arrive in an annealed state at about Rc 25 covered with a black oxide coating.

This steel is strange to work. It must be attacked slowly. It can be sawed, filed, ground, sanded, milled (mfg. says not but we did it successfully) drilled, etc., but it must be done slowly or it will harden and you will be doomed. A high-speed grinding wheel will slowly grind it away as though it were hardened. Slow the wheel down and a coarse grit wheel will remove slivers of metal in a milling action that is much faster. A 6" belt sander with 50 grit alumina/zirconia grit will quickly remove piles of metal if the belt is slowed by a half (I replaced motor with 1750 rpm). A portable belt sander also works as does an angle grinder or even a sharpening system with a slow aggressive wheel. Hand hack sawing is reasonably fast but band sawing at 100 fpm is nice if you have it. Before heat treating sharp internal corners must be rounded and the black oxide removed or it may crack. So, for example, the inside corners of tangs are slightly rounded on the edge of a grinding wheel.

We experienced little distortion during heat-treating. Therefore, it saves time if the backs of chisels are flattened and near finish ground, and the bevels trued. Heat-treating was done at Paul Bos, PaulBos@buckknives.com and included cryo hardening and 2 tempering cycles. The knife makers have never seen chipping on this steel so one might as well harden it as high as it goes, Rc 61-62. The cost was $70 for 20 pieces.

We have not yet determined a totally successful sharpening procedure for the hardened steel. It is by far the most abrasion-resistant material we have ever seen, probably as a result of the vanadium carbides formed as well as cryo treatment. It is much more abrasion resistant than a Hock A2 iron which may indicate that it has merit for plane iron construction. The procedure described in our abrasive sheet sharpening Article (coming soon to the Articles Section) will leave some rogue scratches from larger grit sizes that show up during final polishing. These scratches prevail because aluminum oxide does not abrade the hardened metal at an acceptable rate and determining when the larger scratches have been completely removed from a previous grit is difficult. We've found alumina/zirconia to be fairly effective. The supplier recommended cubic boron nitride (CBN) or diamond as materials for sharpening. It is reported that the ceramic abrasives are effective. Diamonds cut it rapidly but we don't know the best (least costly) way to take advantage of this abrasive. It wears out diamond bench stones unacceptably quickly. Suggestions are needed. Rogue scratches not withstanding, edges can be sharpened to a high degree and establishing a scratch-free microbevel was quickly accomplished with 3M aluminium oxide lapping film. Obvious refinement in edge sharpness is detected through 1 micron abrasive. We have not explored finer abrasives. The grain structure of this steel is reported to be exceptionally fine so we presume it can be sharpened at least as well as the best cutlery steels.

We expect and welcome refinements to these initial trials. Separate articles describe tool construction and chisel tests.