It’s not stainless. In fact a product insert warns you to protect the blade.
Bohler-Uddeholm list the following reasons to use their K390 Microclean steel:
- Good machinability because of uniform mechanical properties,
- Excellent grind ability even with deep engraving in the tool & die center,
- Uniform low dimensional change during heat treatment,
- Non sensitive against overheating or long soak times.
- Optimal EDM characteristic due to uniform carbide distribution.
The Chemistry also looks interesting.
- C 2.4%,
- Cr 4.2%,
- Mo 3.8%,
- V 9%,
- W 1%,
- Co 2%.
I should also note, new steels aren’t simply made by dumping elements together. Tempering, stress relief and hardening cycles have a major part in any production metal. Still, I find these numbers amazing, especially the 9% vanadium and 2.4% carbon!
Strictly speaking chromium levels should be around 11% to be classified as stainless. Chromium forms carbides that stabilize the microstructure, so in ordinary steels you need an excess of chromium to react with carbon and still have enough to protect against rust. Here you have vanadium to form carbides. So is there enough chromium to form the transparent chromium oxide barrier? I don’t know.
I think the K390 steel is going to be a winner. I haven’t had to sharpen it yet, but I have no doubt my Spyderco Sharpmaker is up to the job. I understand you’re going to see K390 steel in a lot of other Spyderco products. I also think you’re going to like it.