About 440C|The hardest of the standard stainless steels. High carbon (0.95-1.20%) means it can heat treat to 58-60 HRC, which puts it in the same hardness range as tool steels. In the annealed state it machines reasonably well, similar to other 400 series alloys. After heat treatment it's extremely difficult to cut. Plan to do all your machining annealed and grind to final dimensions after hardening. Machinability rating is around 40% in annealed condition. Use TiAlN coated carbide and keep tools sharp. The high hardness means excellent wear resistance, so it's used for bearings, valve components, knife blades, nozzles, and injection mold inserts. Corrosion resistance is moderate, better after hardening and polishing. Compare to
416 (much easier to machine but nowhere near the hardness) and D2 tool steel (similar hardness but 440C has better corrosion resistance).
