M4 High Speed Tool Steel for Knife Blades
AISI M4 Tool Steel
Manufacturer: Various (CPM-M4 only by Crucible)
M4, like M2, is a high speed Molybdenum tool steel but with a high Vanadium content as well to improve wear resistance and toughness. There is also an M3 specification, but it has not been used much in knives yet.
The primary difference between M2 and M4 are the increases in Carbon and Vanadium. This results in a superior steel overall with very high wear resistance and strength, and is rather easy to sharpen. Additionally, M4 can take a very nice polished finish as well, though Benchmade is mostly black-coating it now for corrossion resistance.
CPM M4 is Crucible's M4 steel created with their proprietary particle metallury process, and is call CPM Rex M4 HC in full. The HC modification indicates that it is modified with High Carbon. The additional Carbon is
CPM Rex M4 HC Composition