A high performance tool steel which excels at toughness and arguably holds and edge better than any other carbon steel.  Like all CPM steels, CPM M4 is created using Crucible’s patented Crucible Particle Metallurgy process, which provides an extremely homogeneous, stable and grindable product compared to the traditional processes.  CPM M4 provides superbly balances levels of abrasion resistance and toughness through high doses of molybdenum (hence the “M”), vanadium and tungsten together with reasonably high levels of carbon.  It can be hardened to around 62-64 HRC but note M4 is a carbon steel is not considered stainless with relatively low levels of chromium.  So, while this is one of the best steels around for cutting, it has to be properly cared for and may develop a patina over time.  Some manufacturers have resorted to coatings which do help but note they won’t last forever.