What's m2 steel?
Is it like d2?
Harder, softer what?
http://www.cutleryscience.com/reviews/blade_materials.html#T_M2
Apparently, it's a metal used for "high-speed cutting." For example, a power saw. From what it says there, the hardness is retained even at high temperatures, so as a high-speed saw is cutting through something, it will stay hard as it gets hot from the friction.