The way i understand it from purely theoretical sources m2 is a high temperature tool steel high speed steel while d2 is borderline between cold working and high temp.
M2 tool steel knife.
World wide the m2 type is by far the most popular high speed steel having replaced t1 high speed in most applications because of its superior properties and relative economy.
Keep your blade oiled as d2 is prone to rusting and corrosion.
There s no doubt h1 is a specialty steel.
When we call a normal steel stainless it.
Good edge retention toughness and sharpenability d2 has been a popular knife tool steel dating back to wwii and for good reason.
A2 is a mid range air hardening tool steel it s known for its good toughness its tougher than d2 steel or m2 steel and it has a wear resistance in between o1 steel and d2 it s used for punches and dies chuck jaws cutting tools for woodworking tooling for plastic injection dowel pins hammers industrial knives and gage.
M2 high speed steel.
Hs 6 5 2 1 3343 s600 steel e m2 rex m2 skh 51 p6m5 6 6 m2 tool steel.
M2 high speed steel m2 is a tungsten molybdenum high speed steel with a well balanced composition suitable for a wide variety of applications.
This is one of those most ubiquitous steels in knives.