M42 high speed steel, Other Known Names are 1.3247, HS 2-10-1-8, S500, E M42, REX M42®, Dynamax. M42 is a molybdenum series high-speed steel alloy with an additional 8 or 10 percent cobalt, it has superior red hardness and wearing resistance as compared to conventional high-speed steels. This allows for shorter cycle times in production environments due to its higher cutting speeds and from the increase in time between tool changes. M42 steel costs less when compared to those same tools made of carbide.