Chemical composition of martensitic stainless steel, in 0.1% -1.0% C, 12% -27% Cr based on the combination of different ingredients to add molybdenum, tungsten, vanadium, and niobium and other elements. As the organizational structure is the body-centered cubic structure, the strength declined sharply in the high temperature.

      At below 600 ℃, high temperature strength is the highest in all kinds of stainless steel, creep strength also is the highest. 440A has excellent quench hardening property, high hardness steel, it has superior toughness compared with the 440B and 440C steel.  440B is used for cutting tools, measuring tools, bearings and valves, it has higher hardness compared with 440A steel and high toughness compared with 440C. 440C has the highest hardness in all stainless steel and heat-resistant steel, used for nozzles, bearings. 440F is improved  the cutting property of 440C steel, used for the automatic lathe.