The chemical composition of martensitic stainless steel is characterized by the addition of elements such as molybdenum, tungsten, vanadium, and niobium on the basis of different composition combinations of 0.1%-1.0%C and 12%-27%Cr. Because the organizational structure is a body-centered cubic structure, the strength drops sharply at high temperatures. Below 600℃, the high temperature strength is the highest among all kinds of stainless steel, and the creep strength is also the highest. 440A steel has excellent quenching and hardening performance, high hardness, and higher toughness than 440B steel and 440C steel. 440B steel is used for cutting tools, measuring tools, bearings and valves. 440B steel has higher hardness than 440A steel and higher toughness than 440C steel. 440C steel has the highest hardness among all stainless steel and heat-resistant steel, and is used for nozzles and bearings.