From the low temperature tempering martensite. Which is aimed at maintaining the hardened steel of high hardness and high wear resistance under the premise of reducing its quenching stress and brittleness, in order to avoid the use cracked or damaged prematurely. It is mainly used for a variety of high-carbon cutting tools, measuring tools, GB/T9711.1 line pipe, Rolling and carburizing, tempering hardness is generally HRC58-64.