According to the different performance requirements of the workpiece, according to the different tempering temperature, tempering can be divided into the following categories:
(a) low temperature tempering (150-250 degrees)
The tempered microstructure is tempered at low temperature. The purpose is to reduce the quenching internal stress and brittleness in the premise of maintaining the high hardness and high wear resistance of the quenched steel, so as to avoid cracking or premature damage during use. It is mainly used for a variety of high carbon cutting tools, measuring tools, cold punching mould, rolling bearing and carburized parts, after tempering hardness is HRC58 - 64.
(two) medium temperature tempering (350-500 degree)
The tempered microstructure is tempered at medium temperature. The aim is to obtain high yield strength, elastic limit and high toughness. Therefore, it is mainly used in the processing of various springs and hot dies, and the hardness is generally HRC35 - 50 after tempering.
(three) high temperature tempering (500-650 degrees)
The microstructure of tempered steel is tempered bainite. The heat treatment, which combines quenching with high temperature tempering, is called quenching and tempering. The purpose is to obtain the comprehensive mechanical properties of strength, hardness, plasticity and toughness. Therefore, it is widely used in automobile, tractor, machine tools and other important structural parts, such as connecting rod, bolt, gear and shaft. After tempering hardness is commonly hb200-330. The chemical reaction between atmosphere and metals