In the heat treatment process after large-scale production of steel materials, quenching treatment and tempering treatment are the most common and important means in the heat treatment process. After quenching, the hardness of the material structure will be improved, but the newly formed martensite structure will be “very brittle”, which is caused by the nature of martensite itself, On the one hand, the internal stress is generated during the formation of martensite. In order to eliminate the internal stress and obtain the structure with good strength and bremsstrahlung, tempering treatment is generally adopted.
Tempering process is to heat the material to a certain temperature below 723 ° C, which can improve the plasticity of the material, but there may be some reduction in hardness. Generally speaking, the hardness of the steel after tempering treatment will decrease and the toughness will be improved, However, temper brittleness occurs in the two temperature ranges of about 250 ° C-400 ° C and 450 ° c-570 ° C. the former is called “low temperature temper brittleness” and the latter is called “high temperature temper brittleness”, which can also be called “reversible temper brittleness”.