The effect of deep cryogenic treatment on the microstructure evolution and mechanical properties of M2 high speed steel

Abstract Deep cryogenic treatment has been reported to be a beneficial process for improving the properties and microstructure of steels. Generally, deep cryogenic treatment should be combined with tempering to achieve the optimal effects on steels. However, the microscale relationship between deep cryogenic treatment and subsequent tempering is unclear. Therefore, the effects of deep cryogenic treatment combined with various tempering treatments on the mechanical properties and the microstructural evolution of M2 high speed steel are investigated in this work. The results showed that the hardness was increased by deep cryogenic treatment. Furthermore, deep cryogenic treatment improved the thermal stability of steel as the red hardness was maintained to be relatively higher after multiple times of tempering. Deep cryogenic treatment induced the transformation of retained austenite to martensite, which provided more nucleation sites for the precipitation of carbides during the subsequent tempering, and consequently promoted the dispersedly distribution of ultra-fine carbides in the microstructure. The strengthening effects of phase transformation and carbides precipitation were the main reasons for the improvement of mechanical properties of M2 high speed steel.