A study on the effect of temperature and holding time of cryogenic treatment on microstructure and hardness of SKD11 steel

Abstract

This study investigates the effects of cryogenic treatment parameters (temperature and holding time) combined with double tempering on the microstructure and hardness of SKD11 steel. After quenching, the steel samples were subjected to cryogenic treatment at temperatures of -20, -80, and -196°C with holding times of 2, 12, and 24 hours, followed by double tempering at 520°C. The results indicated that cryogenic treatment promotes the transformation of retained austenite into martensite. Furthermore, it enhances the precipitation of fine secondary carbides, which are uniformly distributed within the martensitic matrix. This effect was most pronounced in the specimen treated at -196°C for a 24-hour holding time combined with double tempering. After cryogenic treatment, the hardness of the steel increases with decreasing cryogenic treatment temperature and increasing holding time, reaching its highest value at -196°C for 24 h. Following tempering, the hardness tended to decrease due to carbon depletion from the martensitic matrix resulting from fine carbide precipitation. However, the combination of cryogenic treatment and double tempering still maintains high hardness and promotes the formation of a high density of fine secondary carbides in the tempered martensitic matrix. This is the core factor contributing to the enhancement of the wear resistance of SKD11 steel for cold-work die applications.