Effect of Laser Quenching on Surface Microstructure and Hardness of Different Pretreatment 18CrNiMo7-6 Steel

The quenching-tempering pretreatment and quenching-tempering + pseudo-carburizing pretreatment of 18CrNiMo7-6 steel were carried out, and then laser quenching was carried out under different laser powers (1 000, 1 500, 2 000, 2 500, 3 000, 3 500 W) and different scanning speeds (2, 4, 6, 8, 10, 12 mm·s⁻¹). The effects of laser power and scanning speed on the microstructure, hardness and depth of the surface hardened layer were studied. The results show that after laser quenching, the microstructures of surface hardened layer of quenching-tempering + pseudo-carburizing and quenching-tempering pretreated test steel were both mainly composed of low carbon martensite. With the increase of laser power or the decrease of scanning speed, the hardened layer depth of the two pretreatment test steels increased. The hardened layer depth of the quenching-tempering + pseudo-carburizing pretreatment test steel was larger, and the hardness of the hardened layer was higher. After laser quenching, the hardness of the two pretreatmeet test steel (not higher than 475 HV) was lower than that after carburizing quenching (700 HV).