Process Research of Surface Laser Phase Transformation Hardening for 42CrMo Material

42CrMo is an ultra-high-strength, low-alloy structural steel. To enhance its surface wear resistance and prolong the service life of components, surface strengthening techniques are commonly applied. In this study, a numerical model for the laser phase transformation hardening of 42CrMo was established. The temperature field and metallurgical transformations during the laser phase transformation hardening process were investigated through numerical simulation, and the morphology of the hardened layer after laser surface treatment was predicted. The effects of key process parameters on the temperature field and the characteristics of the hardened layer were identified. The optimal parameters for single-pass laser phase transformation hardening were found to be a laser power of 1200 W, a scanning speed of 20 mm/s, and a spot diameter of 6 mm. The accuracy of the simulation results was validated through laser phase transformation hardening experiments. The results indicate that under these optimal conditions—laser power of 1200 W and a scanning speed of 20 mm/s—the hardening effect is maximized. The surface hardness reaches a maximum of 782 HV0.2, with a cross-sectional hardness peaking at 875 HV0.2, which is three to four times higher than the base material’s hardness, with an average surface hardness of 745 HV0.2.