Abstract: Temperature distribution of unsteady heat transfer during laser quenching of 45 steel was obtained by solving an explicit two-dimensional finite difference equation, and the effect of laser power on the surface temperature after single pass laser quenching was analyzed. Utilizing JMatPro, comprehensive phase transformation curves, as well as temperature-dependent thermophysical properties and phase transformation critical temperatures during heating and cooling processes of the material, were derived. Incorporating both the laser heat source and latent heat of phase transformation, a unsteady heat transfer model for the surface laser quenching of 45 steel was established. This model was then employed to conduct heat transfer analysis under both fixed and moving heat source conditions during laser quenching. The results show that the error of the maximum temperature calculation under fixed heat source condition is within 7%. When the laser irradiation time is 0.5 s and the power is between 1300 W and 2600 W, the surface temperature of the specimen can be effectively controlled between 720 ℃ and liquidus 1495 ℃, ensuring the occurrence of solid phase transformation during laser quenching process. The model is applied to single pass moving heat source laser quenching at high power, which can better reflect the actual temperature change trend.

Key words: laser quenching, unsteady heat transfer, laser heat source, latent heat of phase transformation, critical temperature of phase transformation