Thermodynamic modelling of the surface treatment of a wide thin steel plate with a Gaussian laser beam

摘要

This study develops a thermodynamic model to investigate the quasi-steady thermal process of a wide thin steel workpiece irradiated with a moving Gaussian laser beam. Equations are established for temperature distribution, transformation boundaries, homogenisation time of austenite and cooling rate. The equations are numerically solved with an error of less than 10~(-8). The temperature distributions for various thicknesses are compared with that for infinite thickness at different laser traverse speed. The lag of the peak temperature relative to the centre of laser beam is found to be limited. The conditions to produce full and partial martensite are investigated. The model is verified by comparing the calculated Ac_1 and Ac_3 depths and temperature cycles with the experimental results. For AISI 4340 steel, correction coefficients are applied to the model to produce an empirical equation for temperature cycles above 488.4℃.