Three-dimensional temperature distribution in laser surface hardening processes

Abstract

This paper introduces a new analytical solution to predict transient temperature distributions in a finite thickness plate during laser surface hardening. This analytical solution was obtained by solving a transient three-dimensional heat conduction equation with convection boundary conditions at the surfaces of the workpiece. To calculate the temperature field numerically in laser surface hardening processes, laser beam absorptivity, one of the most important parameters, should first be determined. It was extremely difficult to find an accurate value for laser beam absorptivity owing to the use of coating material on the workpiece surfaces, essentially to improve the efficiency of laser beam power. Therefore, in this paper, absorptivities were measured experimentally under various hardening conditions, including variations in coating thickness, laser beam power and beam travel velocity. Thereafter, to prove the validity of the model, a series of laser surface hardening experiments was performed on medium-carbon steel under various hardening conditions. The hardened layer of the etched cross-sectional view was examined and compared with the isothermal lines predicted by the proposed analytical model, in which the values of the experimentally measured absorptivity were employed. The results showed that the solution predicted well the transient temperature distribution of finite plates with satisfactory accuracy. Also, owing to the simplicity of the solution method, the analytical model developed may be easily implemented for simulation work for analysis and prediction of laser surface hardening processes under various hardening conditions.