Numerical simulation of multi-track laser surface melting of 42CrMo steel

Laser surface melting (LSM) provides benefits over the conventional surface processes, including minimum distortion, high level of hardness and narrow heat-affected zone. One known problem about laser surface melting a large area by multi-track is overlapping. This research is focused on the development of a numerical model to study the effect of overlapping ratio on the hardness and stress distributions in multi-track laser surface melting. The results of hardness calculation have confirmed the microstructure changes in the material and shown that laser surface melting can be regarded as a highly successful method to improve the hardness of the 42CrMo steel. The hardness of the first track of melted area shows a slightly decrease under the effect of tempering by the second laser track. After multi-track laser surface melting, the compressive residual stress exists in the melted zone, while the tensile stress in the heat-affected zone (HAZ) and the boundary of overlapped area may cause the initiation of cracks. With the overlapping ratio increasing, the maximum stress in the surface of the specimen decreases.