Influence of overlapping ratio on hardness and residual stress distributions in multi-track laser surface melting roller steel

Laser surface melting (LSM) has its advantages over the conventional surface processes, including minimum distortion, high hardness and narrow heat-affected zone. Temper softening in overlapping tracks is an important problem to be solved in multi-track LSM large components. In this work, a numerical model is presented in order to study the influence of overlapping ratio on the distributions of hardness and residual stress in multi-track LSM. The results of hardness calculation have confirmed the microstructures evolution in the material and indicated that LSM can be regarded as a highly successful method to improve the hardness of the roller steel. The melted area of the first track shows a slight decrease in hardness under the influence of tempering induced by the second laser track. After multi-track LSM, the residual stress distributed within the melted zone is mainly of the compressive type, while there is tensile residual stress in the heat-affected zone (HAZ) and the boundary of the overlapped area. The maximum stress decreases in the surface of the specimen with the increase in overlapping ratio. The validity of this numerical approach is confirmed by experimental observations. A good agreement is obtained between the calculated results and the experimental ones.