Influence of laser surface treatment on the microstructure distribution, bearing capacity and impact property of 1.0C-1.5Cr steel

A diode laser with a rectangular spot was used to perform laser surface treatment on a 1.0C-1.5Cr steel. Based on the numerical simulation, an empirical equation was developed to predict the peak temperature, and the microstructure distribution was analyzed. The bearing capacity and impact fracture mechanisms were also studied. The results indicated that the relationship between the peak temperature and scanning rate was affected by the depth, and the peak temperature on the outer surface was approximately linear with the reciprocal of the square root of the scanning rate. The higher peak temperature leads to cementite dissolution and coarsening near the outer surface. Cementite dissolution was postponed during the laser surface treatment. The bearing capacity was a combined result of strengthening in the surface region and softening in the heat affect zone. Under a lighter contact load, laser surface treatment had no adverse effect on the bearing capacity. However, under a heavier contact load, the plastic deformation of the heat affect zone slightly decreased the bearing capacity. The impact fracture started at the outer surface of the laser-hardened layer, and propagated intergranularly near the crack source, and then propagated inward through the transgranular fracture. Owing to the stress concentration near the interface between the cementite and martensite matrix, cementite particles tend to appear along the crack propagation path. The decrease in the impact absorbed energy is attributed to the brittleness of the hardened layer and tensile residual stress, and the impact toughness can be improved by preheating.