Microstructure and residual stresses in surface layer of simultaneously laser alloyed and burnished steel

Abstract

The new hybrid method, which combines the laser alloying process with slide burnishing, was investigated and presented in the work. Both treatments were performed on the laser stage in one operation. The experiments were done on carbon steel alloyed with cobalt stellite. The alloying process was conducted with continuous laser CO 2, at different parameters. The single- and multiple-path processes were investigated. The microstructure, microhardness and residual stresses of surface layer after the laser alloying process and laser alloying combined with burnishing were presented. The results of the experimental studies have shown that the proposed new hybrid method allowed for the generation of compressive stresses in surface layer of the alloyed material. The structural analysis has proven that the burnishing process had caused deformation of grains in the 20–30 μm thick zone and increased microhardness of the surface zone material. The X–ray diffraction measurements of residual stresses in surface layer of the samples subjected to the alloying process and burnishing, both in cold and hot conditions, were performed. In the case of multiple-path laser alloying treatment the tensile stresses, approximately 500 MPa, were obtained at the surface. Multiple alloying combined with burnishing generated compressive stresses of about −600 MPa at the surface, substantially improving the surface layer.