Combined Laser-Ultrasonic Surface Hardening Process for Improving the Properties of Metallic Products

Combined laser-ultrasonic hardening and finishing process of large-sized products using laser heat treatment (LHT) followed by the ultrasonic impact treatment (UIT) is proposed. In this study, a medium carbon and chromium tool steels were heat treated by a 1 kW fiber laser with scanning optics and heating temperature control system to improve their surface hardness. A number of experiments are carried out by changing the heating temperature and specimen feed rate while keeping a constant scanning speed and width to produce the hardened layers of different depths. After the LHT, the specimen surfaces were severely deformed by an ultrasonic tool equipped with a seven-pin impact head supplied by a 0.3 kW ultrasonic generator and controlled by a computer-driven machine to form a regular surface microrelief and compressive residual stresses. The results indicate that the combined treatments provide more than triple increase in the surface hardness and formation the compressive residual stresses. Additionally, the LHT + UIT leads to a formation of the regular surface microrelief with minimum surface roughness and high oil holding capacity.