Aspects of Structure and Properties Formation in Steels During Laser-Acoustic Processing

In this study, we discuss the possibilities of improving the quality and properties of steels and alloys surface layers, as well as intensifying the laser treatment process by combining laser heating with the process of surface ultrasonic treatment (UST). It is established that UST after laser processing allows for enhancing the quality of irradiated products by smoothing possible violations of the surface microgeometry. It is revealed that UST of steel before laser treatment is essential for structure formation and hardening of irradiated materials. We establish that during laser-acoustic processing, the surface layers of steels are subjected to low-temperature (with UST) and high-temperature (with pulsed laser irradiation) dynamic effects. We demonstrate that the structure obtained by means of UST possesses increased density of defects in the crystalline structure and a considerable amount of precipitated dispersed carbides. This structure is the most prepared for laser quenching. It is observed that the combination of UST with laser exposure positively affects the material’s strength. This is due to the dynamic polygonization of austenite, the formation of a dispersed substructure, which is characterized by low-angle semipermeable boundaries between individual structural components and is inherited during martensitic transformation in irradiated steel. It is revealed that UST in the cavitation mode enabled to reduce the time of auxiliary operations for eliminating technological impurities before laser irradiation and to improve the quality of steel during laser-acoustic processing. We establish that compared with laser treatment without UST, laser-acoustic treatment increases the depth of the hardened layer by 30%–50% and the hardness of sur- face layers by 10%–15%.