Surface quality improvement of steel parts by combined laser-ultrasonic treatment: determination algorithm of technological parameters

Abstract

To provide the quality of the surface layer and improve operational properties, a combined laser-ultrasonic surface hardening and finishing technology of steel products is proposed. This work is devoted to determining the range of rational parameters of laser heat treatment and ultrasonic impact treatment for enhancing the complex hardening process of AISI 1045 steel and AISI D2 steel. Laser surface transformation hardening was carried out with a constant temperature strategy using a fiber laser and scanning optics at a heating temperature of 1200–1,300 °C and a processing speed of 40–140 mm/min. Ultrasonic surface hardening and finishing were performed on technological equipment with an amplitude of ultrasonic vibration of 18 μm and a load of the ultrasonic tool of 50 N. The ultrasonic treatment duration varied from 60 to 180 s. The results showed that laser-ultrasonic treatment leads to an increase in the hardening intensity by more than 200 %, forming a hardening depth of 200–440 μm. Combined treatment leads to a significant increase in wear resistance due to the formation of ultrafine-grained martensitic microstructure with hardness (58–60 HRC5) in the near-surface layer. The combined laser-ultrasonic hardening process control algorithm for surface treatment of structural and tool steels is proposed, limiting the heating temperature, the duration of laser (ultrasonic) exposure, and the vibration amplitudes of the ultrasonic horn. Laser-ultrasonic treatment will allow the formation of a surface layer with a given set of properties, providing increased wear and corrosion resistance. The developed technology can be used for surface hardening and finishing of large-sized steel products in the mechanical engineering industry.