Experimental study on surface integrity of ultra-high-strength steel by ultrasonic hot rolling surface strengthening

Ultrasonic hot rolling, a newly developed technology of surface modification and multi-field strengthening, is used for surface treatment of ultra-high-strength steel (45CrNiMoVA) at different temperatures, with the temperature as high as 300 °C. Based on the thermal softening and strain rate sensitivity of ultra-high-strength steel, the formation and evolution of surface integrity including surface topography, residual stress and microstructure were analyzed after ultrasonic hot rolling. It is found that ultrasonic hot rolling can still achieve good surface finishing effect, in which rolling pressure and ultrasonic impact play a key role. The residual stress amplitude and the depth of the affected layer are larger under the ultrasonic hot rolling, which is the influence of the ultrasonic impact and the thermal field together. In the temperature range of 150 °C–200 °C, the surface integrity after ultrasonic hot rolling is the best. The reason for the more stable residual stress after ultrasonic hot rolling is work hardening, age hardening, and precipitation hardening.