Investigation on surface integrity and process parameters optimization of carburized 18CrNiMo7-6 steel by induction-heating assisted ultrasonic surface rolling process

The effect of induction-heating assisted ultrasonic surface rolling process (IH-USRP) at different temperatures on the surface integrity of carburized 18CrNiMo7-6 steel was studied. The heating method is induction heating, and the heating temperature range is 100 °C ~ 300 °C. The residual stress, microhardness and surface topography of the modified layer on the sample surface were measured after ultrasonic surface rolling process (USRP). It was found that with the heating temperature increased, the residual compressive stress and the maximum residual compressive stress increased by 29% and 25.5% respectively, and the residual compressive stress depth also increased. The hardness affected layer increased from 1.5 mm to 1.8 mm, and the surface roughness decreased significantly. However, when the heating temperature is higher than the martensitic transformation temperature, the residual compressive stress and microhardness of the sample surface layer decreased, and the surface roughness increased. The process parameters of IH-USRP were optimized by grey correlation analysis method. The optimum process parameters to achieve the best surface integrity are static pressure 400 N, rotate speed 50 r/min, feed rate 0.04 mm/r and heating temperature 250 °C. The significant order of the effect on surface integrity are: static pressure > rotate speed > feed rate > heating temperature.