The Effects of Ultrasonic Impact Modification on the Surface Quality of 20CrNiMo Carburized Steel

Ultra-high residual compressive stress can be introduced via the ultrasonic impact on the basis of transformation hardening, and further enhance the overall performance of 20CrNiMo carburized steel. In order to achieve the best surface quality of 20CrNiMo carburized steel, ultrasonic impact modification testing with varying static loads (900 N, 1200 N, and 1500 N) and rounds (1, 3, and 6) was conducted. By characterizing microhardness, microstructure, the surface roughness and residual compressive stress, the influence of ultrasonic impact modification parameters on its surface quality were analyzed. The experimental results indicated that the static loads and rounds of ultrasonic impact modification had a significant impact on the surface quality. The best surface quality could be obtained after six rounds of ultrasonic impact modification under a static load of 1200 N. In addition, the surface roughness decreased from 0.40 & mu;m to 0.04 & mu;m, the surface microhardness increased from 679 HV0.1 to 1086 HV0.1, and the maximum residual compressive stress of 1195.36 MPa was formed. Furthermore, the surface quality would deteriorate when the static load and ultrasonic impact rounds were increased.