Effects of ultrasonic impact treatment on surface residual stress and electrochemical properties of 42CrMo4 steel

ObjectiveThe effects of different ultrasonic impact treatment time on cross section microstructure, surface residual stress, surface microhardness, and corrosion resistance of 42CrMo4 steel sample was investigated.ResultsThe results showed that after ultrasonic impact, a large amount of plastic deformation occurred on the surface of 42CrMo4 steel sample, which results in that the hardness could be increased. After ultrasonic impact with the time of 8 min, the average surface hardness of the sample reached 262.9 HV, 14.3% higher than the initial hardness. In addition, ultrasonic impact could effectively eliminate residual tensile stress on the sample surface and introduce residual compressive stress. The introduced residual compressive stress increased with the extension of ultrasonic impact treatment time within the range of experimental parameters. When the ultrasonic impact time was 8 min, the maximum residual compressive stress on the <italic>x</italic>-axis and <italic>y</italic>-axis reached -204.2 MPa and -121.5 MPa respectively. The corrosion resistance of the sample can improve after ultrasonic impact treatment. When the ultrasonic impact time was 8 min, the corrosion resistance of the sample was best, and the corrosion current density decreased to 12% of the untreated sample. Ultrasonic impact improved the corrosion resistance of the metal materials by changing the residual stress state on the surface, producing grain refinement effect and plastic deformation.