Effect of ultrasonic surface rolling on microstructural evolution and fretting wear resistance of 20CrMoH steel under different quenching temperatures

Abstract

The influence of ultrasonic surface rolling (USR) treatment on microstructures, residual stress, microhardness and fretting wear behaviors of 20CrMoH steel under different quenching temperatures (740, 840 and 940 °C) was systematically investigated. The results indicated that the maximum hardening layer depth of the USR treated specimen quenched at 740 °C was about 130 μm, accompanied by grain refinement and high-density dislocations. Simultaneously, the microhardness was mostly increased by 212 HV0.2 and the highest surface residual compressive stress (RCS) was up to −649 MPa. The fretting wear mechanisms of the specimens in different treatment states were mainly delamination and oxidative wear. The volume wear loss of the USR treated specimen quenched at 940 °C was reduced by 48% compared with the untreated specimen quenched at 740 °C. This could be benefited from the protection of the oxide layer and the effective prevention of cracks source by the higher surface RCS, as well as the grain refinement and the increase in dislocations caused by USR treatment.