Study on hardness and wear behavior of surface modification layer of 18CrNiMo7-6 alloy steel based on repeated scratch test

ObjectiveTo investigate the hardness and wear resistance of 18CrNiMo7-6 alloy steel and its surface modification layer after carburizing heat treatment.MethodsRepeated scratch tests were conducted using a Vickers indenter on both the 18CrNiMo7-6 alloy steel substrate and the surface modification layer with varying normal loads and number of scratch cycles. Material damage as the scratch cycles increased was observed using the optical microscope. Scratch morphological characteristics, including scratch width, residual depth, and pile-up height, were measured using a three-dimensional profilometry system. Additionally, scratch hardness and wear rate were analyzed.ResultsThe results show that both the scratch width and residual depth of the 18CrNiMo7-6 alloy steel substrate and surface-modified layer increased linearly with the number of scratch cycles. Due to the work-hardening effect induced by repeated scratching, the pile-up height also increased with the number of scratch cycles, although the rate of increase gradually diminished. The scratch width, residual depth, pile-up height, and wear rate of the 18CrNiMo7-6 alloy steel substrate were significantly higher than those of the surface-modified layer, while the scratch hardness was notably lower than those of the surface-modified layer. These findings suggest that the carburized surface-modified layer of 18CrNiMo7-6 alloy steel exhibits superior scratch hardness, a reduced wear rate, and significantly enhanced wear resistance compared to the substrate. The results can provide guidance for research on the construction and performance evolution of surface modification layer.