Unraveling the Friction and Wear Mechanisms of a Medium-Carbon Steel with a Gradient-Structured Surface Layer

This study investigates the enhancement of tribological performance in coarse-grained (CG) 42CrMo steel through the development of gradient-structured (GS) samples using double-sided symmetrical surface mechanical rolling treatment (D-SMRT). Dry reciprocating sliding wear tests are performed against a GCr15 steel counter ball to evaluate the influence of normal load on the wear resistance of CG and D-SMRT samples. Results demonstrate that D-SMRT significantly improves wear resistance under a 5 N load, attributed to the synergistic effects of surface strengthening and microstructure refinement. Characterization of worn surfaces via scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) confirms oxidative wear and abrasive wear as the dominant mechanisms at 5 N. With increasing load, wear transitions to abrasive and fatigue wear for the CG sample, while adhesive wear and plastic deformation dominate in the GS sample. This work concludes that D-SMRT technology effectively enhances the tribological properties of 42CrMo steel under normal loads below 10 N.