Evolution of wear damage in gross sliding fretting of a nitrided high-carbon high-chromium steel

Fretting wear tests were performed to examine the evolution of fretting wear damage of the nitrided high-carbon high-chromium X210CrW12 steel against GCr15 steel ball, and to identify the role of nitrides (converted carbides) in fretting wear characteristics. The nitrided layer was characterized by optical microscope (OM), scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), electron probe microanalyses (EPMA), X-ray diffraction (XRD), and microhardness analysis. The worn surfaces were evaluated by SEM, EDS and 3D optical profiler. The results indicated that the initial carbides in the nitrided layer undergone a transformation into nitrides during nitriding. The nitrided specimens showed excellent wear resistance compared to the steel balls, and their wear damage was mainly caused by the adhesive/abrasive action of oxidized particles. Coarse nitrides led to the rapid wear of steel balls, and acted as barriers against the grooving of oxidized particles. Higher loading conditions of 40 N and 80 N induced the generation of central smooth zone and W-shaped wear scar. The formation of the central smooth zone was very beneficial for reducing the wear rate and friction co-efficient, thus the expected increase in wear volume with increasing applied load from 40 N to 80 N was not observed.