Sliding wear mapping of an ion nitrocarburized low alloy sintered steel

Abstract

A pin on disc wear testing machine was used to assess the tribological behavior of a low alloy sintered steel, with and without a plasma nitrocarburizing surface treatment. Dry and oil impregnated sliding were evaluated. A wide range of speed (0.2–4.0 m/s) and load (4–600 N) was investigated. The system's components (pins, discs and wear debris) were characterized by SEM, optical microscopy and XRD to identify the wear regimes and mechanisms. Wear maps were developed, based on the generated debris characteristics (composition, shape and size). The regimes of mild, severe and transient wear were identified. The transition from mild to severe wear was related to sharp changes of the wear rate. The transient wear regime, interposed between the mild and severe wear regimes, was detected for the base sintered steel at the speeds of 0.5 and 1 m/s in dry sliding for the load ranges 240–320 N and 80–100 N respectively. Oil impregnation of the base sintered steel expanded the mild wear regime towards higher loads throughout the whole sliding speed range compared to dry sliding. The presence of lubricant at the sliding system eliminated the appearance of the transient wear regime. For the plasma surface treatment, the transition loads were slightly higher than the base sintered steel, not consistently though. The beneficial attribute of the compound layer was in terms of reduced wear rate (10−6–10−4 mm3/m) for as long as it remained on the surface. The operating life of the plasma treated sintered steel was further prolonged in the presence of lubricant, impregnated in the sintered material.