Improvement of wear resistance for carbon steel under unlubricated sliding and variable loading conditions

Abstract

Pin-on-disk unlubricated wear tests for 0.35% C steel were conducted in moist air under stepwise loading between low and high levels. The effects of rubbing history under mild or severe wear in the first stage on the transition of wear mode in the second stage were investigated. Under increased loading, in the first stage a highly wear resistant surface is formed by oxidation, work-hardening and flattening of contact surfaces for a long sliding distance under mild wear. In the second stage, the worn surface can bear high loads at which severe wear occurs under constant loading. This brings about a low specific wear rate under quasi-mild wear, which has been newly defined by the authors. The upper critical load (PAcr,i) under increased loading between severe and quasi-mild wear is quite higher than that (PAcr,c) under constant loading, leading to a considerable improvement in wear resistance. Under decreased loading, severe wear for very short sliding distance in the first stage generates unoxidized, roughened worn-surfaces with a highly deformed, hardened layer. In the second stage the worn surface is slightly oxidized at a low load for a long sliding distance, resulting in quasi-mild wear. However the critical load (PAcr,d) under decreased loading is slightly higher than the critical load (PAcr,c) under constant loading, meaning little improvement in wear resistance.