Sliding wear behaviors of medium-carbon high-strength bainitic steel treated by boro-austempering treatment

Boro-austempering treatment is a new process for preparing high-strength bainitic steel with high surface microhardness and high wear resistance. In this study, a Fe-C-Si-Mn-Cr-Mo mediumcarbon bainitic steel with a borided surface layer and carbide-free bainite matrix was prepared by boro-austempering treatment. The microstructure, wear properties, and wear mechanism of the borided layer and bainite matrix were characterized and discussed by optical microscope, scanning electron microscope, micro-scratch experiment, and sliding wear experiments. The results show that the boro-austempering treatment can prominently improve surface microhardness and wear resistance. The surface microhardness reached 1400 HV, and the adhesion force of the borided layer and matrix was 40.2 N. In the rotary sliding wear experiments, the total wear rate of the boro-austempered samples decreased to 48.85 % of the only austempered samples. In addition, the wear mechanism changes from the strong protective mechanism by the borided layer to the weakened protective mechanism at the transition zone, and finally changes to the abrasive wear and adhesive wear of the bainite matrix. Moreover, the friction coefficient of the boroaustempered sample increased from 0.62 to 0.72 and then stabilized during reciprocating sliding wear. Finally, the contact stress theory was adopted to analyze the whole process of the boro-austempered sample during reciprocating sliding wear. Due to the competitive effect of materials parameters of wear medium and friction coefficient, the contact area increased continuously, the contact stress increased first and then decreased, and the maximum stress zone moved to and remained on the worn surface.