Wear and Adhesion Properties of High-Pressure Torsion Processed Carbon Steel

Abstract

High-pressure torsion (HPT) is one of the most promising methods employed to fabricate ultra-fine grained (UFG) materials for use in industrial applications. The aim of this work is to investigate the tribological behavior of UFG carbon steels produced by an HPT. In cases where the counter ball material was tungsten and cobalt cemented carbide (WC-Co), the wear rate (0.2~2.0x10-7 mm2/N) decreased with increasing the Vickers hardness (Hv200~650) for both HPT processed and quenched-tempered (QT) steels. On the other hand, in cases where the counter ball material was high carbon-chromium bearing steel (SUJ2), the wear rate of HPT (1.0~2.5x10-6 mm2/N) increased with increasing the hardness, which was an abnormal wear behavior. There was a tendency that the wear rate increased with an increase of the coefficient of friction, and that the coefficient of friction of HPT was 13-18 % higher than that of QT. Moreover, the adhesion force of HPT was 6-7 times higher than that of QT. Thus we have concluded that the high wear rate of HPT steels in the case of the SUJ2 ball wear tests were due to the high coefficient of friction as a result of the high adhesion force, which was caused by the high density of the grain boundaries in the UFG materials.