Microstructure and Tribological Properties of Sub-Microcrystalline Carbon Steel Produced by Severe Plastic Deformation

The microstructure, hardness, and sliding wear properties of high-pressure torsion (HPT)-processed pure Fe and S45C carbon steel were comprehensively investigated. The grains of Fe and S45C were significantly refined to the submicron size range using the HPT process, and the grain sizes were found to decrease with an increased number of turns (N). The Vickers hardness of HPT-processed specimens increased with increasing N or with distance from the center (i.e., with an increase in the strain), which is attributed to grain refinement. In addition, the hardness of HPT-processed Fe was saturated with a further increase in the number of turns owing to the saturation of grain refinement. However, saturation with hardening was not observed in the case of S45C and the hardness values of S45C were much higher than those of Fe. The wear amount was considerably reduced by HPT processing for both Fe and S45C. A linear correlation was determined between the specific wear rate and the inverse of hardness, which agrees with the Archard wear equation. The experimental results show that the reduction in the wear of Fe and S45C is considered to be due to hardening by the HPT process.