Sliding friction surface microstructure and wear resistance of 9SiCr steel with low-temperature austempering treatment

An extremely fine α single-phase nanocrystalline microstructure was induced in the dry sliding friction surface layer of 9SiCr steel austempered at low temperature. The mean size of nanograins in the top surface layer is about 3 nm, and such fine nanograins had never hitherto been achieved in near surface severe plastic deformation metals and alloys. Grains in the near surface layers coarsen linearly with increasing depth from the top surface. The retained austenite in the surface layer of the austempered sample was decomposed into α phase owing to the action of the shear strain during the dry sliding friction. In addition, the friction surface microstructure and the wear resistance were compared between samples with low-temperature austempering treatment and quenching plus tempering treatment.