Wear Characteristics and Tribofilm Formation Behavior of Carburized Hardened Steel Coated with Manganese Phosphate

This study investigates the MnPh surface treatment applied to improve the tribological properties of steel and rolling fatigue life of gears, focusing on the wear behavior and tribofilm formation during the initial sliding stage.The MnPh-coated layer is almost completely worn off in a short time during sliding, exposing the roughness peaks of the base steel, at which wear mainly occurs.Since the MnPh treatment etches the base steel during the treatment process to roughen the surface, MnPh-treated and MnPh-removed disks are used to match the roughness and morphology of the steel surfaces.The wear rate of the MnPh-treated steel is higher than that of the MnPh-removed steel during the initial sliding stage, following which the wear rate of the MnPh-removed steel increases.The formation of a sulfur-based tribofilm is significant on the MnPh-treated steel, whereas the formation of a calcium-based tribofilm is significant on the MnPh-removed disk.The role of the MnPh treatment is comprehensively discussed through the relationship between the wear behavior and tribofilm formation during the initial sliding stage, which contributes to improving the fatigue life.