Abstract
In this study, the seizure resistance improvement mechanisms of nitrocarburizing, sulphonitriding, and oxynitriding were investigated to obtain design guidelines for further improving seizure resistance surface-treated steel. Roller-on-disk friction tests were conducted under high-temperature and high-contact-pressure conditions, simulating the sliding environment of high-speed gears in electric vehicles. The seizure resistance was evaluated by calculating the frictional heat generation rate per unit area and per unit time from the measured friction coefficient and contact pressure. The results indicate that the friction coefficient of sulphonitriding steel was the lowest, at 0.77 times that of carburizing steel, and that the contact pressure of sulphonitriding steel was also the smallest, at 0.77 times that of carburizing steel. As a result, the frictional heat generation rate of sulphonitriding steel was minimized to 0.73 times that of carburizing steel. These results suggest that sulphonitriding steel exhibits the highest seizure resistance among the surface-treated steels investigated.
