In the present study, high temperature tribological behaviour of gas nitrided 31CrMoV9 steel was investigated. Gas nitriding was carried out in ammonia gas atmosphere at 520uC for 24 h. The wear behaviour of the specimens was studied using a high temperature pin on disc wear tester at 25, 300 and 500uC. The results showed that the wear resistance of the nitrided steel improved by 1?8fold compared with the untreated specimen at room temperature. The wear tests at 300uC and notably at 500uC showed much better improvements in wear behaviour of nitrided steel by about 3?6- and 33fold respectively. Scanning electron microscopy study of worn surfaces indicated that the formation of solid compact layers was responsible for the higher wear resistance of the gas nitrided samples at higher temperatures.
