Tribological Properties Analysis on Nitrided AISI 316L Stainless Steel

AISI 316L stainless steel have been treated by surface hardening technique, which is low temperature nitriding gas treatment in horizontal tube furnace. The environment gas for this treatment is ammonia, which become the source of nitrogen gas that purged into the furnace where the steel is located. The temperature of this treatment is at 450 °C with the variable of 2, 5 and 8 hours nitriding time. The purpose of this investigation is to improve the wear resistance and surface hardness of the stainless steel as the element of tribological properties analysis. Theoretically, the low temperature treatment is to avoid the formation of nitride and carbide precipitation because it can reduce the corrosion resistance of stainless steel. Pin-on disc wear test at dry sliding condition become the standard test to analyze the wear resistance of this nitrided steel according to the ASTM G99-95a standard. The further analysis on tribological properties of nitrided steel are conducting microhardness assessment by Vickers hardness test on the surface of treated steel to identify the improvement of surface hardness by the formation of nitrided layer. This investigation also strongly support by conducting nitrided layer morphology by utilizing Field Emission Scanning Electron Microscope (FESEM) instrument which is to measure the thickness of nitrided layer. Surface morphology of worn region by FESEM also investigated to understand the wear mechanism characteristics of nitrided steel. The results showed that the nitrided layer become more thicker through the extending of time treatments and relatively improved the surface hardness. The nitrided layer characteristic that support the protection oxide layer and resist the wear mechanism is confirmed where the wear resistance improved from the result of coefficient of friction by the pinon disc wear test with the value obtained become lower as the time of treatment is extended. Surface morphology by FESEM investigation on worn region after wear test for untreated and nitrided steels indicates how the wear mechanism influenced the improvement of wear resistance. Untreated samples experienced severe wear while nitrided steel presented only slight abrasion with shallow and narrower wear track.