Novel plasma nitriding–oxidizing duplex treatment of AISI 316 austenitic stainless steel

In this work, plasma nitriding and plasma nitriding–oxidizing treatment have been performed on AISI 316 austenitic stainless steel. In order to evaluate its response to this treatment, their microstructures and wear resistance have been compared with conventional plasma nitrided. The treatment of plasma nitriding was performed at temperature of 450°C for 5h with gas mixture of N2/H2:1/3 whereas plasma nitriding–oxidizing was performed with the same parameters of plasma nitriding and temperature of 450°C with gas mixture of O2/H2:1/5 for 15, 30 and 60min. The structural, mechanical and tribological properties were analyzed using XRD, SEM, microhardness testing and pin-on-disk tribotesting. The results showed that oxidation treatment reduces wear resistance of plasma nitrided sample under high loads. Furthermore the tribological evaluation indicates that by increasing the oxidation time further reduction of wear resistance can be occurred. In addition, it was found that oxidation treatment after plasma nitriding provides an important improvement in the friction coefficient against a AISI 52100 steel pin and reduces surface roughness.