Influence of prior heat treatment on wear resistance of plasma nitrided AISI M2 tool steel

Plasma nitriding behavior and wear resistance of full annealed and quenched-tempered AISI M2 steel samples have been investigated after radio frequency plasma nitriding at 450 °C during 8 hr at 75% N2 + 25 %H2 gas mixture. XRD analysis revealed formation of ε phase on the top surface of the both nitrided samples. Nitrided case depth was determined from cross-sectional microhardness profiles. Sliding wear tests were performed in a ball-on-disk tribometer at 25°C using a 5 mm diameter Al2O3 ball under applied load of 8 N، sliding speed of 0. 05 ms-1، and sliding distance of 1000 m. It was observed that on full annealed samples nitride case has lower surface hardness and thicker case depth. Also after plasma nitriding full annealed samples exhibit higher wear resistance and lower weared material volume than quenched-tempered ones. The results were discussed based on the microhardness and estimated residual stress profiles.