Wear resistance of pulse plasma nitrided AISI 4140 and A355 steels

In this study, the wear resistance of pulse plasma nitrided AISI 4140 and A355 steels was evaluated under dry and lubricated sliding conditions and compared with conventional plasma nitrided samples. After surface characterisation using metallographic, microhardness and surface examination techniques, sliding wear tests were performed on a pin-on-disc machine in which hardened ball bearing steel discs were used as the counterface. The influence of surface treatment, steel composition, and testing conditions on the wear resistance of the surface treated pins was determined. The test results showed that the wear resistance of the investigated steels could be improved by means of plasma and pulse plasma nitriding. However, compared with conventional plasma nitriding, pulse plasma nitriding lead to very similar wear properties of the nitrided steel surface. Also, the steel composition has an important effect on the properties and wear resistance of the plasma nitrided steel surface. Addition of Al, an alloying element with a high affinity to nitrogen, increased the hardness and residual stresses, and improved the wear resistance of the nitrided steel surface.