Microstructure and dry-sliding wear properties of DC plasma nitrided 17-4 PH stainless steel

Abstract

An attempt that the precipitation hardening steel 17-4PH was conducted by DC plasma nitriding (DCPN) is made to develop a kind of candidate material for nuclear reactor. Nitriding process performed at temperature⩽400°C takes effect on creation of the layers composed of S-phase (expanded austenite) and αN′ (expanded martensite). Up to the temperature of 420°C, the S-phase peaks disappear due to the transformation occurrence (S-phase → αN′ + CrN). For the samples nitrided at temperature⩾450°C, no evidence of αN′ is found owing to a precipitation (αN′→α+CrN) taking place. For the 480°C/4h treated sample, it is the surface microhardness that plays the lead role in the wear rate reduction but the surface roughness; while for the 400°C/4h treated sample, it is both of the surface roughness and the S-phase formation. Dry sliding wear of the untreated 17-4PH is mainly characterized by strong adhesion, abrasion and oxidation mechanism. Samples nitrided at 400°C which is dominated by slight abrasion and plastic deformation exhibit the best dry sliding wear resistance compared to the samples nitrided at other temperatures.