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

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 degrees C takes effect on creation of the layers composed of S-phase (expanded austenite) and alpha(N)' (expanded martensite). Up to the temperature of 420 degrees C, the S-phase peaks disappear due to the transformation occurrence (S-phase -> alpha(N)' + CrN). For the samples nitrided at temperature >= 450 degrees C no evidence of alpha(N)' is found owing to a precipitation (alpha(N)' -> alpha + CrN) taking place. For the 480 degrees C/4 h 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 degrees C/4 h 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 degrees 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. (c) 2008 Elsevier B.V. All rights reserved.