The microstructure and properties of 17-4PH martensitic precipitation hardening stainless steel modified by plasma nitrocarburizing

17-4PH martensitic precipitation hardening stainless steel was plasma nitrocarburized at 430 degrees C and 460 degrees C for 8 h. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, microhardness tests, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The results show that the microstructure of plasma nitrocarburized layer is characterized by a Compound layer with no evident diffusion zone. The phases in the 430 degrees C treated layer are mainly of gamma'-Fe4N, nitrogen and carbon expanded martensite (alpha(N)'), and some incipient CrN phases. When the temperature increases up to 460 degrees C, there is no evidence of alpha(N)' phase. The processes of bulk precipitation hardening and surface treatment by plasma nitrocarburizing can be successfully combined in a single-step process on this steel. The hardness of modified layer can reach Lip to 1186HV, which is 3 times higher than that of untreated steel. The wear and corrosion resistance of the specimens can be apparently improved by plasma nitrocarburizing. The 460 degrees C/8 h treated specimen has the best wear and corrosion resistance in the present test conditions. (C) 2009 Elsevier B.V. All rights reserved.