A novel rapid DC plasma nitriding at low gas pressure for 304 austenitic stainless steel

Plasma nitriding is one of the most important surface modification technologies. In this research, D.C. plasma nitriding of 304 austenitic stainless steel was conducted at different gas pressures of 80 Pa, 100 Pa, 120 Pa, 160 Pa and 400 Pa and at the same temperature of 400 degrees C for 8 h with gas mixture of N-2/H-2=24/76. The results showed that the thickness of the nitride layer could be significantly improved by using low gas pressure; the thickest layer of nitride layer was obtained at gas pressure of 100 Pa. And a favorable microstructure of single S-phase without chromium nitrides precipitation in the nitride layers was formed in the rapid D.C. plasma nitriding at low gas pressure; the possible mechanism is that the appropriate gas pressure by the cathodic ion bombardment might favor the nitriding efficiency. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.