Plasma Nitriding of CrMoV Steel for the Enhancement of Hardness and Corrosion Resistance

Abstract

In the plasma ionic environment of nitrogen and hydrogen at 4:1 ratio, nitriding had been realized in the plasma laboratory. Nitriding of steel samples was followed at the lower temperature of 450 °C and also at the higher temperature of 550 °C while the sample was biased at the fixed − 250 V. Steel nitrided at 550 °C had shown a significantly enhanced resistance to corrosion in comparison to that of steel nitrided at 450 °C. X-ray diffraction studies of nitrided steels had shown the presence of nitrides of iron (FexN). Scanning electron microscopic and the electron dispersive spectroscopic analyses (SEM + EDS) of the cross section of the nitrided steels had shown the nitrided layer and the elemental distribution from top to the core. Following structural analysis, microhardness and the potentiodynamic polarization tests were performed. A significant improvement in hardness (~ 1180 Hv) and the case depth ~ 150 µm was obtained after nitriding at the higher temperature. Corrosion resistance was also found to be significantly improved. These achievements might be attributed to the presence of FexN, CrN phases and also to the nitrogen solid solution.