Effects of low and high temperature plasma nitriding on electrochemical corrosion of steel

Abstract

This study concerns plasma nitriding of tool steel at different temperatures and its effects on corrosion resistance. Inside the nitriding reactor steel samples were placed on the sample holder after metallographic polishing and then the vacuum chamber was evacuated to a pressure of 0.5 Pa. At a lower temperature of 450 C and the higher temperature of 550 C nitriding was performed for a fixed duration of 10 h. All the nitrided and the bare steel samples studied under X-ray diffraction (XRD) and scanning electron microscopic analysis/energy dispersive X-ray spectroscopy (EDS). Iron nitride (FexN, x = 2–3, 4) peaks were revealed in the nitrided steels after XRD analyses. EDS revealed the increased amount of nitrogen in the nitrided sample treated at 550 C. For the assessment of corrosion resistance of these steel samples potentiodynamic polarization tests were performed in 3.5% NaCl. On comparison, it was found that the steel nitrided at higher temperature is more effective in enhancing the corrosion resistance.