Effect of Plasma Nitriding on Corrosion Behavior of a High Carbon Low Alloy Steel

Abstract

The present study deals with improvement of corrosion resistance of a low alloy–high carbon steel by pulsed direct current glow discharge mode plasma nitriding. During the nitriding, applied voltage was 540–710 V which resulted in 3–6 A current in the temperature range 450–560°C for a time span of 1–5 hours. The phases formed after nitriding and their morphology were characterized by XRD and SEM analysis. Mostly γ′-Fe4N with a small volume fraction of ε-Fe3N/Fe2N was observed on the surface. Nitride fraction was reported to be more with nitriding time and temperature. These nitrides showed improvement in hardness and wear properties of the steel. Corrosion study revealed that plasma nitriding dramatically improves the corrosion resistance of this ferritic steel in terms of corrosion potential, corrosion current density and resistance to polarization. This improvement was attributed mainly to the formation of nitrides on the surface. Quantitative analysis of the nitrides was done with the help of XRD and the obtained value was found to be linked with corrosion data.