Article: Oxy-Nitriding AISI 304 Stainless Steel by Plasma Electrolytic Surface Saturation to Increase Wear Resistance

Abstract

AISI 304 SS has good corrosion resistance in a variety of environments but does not have good resistance to wear. Aggressive marine environments require materials that can withstand both the biocorrosion and the wear associated with the impact of waves, ocean currents and suspended particles. Oxy-nitriding of stainless steels can be used to increase their hardness and wear resistance. The conventional oxy-nitriding process is lengthy, and the temperature involved can affect the corrosion resistance of the material. To mitigate these problems, it was decided to study an oxy-nitriding process in plasma electrolytic conditions, using aqueous solutions of 20, 30 and 40 wt% urea. The results showed that all the concentrations evaluated gave lower levels of wear than untreated stainless steel. However, considering the amount of urea used and the environmental emissions from the waste generated, a concentration of 20% by weight of urea in the electrolyte is considered sufficient to increase up to three times the wear resistance of stainless steel. XRD, XPS and microscopy analyses showed that, in the main, the outermost layer of the steel surface treated by electrolytic plasma has a morphology of small craters of chromium and iron oxy-nitrides. A nitrogen diffusion layer was also seen below the oxy-nitrided layer.