Influence of alloying elements on the corrosion properties of steels during plasma nitriding process

Plasma nitriding has potential as an industrial process to improve the wear, fatigue and corrosion resistance of steels. It is well known that the corrosion properties of stainless steel deteriorate when treated with temperatures above 450°C. This is because the chromium-alloying element, which is responsible for protection against corrosion, gets converted to chromium nitrides at these temperatures. Whereas low alloy steels and high alloy steels exhibit better corrosion resistance. This is due to the presence of iron nitrides and few chromium nitride phases. In this study an attempt is made to study the effect of alloying elements on the corrosion properties of EN 8 (AISI 1045), En 24 (AISI 4340), AISI H13 and AISI 304 steels during plasma nitriding.

The effects of plasma nitriding on corrosion were investigated by performing potentiodynamic tests on untreated and treated steels. The phases responsible for the improvement in corrosion resistance were detected by X-ray diffractometer. It was found that low alloy steels performed better compared to the other steels because of the presence of Fe4N, Fe3N and other nitrides, which form a dense protective layer responsible for corrosion resistance.