Plasma nitriding on welded joints of AISI 304 stainless steel

Plasma nitriding is widely used for the improvement of the mechanical/tribological properties of various steel components in many applications such as automobile parts, turbine parts, textile machinery parts, etc. However, plasma nitriding on components with welding joints have not been intensively studied so far. In this study, we attempted to study the welded region of AISI 304 stainless steel after carrying out the plasma nitriding process. The plasma nitriding of stainless steel welded joints has been done with a H2:N2 (4:1) gas mixture at 570 and 450 °C for different time durations. The parent and the welded regions were characterized using a microhardness tester, a scanning electron microscope (SEM) and an X-ray diffractometer (XRD) for surface hardness, case depth and phase formation respectively. The results show that the nitrided layer formed on the welded region consists of Fe4N and Fe3N, CrN and γ phases. Also, welded joints using the multiple pass technique gave better nitriding properties compared with that of the single pass technique. There is an improvement in the hardness by 3 times which could be correlated with structural changes and process parameters.

► The effect of plasma nitriding on welded joints of SS 304 steel was investigated. ► Only a marginal increase in hardness values was observed in the weld regions. ► This is attributed to the stress formed during welding. ► Plasma nitriding is feasible on welded joints if welding parameters are controlled.