The effects of severe surface deformation on plasma nitriding of austenitic stainless steel

This paper reports a study on the influence of a modified layer caused by pre-deforming and transforming austenite into martensite, on the plasma nitriding of AISI 304 austenitic stainless steel in the temperature range from 380 to 450 °C. The aim of using the deformed layer with martensite is to produce a thicker nitrided layer and to decrease the processing temperature due to the much faster diffusion of nitrogen in bcc or bct martensite than in fcc austenite, although these two phases have the same chemical composition. The thickness, phase composition and microhardness of nitrided layers formed on the surface of pre-treated and non-treated substrates was investigated, and the difference of the structures of nitrided layers formed on the different surfaces was analyzed by X-ray diffraction (XRD). The results show that the pre-deformed layer with a martensite structure has a great influence on the thickness and phase composition of the nitrided layer.