A study of martensitic stainless steel AISI 420 modified using plasma nitriding

We studied martensitic stainless steel AISI 420, modified using glow discharge plasma nitriding. Microhardness measurements, X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to investigate the surface microhardness, crystal structure, microstructure and chemical bonding in the modified surfaces. High surface microhardness (∼1300 HV) over a case depth of about 60 microns is obtained. Glancing incidence X-ray diffraction (GIXRD) indicates the presence of a predominantly Fe3N phase with dispersed CrN within 2–5 microns on the surface. In addition, using Bragg–Brentano geometry, we measured the presence of a minor phase of Fe4N in the case depth. SEM confirms that the microstructure within 2–5 microns of the surface is different from that of the bulk. XPS shows nitride phase formation on the surface. AES measured over the cross-section of the case depth shows a direct relation of the increased surface microhardness to the high nitrogen content.