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 ińcidence 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.