Microstructural and X-ray diffraction characterization of low-temperature nitrided austenitic stainless steels

Surface treatments of austenitic stainless steels are able to increase surface hardness and wear resistance without compromising the excellent corrosion resistance of these materials only when chromium is essentially retained in solid solution and does not form large amounts of compounds. When nitriding is performed, the formation of large amounts of chromium nitrides is usually avoided carrying out treatments at temperatures lower than about 450 °C. Low-temperature nitriding treatments of austenitic stainless steel produce a modified surface layer consisting of a metastable phase, known as supersaturated or expanded austenite gammaN, S-phase or m-phase, which has high hardness and very good corrosion resistance. Even if the first report on this phase by Ichii et al. dates nearly two decades ago and the working conditions to form this phase are now outlined, its structure is still a matter of debate and has not been completely clarified. In the present research a microstructural and X-ray diffraction study of low-temperature glow-discharge nitrided AISI 316L austenitic stainless steel samples was performed.