Microstructure and Properties of Plasma Source Nitrided AISI 316 Austenitic Stainless Steel

Plasma source nitriding is a relatively new nitriding technology which can overcome those inherent shortcomings associated with conventional direct current plasma nitriding technology such as the arcing surface damage, the edging effect and the hollow cathode effect. There is considerable study on the properties of nitrided samples for laboratorial scale plasma source nitriding system; however, little information has been reported on the industrial-scale plasma source nitriding system. In this work, AISI 316 austenitic stainless steel samples were nitrided by an industrial-scale plasma source nitriding system at various nitriding temperatures (350, 400, 450 and 500 °C) with a floating potential. A high-nitrogen face-centered-cubic phase (γ_N) formed on the surface of nitrided sample surface. As the nitriding temperature was increased, the γ_N phase layer thickness increased, varying from 1.5 μm for the lowest nitriding temperature of 350 °C, to 30 μm for the highest nitriding temperature of 500 °C. The maximum Vickers microhardness of the γ_N phase layer with a peak nitrogen concentration of 20 at.% is about HV _{0.1 N} 15.1 GPa at the nitriding temperature of 450 °C. The wear and corrosion experimental results demonstrated that the γ_N phase was formed on the surface of AISI 316 austenitic stainless steel by plasma source nitriding, which exhibits not only high wear resistance, but also good pitting corrosion resistance.