Fundamental and Innovations in Plasma Assisted Diffusion of Nitrogen and Carbon in Austenitic Stainless Steels and Related Alloys

An improvement of the surface properties of austenitic stainless steels and nickel-based alloys is obtained by low temperature plasma assisted nitriding (PAN), plasma assisted carburizing (PAC) and plasma assisted nitrocarburizing (PANC). At low temperature, PAN treatment produces a peculiar phase usually called expanded austenite, S phase, m phase or γ N phase. Replacing nitrogen by hydrocarbon for conducting a low temperature PAC gives a carburized layer containing the carbon expanded austenite phase (γc). These two phases can simultaneously be obtained by combining hydrocarbon and nitrogen in the gas phase through a low temperature PANC. Several fundamental aspects concerning the expanded austenite phases are presented in this paper.