Expanded Austenite Formation on Stainless Steel via Nitrogen/Hydrogen Atmospheric-Pressure Thermal Plasma Jet

Abstract

Surface layers of expanded austenite (S-phase) are formed on JIS SUS304 austenitic stainless steel by nitrogen doping using a pulsed-arc plasma jet under atmospheric pressure. The characteristics of the formed S-phase strongly depend on the fraction of hydrogen gas in the operating nitrogen/hydrogen gas mixture, i.e., plasma nitriding with a higher hydrogen fraction provides a more uniform but thinner S-phase. Conversely, reductive pretreatment using a high hydrogen fraction prior to nitrogen doping affords a thicker S-phase while maintaining uniformity.