Plasma and Fusion Research

Volume 21, 1306041 (2026)

Letter

Expanded Austenite Formation on Stainless Steel via Nitrogen/Hydrogen Atmospheric-Pressure Thermal Plasma Jet
Ryuta ICHIKI, Takashi FURUKI, Seiji KANAZAWA
Oita University, Oita 870-1192, Japan
(Received 23 March 2026 / Accepted 18 May 2026 / Published 1 September 2026)

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.

Keywords

atmospheric-pressure plasma jet, expanded austenite, stainless steel, nitrogen doping, reductive method

DOI: 10.1585/pfr.21.1306041

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