Abstract
Austenitic stainless steel AISI 304 was nitrided in a low-pressure RF plasma using pure nitrogen. With a treatment of time of 4.0h at $400^{\circ}C$, the nitrogen-rich layer on the sample was $3\mu\textrm{m}$thick and had a hardness of approximately 4.4 times higher than that of untreated material. XRD data showed that as the process temperature rose from 350∼$450^{\circ}C$, the expanded austenite peaks became more prominent while the austenite peaks became weaker. Expanded austenite was transformed to ferrite and CrN at the treatment of$ 500^{\circ}C$. Langmuir probe measurements showed that electron density decreased above $450^{\circ}C$.