Influence of treatment pressure on glow-discharge nitriding of AISI 316L austenitic stainless steel

Austenitic stainless steels are widely used in many industrial fields, owing to their excellent corrosion resistance, but their low hardness may become a limit to their use in several applications. Surface hardening treatments are efficient in increasing surface hardness without compromising corrosion resistance only when chromium is essentially retained in solid solution and does not form large amounts of compounds. Surface alloying with nitrogen is particularly effective when a metastable phase, known as S phase, expanded austenite or supersaturated austenite, is produced, since this phase is able to increase both surface hardness and corrosion resistance. The S phase can be produced by advanced nitriding techniques like plasma nitriding, low-pressure plasma ion-nitriding, plasma immersion ion implantation, which are performed at low pressure, usually in the range 10^-3 - 5 mbar depending on the used technique. The aim of the present research was to study the influence of treatment pressure on the characteristics of the modified surface layers produced by d.c. glow-discharge nitriding on AISI 316L austenitic stainless steel samples.