Nitriding of austenitic stainless steels using plasma immersion ion implantation

Austenitic stainless steels show excellent corrosion resistance, in combination with a rather low hardness and high wear, which is lost during conventional hardening processes at elevated temperatures above 450 degrees C, like plasma nitriding. Here, we present improved hardness and wear behaviour of austenitic stainless steel (X6CrNiMoTi17.12.2 - AlSI 316Ti) implanted with nitrogen plasma immersion ion implantation (PIII) while retaining the corrosion properties. Compared to untreated stainless steel, the hardness can be increased up to a factor 4, depending on the amount of implanted nitrogen. The wear behaviour was improved by 1-2 orders of magnitude. A layer of gamma(N)'-expanded austenite-of mole than 10 mu m was formed in a few hours, as determined with GDOS. Only a very small fraction of chromium nitride, which is not detrimental to the corrosion resistance, was observed with XRD for the samples implanted at 380 degrees C. (C) 1998 Elsevier Science S.A.