Nitriding of austenitic stainless steels using plasma immersion ion implantation

Abstract

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 °C, like plasma nitriding. Here, we present improved hardness and wear behaviour of austenitic stainless steel (X6CrNiMoTil7.12.2 — AISI 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 γ N′—expanded austenite—of more than 10 μm 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 °C.