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Austenitic stainless steel (ASS) is used applied widely owing to its very good corrosion resistance. However, the application of this material as a bearing surface is severely limited by very poor wear and friction behaviour. Consequently, Surface Engineering treatments for austenitic stainless steel are an interesting alternative way to increase the surface hardness and improve the wear resistance. For the purpose of this works, the Surface Engineering design will be classified, very broadly, into three groups : (a) those which coat the substrate: PVD, CVD, etc, (b) those which modify only the structure of the substrate, (c) those which modify the chemical composition and the structure of the substrate: thermochemical, ion implantation, plasma, etc. It is nowadays widely accepted that hard, wear and corrosion resistant surface layers can be produced on ASS by means low temperature nitriding and/or carburizing in a number of different media (salt bath,gas or plasma), each medium having its own strengths and weaknesses. In order to retain the corrosion resistance of austenitic stainless steel, these processes are typically conducted at temperatures below 450ºC and 500ºC, for nitriding and carburizing respectively. The result is a layer of precipitation free austenite, supersaturated with nitrogen and/or carbon, which is usually referred to as Sphase or expanded austenite.
