Corrosion behaviour of low temperature nitrided nickel-free, AISI 200 and AISI 300 series austenitic stainless steels in NaCl solution

Low temperature plasma nitriding was performed on CrNi-based (AISI 316L), CrMn-based (AISI 202) and nickel-free (P558) austenitic stainless steels. For all the used steels modified surface layers consist mainly of S phase without the precipitation of large amounts of nitrides, and they show enhanced surface microhardness and corrosion resistance in NaCl acqueous solution. The different electrochemical corrosion testing techniques evidence that the increase of corrosion potential may be ascribed mainly to nitrogen addition, while regarding the increase of potential, at which localized corrosion phenomena occur, also alloy elements, and in particular Mo, play an important role.