S-phase in stainless steels : an overview

Abstract

The inherent poor tribological behaviour of austenitic stainless steel (ASS) has been a barrier to their wider application under corrosion wear conditions. In 1985 it was discovered that it is possible to create a hard and corrosion resistant modified layer on the surface of ASS by plasma nitriding. This diffused layer was called S-Phase and it is a precipitate free metastable supersaturated solid solution of either nitrogen or carbon. S-Phase has shown a great potential for the improvement in the tribological properties of ASS without any degradation of its corrosion properties. As a result, the last two decades have seen many advances in the field of surface modification of stainless steels. In this paper, the state-of-the-art of surface engineering of ASS in order to create a precipitate free, corrosion and wear resistant S-Phase layer is briefly overviewed. The mechanical, chemical and structural properties of this phase are assessed through a referenced literature review. Finally, future research directions and trends in the ongoing research of S-Phase in stainless steels and other Crcontaining materials are identified and discussed.