Low temperature plasma nitrocarburising of AISI 316 austenitic stainless steel

Plasma nitrocarburising was carried out at a low temperature to improve the surface hardness of AISI 316 austenitic stainless steel without degradation of its corrosion resistance. It was found that nitrogen and carbon atoms can simultaneously be dissolved into the austenite lattice during the nitrocarburising process, forming a nitrogen and carbon supersaturated solid solution, which has a face centre tetragonal (fct) structure (i.e. the S phase). GDS analysis showed that the maximum nitrogen and carbon concentrations in the nitrocarburised S-phase layer occur at different depths from the surface. The nitrocarburised layers have not only high hardness like the nitrided layer, but also high thickness and gradually reduced hardness profile like the carburised layer.