• plasma nitriding;
  • S-phase;
  • stainless;
  • austenitic;
  • XPS

The current study focuses on the characterization of the nitrided layer, formed in American Iron and Steel Institute (AISI) 304L and AISI 904L austenitic stainless steels by industrial low-temperature plasma nitriding, using combined analysis techniques. The study highlighted that the evolution of the microstructure of the nitrided layers is influenced by surface finishing prior to nitriding, alloying elements and nitriding conditions, all factors affecting S-phase formation and nitrogen (N) diffusion mechanisms. The chemical bonding characteristics of Cr 2p3/2 and N 1s as revealed by XPS show a shift in binding energy between expanded austenite (S-phase) and CrN-like compounds. S-phase has proven to be more stable in 904L, whereas residual and/or induced ferrite/martensite in 304L acts as a barrier for its development. © 2014 The Authors. Surface and Interface Analysis published by John Wiley & Sons, Ltd.