Phase transformation induced by high nitrogen content solid solution in the martensitic stainless steels

A high density plasma nitriding experiment was performed on a circular disk specimen of martensitic stainless steel at the temperature of 673 K for 14.4 ks. The nitrided thickness was 80 μm in depth from the surface with a high surface nitrogen concentration of 31 at%. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDX) and, electron backscattering diffraction (EBSD) were used to analyze the microstructure, the nitrogen content distribution, the phase formation, the grain size, and the straining in the specimen. Phase transformation from martensitic to austenitic phases took place together with high straining as well as grain size refinement.