Effect of nitrogen addition on the stacking-fault energies in Si-added austenitic stainless steel

Austenitic stainless steels have superior room temperature and high temperature strengths, strongly influenced by stacking-faults in the steel microstructure. Nitrogen addition makes substantial contribution to room temperature and high temperature strengths, so it is essential to consider the effect of nitrogen on the stacking-fault energies (SFE) to understand strength mechanism of the steel and to enhance the strength. In this study, SFE were measured by weak-beam TEM method, and deformation mechanisms of nitrogen-added austenitic stainless steels at room temperature and at high temperature (1 173 K) were discussed in terms of SFE in Si-added austenitic stainless steel (Fe-19 wt%Cr-13 wt%Ni-0.05 wt%C-3 wt%Si-x wt%N). Nitrogen addition resulted in the decrease of SFE, which changed dislocation structures at room temperature and at 1 173 K. At room temperature, nitrogen addition resulted in dislocation localization, and at 1 173 K, all samples formed the sub-grain structure, caused by the dislocation recovery. It was revealed that the increase of nitrogen content resulted in the increase of the dislocation density in the sub-boundary, which indicates that the decrease of SFE contributes to the high temperature strength.