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 (1173 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 1173 K. At room temperature, nitrogen addition resulted in dislocation localization, and at 1173 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.