Effects of nitrogen on the microstructure and mechanical properties of an austenitic stainless steel with incomplete recrystallization annealing

A 304 N austenitic stainless steel possessing excellent performance through the addition of nitrogen, combined with deformation and incomplete recrystallization annealing processes was obtained. The results reveal that the solid solution of 0.15 wt% nitrogen in austenite tremendously enhances the yield strength of the 304 N sample (from 285 MPa to 581 MPa) while maintaining sufficiently high elongation (about 50%). Compared with the 304 reference steel, the interstitial nitrogen not only brings significant solid solution strengthening effect, but also greatly stabilizes the austenite, so as to avoid stress-induced martensitic transformation at the early elastic stage that leads to premature yielding. Moreover, nitrogen promotes recrystallization process and dislocation planar slip, which effectively improves the capacity to accommodate dislocations of austenite and sustains high flow stress under equivalent strain level, thus maintaining high elongation of the steel. This study is a new attempt to develop high strength and ductility stainless steels without changing the chemical composition of materials.