Effect of nitrogen content on mechanical properties of 316L(N) austenitic stainless steel

Abstract

Increasing the yield strength of 316L(N) stainless steel is both scientifically and commercially crucial. In this study, five 316L(N) stainless steels with different nitrogen contents were melted and specimens with grain size from 5 μm to 320 μm were obtained by cold rolling and heat treatment. The yield strength was examined through tensile tests. The microstructure was investigated using electron-backscatter diffraction, transmission electron microscopy, and X-ray diffraction. The fracture morphology was studied by scanning electron microscopy. Nitrogen improved the coefficient in the Hall–Petch equation. As the nitrogen content increased from 0.008 wt% to 0.34 wt%, the coefficient K increased from 363 MPa μm0.5–1895 MPa μm0.5 and the coefficient σ0 increased from 168 MPa to 331 MPa, resulting in an improvement of yield strength from 249 MPa to 757 MPa (grain size of 20 μm). Planar slips and stacking faults were found in deformation structures of 316L(N) steel with higher nitrogen content, which is underlying factors for the significant improvement of yield strength. Strain-induced martensite near the fracture surface contributed to the plasticity of 316L(N) steel. This study discusses the contribution of nitrogen, including solution strengthening, stacking fault energy, and short-range ordered structure to strength enhancement. It provides a valuable reference for developing new austenitic stainless steel with an optimal strength–plasticity combination.