Fatigue Crack Growth Behavior of Nitrogen-Alloyed Low-Carbon Austenitic Stainless Steel at Room Temperature

Fatigue crack growth (FCG) behavior of SS 316L with different nitrogen contents (0.078 wt.% to 0.22 wt.%) was studied at room temperature under different load ratios ( R ) 0.1 to 0.7. The variation of crack growth rate (d a /d N ) was analyzed in terms of crack growth mechanism operating under both regimes. With variation of nitrogen content, variation of Δ K th was observed; 0.12 (12 N) and 0.14 (14 N) variants showing minimum and maximum Δ K th , respectively. This was correlated with changes in stacking fault energy (SFE) of the material with nitrogen content. The influence of other factors such as tensile strength, modulus, and microstructure, along with substructural changes during crack growth, were studied. In the 14 N nitrogen variant, the propensity for planar slip and better slip reversibility, originating from a relatively lower SFE, were attributed to a higher Δ K th .