Influence of Nitrogen on Grain Size-Dependent Sensitisation and Corrosion Resistance of 316L (N) Austenitic Stainless Steels

Influences of grain size and low energy Σ boundaries on intergranular corrosion (IGC) resistance of low and high nitrogen containing 316L austenitic stainless steel (ASS) have been investigated in this study after solutionising and sensitisation heat treatments. With increase in solutionising temperature, an increase in average grain size with a larger distribution (larger standard deviation) was also observed. Variation of grain size was larger in the low nitrogen containing ASS as compared to that of high nitrogen containing ASS. Full width half maximum (FWHM) was observed to increase with increasing solutionising temperature and grain size in both the steels. However, relatively finer grains accompanied by higher FWHM were observed in high nitrogen containing ASS. The IGC resistance of solutionised and sensitised steels was studied using double-loop electrochemical potentiokinetic reactivation (DL-EPR) method. It was observed that the degree of sensitisation (DOS) had reduced significantly in high nitrogen containing ASS after sensitisation heat treatments. Improved IGC resistance of steel with increased nitrogen content could be attributed to the increased fraction of low energy Σ boundaries. © 2022, The Indian Institute of Metals - IIM