Influence of solution-annealing and stress-relieving on the pitting corrosion resistance of modified 316N SS weld metals: A study using EN technique

This paper presents the pitting corrosion resistance of AISI 316LN SS Weld joints in the (i) as-welded and (ii) post-weld heat-treated condition. The weld metal contains 0.055% carbon and 0.13% nitrogen in order to have improved creep strength. The welded components are subjected to (i) solution annealing at 1050 °C, (ii) stress relieving at 750 °C or (iii) dimensional stabilization at 550 °C depending upon the fabrication route. These welds are exposed to marine/coastal environment at various stages of fabrication, inspection, storage and commissioning after these heat-treatments, which may lead to pitting corrosion. Hence an attempt was made to understand the influence of microstructural change arising due to the post-weld heat-treatments on the susceptibility of these materials to pitting corrosion. Potentiodynamic polarisation as well as electrochemical noise (EN) studies were conducted in 0.5 M sodium chloride solution in open atmosphere. Shot-noise analysis, Weibull probability plots and the 3 dimensional plots using shot-noise parameters were used to assess the susceptibility to pitting corrosion. It has been established that solution annealing improves the pitting corrosion resistance whereas stress relieving as well as dimensional stabilization heat-treatments make the weld joints more prone to pitting. The localized corrosion resistance was correlated to the microstructural changes resulted during the various heat-treatments.