Influences of niobium and solution treatment temperature on pitting corrosion behaviour of stabilised austenitic stainless steels

Effects of niobium and solution treatment temperature on pitting corrosion of Super304H austenitic stainless steels were investigated by potentiodynamic and potentiostatic polarization tests and surface analysis. Results indicated that niobium in solid solution stabilised passive films against pit initiation and formed insoluble niobium-rich corrosion products partially covering pit walls inhibiting pit growth, whereas niobium as carbonitride accelerated metastable pit growth by reducing nitrogen in austenite matrix. Niobium additions more than a critical amount ennobled the pitting potential of Super304H. Moreover, increasing solution treatment temperature increased pitting potential for niobium-bearing Super304H samples but had little influence on that for niobium-free ones.