Investigation of the Microstructure Dependence of Critical Pitting Temperature and Pitting Potential in a 2205 Duplex Stainless Steel

Dependence of 2205 duplex stainless steel pitting resistance on its microstructure was investigated using microstructural examinations and potentiodynamic and potentiostatic polarization techniques. An as-received hot-rolled alloy was subjected to different heat treatments to understand how microstructural characteristics individually affect the corrosion resistance in terms of critical pitting temperature (CPT), pitting potential (Epit), and metastable pitting characteristics. Results revealed that there is a transition temperature interval for the 2205 DSS. By promoting pit initiation and pit propagation, the Widmanstätten structure significantly deteriorated both CPT, by 10 °C, and Epit, compared to the as-received hot-rolled specimen. The σ phase appearance was also associated with a minor drop in CPT, but a considerable reduction in Epit as it increased the occurrence frequency of metastable pits. The specimen having equiaxed grains had the highest CPT, underwent stable pitting at 47 °C, but still it had a low Epit compared to the hot-rolled specimen due to its higher occurrence frequency of metastable pits. The formation of the Widmanstätten austenite needles weakened the ferrite phase in terms of the pitting resistance by reducing the contents of Cr and Mo in it and made it more susceptible to pit propagation.