Effect of annealing at 1100°C on the pitting corrosion in SDSS

Pitting corrosion initiation sites were investigated in superduplex stainless steels (SDSS) annealed at 1100 °C for 72 h and 700 h using EBSD maps, SEM, cyclic potentiodynamic polarisation tests and optical images. The extension of boundaries with rational interfaces (Kurdjumov-Sachs and Nishiyama-Wassermann) increases with increasing annealing time. The fraction of low-Σ3 CSL interfaces in the austenite phase increases with the annealing time. The pitting potential (E_pit) was slightly higher for the samples annealed during 72 h, while those annealed during 700 h showed a pitting potential similar that of the untreated samples. Pitting were observed at different locations of the microstructure depending of the annealing time at 1100°C. It is shown that increasing the density of low-energy interfaces in this alloy improves the pitting corrosion resistance of the weakest phase in chloride-rich media. The article focuses on the interaction between PREN values, determined by the chemical composition of the weakest phase (austenite), and the character of the interfaces during the prolonged annealing.