Study on the Microstructure and Alternating Current Corrosion Behavior of SAF2507 Super-Duplex Stainless Steel in 3.5%NaCl Solution

The effect of solution annealing temperature on microstructure and the corresponding AC (alternating current) corrosion behavior was investigated by electrochemical impedance spectroscopy, polarization curve, Mott–Schottky curve and immersion test. With or without AC application, the 2507 SDSS (super-duplex stainless steel) samples annealed at various temperatures exhibit a difference in corrosion resistance. Among them, the corrosion resistance first increases and then decreases as the annealing temperature increases, that is, the 2507 SDSS annealed at 1060 °C has the optimum corrosion resistance, followed by the specimen annealed at 1000 °C, and finally the specimen at 1120 °C. The variation trends of Rct, Rf and ip can verify the above law. The σ phase and an excessive amount of α phase within the microstructure can decrease the corrosion resistance. Additionally, the stability and protective property of passive film formed on the electrode surface is associated with the microstructure of 2507 SDSS. An imposed AC can decrease the passivity of 2507 SDSS and damage the film formed on the sample surface. Furthermore, the corrosion rate and pitting sensitivity of the SDSS increase with the increasing AC current density.