Galvanic corrosion between the constituent phases in duplex stainless steel

The exclusive single-phase with the exact chemical composition of the constituent phase in 2205 duplex stainless steel (DSS) could be prepared using selective dissolution method. The respective electrochemical behavior of each constituent phase could then be measured. The experimental results showed that the two distinct peaks in the active-to-passive transition region of the polarization curve determined in 2 M H₂SO₄ + 0.5 M HCl mixed solution were actually corresponded to the respective anodic peaks of the single austenite and ferrite phases. A polarity reversion was found between austenite and ferrite phases in mixed H₂SO₄ + HCl solution and HNO₃ solution. Galvanic current measurements also revealed that austenite was anode in HNO₃ solution, but became cathode when exposed in 2 M H₂SO₄ + 0.5 M HCl mixed solution.