Localized Corrosion of Thermally Aged Cast Duplex Stainless Steel for Primary Coolant Pipes of Nuclear Power Plant

Localized corrosion of cast duplex stainless steel Z3CN20.09M, which used widely in primary coolant pipes of nuclear power plants, has been investigated after thermally aged at 400 °C for 100, 300, 1000 and 3000h by making use of electrochemical method. Double loop electrochemical potentiodynamic reactivation (DL-EPR) and potentiodynamic polarization tests were used for assessing intergranular corrosion (IGC), pitting and general corrosion resistance, respectively. The experimental results showed that the general corrosion resistance of Z3CN20.09M did not change almost with increase of thermal aging time, however, IGC and pitting corrosion resistance decreased. In the polarization curves, the peak anodic current density of general corrosion was not found to change almost with increase of thermal aging time, but DL-EPR results showed that the value of Ir/Ia increased. The deterioration in localized corrosion resistance of thermally aged specimen was directly related to the precipitation of alpha prime phase in ferrite by spinodal decomposition.