Effect of spinodal decomposition on the pitting corrosion resistance of Z3CN20.09M duplex stainless steel

The microstructural characterization and pitting corrosion behavior of Z3CN20.09M duplex stainless steel were investigated by TEM, potentiodynamic polarization, and electrochemical impedance spectroscopy after thermal aging at 475 degrees C for 0, 500, 1000, 2000, and 3000 h. The results showed that the ferrite in the steel decomposes into coherent Cr-rich, Fe-rich, and G phases. No any precipitates were found in the austenite during the thermal aging process. It is revealed that the pitting resistance of this steel has a negative relationship with increasing aging time and the priority nucleation position changes before and after the thermal aging process. The composition fluctuation region adjacent to the G phase and the Cr-depleted region around the Cr-rich phase are preferential to form pits. Therefore the G phase precipitation and the formation of Cr-depleted region are harmful to the pitting resistance of the steel.