Investigation of the pitting corrosion behavior between the constituent phases in F53 super duplex stainless steel in acidified chloride environments

摘要

The pitting corrosion behaviors between the constituent phases in F53 super duplex stainless steel (SDSS) in acidified chloride environments were investigated using a critical pitting corrosion temperature test, a potentiodynamic anodic polarization test, and the microstructure analyses through a SEM-EDS and a SAM. As the solution annealing temperature decreased from 1150℃ to 1050℃, the γ-phase fraction increased whereas the α-phase fraction decreased. The pitting potential and the critical pitting temperature increased with a decrease of solution annealing temperature, thereby increasing the resistance to pitting corrosion. The pitting corrosion of the SDSS was selectively initiated at the γ-phases because the PREN (pitting resistance equivalent number, PREN = %Cr+3.3%Mo+30%N) value of the γ-phase is much larger than that of the α-phase, irrespective of the solution annealing temperature. The pitting corrosion was finally propagated from the α-phase to the γ-phase. The decrease of solution annealing temperature enhanced the resistance to pitting corrosion greatly in acidified chloride environments due to a decrease of PREN difference between the γ-phase and the α-phase, that is, a decrease of PREN_γ by dilution of N in γ-phase with an increase in the γ-phase volume fraction and an increase of PREN_α by enrichment of Cr and Mo in the α-phase with a decrease in the α-phase volume fraction.