Effect of cooling rate on segregation characteristics of 254SMO super austenitic stainless steel and pitting corrosion resistance under simulated flue gas desulfurization environment

The segregation behavior and pitting corrosion resistance under simulated flue gas desulfurization (FGD) environment of 254SMO super austenitic stainless steel (SASS) under different cooling rates were investigated by scanning electron microscopy (SEM), backscattering (BSD), electron probe microanalysis (EPMA) combined with electrochemical analysis and XPS. With the increase in cooling rate, the segregation degree of Cr, Mo and Ni in 254SMO decreased first and then increased, the pitting corrosion resistance showed a trend of first increasing and then decreasing, and the passive film was mainly composed of Cr 2 O 3 , Cr(OH) 3 , Fe 2 O 3 , Fe(OH) 3 , MoO 3 , NiO and NiOOH. At higher or lower cooling rate, the proportion of protective Cr 2 O 3 was less, which led to a decrease in the protection of the passivation film, and the corrosion resistance was reduced. That is, the lightest segregation degree and the best pitting corrosion resistance of 254SMO at 100 °C/min. In addition, the corrosion mechanism of 254SMO in simulated FGD environment was discussed.