Role of MnS in the intergranular corrosion and depassivation of sensitized Type 304 stainless steel

During polarization in 1 M NaCl (pH 5.4), intergranular corrosion of sensitized re-sulfurized Type 304 stainless steel occurred after pit initiation at MnS inclusions. Intergranular corrosion occurred when the pitting corrosion reached a Cr-depleted region along the sensitized grain boundaries. During depassivation under open-circuit conditions in 1 M NaCl (pH 1.0), MnS dissolution occurred as the first step, and the second step was the initiation of intergranular corrosion. Finally, dissolution of the steel matrix occurred. The role of MnS in the initiation of intergranular corrosion and depassivation of sensitized steel is discussed.