Effect of Sensitization on Pitting Corrosion at MnS and CrS in Type 304 Stainless Steel

The effect of sensitization on the pitting potentials at MnS and CrS inclusions in Type 304 stainless steels was assessed. For Type 304 containing MnS inclusions, MnS dissolution was observed approximately 0.3 V, and the pitting potential at MnS was in the passive region and decreased by sensitization. Based on the pit morphology, the pit initiation at MnS inclusions is thought to be caused by the transition from passive to active state of the steel matrix. In contrast, the pitting potential at CrS inclusions was located in the transpassive region, and no decrease in the pitting potential was observed due to sensitization. These mechanisms were analyzed based on the effect of the Cr concentration on the active dissolution and transpassive dissolution of the steel.