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

Abstract

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.

Corrosion Behavior of Sensitized AISI 304 Stainless Steel in Acid Chloride Solution

“…The polarization curves with the passive anodic branches typical for passivating metals (as received 20, SP 20 and as received 50) are evaluated by the pitting potentials E p [ 19 , 20 , 21 , 29 ] and by the corrosion potentials E corr determined directly from PP curves. E p values were determined as the potentials of strong permanent increase of the current density in the passivity region, which indicates a breakdown of the passive film and the onset of the stable pit growth.…”

“…Microstructure of as received AISI 304 SS ( Figure 1 ) observed by OM is polyhedral, austenitic with numerous twins that could be related to annealing or rolling. According to the chemical composition of SS, visible inclusions could contain Mn [ 14 , 20 , 21 ].…”

“…Currently, the relation between sensitization and the pitting corrosion susceptibility of austenitic SSs is the subject of numerous studies [ 13 , 14 , 19 , 20 , 21 , 22 , 23 ]. In addition to the effect of chromium-depleted zones, the authors of [ 14 , 20 , 21 ] presented the role of MnS inclusions on the pitting corrosion initiation of sensitized austenitic SSs.…”

“…Currently, the relation between sensitization and the pitting corrosion susceptibility of austenitic SSs is the subject of numerous studies [ 13 , 14 , 19 , 20 , 21 , 22 , 23 ]. In addition to the effect of chromium-depleted zones, the authors of [ 14 , 20 , 21 ] presented the role of MnS inclusions on the pitting corrosion initiation of sensitized austenitic SSs. According to the available references, most electrochemical PP tests were carried out on the ground surface in pH neutral chloride solutions at room temperature [ 14 , 19 , 20 , 21 ].…”

“…In addition to the effect of chromium-depleted zones, the authors of [ 14 , 20 , 21 ] presented the role of MnS inclusions on the pitting corrosion initiation of sensitized austenitic SSs. According to the available references, most electrochemical PP tests were carried out on the ground surface in pH neutral chloride solutions at room temperature [ 14 , 19 , 20 , 21 ]. The authors of [ 22 ] compared the effect of various mechanical surface treatments on the pitting corrosion resistance of sensitized AISI 304 SS in 3.5 wt % solution at 23 and 50 °C.…”