Revisiting Cl-Induced Degradation of MnS Inclusions Using DFT

Cl-induced passivity breakdown is one of the major causes of corrosion for ferrous alloys. On a passive layer, manganese sulfide (MnS) inclusions are known to be the preferred sites for pit initiation. While the breakdown process has been examined, relatively less effort has been devoted to discovering ways to mitigate the harmful process. Using DFT + U and ab initio molecular dynamics (AIMD) calculations, we investigated the initial stages of the Cl-induced degradation of MnS inclusions. We found that Cl adsorption on the MnS inclusion would lead to the formation of an amorphous Mn x Cl y S z complex on the surface. With increased Cl concentration, a thinned MnS inclusion could be formed. More importantly, we examined the effects of alloying Cr, Fe, and Mo on the inclusion against Cl-induced degradation. Our calculations showed that the addition of Mo can effectively mitigate the degradation process, suggesting a potential way to improve the corrosion resistance of ferrous alloys.