Operando electrochemical TEM, ex-situ SEM and atomistic modeling studies of MnS dissolution and its role in triggering pitting corrosion in 304L stainless steel

Insights into the roles of geometry, size, and composition on MnS inclusion dissolution to initiate pits in 304L SS were obtained by combining operando and ex-situ electron microscopy, EDS, and atomistic modeling. The majority of thirty MnS on SS surface did not undergo dissolution even after over a week of exposure, and only a small number caused an attack of SS. Operando TEM during potentiodynamic polarization confirmed that MnS attack was followed by corrosion of the nearby SS substrate. Atomistic modeling revealed that elemental variations in the surface composition may play a role in differentiating pitting initiation by sulfur species. •Ex-situ SEM/EDS and ex-situ STEM/EDS to study MnS dissolution.•Quantitative chemical and geometric analysis of the MnS inclusions exposed to NaCl solutions.•Stainless matrix corrosion attack resulted from MnS dissolution.•Operando electrochemical TEM: electrochemical measurements and in-situ TEM to monitor MnS dissolution causing pitting initiation.•By atomistic modeling: shown differentiation of surface site susceptibility to S2- and Cl- adsorption caused the pit initiation.