Effect of atmospheric aging on dissolution of MnS inclusions and pitting initiation process in type 304 stainless steel

Microelectrochemical measurements were performed to ascertain the effects of atmospheric exposure on pitting at MnS inclusion on Type 304 stainless steel. The exposure to air at 298 K and 50% RH for 30 and 90 days improved the resistance of the investigated steel to pitting. The thickness of the oxide film on the inclusions increased with the exposure time, and the dissolution of the inclusion was suppressed during anodic polarization in NaCl and Na2SO4 solutions. The 90 days exposure effectively inhibited the trench formation at the MnS/steel boundaries, making the inclusions less active as the initiation sites for pitting.