The Role of Sulfide Inclusion Morphology in Pit Initiation of Several Type 300 Series Stainless Steels

Pitting potential measurements have been made on several single phase Type 300 series stainless steels and duplex Type 304L alloy by the potentiodynamic test method. The heat of Type 316L stainless steel examined was more susceptible to pit initiation than the heat of Type 304L stainless steel that was studied. Several heat treatments were examined, and the effects of chloride ion concentration, pH, and temperature of the electrolyte on the pit initiation of single phase and duplex alloys were investigated. The effects of heat treatment demonstrate the importance of the morphology of sulfide inclusions that are exposed to the electrolyte. The sulfide dissolution kinetics, which are presumed to control the pit initiation process, are influenced by the morphology of the inclusions exposed to the electrolyte, the time constraints of the various pitting corrosion test methods, the temperature and composition of the bulk electrolyte, and the spectrum of sulfide inclusion compositions present in the alloy.