Effects of Sulfur Compounds on the Pitting Behavior of Type 304 Stainless Steel in Near-Neutral Chloride Solutions

Abstract

Abstract Pitting potentials have been measured potentiodynamically for Type 304 stainless steel in neutral or mildly acidic solutions containing 0.25M NaCl and various concentrations of sulfur species from 0 to 2 molar. Additions of 0.01 to 0.02M Na2S2O3 lowered the pitting potential by more than 300 mV, while additions of more than 0.5M Na2S2O3 inhibited pitting. KSCN showed similar but less marked effects, while increasing Na2S additions up to 0.1 molar (giving H2S and HS− at neutral pH) caused an increasing reduction in the pitting potential. Additions of Na2S4O6 up to 0.05M promoted pitting, but addition of 0.01 M Na2SO3 had no effect. Parallel pitting potential measurements using a scratch technique gave lower values for the sulfur containing solutions but a higher value for the plain chloride solution; this effect of surface deformation was also reflected in the results obtained potentiodynamically on abraded and electropolished surfaces.