THE EFFECT OF ELECTROLYTE-COMPOSITION ON THE PITTING AND REPASSIVATION BEHAVIOR OF AISI 304 STAINLESS-STEEL AT HIGH-TEMPERATURE

The pitting potential E'p and the repassivation potential ER for AISI 304 stainless steel have been determined by stepwise cyclic polarization in deaerated NaCl solution of various concentrations from 0.01 to 2 M at 150 and 250 C. Repeated determination of E'p and ER showed that E'p scattered in accordance with normal distribution function and that ER could be determined uniquely when the concentration of NaCl was above 0.5 M, while it decreased with the growth of pits below 0.1 M. The mean value of E'p, E'p,mean and the most negative value of ER, ER,min were expressed by the conventional form as a function of concentration of chloride: E = A - Blog[Cl-]. The effect of sulfate and hydroxide ions on E'p and ER has also been studied at 150 C. The results showed that both sulfate and hydroxide ion suppressed the initiation of pitting, while ER was shifted to nobler values only by sulfate ion. The role of these anions is discussed to account for these observations. © 1990.