EFFECT OF EXTERNALLY ADDED MOLYBDATE ON REPASSIVATION AND STRESS-CORROSION CRACKING OF TYPE-304 STAINLESS-STEEL IN HYDROCHLORIC-ACID

The effect of externally added molybdate (MoO42-) on the repassivation and SCC behavior of type 304 (UNS S30400) stainless steel (SS) was in vestigated in 1 M hydrochloric acid (HCl) at open-circuit potential (O CP). With the addition of MoO42-, the time to failure initially decrea sed hut then gradually increased. From studies using potential-vs-time data, the scratching electrode technique, and electron spectroscopy f or chemical analysis (ESCA), the initial decrease in the time to failu re at lower MoO42- concentrations was attributed to an increase in the cathodic reaction rate and a consequent increase in anodic dissolutio n. The increase in the time to failure at higher MoO42- concentrations was attributed to the reduction in anodic dissolution with a strong t endency for MoO42- deposition on the bare metal surface.