Effect of externally added molybdate on repassivation and stress corrosion cracking of type 304 stainless steel in hydrochloric acid

Abstract

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