Hydrogen-facilitated anodic dissolution of austenitic stainless steels

Effects of hydrogen in alloys on their anodic polarization curves and the dissolution behavior of types 304 and 310 (UNS 30400 and UNS 31000) stainless steels (SS) in 0.5 M sulfuric acid (H2SO4) + 0.1 M hydrochloric acid (HCl) solution were studied. Electrochemical polarization curves obtained from both alloys showed hydrogen increased the anodic currents in the active and transpassive regions, widened the active potential zone, and narrowed the passive zone. The higher the hydrogen concentrations in the alloys, the greater the hydrogen effect was shown to be. Hydrogen charging induced martensite transformation. The martensite phase was dissolved preferably. Inductively coupled plasma (ICP) was used to determine the ion concentrations of iron (Fe), chromium (Cr), and nickel (Ni) dissolved in the test solution. Results showed hydrogen greatly increased the dissolution rates of both alloys in the transpassive region by hindering chromium enrichment in surface films, thus weakening the passivity and repassivation capabilities of the alloys.