The effects of the valence of sulfur in sulfur oxyanions on the passivation behavior of Alloys 600 and 690 in various heat treatments was studied at 25°C and 95°C using the potentiodynamic polarization method; the effects of scanning rate of the potential, valence of sulfur oxyanions, pH, alloy composition and alloy heat treatment were investigated. In general, the stability of passive films was found to decrease with the decrease of sulfur valence from +6 to -2. Alloy 690 in the thermally treated condition tended to be more stable that the various heat treatments of Alloy 600. Examination of surfaces after polarization over the potential range showed that intergranular corrosion occurred mainly in solutions of...
Key words: Alloy 600, Alloy 690, sulfur-containing ions, passivation, kinetic instability, transient current, stress corrosion cracking.