Intergranular Attack Observed in Radiation-Enhanced Corrosion of Mild Steel

Experiments were conducted to determine the effects of gamma radiation on the corrosion of AISI⁽¹⁾ 1018 mild steel in deaerated brine solutions of various sodium, magnesium, and chloride ion concentrations. Immersed metal specimens were irradiated at an exposure rate of 3 x 10⁵ R/h (0.3 MR/h) for up to 1250 h at a temperature of ~25 C. The corrosion rates of the irradiated specimens were found to be roughly a factor of 10 greater than the rates for the non-irradiated specimens. The radiation-enhanced corrosion rate was also found to have increased with the chloride concentration. Electron micrographs revealed that the surface morphology of the specimens exposed to irradiated brines differed greatly from the non-irradiated specimens. The non-irradiated specimens had undergone uniform corrosion, while the irradiated specimens exhibited intergranular corrosion (IGC), a phenomenon not yet observed in mild steel. An explanation for this observation is offered in terms of the relative rates of formation and recombination of radiolytic species.