Evaluation of Radiation-Induced Sensitization of Austenitic Stainless Steels Using Electrochemical Potentiokinetic Reactivation Technique

The electrochemical potentiokinetic reactivation (EPR) test technique was applied to the determination of radiation-induced sensitization in a neutron-irradiated (420°C. 9 displacements per atom [dpa]) titanium-modified, austenitic stainless steel. Miniaturized specimens (3 mm diam by 0.25 mm thick) in both the solution-annealed and 25% cold-worked conditions were irradiated and tested by the single-loop EPR test technique. The degree of sensitization (DOS) was calculated in terms of the reactivation charge (Pa). The Pa value was increased by the irradiation as compared to control specimens thermally aged at the irradiation temperature. Grain boundary etching was observed on the specimen surface after EPR testing. Subsequent x-ray microanalysis by analytical electron microscopy (AEM) revealed that chromium depletion at grain boundaries had occurred. These results suggest the occurrence of radiation-induced sensitization associated with chromium depletion at grain boundaries. However, the post-EPR examination of the specimen surfaces showed that etching had also occurred across the face of the grains as well as at grain boundaries. This indicates that the Pa value normalized by the total grain boundary area, which is an accepted EPR–DOS criterion, cannot be directly used as an indicator of the DOS in determining the susceptibility of this irradiated material to intergranular stress corrosion cracking (IGSCC). Further investigations are necessary to correlate the results in this study to the IGSCC susceptibility of the irradiated stainless steel.