NEW MECHANISMS TOWARD MITIGATING IRRADIATION-ASSISTED STRESS CORROSION CRACKING OF ADDITIVELY MANUFACTURED AND CONVENTIONAL AUSTENITIC STAINLESS STEEL

Irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels (SSs) remains one of the most critical material degradation issues in light water reactors (LWRs). This study presents new alloy design strategies and mechanisms to develop IASCC-resistant stainless steels. Additive manufacturing provides not only new mechanisms to suppress IASCC but also high-throughput means to support alloy exploration. New SS design concepts are demonstrated to significantly enhance IASCC resistance, and mechanistic insights are proposed.

In the first part of this study, we systematically explored the root cause of the superior IASCC resistance of additively manufactured 316L SS after the hot isostatic pressing (HIP) in high-temperature water, compared to 316L SS in other forms. It was found that the overall radiation hardening was not an accurate measure of IASCC susceptibility. A decreased strain localization along grain boundaries, caused by dislocation channel broadening, was identified as the main reason for the IASCC resistance. The phenomenon was further confirmed through in situ straining tests under the TEM. The second part developed a high-throughput approach utilizing directed energy deposition (DED) to accelerate alloy design and testing for improving IASCC resistance. We explored the effects of reactive elements (REs), such as Hf, Ti, and Y, on the IASCC of 316L SS. All of these REs suppressed the radiation hardening, radiation damage, and IASCC of 316L SS, although their contributions varied with concentrations. It is suggested that radiation-induced segregation is not necessary to cause IASCC, while hardness and strain localization exhibited a stronger correlation to the IASCC. Finally, based on the roles of these reactive elements, a new type of SS was developed, which exhibited superior resistance to stress corrosion cracking (SCC) and IASCC. The low level of radiation damage and high corrosion resistance were considered the primary factor.