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). The 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. The dominant IASCC mechanisms under different situations will be discussed. 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 underlying mechanisms to mitigate IASCC are discussed in detail.