The role of dislocation channeling in IASCC initiation of neutron irradiated stainless steel

- MnS inclusions enhance susceptibility to IASCC initiation.
- Local stress (typically caused by an intersecting dislocation channel) was required to cause cracking at a MnS inclusion.
- The remotely applied stress at which IASCC initiation occurred decreased with increasing irradiation dose.
- IASCC resistant alloys were more likely to transmit dislocation channels across grain boundaries.

This study intended to understand how dislocation channeling affects IASCC initiation using a novel four-point bend test. Stainless steels used in this study (irradiated in the BOR-60 reactor) included a commercial purity 304L alloy irradiated to 5.5, 10.2, and 47.5 dpa, and two high purity alloys, Fe18Cr12Ni and Fe18Cr25Ni, irradiated to ∼10 dpa. IASCC was enhanced by MnS inclusions, which dissolve in the NWC environment and form oxide caps, creating a crevice condition with a high propensity for crack initiation. Stress concentration at the grain boundary intersecting these sites induced crack initiation, resulting from discontinuous dislocation channels (DC). Stress to initiate IASCC decreased with dose due to earlier DC initiation. The HP Fe18Cr12Ni alloy had low IASCC susceptibility and the high Ni alloy did not crack. The difference was attributed to the propensity for DCs to transmit across grain boundaries, which controls stress accumulation at DC - grain boundary intersections.