Macro-Scale strain localization in highly irradiated stainless steel investigated using digital image correlation

Low-temperature radiation hardening and embrittlement is a major life-limiting radiation effect in austenitic stainless steels (AuSS). A strain-induced phase transformation to martensite is observed during plastic deformation of low-Ni AuSS, often increasing strain hardening and reducing ductility. However, in this paper we show an unexpectedly high ductility of 18-37% during room-temperature mechanical testing of a 0.12C-18Cr-10Ni-0.8Ti AuSS (AISI 321 analogue) cut from the hexagonal wrapper of a fuel assembly irradiated in the BN-350 sodium-cooled fast reactor located in Aktau, Kazakhstan. Using digital image correlation, we reveal two completely different deformation mechanisms in samples with the same chemical composition, irradiated to very similar doses. The roles of the martensitic. gamma -> alpha' transformation and neutron irradiation parameters explain the differences between plastic deformation mechanisms in the specimens.