b'2019 | ANNUAL REPORTFigure 4. G-phase (Mn-Ni-Si) precipitates in irradiatedferrite phases.ferrite would decrease subsequently.saturate at 5 dpa. The discrepancy Limited study showed that the cracksis attributed to the austenite phase initiate in hardened ferrite phase andbecoming hardened and embrittled propagate along the phase boundary,and essentially determiningthe bulk which reduce the overall fracturemechanical properties.toughness of the material [10]. TheThe correlation between the micro-APT microstructure characterizationstructural changes and mechanical on the 3 dpa irradiated duplex stain- responses was established through less steel clearly displayed that thethe mechanistic understanding and neutron irradiation introduced veryfinite element modeling developed in similar phase evolutions in the ferritethe project. Prediction can be made phase as compared with thermalbased on the microstructural data aging. With additional data collectedfrom small samples exposed to long-from the samples irradiated at 5, 10,term thermal aging with or without 20 and 40 dpa, it was found thatneutron irradiation conditions, that neutron irradiation induced spinodalnormally poses significant challenges decomposition started to saturate atin experimental measurements due between 10 and 20 dpa. However, itto the limit of surveillance samples. is generally agreed that the decreaseBy simply characterizing the micro-of bulk fracture toughness starts to 51'