Morphology and elemental composition of a new iron-rich ferrite phase in highly irradiated austenitic steel

Merezhko D.A. Gussev M.N. Merezhko M.S. Rofman O.V. Rosseel T.M. Garner F.A.
1 July 2022 Acta Materialia Inc

Scripta Materialia
2022 #215

Elemental composition and morphology of a previously unidentified radiation-induced ferrite phase were investigated in a 300-series steel irradiated by neutrons in-service up to 57.6 dpa. Specimens of 18Cr-10Ni-Ti stainless steel (AISI 321 analog) were cut from a hexagonal wrapper of a fuel assembly irradiated in the BN-350 sodium-cooled fast reactor. An Fe-rich bcc-phase was observed primarily on grain boundaries. In this phase, the concentration of Cr is ∼8–12% (compared to ∼19% in the matrix), the concentration of Ni is ∼1.5–3% (∼9% in the bulk material), and the concentration of Mn is ∼0.23% (1.3% in the matrix). This Fe-rich phase is distinctly different from the retained-ferrite phase, commonly found in commercial austenitic steels. The extensive appearance of this Fe-rich ferrite on grain boundaries suggests that enhanced surface–intergranular corrosion may occur in water-cooled power reactors, arising from the low Ni, Mn, and Cr concentrations in this phase.

Austenitic steels , Corrosion , Ferrite phases , Grain boundaries , Irradiation-induced phase transformation

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Laboratory of Radiation Materials Science, Institute of Nuclear Physics, Almaty, 050032, Kazakhstan
Nuclear Energy and Fuel Cycle Division, Oak Ridge National Laboratory, Oak Ridge, 37831, TN, United States
Material Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, 37831, TN, United States
Radiation Effects Consulting, Richland, 99354, WA, United States
Texas A&M University, College Station, 77843, TX, United States

Laboratory of Radiation Materials Science
Nuclear Energy and Fuel Cycle Division
Material Science and Technology Division
Radiation Effects Consulting
Texas A&M University

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