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

D. A. Merezhko; M. N. Gussev; M. S. Merezhko; O. V. Rofman; T. M. Rosseel; F. A. Garner

doi:10.1016/j.scriptamat.2022.114690

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

D. A. Merezhko, M. N. Gussev, M. S. Merezhko, O. V. Rofman, T. M. Rosseel, F. A. Garner

Nuclear Fuel Element Performance

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6 Scopus citations

Abstract

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.

Original language	English
Article number	114690
Journal	Scripta Materialia
Volume	215
DOIs	https://doi.org/10.1016/j.scriptamat.2022.114690
State	Published - Jul 1 2022

Funding

The research was funded by the Ministry of Education and Science of the Republic of Kazakhstan (Grant no. AP08052488). This research was supported in part by the US Department of Energy , Office of Nuclear Energy, Light Water Reactor Sustainability Program under contract DE-AC05–00OR22725 with UT-Battelle LLC via Oak Ridge National Laboratory. The authors wish to express their gratitude and appreciation to the leadership of recently deceased Prof. Oleg P. Maksimkin (Institute of Nuclear Physics, Almaty, Kazakhstan) in providing resources to conduct this experiment.

Funders	Funder number
Office of Nuclear Energy, Light Water Reactor Sustainability Program	DE-AC05–00OR22725
U.S. Department of Energy
Oak Ridge National Laboratory
Ministry of Education and Science of the Republic of Kazakhstan	AP08052488

Keywords

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

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10.1016/j.scriptamat.2022.114690

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

abstract = "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.",

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

author = "Merezhko, {D. A.} and Gussev, {M. N.} and Merezhko, {M. S.} and Rofman, {O. V.} and Rosseel, {T. M.} and Garner, {F. A.}",

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AU - Merezhko, D. A.

AU - Gussev, M. N.

AU - Merezhko, M. S.

AU - Rofman, O. V.

AU - Rosseel, T. M.

AU - Garner, F. A.

PY - 2022/7/1

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N2 - 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.

AB - 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.

KW - Austenitic steels

KW - Corrosion

KW - Ferrite phases

KW - Grain boundaries

KW - Irradiation-induced phase transformation

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ER -

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

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