Crack Initiation Mechanism in Non-ductile Cracking of Irradiated 304L Stainless Steels under BWR Water Environment

Takeo Onchi, Kenji Hohi, Marta Navas, Wade Karlsen

    Research output: Contribution to journalArticleScientificpeer-review

    8 Citations (Scopus)

    Abstract

    The deformation behavior and initiation mechanisms of intergranular (IG) and transgranular (TG) cracks in irradiated 304L stainless steel were studied by slow-strain-rate tensile tests in inert gas and simulated BWR water environments, followed by fractographic and microstructural examinations. Neutron irradiation was made in test reactors to fluences of up to 6.2x1020 n/cm2 (E>1 MeV). Intergranular cracking occurred in water above a critical neutron fluence of around 1 × 1020 n/cm2, based on the results of the SSRT tests and SEM fractography. That critical fluence is mechanistically supported by irradiated, deformed microstructures exhibiting dislocation channeling at that fluence, while radiation-induced Cr depletion at the grain boundaries was minor. Transgranular cracking of the irradiated material occurred in water below the critical fluence, initiating in the non-uniformly strained surface region of the test bar in the later stages of plastic deformation. The initiation of TG cracking is hypothesized to be related to a high density of deformation twins. Intergranular cracking is proposed to have initiated where localized slip bands terminated at grain boundaries, while TG cracking is inferred to have initiated at deformation twin boundaries. High stress and strain concentrations at grain/twin boundaries would be the common cause of non-ductile crack initiation.
    Original languageEnglish
    Pages (from-to)851-865
    Number of pages5
    JournalJournal of Nuclear Science and Technology
    Volume43
    Issue number8
    DOIs
    Publication statusPublished - 2006
    MoE publication typeA1 Journal article-refereed

    Keywords

    • 304L stainless steel
    • neutron irradiation
    • intergranular cracking
    • transgranular cracking
    • plastic deformation localization
    • dislocation channeling
    • deformation twins
    • grain boundary
    • twin boundary
    • stress and strain concentration

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