Effect of machining on near surface microstructure and the observation of martensite at the fatigue crack tip in PWR environment of 304L stainless steel

Zaiqing Que (Corresponding Author), Caitlin Huotilainen, Tiia Seppänen, Jari Lydman, Ulla Ehrnstén

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    Abstract

    This work highlighted that a ground surface finish and the exposure to a pressurised water reactor (PWR) environment result in a decreased low-cycle fatigue lifetime, an enhanced fatigue crack initiation and an accelerated fatigue crack growth rate of 304 L austenitic stainless steel. A ground surface finish promotes fatigue crack initiation and short crack growth especially in a water environment, due to the highly deformed underlying microstructure with high-angle grain boundaries and the grinding marks on surface. Martensite was observed in the vicinity of secondary crack tips in specimens tested in a simulated PWR primary side environment. The aggregated presence of α′- and ε-martensite in the vicinity of the fatigue crack tip can enhance the material's susceptibility to hydrogen-assisted fatigue cracking. Martensite formation was rarely observed in specimens exposed to high temperature air. The phase transformation from γ-austenite to αꞌ-martensite in the PWR primary environment occurred via the intermediate ε-martensite phase.
    Original languageEnglish
    Article number153399
    JournalJournal of Nuclear Materials
    Volume558
    DOIs
    Publication statusPublished - Jan 2022
    MoE publication typeA1 Journal article-refereed

    Keywords

    • Environmentally assisted fatigue
    • Hydrogen
    • Martensite formation
    • Stainless steels
    • Surface finish

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