Volume 6, Issue 5 (May 2009)

    Effect of Ta Rich Inclusions and Microstructure Change During Precracking on Bimodal Fracture of Reduced-Activation Ferritic/Martensitic Steels Observed in Transition Range

    (Received 29 February 2008; accepted 18 March 2009)

    Published Online: 2009

    CODEN: JAIOAD

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    Abstract

    The master curve method for analyzing fracture toughness data depends on the assumption that the fracture initiation points are homogeneously distributed and fracture initiation is independent of test temperature. The reduced-activation ferritic/martensitic steels, such as F82H (Fe-8Cr-2W-0.2V-0.04Ta), form Al2O3-Ta(V,Ti)O composite inclusions and its distribution is not homogeneous throughout one heat, and this microstructural inhomogeneity appears to be correlated with bimodal facture of F82H in the transition range. To investigate this possibility, 1TCT fracture toughness specimens of F82H-IEA steel were fatigue precracked and sliced through the specimen thickness for microstructure analysis around the crack. It was found that the crack penetration was straight in the beginning, and then tended to follow a prior austenite grain boundary and finally to branch into two or three different directions. In addition, the microstructures around the crack and ahead of the crack formed a cell structure and became softer than nearby regions, which is typical for fatigue-loaded F82H. Possible mechanisms for how this cell structure ahead of cracks affects fracture toughness are suggested.


    Author Information:

    Tanigawa, Hiroyasu
    Japan Atomic Energy Agency, Tokai, Ibaraki

    Sokolov, Mikhail A.
    Metals & Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN

    Sawahata, Atsushi
    Ibaraki Univ., Hitachi, Ibaraki

    Hashimoto, Naoyuki
    Hokkaido Univ., Sapporo, Hokkaido

    Ando, Masami
    Japan Atomic Energy Agency, Tokai, Ibaraki

    Shiba, Kiyoyuki
    Japan Atomic Energy Agency, Tokai, Ibaraki

    Enomoto, Masato
    Ibaraki Univ., Hitachi, Ibaraki

    Klueh, Ronald L.
    Metals & Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN


    Stock #: JAI101728

    ISSN: 1546-962X

    DOI: 10.1520/JAI101728

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    Author
    Title Effect of Ta Rich Inclusions and Microstructure Change During Precracking on Bimodal Fracture of Reduced-Activation Ferritic/Martensitic Steels Observed in Transition Range
    Symposium Fifth Symposium on Small Specimen Test Techniques, 2007-02-01
    Committee E10