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    Micromechanisms of Ductile Stable Crack Growth in Nuclear Pressure Vessel Steels

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    The objective of this work was to investigate the relationship between the micromechanisms of ductile crack growth, the microstructural constituent phases present in nuclear pressure vessel steel, and the observed fracture behavior as determined by impact and fracture mechanics tests.

    Results from a microstructural and mechanical property comparison of an A508 Class 3 pressurized water reactor nozzle forging cutout and a 150-mm-thick A533B Class 1 plate are reported. The variation of upper-shelf toughness between the two steels and its orientation sensitivity are discussed on the basis of inclusion and precipitate distributions. Inclusion clusters in A533B, deformed to elongated disks in the rolling plane, have a profound effect on short transverse fracture properties.

    Data derived using the multi-specimen J-integral method to characterize the initiation of ductile crack extension and resistance to stable crack growth are compared with equivalent Charpy results. Results of the JR-curve analyses indicate (1) that the A533B short transverse crack growth resistance is approximately half that observed from transverse and longitudinal specimen orientations, and (2) that the A508 initiation toughness and resistance to stable crack growth are insensitive to position through the forging wall, and are higher than exhibited by A533B at any orientation in the midthickness position.


    elastic-plastic fracture, J-integral fracture mechanics, crack growth tearing resistance, inclusions, steels, crack initiation toughness

    Author Information:

    Belcher, WPA
    Metallurgist, National Nuclear Corporation, Ltd., Whetstone, Leicester

    Druce, SG
    Senior scientific officer, Atomic Energy Research Establishment, Harwell, Oxfordshire

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP36796S