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    The Effects of Metallurgical and Irradiation Variables on the Postirradiation Annealing Kinetics of Pressure Vessel Steels

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    Microhardness measurements were carried out following irradiation and isothermal postirradiation annealing at 375, 425, and 450°C for times up to 600 h on a set of steels representing a range of compositions, microstructures, fluxes, fluences, and irradiation temperatures. Following an initial drop in hardness, radiation anneal hardening peaks were frequently observed in copper-bearing alloys at times which decreased with increasing annealing temperature. Overall, however, both residual hardening and effects of the embrittlement variables decreased with increasing annealing time and temperature, as expected. In the copper-bearing commercial alloys, full, or nearly full, recovery was observed only at 450°C beyond about 50 h. Full recovery was observed in the low-copper commercial alloys at all annealing temperatures. The short-term recovery increment increased with increasing flux, fluence, and nickel content and decreasing irradiation temperature. Residual hardening after long-term annealing systematically increased with lower flux, higher fluences, and higher copper and nickel content. The residual hardness was also significantly larger for a simple copper-bearing ferritic model steel than for any of the complex commercial alloys. The results of this study are qualitatively consistent with a multiple feature model of embrittlement involving point defect-solute cluster complexes and copper-rich precipitates. We propose an explanation for what has up until now been a significant discrepancy in our understanding of how embrittlement develops during irradiation and how it recovers during annealing. This insight will provide a physical basis for constructing quantitative annealing models.


    pressure vessel steels, embrittlement, hardening, postirradiation annealing

    Author Information:

    Mader, E
    University of California, Santa Barbara, CA

    Lucas, GE
    University of California, Santa Barbara, CA

    Odette, GR
    University of California, Santa Barbara, CA

    Committee/Subcommittee: E10.08

    DOI: 10.1520/STP17867S