STP1405

    Review of Phosphorus Segregation and Intergranular Embrittlement in Reactor Pressure Vessel Steels

    Published: Jan 2001


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    Abstract

    This paper presents a systematic review of the behavior of phosphorus (P), highlighting the implications of P segregation to grain boundaries under neutron irradiation. The review focuses on Mn-Mo-Ni steels employed in US pressurized water reactors (PWRs), and other PWRs worldwide. Segregation of P to grain boundaries in reactor pressure vessel (RPV) steels can occur during fabrication (especially during the slow cooling stage of a post-weld heat treatment), and as a result of in-service exposure to high operating temperature and irradiation. This segregation of P to grain boundaries can promote a change in the brittle fracture mode from transgranular (TGF) to intergranular (IGF), and a degradation in the mechanical properties. In US RPV steels, most data are on thermal aging of the heat-affected zone (HAZ). Studies in coarse-grained HAZ have shown that the embrittlement arising from segregation of P to grain boundaries is approximately linearly related to the proportion of the brittle fracture that is IGF, and/or the P concentration at the grain boundary. Data are sparse on the effect of irradiation at 288°C on P segregation, and on the contribution of IGF to the total shift in the 41J transition temperature, T41J. In general, the bulk P content appears to be less than about 0.028 wt% P, with base metals having lower levels than weldments. In addition, the consequences of vessel annealing are considered at temperatures around 475°C. It is certain that the annealing treatment will have the consequence of reducing the irradiation hardening, but may significantly increase the grain boundary phosphorus coverage and the likelihood of IGF.

    Keywords:

    phosphorus segregation, intergranular embrittlement, grain boundaries, HAZ, thermal anneal heat treatment


    Author Information:

    English, CA
    Technical Staff, AEA Technology, Nuclear Science, Harwell, Didcot, Oxfordshire

    Ortner, SR
    Technical Staff, AEA Technology, Nuclear Science, Harwell, Didcot, Oxfordshire

    Gage, G
    Technical Staff, AEA Technology, Nuclear Science, Harwell, Didcot, Oxfordshire

    Server, WL
    President, ATI Consulting, Dublin, CA

    Rosinski, ST
    Project Manager, EPRI, Charlotte, NC


    Paper ID: STP10531S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP10531S


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