STP1447: Grain Boundary Phosphorous Segregation and Its Influence on the Ductile Brittle Transition Temperature in Reactor Pressure Vessel Steels

    Kimura, A
    Professor, Graduate Student, and Research Associate, IAE, Kyoto University, Kyoto,

    Shibata, M
    Professor, Graduate Student, and Research Associate, IAE, Kyoto University, Kyoto,

    Kasada, R
    Professor, Graduate Student, and Research Associate, IAE, Kyoto University, Kyoto,

    Nakata, H
    Senior Researcher, Institute of Nuclear Safety System, Inc., Fukui,

    Fujii, K
    Senior Researcher, Institute of Nuclear Safety System, Inc., Fukui,

    Fukuya, K
    Senior Researcher, Institute of Nuclear Safety System, Inc., Fukui,

    Pages: 14    Published: Jan 2004


    Abstract

    The materials used for this work were two sorts of reactor pressure vessel (RPV) steels, which contain different amounts of phosphorous (P), namely 0.011 and 0.002 wt%. The specimens for Charpy V-notch (CVN) impact test, Auger electron spectroscopy (AES), and tensile test were thermally aged at 400, 450, and 500°C for 1000, 3000, and 5000 h. After the thermal aging, the AES specimens were broken in the AES chamber to measure the P concentration at grain boundaries. The AES measurements for as-received specimens were carried out following hydrogen charging so that grain boundary facets were available even without P segregation. The AES measurements revealed that the peak height ratio (PHR) of P/Fe at the grain boundaries of the high-P steel were 0.066, 0.141, and 0.120 in the specimens aged at 400°C for 3000 h, 450°C for 3000 h, and 500°C for 1000 h, respectively. The ductile-brittle transition temperature (DBTT) was measured for the aged specimens, and the ▵DBTT of 15K was observed only for the specimen aged at 450°C for 3000 h, although no changes in the hardness and tensile properties were observed. The grain boundary fracture ratio (GBFR) increased with increasing the PHR of P/Fe. Grain boundary fracture mode was located at the area close to the V-notch root. There was a good relationship among PHR, GBFR, and DBTT, indicating directly that the shift in the DBTT was due to grain boundary embrittlement caused by P segregation.

    Keywords:

    grain boundary fracture ratio, DBTT shift, grain boundary phosphorous segregation, non-hardening embrittlement, synergistic effects


    Paper ID: STP11257S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP11257S


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