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    The Effects of Mechanical Stress Gradients on Irradiation-Induced Embrittlement of Pressure Vessel Steel

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    The role of cracks and locally elevated stress fields in enhancing embrittlement in nuclear pressure vessel steels is assessed. The (elastic) stress field surrounding a crack tip can attract oversized or reject undersized solute atoms. The extent of the attraction or rejection depends on the size difference between the solvent and the solute atom, the temperature, the diffusivity of the solute, and the applied stress intensity. Under certain conditions, it is possible for solute atoms to concentrate near the crack tip and influence its growth. In the present study, a kinetic model for the concentration of solute atoms at crack tips is developed. This model is applied to the examination of the kinetics of enhanced concentrations of copper (Cu), sulfur (S), and phosphorus (P) near crack tips in ferrite. The effects of irradiation on the kinetics of the concentration process are also modeled. Finally, the consequences of such solute concentrations for fracture properties are examined in light of both the potential elevation in yield strength and the lowering of fracture strength. The consequences are found to be significant in pressure vessel steels at typical reactor vessel operating temperatures when irradiation enhanced diffusion accelerates the segregation process.


    fracture, stress concentration, radiation-enhanced diffusion, radiation-induced segregation, pressure vessel steels, atom size, embrittlement

    Author Information:

    Stubbins, James F.
    Associate professor, University of Illinois, Urbana, IL

    Ougouag, Abderrafi M.
    Assistant professor, University of Illinois, Urbana, IL

    Williams, John G.
    Associate professor, University of Illinois, Urbana, IL

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP49457S