STP1366

    Embrittlement, Hardening, and Grain Boundary Composition in an Fe-P-C Alloy after Irradiation or Thermal Aging

    Published: Jan 2000


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    Abstract

    An Fe-1200ppmP-30ppmC alloy has been examined after aging and irradiation exposure at 240°C. Thermal aging for 97 days reduced the yield stress by 10% but increased the 40J Charpy transition temperature by 50°C. Irradiation for a similar duration, in a highly thermalised neutron spectrum at 5.8 ± 1.7×10-11dpa/sec, increased both the yield stress by 15% and the transition temperature by 70°C. Longer irradiation, in spectra with or without the high thermal fraction, produced additional hardening but little extra embrittlement. Irradiation and aging gave a fivefold increase in the fraction of brittle intergranular fracture. Auger Spectroscopy showed that the P grain boundary monolayer coverage was virtually unchanged for all start-of-life, aging and irradiation conditions. In contrast, the C coverage reduced by 50% during the initial aging or irradiation, but changed little after longer irradiations. Grain boundary N increased initially but then stabilised. No grain boundary S occurred. Transmission microscopy revealed some dislocation loops and small regions of strain contrast in the grains after irradiation but no P-rich precipitates were seen. From this, and other published work, it is concluded that irradiation hardening arises from dislocation loops and possibly from P-rich cluster formation. Embrittlement developed due to loss of C from the grain boundaries, rather than from changes to the boundary P content. Loss of C reduced the boundary fracture stress but embrittlement was independent of the matrix strength. For the irradiation conditions examined, there was no evidence of irradiation-induced grain boundary P segregation.

    Keywords:

    Embrittlement, hardening, irradiation, neutron spectra, thermal aging, iron alloy, phosphorus, carbon, intergranular fracture, grain boundary composition


    Author Information:

    Jones, RB
    Irradiation Team Leader and Research Officer, Materials Group, Integrity and Engineering Branch at BNFL Magnox Generation, Berkeley Centre, Berkeley, Glos,

    Cowan, JR
    Irradiation Team Leader and Research Officer, Materials Group, Integrity and Engineering Branch at BNFL Magnox Generation, Berkeley Centre, Berkeley, Glos,

    Corcoran, RC
    Research Officer, Electron Optics Team, Nuclear Facilities Branch at BNFL Magnox Generation, Berkeley Centre, Berkeley, Glos,

    Walmsley, JC
    SINTEF Materialteknologi, Trondheim,


    Paper ID: STP12409S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP12409S


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