STP484: Effect of Fast Neutron Irradiation on the Creep Rupture Properties of Type 304 Stainless Steel at 600 C

    Bloom, EE
    Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Stiegler, J
    Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Pages: 16    Published: Jan 1970


    Abstract

    The creep rupture properties of Type 304 stainless steel have been determined at 600 C after irradiation at temperatures in the range from 370 to 600 C to fast neutron fluences of 1×1021 to 6.7×1022 n/cm2, E >0.1 MeV. The microstructures were characterized by electron microscopy. Irradiation at 370 to 470 C caused a decrease in ductility and rupture life which became larger with increasing fast neutron fluence. The irradiated specimens fractured along the grain boundaries with no evidence of deformation within the matrix. A specimen irradiated at 410 C to 6.7×1022 n/cm2 ruptured in 0.5 h with 0.1 percent elongation, as compared to a rupture life of 185 h and elongation of 19.7 percent for the unirradiated material tested at the same stress. Specimens irradiated at 600 C to fluences from 2.5 to 3.5 ×1022 n/cm2 exhibited decreased ductilities and creep rates and essentially the same rupture lives as unirradiated specimens.

    The increased tendency for grain boundary fracture, and thus reduced ductility and rupture life, appears to result from the effects of the irradiation produced voids and dislocations upon deformation processes, which effects would be inoperative in an unirradiated specimen. The voids and dislocations prevent dislocation motion within the matrix. Regions along grain boundaries are denuded of these defects and grain boundary sliding occurs, leading to stress concentrations and the initiation of grain boundary cracks. The presence of helium at the boundaries may increase the rate of crack propagation.

    Keywords:

    neutron irradiation, neutron flux, fast neutrons, radiation effects, cracking (fracturing), crack propagation, deformation, ductility, microstructure, crystal lattices, crystal dislocations, voids, grain boundaries, creep rupture strength, creep rupture tests, austenitic stainless steels, fast reactors (nuclear), nuclear fuel cladding


    Paper ID: STP26643S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP26643S


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