STP426

    Dose Rate, Annealing, and Stress Relaxation Studies of Radiation Hardening in Iron

    Published: Jan 1967


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    Abstract

    A study of the specific effect of dose rate on the increase in yield stress of a vacuum-melted iron was carried out by irradiating tensile specimens at dose rates from 2 × 1011 to 3 × 1013 neutrons/cm2 sec (E > 1 Mev) at 95 C in the poolside of the Oak Ridge Research Reactor. For a dose of 4.6 × 1018 neutrons/cm2 (E > 1 Mev), a three-fold increase in yield stress occurred, but there was no variation with dose rate in the range investigated. The possible significance of the absence of a dose rate effect is discussed in general terms. The annealing of the radiation hardening was found to take place at temperatures of 300 to 400 C with an activation energy of about 3 ev. This range of temperatures coincides with that observed for the dissociation of nitrogen from radiation-produced traps after electron irradiation. Several models for the annealing process are considered. Stress relaxation measurements on unirradiated and irradiated iron and iron-silicon are described. Evidence for the existence of an internal or threshold stress, which must be exceeded for macroscopic dislocation motion, is cited. It is pointed out that the major cause of radiation hardening is the increase in this stress. When account is taken of the increase in internal stress upon irradiation, the stress relaxation experiments indicate no change in the activation volume for plastic deformation.

    Keywords:

    neutrons, dose rate, iron, iron-silicon, tension tests, radiation hardening, yield stress, internal stress, annealing, interstitial impurity, stress relaxation, dislocations, radiation effects


    Author Information:

    Hinkle, N. E.
    Development engineer, metallurgist, and head of the Radiation Metallurgy Section, Solid State Div., Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Ohr, S. M.
    Development engineer, metallurgist, and head of the Radiation Metallurgy Section, Solid State Div., Oak Ridge National Laboratory, Oak Ridge, Tenn.

    Wechsler, M. S.
    Development engineer, metallurgist, and head of the Radiation Metallurgy Section, Solid State Div., Oak Ridge National Laboratory, Oak Ridge, Tenn.


    Paper ID: STP41338S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP41338S


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