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Studies involving the application of the instrumented Charpy impact test are presented. The studies were concerned with the effect of strain rate, alloying, and irradiation on the ductile-brittle transition temperature (DBTT) and fracture behavior of pressure vessel steels.
The effect of strain rate on a 0.02C and 0.02C-3.5Ni steel was evaluated by comparing instrumented Charpy tests with three-point slow bend tests on Charpy V-notch specimens. Increasing the strain rate (1) increased the DBTT, (2) increased the yield stress, and (3) decreased the temperature dependence of the yield stress. The strain rate sensitivity of the yield stress was mainly responsible for the increase in the DBTT.
The instrumented Charpy test was used to determine why small nickel additions to steel are so effective in lowering the ductile-brittle transition temperature. The decrease in the DBTT was shown to be related to the decrease in the strain rate and temperature dependence of the yield stress produced by nickel.
The effect of irradiation on A212-B steel was evaluated by use of the instrumented Charpy impact test. Irradiating A212-B steel at approximately 260 C to a fluence of 9.4 × 1018 n/cm2 (>1 Mev) increased the DBTT 56 C. Irradiation increased the dynamic yield stress 30 percent but reduced the strain rate sensitivity of the yield stress. The increase in the ductile-brittle transition temperature was shown to be almost entirely due to the radiation-induced increase in the dynamic yield stress.
impact tests, fracture (materials), irradiation, strain rate, pressure vessel steels, bend tests, evaluation, tests
Division chief, Battelle Memorial Institute, Columbus, Ohio