The thermal cycling, irradiation behavior, and fabrication characteristics of U are strongly dependent upon grain size; a smaller grain size yields the better properties. Grain refinement of cast U may be accomplished either by hot working in the high alpha temperature range or by heat treatment; refinement by the latter method was the object of this investigation. The variables studied were time, temperature, specimen size, multiple quenching, and alphaannealing after quenching. The results of the investigation have led to the following conclusions, within the scope of the experimental conditions. The grain size of cast U may be appreciably refined by beta-quenching. Time and temperature in the beta phase are not significant in determining the final alpha grain size. Multiple beta-quenches (two to four times) produce better grain size refinement than a single quench. Alpha-annealing after beta-quenching causes recrystallization, but does not greatly affect the grain size. Gamma-quenching is not recommended as a practical heat treatment. (auth)

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