When U is heat treated at low beta-phase temperatures and air cooled, the rate of loss of preferred orientation is markedly less than the rate of coarsening of the grain structure. A coarse-grained structure cannot therefore be taken as an infallible indication of satisfactory heat treatment. The final grain size of incompletely transformed metal is essentially equal to or larger than the starting grain size. Large-grained specimens can not be refined by interruption of the transformation at an intermediate stage. (auth)