Transformation kinetics and heat treatment of U-Cr alloys

The kinetics of β-to-α transformation in nucleation and growth mechanism, and the effect of the conditions of heat treatment on grain size have been studied on the alloys containing from 0.25 to 1.0 a/o Cr. Nearly constant activation energies, which vary from 32 to 38 kcal/g-atom with the content of alloying element, correspond to the temperature regions below the noses of T-T-T diagrams. And more effect of isothermal transformation temperature on grain size was observed in the temperature region above the nose of T-T-T diagram than bellow, but the effect of the content of alloying element is not conspicuous in whole temperature region, so far as nucleation and growth mechanism is concerned. As grain size is, in general, discontinuously increased by martensitic transformation, the lower limit of temperature which produces fine structure in isothermal transformation is correspondence to the upper limit of the beginning of martensitic transformation. Ms (β-to-α) temperatures are determined with alloys containing from 0.25 to 1.0 a/o Cr. (author)