Abstract: "The heat-treatment behavior of zirconium alloys containing 7 to 70 w/o uranium is described. The effect of oxygen contamination on the structure and hardness of these alloys is outlined. It is shown that in the initial stages pf transformation of beta zirconium-uranium solid solution into the low-temperature phases a potent hardening reaction occurs in alloys containing 20 to 70 w/o uranium. In this reaction the hardness may rise from 200 DPH characteristic of retained beta to values in excess of 400 DPH. Practical heat treatments have been developed which produce relatively soft alloys. The microstructures and hardnesses produces by these treatments are shown."