Effect of cooling rate on gleeble hot ductility of udimet alloy 720 billet

Abstract

Conversion of highly-alloyed γ′-hardened disk alloys such as UDIMET alloy 720 from cast ingot into billet requires a detailed knowledge of the hot working process window. Hot workability of billet stock was assessed by Gleeble tension testing. The effects of test temperature and, in particular, cooling rate from the prior annealing temperature to the test temperature on hot ductility were systematically studied. High cooling rates on the order of 30 °C / s as realized in the Gleeble tester resulted in a dramatic drop in hot ductility. Much slower cooling rates, representative of industrial conversion operations, resulted in acceptable ductility of greater than 60 %. Microstructures of the as-supplied billet stock and in the various tested conditions were characterized. The measured significant differences in hot ductility are rationalized by the dominant deformation mechanisms observed microscopically.