Abstract:To improve the hot workability of hard-deformed superalloy U720Li, the effect of holding time before deformation (5 and 10 min) on hot deformation behavior was investigated by hot compression tests. Results show that the flow stress increases with increase in strain rate, while decreases with increase in deformation temperature and holding time. Based on the obtained Arrhenius-type constitutive models, the calculated peak stresses are in good agreement with experimental values, indicating that this model can accurately predict the hot deformation behavior of U720Li alloy, and the deformation activation energies for the holding time of 5 and 10 min were calculated to be 992.006 and 850.996 kJ·mol-1, respectively. Moreover, processing maps of U720Li alloy with these two holding durations were constructed. Through observation of deformation microstructures in each domain of the processing maps, the optimal hot working conditions for the holding time of 5 min are determined to be 1090?1110 °C/ 1?10 s-1 and 1146?1180 °C/1?10 s-1, and the optimal hot working conditions for the holding time of 10 min are 1080?1090 °C/1?10 s-1 and 1153?1160 °C/1?10 s-1, indicating that the safe processing window can be obviously enlarged by shortening the holding time reasonably. In the absence of cracking, the dynamic recrystallization (DRX) grain size increases gradually with increasing the deformation temperature and holding time, but it first decreases and then increases with the increase in strain rate. When the deformation temperature is below 1100 °C, the DRX mechanism is mainly the particle-induced continuous DRX. As the temperature is raised to above 1130 °C, the main DRX mechanism changes to discontinuous DRX.