The research on the constitutive modeling and hot working characteristics of as-cast V–5Cr–5Ti alloy during hot deformation

Abstract

Isothermal compression tests of as-cast V–5Cr–5Ti vanadium alloy are conducted in the deformation temperature ranging from 1150 to 1400 °C with an interval of 50 °C, strain rate ranging from 0.001 to 1 s−1 and height reductions of 55% on a computer controlled thermal simulation machine. The hot deformation behavior of as-cast is characterized based on the analysis of the stress–strain behaviors, the constitutive equations and process map for obtaining optimum processing parameters and achieving desired microstructure during hot working. A constitutive equation by which the flow stress was expressed as a function of strain rate and deformation temperature was established and the apparent activation energy of deformation was calculated to be 428.480 kJ/mol. The processing maps are constructed at the true strain of 0.5 and 0.7 based on dynamic materials model (DMM) to delineate the safe and unsafe regions in the axes of temperature and strain rate. The area of unsafe region increases with the increasing of strain. These instability domains exhibited localized flow and cracking along grain boundaries which should be taken care of during hot processing. The recommended domain is in the condition of the temperature range of 1250–1400 °C and strain rate range of 0.001–0.02 s−1. And in this state the main soften mechanism is dynamic recovery. It is worth noting that when as-cast V–5Cr–5Ti alloys deformed in the recommended deformation zone, the continuous dynamic recrystallization occurred, which display the feature of serrate grain boundaries and the equiaxed grains in the grain boundaries. Microstructure observation of deformed specimens validated the applicability of the processing map at obtaining the optimum processing parameters of as-cast V–5Cr–5Ti alloy.