Calculation of activation energy at hot plastic deformation conditions

Abstract

For the experiments to determine deformation resistance under heat, a steel with the addition of boron, officially designated as BCT steel, was used. This designation characterizes steel that does not belong to the standardized steel brands. Determining the deformation resistance was carried out using a hardening dilatometer DIL805A/D, which is supplemented with a hydraulic unit. This enables compression tests during high-temperature forming. The deformation mode allows the material to be formed under defined conditions. Such conditions are strain value, strain temperature and strain rate. The deformation resistance for the test matrix 5x5, deformation temperatures (800, 900, 1000, 1100, 1200 °C) and deformation rates (0.001, 0.01, 0.1, 1, 10 s^-1) were experimentally determined. A mathematical model was used to evaluate the measured data, which describes the deformation curve depending on the deformation. Furthermore, equations were used to calculate the basic deformation resistance depending on two variables: degree of deformation and temperature of deformation, while the rate of deformation was constant. Appropriate mathematical equations and their graphical visualization are given for the five deformation rates. The Garofalo equation is used to calculate the activation energy of plastic deformation under heat. This equation is further extended by the deformation variable. Based on the results of the physical simulation of the compression process, a mathematical simulation of the compression process was performed. From the deformation curves, after the mathematical simulation of the compression process, it was possible to calculate the activation energy of plastic deformation for different temperatures. Subsequent visualization of the activation energy values showed its dependence on the deformation temperature. The mathematical description showed that the activation energy of plastic deformation is dependent on the deformation temperature, which proves that it is not a constant value as has been published so far.