A Comparative Study on the Activation Energy for Hot Deformation of 5CrNiMoV and S34MnV Steel

Background: The value of the activation energy is dependent on deformation conditions and sensitive to the difference in the alloying element. The research on the evolution of the activation energy with strain and alloying elements plays an important role in analyzing the mechanism of hot deformation. Objective: The purpose was to clarify the activation energy evolution with strain, to analyze the strengthening or softening mechanism of each element, and acquire an empirical equation for medium carbon steels to quantitatively describe the effect of each element on activation energy. Methods: Hot compression tests of the two medium carbon steel were conducted. The value of activation energy at different strain was obtained by fitting the experiment results. Through the analysis of medium carbon steels with different compositions in published papers, the empirical relationship between thermal activation energy and chemical composition can be fitted. Results: It was found that the activation energy showed significant dependence on the strain and chemical composition. The activation energy’s evolution with strain was revealed. An empirical expression for medium carbon steels was proposed to characterize the influence of the chemical composition on the activation energy. It was found that the microalloying elements Nb, Ti, V and Mo, as the main solution strengthener and precipitation strengthener, have a positive effect on the activation energy. Conclusion: The evolution of the activation energy with strain was revealed, and the corresponding hot deformation mechanism was analyzed through the activation energy. An empirical expression was acquired to characterize the influence of the chemical composition on the activation energy for medium carbon steels, which would be used for the research on new materials.