:
Hot compression tests on 5CrNiMoV and S34MnV steel at temperature of 1030, 1130, 1230℃ and strain rates
of 0.001, 0.01, 0.1s-1, were carried out to analyze the activation energy for hot deformation. The activation energy of
5CrNiMoV and S34MnV steels was respectively calculated with reference to σp and σs. It was found that the activation
energy showed significant dependence on the strain and chemical composition. The activation energy was obtained based
on different stresses corresponding to the true strain 0.1-0.7 and its evolution with strain was revealed. Besides, an
empirical expression for medium carbon steels was proposed to characterize the influence of the chemical composition on
the activation energy. It indicated 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 by restraining the grain boundary migration
and thus inducing the retardation of DRX. C is the dominating element for decreasing the activation energy by increasing
the self-diffusion and decreasing the segregation of other alloying atoms. Compared with the alloying element content in
S34MnV steel, relatively higher alloying element content in 5CrNiMoV steel, especially higher alloying element Mo,
probably contributed to higher activation energy.
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 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 composition 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 acquied 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.
