Rate-controlling mechanisms of hot deformation in a medium carbon vanadium microalloy steel

Isothermal compression tests were carried out on a medium carbon vanadium microalloy steel (roughly Fe-0.33C-1.5Mn-0.1 V, wt%) by using a Gleeble-1500 simulator. Based on constitutive analysis including an Arrhenius term, activation energy for hot working was calculated and used to evaluate the rate-controlling mechanism of hot deformation. At low strain rates (0.1–1 s−1), the activation energy for hot working (287.4 kJ/mol) is very close to the austenite lattice self-diffusion activation energy, indicating that the rate-controlling mechanism is dislocation climb. While at high strain rates (10–30 s−1), the activation energy becomes very high (500.6 kJ/mol), and activation volume is better used under such conditions. Then, activation volume analysis based on both Schöck model and Kocks–Argon–Ashby model demonstrates that the rate-controlling mechanism at high strain rates is cross slip. That is, the rate-controlling mechanisms of hot deformation for the medium carbon vanadium microalloy steel at high and low strain rates are intrinsically different. Inspired by the findings above, processing map analysis based on dynamic materials model was further preceded and different peak domains of power dissipation efficiency in high and low strain rate regimes were found.