Dynamic Recrystallization Behavior of Vanadium Micro-alloyed Forging Medium Carbon Steel

The dynamical recrystallization of Micro-alloyed forging steel was investigated at deformation temperatures of 850-1150 degrees C and strain rates of 0.01-5 s(-1) on a Gleeble-1500 dynamic thermo-mechanical simulator. The stress-strain curves at lower strain rates are typical of the occurrence of DRX and exhibit a peak in the flow stress before reaching steady state. The critical strain for the initiation of DRX has been estimated through the analysis of stress-strain curves and the result showed that the critical strain was correlated to the peak strain by epsilon(c) = 0.68 epsilon(p). Utilizing the peak stresses up measured from the stress-strain curves, constitutive equation governing the dynamic recrystallization has been analyzed and activation energy was determined to be Q = 379 kJ/mole, which was significantly, larger than that of same composition of V-micro alloyed steel. The grain size was refined from 140 mu m to 8-60 mu m by DRX. The dynamically recrystallized grain size has been measured and the result showed that logarithm of grain size appeared to be linearly decreasing with the increase in the logarithm of Zener-Holloman parameter Z = epsilon-exp(Q/RT). However, when the logarithm of grain size was plotted in terms of the inverse of deformation temperature, i.e. 1/T, the plot showed a significant deviation from the linearity expected from the above linear relationship.