The dynamical recrystallization of Micro-alloyed forging steel was investigated at deformation temperatures of 850-1150°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 εc = 0.68εp. Utilizing the peak stresses σp 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 μm to 8–60 μm 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 = ε ′ 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.
2014 by The Iron and Steel Institute of Japan