Determination of critical conditions for dynamic recrystallization of a microalloyed steel

A low carbon Nb–Ti microalloyed steel was subjected to hot torsion testing over the range of temperatures from 900 to 1100 °C and strain rates from 0.01 to 1 s−1 to characterize its hot deformation behavior. The initiation and evolution of dynamic recrystallization were investigated by analyzing of hot flow curves. Two important dynamic recrystallization parameters, the critical strain and the point of maximum dynamic softening, derived from strain hardening rate- stress curves. These parameters then were used to predict the dynamic recrystallized fraction. The results showed that the critical stress and strain increase with decreasing deformation temperature and increasing strain rate. The hot deformation activation energy of the steel investigated in the present work is 375 kJ/mol, and the expression for steady state flow stress isσSS=0.07Z0.14=0.07⋅ε˙ exp375,000RT0.14The volume fraction of dynamic recrystallization as a function of processing variables was established. It was found that the model used for predicting the kinetic of dynamic recrystallization is in good agreement with the data directly acquired from experimental flow curves.