Dynamic recrystallization behaviour of Nb-Ti microalloyed steels

The dynamic recrystallization (DRX) behavior of Nb-Ti microalloyed steels was investigated by isothermal single compression tests in the temperature range of 900-1 150 degrees C at constant strain rates of 0.1-5 s(-1). DRX was retarded effectively at low temperature due to the onset of dynamic precipitation of Nb and Ti carbonitrides, resulting in higher values of the peak strain. An expression was developed for the activation energy of deformation as a function of the contents of Nb and Ti in solution as well as other alloying elements. A new value of corrective factor was determined and applied to quantify the retardation produced by increase in the amount of Nb and Ti dissolved at the reheating temperature. The ratio of critical strain to peak strain decreases with increasing equivalent Nb content. In addition, the effects of Ti content and deformation conditions on DRX kinetics and steady state grain size were determined. Finally, the kinetics of dynamic precipitation was determined and effect of dynamic precipitation on the onset of DRX was clarified based on the comparison between precipitate pinning force and recrystallization driving force.