Recrystallization kinetics of microalloyed steels determined by two mechanical testing techniques

Data on the static and post-dynamic recrystallization have been determined in five Ti-microalloyed steels. Both the stress relaxation and interrupted deformation techniques have been employed. The effect of a strain rate change on the flow stress and the subsequent softening kinetics was also investigated. A reasonable agreement is obtained between the results of both the stress relaxation and double-compression methods, which further confirms the reliability of the stress relaxation technique. The results indicate that steels with plain Ti or with Ti-Ni-V or Ti-Ni-Cu alloying recrystallize at temperatures above 900 degrees C (pass reduction greater than or equal to 0.15) for interpass times characteristic of plate rolling, but Nb (ca. 0.03%) retards the recrystallization rate so that the final rolling temperature should be about 1000 degrees C for full recrystallization between passes. The characteristics of static and metadynamic recrystallization are distinctly different. Softening becomes independent of strain and highly dependent on the strain rate even at strains leading to a small fraction of dynamic recrystallization. Nb has only a small retarding effect in metadynamic recrystallization. The flow stress level and softening kinetics are independent of the strain rate history only being dependent on the final strain rate.