Effect of delay time on microstructural evolution during warm rolling of Ti-Nb-IF steel

The effect of delay time with constant first finishing pass temperature (800°C) has been investigated by means of multi-pass torsion tests on Ti-Nb-IF steel. All the tests have been carried out at a strain rate of 2 s-1 with 11 passes and 0.3 strain each pass. During the final pass, the dynamic recrystallization occurs to a degree that depends on the delay time. In short interpass time (1 s) and at these temperatures (T&le 800°C), there is not enough time to start the static recrystallization, therefore, the accumulation of strain occurs and after some passes, the strain reaches a critical strain for starting the dynamic recrystallization. In this study, the change of mean flow stress during each pass and also the microstructural observation confirm that the dynamic recrystallization occurs after some passes in the ferrite phase of this steel. The stress-strain curves with constant temperature were obtained by using a kinetic model and the compensation of the increasing mean flow stress with decreasing temperature. Thus, this result also confirms that the dynamic recrystallization occurs in warm rolling of this IF steel. The chemical composition of the Ti-Nb-IF steel is C-Si-Mn-S-N-Ti-Nb.