Use of in-situ laser-ultrasonics measurements to develop robust models combining deformation, recovery, recrystallization and grain growth

The hot deformation and subsequent annealing of two C-Mn steels have been investigated using a Gleeble 3500 simulator. The flow stress during deformation and subsequent relaxation stress were recorded. The grain size evolution was simultaneously evaluated by the in-situ laser-ultrasonic (LUS) measurements. The LUS data allowed clear identification of the dominant annealing phenomena. Excellent correlation was obtained between stress relaxation and laser-ultrasonic data, which provided additional confidence in the identification of the processes taking place. The solute drag effect of niobium led to the delayed onset and completion of recrystallization. Lower temperature generally slowed down the kinetics. Robust models combining deformation, recovery, recrystallization and grain growth have been developed and validated against the experimental data. The onset of recrystallization can be predicted precisely, as well as the time for recrystallization completion. As can be seen, the models are in good agreements with both the mechanical (stress evolution) and grain-size (laser-ultrasonic) data.