Evolution of Austenite Recrystallization and Grain Growth Using Laser Ultrasonics

Laser ultrasonics is a noncontacting technique with which the attenuation of ultrasonic signals can be measured and related to the grain size of the investigated material. In the present article, a laser-ultrasonic grain-size measurement technique previously developed for various C-Mn and microalloyed steels has been extended to examine austenite recrystallization and subsequent grain growth following hot deformation. The ultrasonic measurements were conducted on a low-carbon (0.05 wt pct) steel that contains Mn, Mo, and Nb as the three main alloying/microalloying elements. The grain-size data measured by ultrasonic experiments were analyzed to quantify the effect of deformation conditions on the evolution of recrystallized grain size and subsequent grain growth. A significant effect of deformation temperature, applied strain, and initial grain size on the grain-size evolution was observed, while strain rate had a negligible effect. Phenomenological modeling approaches were employed to describe the recrystallized grain-size and grain-growth behavior of the present steel.