Laser-ultrasonic measurements are performed during the annealing of cold-worked low-carbon steel at temperatures between 590°C and 610°C. During annealing, the ultrasound velocity behaves in a peculiar way, first decreasing and then increasing to a final value. The recrystallized fraction evaluated by metallography indicates that recrystallization occurs during both the decrease and the increase in longitudinal velocity. Texture evaluated using laser ultrasonics suggests that the peculiar behavior of the velocity might be due to two different regimes of texture evolution. Internal friction, investigated through ultrasound absorption measurements, is also revealed to be very sensitive to the annealing process. This internal friction is attributed to magnetomechanical effects that are also known to decrease the ultrasonic longitudinal velocity and probably contribute to the observed peculiar behavior of the velocity. From this work, we conclude that, although there remains much work to do to explain our observations, both the longitudinal velocity and internal friction measurements are promising approaches for the development of an online sensor to characterize annealing using laser-ultrasonics.
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