Laser-Ultrasonic Characterization of the Annealing Process of Low-Carbon Steel

Abstract

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.

Laser-Ultrasonics: From the Laboratory to Industry

“…Laboratory use of laser-ultrasonics with such a simulator as well as on-line application appears presently near commercialization. It should also be noted that laser-ultrasonics could provide on a metal processing line, at the hot stage (hot rolling) or at lower temperature near finishing (cold rolling, annealing) further information such as texture (or anisotropy), distribution between various phases, degree of recrystallisation and information on the mechanical properties [82,83]. Laser-ultrasonics has been in particular tested on a finishing line by IMI/NRC under support of the American Iron and Steel Institute material with the purpose of measuring these properties.…”

Laser Ultrasonic Thickness Measurements of Very Thick Walls at High Temperatures

“…It has been not only applied to laboratory measurements [1][2][3][4][5], but was also demonstrated and is actually used on production lines [6][7][8]. Although this technique has the unique capability of allowing material characterization during processing and at elevated temperatures, and this has been reported many times [1][2][3][4][5][6][7][8], more straightforward applications, like measuring thickness, are often the most needed by industry. In this case it should be noted that the technique is now commercially used for measuring the wall thickness and eccentricity of seamless tubes in production [6].…”