Monitoring austenite decomposition by ultrasonic velocity

The ultrasonic longitudinal velocity measured by the laser-ultrasonic technique is compared to dilatometry for the monitoring of austenite decomposition of low alloy steels. It is demonstrated that the technique could be an interesting alternative to dilatometry. The temperature dependence of the ultrasonic velocity and the various phases in steels is determined and used to calculate the decomposed austenite by a simple law of mixtures approximation. As a non-destructive and non-contact technique, laser-ultrasonics can be applied to monitor austenite transformation of real products in an industrial production line, which would be much more difficult with dilatometry.