Influence of steel heat treatment on ultrasonic absorption measured by laser ultrasonics

Laser ultrasonics is combined with the reverberation technique to measure ultrasound absorption during thermal cycles applied to medium-carbon steel samples. During heating to the austenitic phase, a small Snoek peak is observed around 360 °C at 10 MHz along with a signature of the ferromagnetic to paramagnetic transition near 768 °C. Upon cooling, the behavior of the internal friction is much different from that of heating: reduced high-temperature absorption, delayed phase transition, smaller magnetoelastic contribution and stronger Snoek peak are observed. The austenitizing temperature is found to have primary importance on the internal friction behavior during cooling. These measurements show that ultrasound absorption measurements using laser ultrasonics could serve as a basis for a technique to characterize the microstructure evolution of steel in various temperature ranges.