Phase Transformation Ratio Measurement of Steel Sheets Using Laser-Based Ultrasonics

A material property measurement system of steel sheet using laser-based ultrasonics has been developed. The system consists of pulsed Nd:YAG laser for ultrasonic generation, CW single frequency laser and multi-channel interferometer for ultrasonic detection. The system can measure the frequency of S1 Lamb wave mode of zero group velocity (S1f) without ablative damages on the steel surface. Since the S1f value is theoretically related to longitudinal and shear wave velocities, the system has a potential to evaluate the material property. To evaluate the applicability of the system to real steel production line, the system was installed in hot rolling pilot plant of steel samples. As the results, it was demonstrated that the system could evaluate the phase transformation ratio of steel sheets, even in the environment of hot rolling pilot plant.