Measurement of Grain Size of Hot-rolled Steel Sheets Using Laser-Based ultrasonics

The relationship between grain size of hot-rolled steel sheet and ultrasonic attenuation coefficient has been evaluated in laboarory and pilot plant using laser-based ultrasonic technology. For the measurement of ultrasonics in pilot plant, the Fabry-Perot interferometer was optimized to increase the signal to noise ratio. Also, the efficiency of ultrasonic generation using multiple laser pulses was evaluated experimentally for generation of ultrasonics in slightly ablative condition. The prototype measurement system was installed in pilot rolling plant and ultrasonic signals were measured during hot-rolling process. According to the results of laboratory and pilot plant, possibility of on-line measurement of grain size of hot-rolled steel sheet in production line has been confirmed.