Ultrasonic inclusion and pore classification in rolled and unrolled steel samples

The feasibility of an ultrasonic method to discriminate inclusions and pores (foreign bodies, FBs) in rolled and unrolled steel samples was studied. A 10 MHz point-focused transducer was used to scan immersed steel samples in pulse-echo mode to detect FBs. The differences in RF-echo amplitude and frequency content allowed discriminating inclusions from pores in the steel samples. Optical microscopy and scanning electron microscopy served as reference methods on cut samples to verify the classification after the ultrasonic measurement. The FB classification method was tested on 24 inclusions and 16 pores from rolled samples. All FBs were correctly classified indicating that this method is feasible for FB classification in rolled steel samples. In the unrolled samples, differences in calcium-aluminate (CaAl) inclusion and pore spectra at 16 MHz should allow CaAl discrimination from pores.