Detection and Imaging of Nonmetallic Inclusions in Continuously Cast Steel Plates by Higher Harmonics

Abstract

Nonmetallic inclusions within coarse columnar dendrites in continuously cast steel plates were detected and imaged by a nonlinear ultrasonic imaging technique. The nonlinear response of the inclusion/steel interface to tensile and compressive stress results in waveform distortion of the incident tone-burst wave, namely, higher harmonics in the frequency domain. By extracting the second harmonic with a band-pass filter and mapping the amplitude, small nonmetallic inclusions trapped at the bottom of coarse columnar dendrites were detected and imaged.