Abstract
Samples made of SCM415 bulk with hole defects of different depth were annealed at 855°C for two hours. A ferromagnetic oxide scale was produced and the defects were measured by EMAT using magnetostrictives. Their resulting images of defects were very noisy and blurred. First, we performed noise-reduction on a sample with internal defects 10mm, 20mm, 30mm and 40mm deep. The echo signals were identified clearly. Second, we developed a theory of ultrasonic wave propagation and measured the response function. A sample with hole defects of different diameters was prepared and image reconstruction was applied.
