Nondestructive magnetic methods are widely using to inspect the surface defects in steel products such as the billets, wire rods and tubes. In the case of thin steel sheet, we can classify the defects of steel sheet to the surface defects and the internal defects. On the other hand the surface defects can be detected by the optic methods, inspecting the internal defects, such as the nonmetallic inclusions that cause cracking of 2-piece steel can during the flanging process, is quite difficult.