2014 年 63 巻 1 号 p. 37-43
Recently, steel can manufacturing requires higher quality steel because otherwise minute non-metal inclusions in thin sheets could cause cracks and result in a burst during the pressurization after the pressing process. Quality testing is already incorporated during the final process in steel plants, but if there was another inspection in an earlier step, at the hot strip mill for example, then the mass manufacture of non-conforming products could be avoided and the maintenance of quality control would be more efficient. Magnetic Flux Leakage Testing (MFLT) has been developed using different magnetizing, in order to detect inclusion defects in hot-rolled steel plates. In the analysis of the noise factors in MFLT, the signals generated from the scale layer on a steel surface were found to be dominant. A different magnetizing force method is used to decrease this overpowering noise level in MFLT. In this paper, it is confirmed that inclusions, larger than 160μm in diameter and less than 0.45mm in depth, can be detected.