| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a manufacturing method of a hot-rolled steel sheet using a magnetic leakage flux test by which flaws are detected with high accuracy even when the flaws are very small and unwanted magnetic fluxes, that is, noises are large. SOLUTION: The manufacturing method of the hot-rolled steel sheet having a stage where hot rolling is performed, a stage where flaw detection is performed by the magnetic leakage flux test and a stage where the position on the steel sheet where the detected flaw is present is specified is provided. The stage where the flaw detection is performed consists of a stage for successively magnetizing a ferromagnetic body to plural different intensities of magnetization to the steel sheet after rolling, a stage for detecting the magnetic flux which leaks from the same position of the ferromagnetic body which is magnetized to the each intensity of magnetization with a magnetic sensor and a stage for performing arithmetic processing of the output signal of the magnetic sensor corresponding to the intensity of each magnetization so as to emphasize a signal due to the flaw inside the ferromagnetic body.</p> |
