| 摘要 |
PROBLEM TO BE SOLVED: To provide a simple method for discriminating surface defects whereby types of streaky defects clearly appearing at surfaces of hot dip galvanized carbon steel sheets are simply discriminated. SOLUTION: There are included a process of detecting the streaky defect and calculating a defect length (L) and a defect width (w), a process of calculating a pressure slab ratio (ts/tp) from a slab thickness (ts) before the steel sheet is rolled and a steel sheet thickness (tp) after the steel sheet is rolled, a process of comparing a ratio (L/w) of the defect length (l) and the defect width (w) with the pressure slab ratio (ts/tp), discriminating that the detected streaky defect is caused by biting foreign matters after a hot rolling rough mill when (L/w)<(ts/tp) is held, and that the detected streaky defect is caused by a slab surface layer hole when 2×(ts/tp)<=(L/w) is held, and reserving the discrimination for the defect in the other cases than the above.
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