| 摘要 |
PROBLEM TO BE SOLVED: To make a mill scale to be a uniform color tone throughout its length, of which the composition and thickness vary according to temperature and oxidizing atmosphere in the forming stage of a steel sheet. SOLUTION: The uniform dark-violet hot-rolled steel sheet is characterized by having a scale thickness of 10μm or less, after being hot rolled in a hot rolling process, then cooled, and wound up, and having a color tone of 15<=L*<=40, -2<=a*<=2, and -5<=b*<=-3 in color specification by L*a*b*, for the scale on the surface. The steel material includes, by mass%, 0.01-0.2 C, 0.3 or less Si, 0.05-2 Mn, 0.1 or less P, 0.02 or less S, 0.1 or less Al, 0.01 or less N, and the balance Fe. The manufacturing method comprises winding up the steel material after roughing rolling it, then finish rolling it continuously by sequentially joining the end of the strip with the top of the following strip, after rewinding the coil, then water cooling it to 300-650 deg.C at 30 deg.C/s or more rapidly, and winding it up after 2-15 seconds.
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