Hot-rolled steel sheet and method for manufacturing same
A hot-rolled steel sheet not exceeding a coil opener allowable load during unwinding includes a steel sheet cut in unsteady portions at its longitudinal head and tail ends in a cutting step after a rough rolling step, having a width of 1,200 mm to 2,300 mm, a thickness of 13 mm to 25.4 mm, and at least an API standard X65-grade strength, and used in a state of being unwound after having been wound around a coil. A longitudinal end corresponding to the unwinding start includes a portion at its widthwise center recessed inwards in the longitudinal direction with respect to its two widthwise ends, the two widthwise ends projection sizes with respect to the recessed portion at the widthwise center are 20 to 295 mm, and the sum of the widths of projecting portions at the two widthwise ends is set to ¼ to ½ of the sheet width.
1. A hot-rolled steel sheet having
a width that is in a range of from 1,200 mm to 2,300 mm,
a thickness that is in a range of from 13 mm to 25.4 mm,
a strength that is at least an API standard X65-grade strength,
a longitudinal head end, and
a longitudinal tail end,
wherein:
the hot-rolled steel sheet is cut in portions at the longitudinal head end and the longitudinal tail end after rough rolling,
at least one of the longitudinal head end and the longitudinal tail end includes two widthwise end portions and a recessed portion at a widthwise center, the recessed portion is recessed inwards in a longitudinal direction with respect to the two widthwise end portions,
in the longitudinal direction, a longitudinal height of each of the two widthwise end portions with respect to the recessed portion is in a range of from 20 mm to 295 mm,
a sum of widths of the two widthwise end portions is in a range of from ¼ to ½ of the width of the sheet, and
the hot-rolled steel sheet is configured to be used in an unwound state after having been wound around a coil.
2. A method for manufacturing the hot-rolled steel sheet according to claim 1 , the method comprising:
rough rolling a steel sheet, the rough rolling includes width reduction rolling and horizontal rolling so as to shape a crop portion that is formed on a trailing end of the steel sheet in a transport direction into a fish tail-shaped structure such that a minimum length L (mm) from the recessed portion to a tip in the fish tail-shaped structure satisfies:
(2X+5)≤L≤300 (1)
where
X is a maximum error (mm) of a cut position of a crop shear, and
0≤X≤90;
cutting the rough-rolled steel sheet with the crop shear in the crop portion such that the rough-rolled steel sheet is cut at a target cut position that is between the recessed portion and the tip;
finish rolling the cut steel sheet; and
winding the finished-rolled steel sheet.
3. The method according to claim 2 , wherein the target cut position is set between a position X mm from the recessed position toward the tip and a position (X+5) mm from the tip of toward the recessed portion.