Abstract: This internal oxide layer thickness estimation device estimates a thickness of an internal oxide layer formed in a hot-rolled steel sheet.

Abstract: An internal oxidation starting temperature, estimation device estimates an internal oxidation starting temperature which is a minimum temperature required for an internal oxide layer to grow on a surface of an easily oxidizable element-containing hot-rolled steel sheet including Si, Mn, or Al or any combination thereof. The internal oxidation starting temperature estimation device includes an internal, oxidation starting temperature estimation unit that estimates the internal oxidation starting temperature on the basis of concentrations of the Si, the Mn, and the Al included in the easily oxidizable element-containing hot-rolled steel sheet.

Abstract: Flatness of a hot-rolled steel sheet in a coil is improved when the hot-rolled steel sheet is wound with a mandrel in a hot-rolling process to manufacture a coil. The mandrel has a protruding shape with a center portion in an axial direction protruding from both end portions when seen from a lateral side in the axial direction. Regarding a peripheral length difference, which is a difference between a peripheral length of the center portion of the mandrel and a peripheral length at a predetermined distance from the center portion, the ratio of the peripheral length difference to the peripheral length of the center portion is preferably 0.0002 to 0.012. The protruding shape may be a trapezoidal shape or a polynomial function shape.

Abstract: A coil skid on which a hot-rolled coil 1 obtained by coiling a hot-rolled steel sheet is placed includes: at least two or more layers of a metal plate 11 and at least two or more layers of a heat insulating material 12 each stacked alternately, in which the metal plate 11 is in contact with the hot-rolled coil 1. The uneven cooling of an outer peripheral portion of the hot-rolled coil caused by the coil skid is prevented while ensuring the strength of the coil skid, to thereby inhibit the uneven hardness in the longitudinal direction of the hot-rolled coil resulting from this uneven cooling.

Abstract: Flatness of a hot-rolled steel sheet in a coil is improved when the hot-rolled steel sheet is wound with a mandrel in a hot-rolling process to manufacture a coil. The mandrel has a protruding shape with a center portion in an axial direction protruding from both end portions when seen from a lateral side in the axial direction. Regarding a peripheral length difference, which is a difference between a peripheral length of the center portion of the mandrel and a peripheral length at a predetermined distance from the center portion, the ratio of the peripheral length difference to the peripheral length of the center portion is preferably 0.0002 to 0.012. The protruding shape may be a trapezoidal shape or a polynomial function shape.

Abstract: A provisional elongation strain difference distribution ??(x) of a metal strip during rolling is found under conditions in which out-of-plane deformation of the metal strip is restrained. A critical buckling strain difference distribution ??cr(x) is found based on the provisional elongation strain difference distribution ??(x), a strip thickness and strip width of the metal strip, and tension acting on the metal strip at exit from a rolling mill. When the provisional elongation strain difference distribution ??(x) exceeds the critical buckling strain difference distribution ??cr(x), the difference between the provisional elongation strain difference distribution ??(x) and the critical buckling strain difference distribution ??cr(x) is found, and added to the provisional elongation strain difference distribution ??(x) to find a true elongation strain difference distribution ???(x).

Abstract: A provisional elongation strain difference distribution ??(x) of a metal strip during rolling is found under conditions in which out-of-plane deformation of the metal strip is restrained. A critical buckling strain difference distribution ??cr(x) is found based on the provisional elongation strain difference distribution ??(x), a strip thickness and strip width of the metal strip, and tension acting on the metal strip at exit from a rolling mill. In cases in which the provisional elongation strain difference distribution ??(x) exceeds the critical buckling strain difference distribution ??cr(x), the difference between the provisional elongation strain difference distribution ??(x) and the critical buckling strain difference distribution ??cr(x) is found, and this difference is added to the provisional elongation strain difference distribution ??(x) to find a true elongation strain difference distribution ???(x).

Abstract: The apparatus for cooling a hot-rolled steel sheet of the invention includes a thermometer that measures the temperature of the hot-rolled steel sheet; a shape meter that measures a shape of the hot-rolled steel sheet; a top side cooling device that cools a top surface of the hot-rolled steel sheet in a cooling section; a bottom side cooling device that cools a bottom surface of the hot-rolled steel sheet in the cooling section; and a control device that controls at least one of an amount of heat dissipated from the top surface by cooling and an amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet in the cooling section by controlling the top side cooling device and the bottom side cooling device based on temperature measurement results and shape measurement results.

Abstract: A method for manufacturing a steel sheet of the invention includes a hot-rolling process in which a steel material is hot-rolled using a finishing mill so as to obtain a hot-rolled steel sheet; and a cooling process in which the hot-rolled steel sheet is cooled. The hot-rolling process includes a target steepness-setting process in which a target steepness of the edge wave shape is set based on first correlation data indicating a correlation between a steepness of the edge wave shape of the hot-rolled steel sheet and a temperature standard deviation Y; and a shape-controlling process in which operation parameters of the finishing mill are controlled so as to match the steepness of the edge wave shape with the target steepness.

Abstract: The method for cooling a hot-rolled steel sheet of the invention includes a target ratio-setting process in which a top and bottom heat transfer coefficient ratio X1, at which a temperature standard deviation Y becomes a minimum value Ymin, is set as a target ratio Xt based on correlation data between a top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet and the temperature standard deviation Y of the hot-rolled steel sheet; and a cooling control process in which at least one of an amount of heat dissipated from a top surface by cooling and an amount of heat dissipated from a bottom surface by cooling of the hot-rolled steel sheet in the cooling section is controlled so that the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet in the cooling section matches the target ratio Xt.

Abstract: A cooling apparatus for hot rolling is installed on a downstream side of a finishing mill of a continuous hot rolling mill, and cools a steel sheet rolled by the finishing mill while being conveyed. The cooling apparatus includes first pinch rolls which, during an interval when the steel sheet fed out from a final stand of the finishing mill moves from a position of the final stand to a position where a surface temperature of the steel sheet reaches 850° C. or less, pinch the steel sheet while applying tension of 3.9 MPa or greater.

Abstract: A method for manufacturing a steel sheet of the invention includes a hot-rolling process in which a steel material is hot-rolled using a finishing mill so as to obtain a hot-rolled steel sheet; and a cooling process in which the hot-rolled steel sheet is cooled. The hot-rolling process includes a target steepness-setting process in which a target steepness of the edge wave shape is set based on first correlation data indicating a correlation between a steepness of the edge wave shape of the hot-rolled steel sheet and a temperature standard deviation Y; and a shape-controlling process in which operation parameters of the finishing mill are controlled so as to match the steepness of the edge wave shape with the target steepness.

Abstract: The method for cooling a hot-rolled steel sheet of the invention includes a target ratio-setting process in which a top and bottom heat transfer coefficient ratio X1, at which a temperature standard deviation Y becomes a minimum value Ymin, is set as a target ratio Xt based on correlation data between a top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet and the temperature standard deviation Y of the hot-rolled steel sheet; and a cooling control process in which at least one of an amount of heat dissipated from a top surface by cooling and an amount of heat dissipated from a bottom surface by cooling of the hot-rolled steel sheet in the cooling section is controlled so that the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet in the cooling section matches the target ratio Xt.

Abstract: The apparatus for cooling a hot-rolled steel sheet of the invention includes a thermometer that measures the temperature of the hot-rolled steel sheet; a shape meter that measures a shape of the hot-rolled steel sheet; a top side cooling device that cools a top surface of the hot-rolled steel sheet in a cooling section; a bottom side cooling device that cools a bottom surface of the hot-rolled steel sheet in the cooling section; and a control device that controls at least one of an amount of heat dissipated from the top surface by cooling and an amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet in the cooling section by controlling the top side cooling device and the bottom side cooling device based on temperature measurement results and shape measurement results.

Abstract: A cooling apparatus for hot rolling is installed on a downstream side of a finishing mill of a continuous hot rolling mill, and cools a steel sheet rolled by the finishing mill while being conveyed. The cooling apparatus includes first pinch rolls which, during an interval when the steel sheet fed out from a final stand of the finishing mill moves from a position of the final stand to a position where a surface temperature of the steel sheet reaches 850° C. or less, pinch the steel sheet while applying tension of 3.9 MPa or greater.

Abstract: The oxide film thickness of the steel material surface (dH2O+do2) is made to become 15 nm or less where post-treatment after water-cooling is not needed by suitably setting the conditions of the water-cooling start temperature (Ti), water-cooling end temperature (To), steel material thickness (d), concentration of solute oxygen in the cooling water (Do), and cooling rate (CR) in the equation of dH2O+do2=7.98×10?4(Ti?To)dDo+{5.50×10?3(Ti2?To2)?6.51(Ti?To)}/CR.

Abstract: The oxide film thickness of the steel material surface (dH2O+do2) is made to become 15 nm or less where post-treatment after water-cooling is not needed by suitably setting the conditions of the water-cooling start temperature (Ti), water-cooling end temperature (To), steel material thickness (d), concentration of solute oxygen in the cooling water (Do), and cooling rate (CR) in the equation of dH2O+do2=7.98×10?4(Ti?To)dDo+{5.50×10?3(Ti2?To2)?6.51 (Ti?To)}/CR.

Abstract: Suppression and removal of scales are efficiently carried out in a steel material hot rolling process and the time of pickling treatment as a successive step is greatly shortened. In a water cooling step of metallic material 11 at a temperature of 100° to 1,200° C., scales are removed by applying a direct current or an alternating current to metallic material 11 at 0.1 to 105 A/m2 of unit surface area from pinch rolls 2 to rolls 6 or apron guides 7 on the outlet side of a hot rolling mill 1 and/or by injecting cooling water at a pH value of −2 to 4 onto the metallic material 11 from cooling headers 4 and apron guides 7.