Abstract: A water-blocking apparatus for cooling water for a hot-rolled steel sheet according to the present invention, which blocks cooling water sprayed onto a hot-rolled steel sheet at a sprayed water density of higher than 4 m3/m2/min and equal to or less than 10 m3/m2/min when the hot-rolled steel sheet is cooled after finish rolling of a hot-rolling process, includes: a plurality of water-blocking nozzles which spray water-blocking water onto the hot-rolled steel sheet. Impact areas of the water-blocking water respectively sprayed from the water-blocking nozzles are continuously lined up in a straight line in a width direction of the hot-rolled steel sheet on a surface of the hot-rolled steel sheet and the adjacent impact areas partially overlap.

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 water-blocking apparatus for cooling water for a hot-rolled steel sheet according to the present invention, which blocks cooling water sprayed onto a hot-rolled steel sheet at a sprayed water density of higher than 4 m3/m2/min and equal to or less than 10 m3/m2/min when the hot-rolled steel sheet is cooled after finish rolling of a hot-rolling process, includes: a plurality of water-blocking nozzles which spray water-blocking water onto the hot-rolled steel sheet. Impact areas of the water-blocking water respectively sprayed from the water-blocking nozzles are continuously lined up in a straight line in a width direction of the hot-rolled steel sheet on a surface of the hot-rolled steel sheet and the adjacent impact areas partially overlap.

Abstract: The present invention provides a method of cooling a hot-rolled steel strip which has passed through a finishing rolling, including: cooling the hot-rolled steel strip from a first temperature of not lower than 600° C. and not higher than 650° C. to a second temperature of not higher than 450° C. with cooling water having the water amount density of not lower than 4 m3/m2/min and not higher than 10 m3/m2/min, wherein with respect to the area of the target surface, the area of a portion where a plurality of spray jets of the cooling water directly strikes on the target surface is at least 80%.

Abstract: The present invention provides a method of cooling a hot-rolled steel strip which has passed through a finishing rolling, including: cooling the hot-rolled steel strip from a first temperature of not lower than 600° C. and not higher than 650° C. to a second temperature of not higher than 450° C. with cooling water having the water amount density of not lower than 4 m3/m2/min and not higher than 10 m3/m2/min, wherein with respect to the area of the target surface, the area of a portion where a plurality of spray jets of the cooling water directly strikes on the target surface is at least 80%.

Abstract: The present invention provides a method for cooling a hot-rolled steel strip after a finishing rolling in which a transportation speed varies, the method including: setting a transportation-speed changing schedule on the basis of a temperature of a steel strip before the finishing rolling and a condition of the finishing rolling; performing a first cooling in which the hot-rolled steel strip is cooled under a film boiling state in a first cooling section; performing a second cooling in which the hot-rolled steel strip is cooled with a water amount density of not less than 2m3/min/m2 in a second cooling section; and coiling the hot-rolled steel strip, in which a cooling condition is controlled in the first cooling so as to satisfy 0.8?(T2a??T2a)/?Tx?1.2.

Abstract: The present invention provides a method of cooling a hot-rolled steel strip which has passed through a finishing rolling, including: cooling the hot-rolled steel strip from a first temperature of not lower than 600° C. and not higher than 650° C. to a second temperature of not higher than 450° C. with cooling water having the water amount density of not lower than 4 m3/m2/min and not higher than 10 m3/m2/min, wherein with respect to the area of the target surface, the area of a portion where a plurality of spray jets of the cooling water directly strikes on the target surface is at least 80%.

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 present invention provides a method for cooling a hot-rolled steel strip after a finishing rolling in which a transportation speed varies, the method including: setting a transportation-speed changing schedule on the basis of a temperature of a steel strip before the finishing rolling and a condition of the finishing rolling; performing a first cooling in which the hot-rolled steel strip is cooled under a film boiling state in a first cooling section; performing a second cooling in which the hot-rolled steel strip is cooled with a water amount density of not less than 2 m3/min/m2 in a second cooling section; and coiling the hot-rolled steel strip, in which a cooling condition is controlled in the first cooling so as to satisfy 0.8?(T2a??T2a)/?Tx?1.2.

Abstract: The present invention provides a method of cooling a hot-rolled steel strip which has passed through a finishing rolling, including: cooling the hot-rolled steel strip from a first temperature of not lower than 600° C. and not higher than 650° C. to a second temperature of not higher than 450° C. with cooling water having the water amount density of not lower than 4 m3/m2/min and not higher than 10 m3/m2/min, wherein with respect to the area of the target surface, the area of a portion where a plurality of spray jets of the cooling water directly strikes on the target surface is at least 80%.

Abstract: A method for controlling the cooling of a steel sheet characterized by controlling the end-of-cooling temperature in a cooling process from the Ae3 or above temperature of the steel sheet, during which; preliminarily obtaining enthalpies (H? and H?) of an austenite phase and ferrite phase respectively at some temperature, obtaining a gynamic enthalpy (Hsys) defined by formula (1) with an untransformed fraction (X?) of austenite in accordance with a target temperature pattern, predicting the temperature by using a gradient of this dynamic enthalpy with respect to temperature as a dynamic specific heat and controlling the cooling of the steel sheet: Hsys=H?(X?)+H?(1?X?).

Abstract: A method for controlling the cooling of a steel plate, characterized in that, in the control of the temperature at the end of cooling in the process of the cooling of a steel plate from the Ae3 temperature or higher, the enthalpies (H? and H?) of the austenite and ferrite phases at respective temperatures are determined in advance, a dynamic enthalpy (Hsys) defined by the formula (1) is determined from the proportion (X?) of untransformed austenite being determined in the correspondence to an objective temperature pattern, and a temperature of the steel plate is predicted by using an inclination of the above dynamic enthalpy to temperature as a dynamic specific heat for controlling the cooling of the steel plate. Hsys=H? (X?)+H? (1?X?) . . .