Abstract: A method for continuously casting steel capable of reducing center segregation that occurs in a slab. In a section in a continuous casting machine in a slab withdrawal direction, a section from a start point at which the average value of solid phase ratios along a thickness direction at a widthwise center of a slab is within a range of 0.4 or more and 0.8 or less to an end point at which the average value of solid phase ratios along the thickness direction at the widthwise center of the slab is greater than the average value of solid phase ratios at the start point and is 1.0 or less is set as a first section. The slab is cooled by water in the first section at a water flow rate per surface area of the slab within a range of 50 L/(m2×min) or more and 2,000 L/(m2×min) or less.

Abstract: The hardness of a rail after the rail having a temperature equal to or higher than an austenite region temperature is forcibly cooled in a cooling facility is predicted. A plurality of sets of data for learning composed of a cooling condition data set and output data of hardness are acquired using a model that performs computing by using a cooling condition data set having at least a surface temperature of the rail before the start of cooling and the operating conditions of the cooling facility as input data and the hardness inside the rail after the forced cooling as output data.

Abstract: A method for continuously casting steel capable of reducing center segregation that occurs in a slab. In a section in a continuous casting machine in a slab withdrawal direction, a section from a start point at which the average value of solid phase ratios along a thickness direction at a widthwise center of a slab is within a range of 0.4 or more and 0.8 or less to an end point at which the average value of solid phase ratios along the thickness direction at the widthwise center of the slab is greater than the average value of solid phase ratios at the start point and is 1.0 or less is set as a first section. The slab is cooled by water in the first section at a water flow rate per surface area of the slab within a range of 50 L/(m2×min) or more and 2,000 L/(m2×min) or less.

Abstract: A method of cooling control for a steel plate, a cooling control device, and a method of manufacturing a steel plate, which adjust an upper/lower water ratio and prevent C-warping during cooling. The method of cooling control includes: determining an upper/lower water ratio of a steel plate being cooled wherein at least one of a C-warping amount and a curvature is within a target permissible range, based on a past operating condition, a past upper/lower water ratio when cooling under the past operating condition has been implemented, and at least one of a past C-warping amount and a past curvature measured by a shape measuring meter at an outgoing side of a cooling zone when the cooling under the past operating condition is implemented; and adjusting an amount of cooling water to be blown onto the steel plate to reach the upper/lower water ratio.

Abstract: 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.

Abstract: A production equipment line for a hot-rolled steel strip comprises a rough rolling mill comprising rough rolling mills for hot rolling a material, which is heated to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill comprising finish rolling mills for controlled-rolling the material to a final sheet thickness. At least one of the rough rolling mills is a reversible rolling mill. The production equipment line is provided on an upstream side of the reversible rolling mill with one of a slow cooling apparatus for slowly cooling at a water volume density of less than 1000 L/min·m2 and a rapid cooling apparatus for rapidly cooling after the slow-cooling at a water volume density of not less than 1000 L/min·m2 and the other of the slow cooling apparatus and rapid cooling apparatus on a downstream side of the reversible rolling mill.

Abstract: A production equipment line for a hot-rolled steel strip comprises a rough rolling mill group comprised of plural rough rolling mills for hot rolling a material which is heated up to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill group comprised of plural finish rolling mills for controlled-rolling the material to a final sheet thickness, wherein at least one of the plural rough rolling mills is a reversible rolling mill. The production equipment line for a hot-rolled steel strip is provided with a slow cooling apparatus for slowly cooling the material at a water volume density of less than 1000 L/min·m2 and a rapid cooling apparatus which is arranged next to the slow cooling apparatus and rapidly cools the material after the slow-cooling at a water volume density of not less than 1000 L/min·m2.

Abstract: A method for manufacturing a hot-rolled steel sheet having a large thickness and a large width, a larger sheet width and a lower temperature can stably be cut at a cutting load equal to that of a conventional steel sheet having a usual sheet thickness, a usual sheet width and a usual temperature. In a rough rolling step, the steel sheet is formed so that the shortest length L (mm) from a concave portion bottom to a convex portion top of the fishtail shape satisfies Equation (1) mentioned below, and an intermediate portion between the concave portion bottom and the convex portion top, defined as a desired cutting location, is cut: (2X+30)?L?300??(1), in which X is a maximum deviation (mm) of the cutting location of a crop cutting machine and 0?X?90.

Abstract: 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.

Abstract: A production equipment line for a hot-rolled steel strip comprises a rough rolling mill comprising rough rolling mills for hot rolling a material, which is heated to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill comprising finish rolling mills for controlled-rolling the material to a final sheet thickness. At least one of the rough rolling mills is a reversible rolling mill. The production equipment line is provided on an upstream side of the reversible rolling mill with one of a slow cooling apparatus for slowly cooling at a water volume density of less than 1000 L/min·m2 and a rapid cooling apparatus for rapidly cooling after the slow-cooling at a water volume density of not less than 1000 L/min·m2 and the other of the slow cooling apparatus and rapid cooling apparatus on a downstream side of the reversible rolling mill.

Abstract: A production equipment line for a hot-rolled steel strip comprises a rough rolling mill group comprised of plural rough rolling mills for hot rolling a material which is heated up to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill group comprised of plural finish rolling mills for controlled-rolling the material to a final sheet thickness, wherein at least one of the plural rough rolling mills is a reversible rolling mill. The production equipment line for a hot-rolled steel strip is provided with a slow cooling apparatus for slowly cooling the material at a water volume density of less than 1000 L/min·m2 and a rapid cooling apparatus which is arranged next to the slow cooling apparatus and rapidly cools the material after the slow-cooling at a water volume density of not less than 1000 L/min·m2.

Abstract: Provided are a cooling method and a cooling apparatus that, in the cooling of a hot-rolled steel strip, regulates the amount of cooling water in a two-stage manner for each set of headers in the width direction and changes the rate at which the steel strip is cooled, in a multistage manner by a simple method, and that is effective particularly in cooling the lower surface of the steel strip, where space is narrow. The spray nozzles 5 are arranged in a row in the width direction of the steel strip at a predetermined pitch. Two systems of cooling headers 6 are arranged for one set so that spray nozzles 5 adjacent in the width direction can be supplied with cooling water from different pipe systems, and a spray valve 7 is attached to each cooling header 7 so that spraying/stop of spraying of cooling water can be individually performed.

Abstract: A method for manufacturing a hot-rolled steel sheet having a large thickness and a large width, a larger sheet width and a lower temperature can stably be cut at a cutting load equal to that of a conventional steel sheet having a usual sheet thickness, a usual sheet width and a usual temperature. In a rough rolling step, the steel sheet is formed so that the shortest length L (mm) from a concave portion bottom to a convex portion top of the fishtail shape satisfies Equation (1) mentioned below, and an intermediate portion between the concave portion bottom and the convex portion top, defined as a desired cutting location, is cut: (2X+30)?L?300??(1), in which X is a maximum deviation (mm) of the cutting location of a crop cutting machine and 0?X?90.

Abstract: Provided are a cooling method and a cooling apparatus that, in the cooling of a hot-rolled steel strip, regulates the amount of cooling water in a two-stage manner for each set of headers in the width direction and changes the rate at which the steel strip is cooled, in a multistage manner by a simple method, and that is effective particularly in cooling the lower surface of the steel strip, where space is narrow. The spray nozzles 5 are arranged in a row in the width direction of the steel strip at a predetermined pitch. Two systems of cooling headers 6 are arranged for one set so that spray nozzles 5 adjacent in the width direction can be supplied with cooling water from different pipe systems, and a spray valve 7 is attached to each cooling header 7 so that spraying/stop of spraying of cooling water can be individually performed.

Abstract: A hot rolled steel sheet cooling apparatus includes a gradual cooling header 2 including a rod-like cooling water nozzle 3 for gradual cooling and a rapid cooling header 4 including a rod-like cooling water nozzle 5 for rapid cooling such that the headers constitute a cooling unit 9. The cooling unit 9 includes an elevating unit 7 capable of moving upward and downward in unison with the cooling unit. In cooling the upper surface of a hot rolled steel sheet (hot rolled steel strip or steel plate), uniform and stable cooling is achieved while both of high cooling rate and low cooling rate are ensured.

Abstract: A method for manufacturing a high strength hot rolled steel sheet includes heating a slab to a temperature in the range of 1150 to 1300° C.; hot rolling the slab with a finishing rolling temperature being in the range of 800 to 1000° C.; cooling the steel sheet at a mean cooling rate of 30° C./s or higher to a cooling termination temperature in the range of 525 to 625° C.; suspending cooling for a time period in the range of 3 to 10 seconds; cooling the steel sheet in such a manner that cooling of the steel sheet is nucleate boiling; and coiling the steel sheet at a temperature in the range of 400 to 550° C.

Abstract: A method for cooling a hot strip conveyed on a run-out table after finishing, including ejecting rod-like flows of cooling water from nozzles to the upper surface of the steel strip such that the flows are inclined toward a traveling direction of the steel strip, and draining the cooling water using draining means disposed downstream of the nozzles.

Abstract: A hot-strip cooling device for cooling a hot strip that has been subjected to finish rolling while being conveyed over a run-out table. The device includes a plurality of cooling nozzles that are disposed above a steel strip and eject rod-like flows of coolant at an ejection angle tilted toward the upstream side in a steel-strip traveling direction; and purging means that is disposed on the upstream side with respect to the cooling nozzles and purges the coolant that has been ejected from the cooling nozzles and resides on the steel strip.

Abstract: A cooling device and a cooling method for a hot strip allow uniform and stable cooling of the strip at a high cooling rate when supplying the coolant to the upper surface of the hot strip. The cooling device includes an upper header unit 21 for supplying a rod-like flow to the upper surface of the strip 10. The upper header unit 21 is formed of the first upper header group including plural first upper headers 21a arranged in a conveying direction and a second upper header group including plural second upper headers 21b arranged in the conveying direction. The cooling device is provided with an ON-OFF mechanism 30 to allow each of the upper headers 21a and 21b of the first and the second upper header groups to independently execute the ON-OFF control (start/end injection control) of an injection (feeding) of the rod-like flow.

Abstract: A cooling device and cooling method for a hot-rolled strip in which the strip can be uniformly cooled from a leading edge to a trailing edge with coolant by properly realizing a great cooling ability and a stable cooling zone.