EP2764932B1 - Kühlverfahren für ein heissgewalztes stahlblech - Google Patents

Kühlverfahren für ein heissgewalztes stahlblech Download PDF

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Publication number
EP2764932B1
EP2764932B1 EP12873475.3A EP12873475A EP2764932B1 EP 2764932 B1 EP2764932 B1 EP 2764932B1 EP 12873475 A EP12873475 A EP 12873475A EP 2764932 B1 EP2764932 B1 EP 2764932B1
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EP
European Patent Office
Prior art keywords
cooling
hot
steel sheet
rolled steel
temperature
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EP12873475.3A
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English (en)
French (fr)
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EP2764932A4 (de
EP2764932A1 (de
Inventor
Tooru Akashi
Shingo Kuriyama
Takeo Itoh
Fuminori Tasaki
Koji Noguchi
Hitoshi Nikaido
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • B21B37/76—Cooling control on the run-out table

Definitions

  • the present invention relates to a method for cooling a hot-rolled steel sheet in which a hot-rolled steel sheet hot-rolled using a finishing mill is cooled.
  • FIG. 21 is a view schematically illustrating a method for manufacturing a hot-rolled steel sheet of the related art.
  • a slab S obtained by continuously casting molten steel having an adjusted predetermined composition is rolled using a roughing mill 201, and then, furthermore, hot-rolled using a finishing mill 203 constituted by a plurality of rolling stands 202a to 202d, thereby forming a hot-rolled steel sheet H having a predetermined thickness.
  • the hot-rolled steel sheet H is cooled using cooling water supplied from a cooling apparatus 211, and then coiled into a coil shape using a coiling apparatus 212.
  • the cooling apparatus 211 is generally a facility for carrying out so-called laminar cooling on the hot-rolled steel sheet H transported from the finishing mill 203.
  • the cooling apparatus 211 sprays the cooling water on the top surface of the hot-rolled steel sheet H moving on a run-out table from the top in the vertical direction in a water jet form through a cooling nozzle, and, simultaneously, sprays the cooling water on the bottom surface of the hot-rolled steel sheet H through a pipe laminar in a water jet form, thereby cooling the hot-rolled steel sheet H.
  • JP 2005-74463A discloses a technique of the related art which reduces the difference in surface temperature between the top and bottom surfaces of a thick steel sheet, thereby preventing the shape of the steel sheet from becoming defective.
  • the water volume ratio of cooling water supplied to the top surface and the bottom surface of the steel sheet is adjusted based on the difference in surface temperature obtained by simultaneously measuring the surface temperatures of the top surface and the bottom surface of the steel sheet using a thermometer when the steel sheet is cooled using a cooling apparatus.
  • JP H05-337505A discloses a technique that cools a rolled material between two adjacent stands in a finishing mill using a sprayer, thereby beginning and completing the ⁇ - ⁇ transformation of the rolled material so as to prevent sheet-threading performance between the stands from deteriorating.
  • JP 2005-271052A discloses a technique that measures the steepness at the tip of a steel sheet using a steepness meter installed on the exit side of a mill, and prevents the steel sheet from being perforated by adjusting the flow rate of cooling water to be different in the width direction based on the measured steepness.
  • JP 2003-48003A discloses a technique that aims to solve a wave-shaped sheet thickness distribution in the sheet width direction of a hot-rolled steel sheet and to make uniform the sheet thickness in the sheet width direction, and controls the difference between the maximum heat transmissibility and the minimum heat transmissibility in the sheet width direction of the hot-rolled steel sheet to be in a range of predetermined values.
  • the hot-rolled steel sheet H manufactured using the manufacturing method illustrated in FIG. 21 forms a wave shape in the rolling direction (the arrow direction in FIG. 22 ) on transportation rolls 220 in the run-out table (hereinafter sometimes referred to as "ROT") in the cooling apparatus 211 as illustrated in FIG. 22 .
  • the top surface and the bottom surface of the hot-rolled steel sheet H are not uniformly cooled. That is, there was a problem in that, due to cooling deviation caused by the wave shape of the hot-rolled steel sheet H, it became impossible to uniformly cool the steel sheet in the rolling direction.
  • JP H06-328117A discloses a technique that, in a steel sheet formed into a wave shape in the rolling direction, makes uniform the cooling capabilities of top portion cooling and bottom portion cooling so as to minimize the influence of the distance between soaked water on the top portion of the steel sheet and a table roller at the bottom portion in order to uniformly cool the steel sheet.
  • US 2012/0318478 A1 discloses a method for cooling sheet metal by means of a cooling section having multiple coolant dispensing devices for cooling upper and lower faces of a sheet metal, in which the cooling achieves a predefined target state of the sheet metal at a reference point at and/or after the exit from the cooling section, wherein coolant dispensing for a first and a second coolant dispensing device is determined, wherein the first and the second coolant dispensing devices are arranged opposite the sheet metal, and the coolant dispensing for the first and second coolant dispensing devices is determined based on a predefined flow of heat to be dissipated from the sheet metal side that faces the respective coolant dispensing device, with a surface temperature of the respective sheet metal side being taken into account.
  • the portions that locally come into contact with the transportation rolls 220 or the aprons become more easily cooled than other portions due to heat dissipation by contact. Therefore, there was a problem in that the hot-rolled steel sheet H was ununiformly cooled. That is, in Patent Document 1, the fact that the wave shape of the hot-rolled steel sheet causes the hot-rolled steel sheet to locally come into contact with the transportation rolls or the aprons and the contact portions becomes easily cooled due to heat dissipation by contact is not taken into consideration. Therefore, there are cases in which it is impossible to uniformly cool a hot-rolled steel sheet having a wave shape formed as described above.
  • JP H05-337505A is to make (soft) ultra low carbon steel having a relatively low hardness undergo ⁇ - ⁇ transformation between stands in a finishing mill, and does not aim at uniform cooling.
  • the invention of Patent Document 2 does not relate to cooling in a case in which a rolled material has a wave shape in the rolling direction or a rolled material is a steel material that is so-called high tensile strength steel having a tensile strength (TS) of 800 MPa or more, and therefore there is a concern that uniform cooling may not be possible in a case in which a rolled material is a hot-rolled steel sheet having a wave shape or a steel material having a relatively high hardness.
  • TS tensile strength
  • Patent Document 3 also does not take a hot-rolled steel sheet having a wave shape in the rolling direction into consideration, and there are cases in which it is not possible to uniformly cool a hot-rolled steel sheet as described above.
  • JP 2003-48003A is the cooling of a hot-rolled steel sheet immediately before roll bites in the finishing mill, and therefore it is not possible to apply the cooling to a hot-rolled steel sheet which has undergone finish-rolling so as to have a predetermined thickness.
  • Patent Document 4 also does not take a hot-rolled steel sheet having a wave shape in the rolling direction into consideration, and there are cases in which it is not possible to uniformly cool a hot-rolled steel sheet in the rolling direction as described above.
  • the cooling capability of the top portion cooling includes not only cooling by the cooling water supplied to the steel sheet from a top portion water supply nozzle but also cooling by the soaked water in the top portion of the steel sheet. Since the soaked water is influenced by the steepness of the wave shape formed in the steel sheet or the sheet-threading speed of the steel sheet, strictly, it is not possible to specify the cooling capability of the steel sheet by the soaked water. Thus, it is difficult to accurately control the cooling capability of the top portion cooling. Therefore, it is also difficult to make the cooling capabilities of the top portion cooling and the bottom portion cooling equivalence.
  • the patent document describes an example of a method for determining the cooling capabilities when the cooling capabilities of the top portion cooling and the bottom portion cooling are made uniform, but does not disclose ordinary determination methods. Therefore, in the cooling method of Patent Document 5, there are cases in which it is not possible to uniformly cool a hot-rolled steel sheet.
  • the present invention has been made in consideration of the above problems, and an object of the present invention is to uniformly cool a hot-rolled steel sheet hot-rolled using a finishing mill.
  • the present invention employs the following means for solving the problems and achieving the relevant object.
  • the present inventors found that the temperature standard deviation Y can be minimized (that is, the hot-rolled steel sheet can be uniformly cooled) by controlling the top and bottom heat transfer coefficient ratio X to a specific value.
  • a top and bottom heat transfer coefficient ratio X1 at which the temperature standard deviation Y becomes a minimum value Ymin, is set as the target ratio Xt based on the correlation data of the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y of the hot-rolled steel sheet, which have been experimentally obtained in advance, and at least one of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet 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, it is possible to uniformly cool the hot-rolled steel sheet which has been hot-rolled using a finishing mill so as to have a wave shape.
  • FIG. 1 schematically illustrates an example of a hot rolling facility 1 for realizing the method for cooling a hot-rolled steel sheet in the present embodiment.
  • the hot rolling facility 1 is a facility aimed to sandwich the top and bottom of a heated slab S using rolls, continuously roll the slab to make the slab as thin as a minimum of 1 mm, and coil the slab.
  • the hot rolling facility 1 has a heating furnace 11 for heating the slab S, a width-direction mill 16 that rolls the slab S heated in the heating furnace 11 in a width direction, a roughing mill 12 that rolls the slab S rolled in the width direction from the vertical direction so as to produce a rough bar, a finishing mill 13 that further continuously hot-finishing-rolls the rough bar to a predetermined thickness, a cooling apparatus 14 that cools the hot-rolled steel sheet H hot-finishing-rolled using the finishing mill 13 using cooling water, and a coiling apparatus 15 that coils the hot-rolled steel sheet H cooled using the cooling apparatus 14 into a coil shape.
  • the heating furnace 11 is provided with a side burner, an axial burner and a roof burner that heat the slab S brought from the outside through a charging hole by blowing flame.
  • the slab S brought into the heating furnace 11 is sequentially heated in respective heating areas formed in respective zones, and, furthermore, a heat-retention treatment for enabling transportation at an optimal temperature is carried out by uniformly heating the slab S using the roof burner in a soaking area formed in a final zone.
  • a heating treatment in the heating furnace 11 completely ends, the slab S is transported to the outside of the heating furnace 11, and moved into a rolling process by the roughing mill 12.
  • the roughing mill 12 passes the transported slab S through gaps between columnar rotary rolls provided across a plurality of stands.
  • the roughing mill 12 hot-rolls the slab S only using work rolls 12a provided at the top and bottom of a first stand so as to form a rough bar.
  • the rough bar which has passed through the work rolls 12a is further continuously rolled using a plurality of fourfold mills 12b constituted by a work roll and a back-up roll.
  • the rough bar is rolled into a thickness of approximately 30 mm to 60 mm, and transported to the finishing mill 13.
  • the finishing mill 13 finishing-rolls the rough bar transported from the roughing mill 12 until the thickness becomes approximately several millimeters.
  • the finishing mill 13 passes the rough bar through gaps between top and bottom finish rolling rolls 13a linearly arranged across 6 to 7 stands so as to gradually reduce the rough bar.
  • the hot-rolled steel sheet H finishing-rolled using the finishing mill 13 is transported to the cooling apparatus 14 using the transportation rolls 32 described below.
  • the cooling apparatus 14 is a facility for carrying out so-called laminar cooling on the hot-rolled steel sheet H transported from the finishing mill 13. As illustrated in FIG. 2 , the cooling apparatus 14 has a top side cooling apparatus 14a that sprays cooling water from cooling holes 31 on the top side to the top surface of the hot-rolled steel sheet H moving on the transportation rolls 32 in a run-out table, and a bottom side cooling apparatus 14b that sprays cooling water from cooling holes 31 on the bottom side to the bottom surface of the hot-rolled steel sheet H. A plurality of the cooling holes 31 is provided in the top side cooling apparatus 14a and the bottom side cooling apparatus 14b respectively.
  • a cooling header (not illustrated) is connected to the cooling hole 31.
  • the number of the cooling holes 31 determines the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b.
  • the cooling apparatus 14 may be constituted by at least one of a top and bottom split laminar, a pipe laminar, spray cooling and the like.
  • a section in which the hot-rolled steel sheet H is cooled using the cooling apparatus 14 corresponds to a cooling section in the present invention.
  • the coiling apparatus 15 coils the hot-rolled steel sheet H cooled using the cooling apparatus 14 at a predetermined coiling temperature as illustrated in FIG. 1 .
  • the hot-rolled steel sheet H coiled into a coil shape using the coiling apparatus 15 is transported to the outside of the hot rolling facility 1.
  • a wave shape having a surface height (wave height) changing in the rolling direction is formed in the hot-rolled steel sheet H hot-rolled using the finishing mill 13 as illustrated in FIG. 17 .
  • the influence of soaked water remaining on the hot-rolled steel sheet H will be ignored when cooling the hot-rolled steel sheet H. Actually, as a result of investigation by the inventors, it was found that the soaked water remaining on the hot-rolled steel sheet H has little influence.
  • the method for cooling a hot-rolled steel sheet of the present embodiment has two processes of a target ratio-setting process and a cooling control process.
  • 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 indicating a correlation between a top and bottom heat transfer coefficient ratio X, which is a ratio of heat transfer coefficients of the top and bottom surfaces of the hot-rolled steel sheet H, and the temperature standard deviation Y during or after cooling of the hot-rolled steel sheet H, which have been experimentally obtained in advance under conditions in which the steepness and the sheet-threading speed of the hot-rolled steel sheet H are set to constant values.
  • 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 H in the cooling section is controlled so that the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet H in the cooling section (a section in which the hot-rolled steel sheet H is cooled using the cooling apparatus 14) matches the target ratio Xt.
  • the correlation data used in the target ratio-setting process is experimentally obtained in advance using the hot rolling facility 1 before actual operation (before the hot-rolled steel sheet H is actually manufactured as a product).
  • a method for obtaining the correlation data used in the target ratio-setting process will be described in detail.
  • the cooling capability (top side cooling capability) of the top side cooling apparatus 14a and the cooling capability (bottom side cooling capability) of the bottom side cooling apparatus 14b of the cooling apparatus 14 are adjusted respectively in advance.
  • the top side cooling capability and the bottom side cooling capability are adjusted using the heat transfer coefficient of the top surface of the hot-rolled steel sheet H, which is cooled using the top side cooling apparatus 14a, and the heat transfer coefficient of the bottom surface of the hot-rolled steel sheet H, which is cooled using the bottom side cooling apparatus 14b.
  • the temperature difference herein refers to the difference between the temperature of the hot-rolled steel sheet H, which is measured using a thermometer on an entry side of the cooling apparatus 14, and the temperature of cooling water used in the cooling apparatus 14.
  • the computed heat transfer coefficient of the hot-rolled steel sheet H is classified into the heat transfer coefficient of the top surface and the heat transfer coefficient of the bottom surface of the hot-rolled steel sheet H.
  • the heat transfer coefficients of the top surface and the bottom surface are computed using a ratio that is obtained in advance, for example, in the following manner.
  • the heat transfer coefficient of the hot-rolled steel sheet H in a case in which the hot-rolled steel sheet H is cooled only using the top side cooling apparatus 14a and the heat transfer coefficient of the hot-rolled steel sheet H in a case in which the hot-rolled steel sheet H is cooled only using the bottom side cooling apparatus 14b are measured.
  • the amount of cooling water from the top side cooling apparatus 14a and the amount of cooling water from the bottom side cooling apparatus 14b are set to be equal.
  • the inverse number of the ratio between the measured heat transfer coefficient in a case in which the top side cooling apparatus 14a is used and the heat transfer coefficient in a case in which the bottom side cooling apparatus 14b is used becomes a top and bottom ratio of the amount of cooling water of the top side cooling apparatus 14a and the amount of cooling water of the bottom side cooling apparatus 14b in a case in which a top and bottom heat transfer coefficient ratio X, which will be described below, is set to "1".
  • top and bottom heat transfer coefficient ratio X is computed by multiplying the amount of cooling water of the top side cooling apparatus 14a or the amount of cooling water of the bottom side cooling apparatus 14b when cooling the hot-rolled steel sheet H by the top and bottom ratio of the amounts of cooling water obtained in the above manner.
  • the heat transfer coefficients of the hot-rolled steel sheet H cooled only using the top side cooling apparatus 14a and only using the bottom side cooling apparatus 14b are used, but the heat transfer coefficient of the hot-rolled steel sheet H cooled using both the top side cooling apparatus 14a and the bottom side cooling apparatus 14b may be used. That is, the heat transfer coefficients of the hot-rolled steel sheet H in a case in which the amounts of cooling water of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b are changed are measured, and the ratio of the heat transfer coefficients of the top surface and the bottom surface of the hot-rolled steel sheet H may be computed using the ratio of the heat transfer coefficients.
  • the heat transfer coefficients of the hot-rolled steel sheet H are computed, and the heat transfer coefficients of the top surface and the bottom surface of the hot-rolled steel sheet H are computed based on the above ratio of the heat transfer coefficients of the top surface and the bottom surface of the hot-rolled steel sheet H (top and bottom heat transfer coefficient ratio X).
  • top side cooling apparatus 14a and the bottom side cooling apparatus 14b are adjusted respectively using the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet H based on FIG. 3 .
  • the horizontal axis of FIG. 3 indicates a ratio of an average heat transfer coefficient of the top surface to an average heat transfer coefficient of the bottom surface of the hot-rolled steel sheet H (that is, equivalent to the top and bottom heat transfer coefficient ratio X), and the vertical axis indicates a standard deviation of temperature between the maximum temperature and the minimum temperature of the hot-rolled steel sheet H in the rolling direction (temperature standard deviation Y).
  • FIG. 3 shows data (correlation data) indicating the correlation between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y which are obtained by actually measuring the temperature standard deviation Y of the cooled hot-rolled steel sheet H while changing the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet H by adjusting the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b under conditions in which the steepness of the wave shape of the hot-rolled steel sheet H and the sheet-threading speed of the hot-rolled steel sheet H are set to constant values.
  • the steepness of the wave shape of the hot-rolled steel sheet H refers to a value obtained by dividing the amplitude of the wave shape by the length of a cycle in the rolling direction.
  • FIG. 3 is correlation data between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y which are obtained under conditions in which the steepness of the hot-rolled steel sheet H is set to 2% and the sheet-threading speed is set to 600 m/min (10 m/sec).
  • the temperature standard deviation Y may be measured during the cooling of the hot-rolled steel sheet H, or may be measured after the cooling.
  • the target cooling temperature of the hot-rolled steel sheet H is a temperature of 600°C or higher, for example, 800°C.
  • the top and bottom heat transfer coefficient ratio X1 at which the temperature standard deviation Y becomes the minimum value Ymin, is set as the target ratio Xt based on the correlation data experimentally obtained in advance as described above.
  • the correlation data may be prepared in a form of data (table data) that indicate the correlation between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y using a table (table form), or may be prepared in a form of data that indicate the correlation between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y using a mathematical formula (for example, regression formula).
  • the correlation data are prepared in a form of data indicating the correlation between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y using a regression formula
  • the regression formula may be derived by linearly regressing the line.
  • the minimum value Ymin of the temperature standard deviation Y is searched using a variety of methods, for example, a binary method, a golden section method and random search which are generally known search algorithms.
  • the top and bottom heat transfer coefficient ratio X1 at which the temperature standard deviation Y of the hot-rolled steel sheet H becomes the minimum value Ymin is derived in the above manner based on the correlation data illustrated in FIG. 3 .
  • the regression formulae of the temperature standard deviations Y of the hot-rolled steel sheet H in the rolling direction with respect to the top and bottom heat transfer coefficient ratio X may be obtained respectively on both sides of an equal point above and below the average heat transfer coefficient.
  • FIG. 4 illustrates a standard case in which mutually different regression lines are obtained on both sides of the minimum value Ymin of the temperature standard deviation Y.
  • first, temperature standard deviations Ya, Yb and Yc actually measured at a point, b point and c point which is in the center between the a point and the b point are extracted respectively.
  • the center between the a point and the b point indicates the c point at which a value between the top and bottom heat transfer coefficient ratio Xa at the a point and the top and bottom heat transfer coefficient ratio Xb at the b point is present, and this shall apply below.
  • Ya and Yb is the temperature standard deviation Yc closer is determined. In the embodiment, Yc is closer to Ya.
  • a temperature standard deviation Yd at a d point between the a point and the c point is extracted.
  • Yd is closer to Yc.
  • a temperature standard deviation Ye at an e point between the c point and the d point is extracted.
  • Ye closer is determined. In the embodiment, Ye is closer to Yd.
  • a minimum point f (minimum value Ymin) of the temperature standard deviation Y of the hot-rolled steel sheet H is specified.
  • the above computation needs to be carried out, for example, five times.
  • the minimum point f may be specified by dividing the range of the top and bottom heat transfer coefficient ratio X of a search target into 10 sections, and carrying out the above computation in each of the sections.
  • the top and bottom heat transfer coefficient ratio X may be corrected using the so-called Newton's method.
  • a partial difference between the top and bottom heat transfer coefficient ratio X with respect to the actual value of the temperature standard deviation Y and the top and bottom heat transfer coefficient ratio X at which the temperature standard deviation Y becomes zero is obtained using the above-described regression formula, and the top and bottom heat transfer coefficient ratio X when cooling the hot-rolled steel sheet H may be amended using the partial difference.
  • the top and bottom heat transfer coefficient ratio X1 at which the temperature standard deviation Y of the hot-rolled steel sheet H becomes the minimum value Ymin (Xf in FIG. 4 ) is derived as described above.
  • Ymin minimum value Ymin
  • the top and bottom heat transfer coefficient ratio X1 at which the temperature standard deviation Y of the hot-rolled steel sheet H becomes the minimum value Ymin is "1". Therefore, in a case in which the correlation data as illustrated in FIG. 3 is obtained, the target ratio Xt is set to "1" in the target ratio-setting process during an actual operation in order to minimize the temperature standard deviation Y, that is, in order to uniformly cool the hot-rolled steel sheet H.
  • At least one of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet H in the cooling section is controlled so that the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet H in the cooling section matches the target ratio Xt (that is "1 ").
  • the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet H may be equaled by, for example, adjusting the cooling capability of the top side cooling apparatus 14a and the cooling capability of the bottom side cooling apparatus 14b to be equal.
  • the numerator is the heat transfer coefficient of the hot-rolled steel sheet H on the top surface
  • the denominator is the heat transfer coefficient of the hot-rolled steel sheet H on the bottom surface.
  • the condition under which the temperature standard deviation Y becomes the minimum value Ymin is considered as "A”
  • the condition under which the difference of the standard deviation from the minimum value becomes 10°C or less, that is, the operation becomes preferable as described below is considered as "B”
  • the condition under which the computation is heuristically carried out in order to obtain the above-described regression formula is considered as"C".
  • top and bottom heat transfer coefficient ratio X1 at which the evaluation becomes "A”, that is, the temperature standard deviation Y of the hot-rolled steel sheet H becomes the minimum value Ymin is "1".
  • Top and bottom heat transfer coefficient ratio X Temperature standard deviation Y(°C) Difference of standard deviation from minimum value (°C) Evaluation 1.6/1.0 33.2 30.9 C 1.2/1.0 14.6 12.3 C 1.1/1.0 8.5 6.2 B 1.0/1.0 2.3 0.0 A 1.0/1.1 6.1 3.8 B 1.0/1.2 9.8 7.5 B 1.0/1.6 28.7 26.4 C
  • the temperature standard deviation Y of the hot-rolled steel sheet H converges at least in a range of the minimum value Ymin to the minimum value Ymin+10°C, it can be said that the variations in yield stress, tensile strength and the like are suppressed within the manufacturing permissible ranges, and the hot-rolled steel sheet H can be uniformly cooled. That is, in the target ratio-setting process, the top and bottom heat transfer ratio X at which the temperature standard deviation Y converges in a range of the minimum value Ymin to the minimum value Ymin+10°C may be set as the target ratio Xt based on the correlation data experimentally obtained in advance.
  • the manufacturing permissible range is set to a range in which the temperature standard deviation Y of the hot-rolled steel sheet H is the minimum value Ymin to the minimum value Ymin+10°C in order to remove the influence of the noise.
  • the temperature standard deviation Y can be converged in a range of the minimum value Ymin to the minimum value Ymin+10°C by setting the top and bottom heat transfer coefficient ratio X with an evaluation of "B" as the target ratio Xt.
  • the values in the horizontal axis are replaced by the top and bottom sprayed water density ratio, and the regression formula of the temperature standard deviation Y of the hot-rolled steel sheet H with respect to the top and bottom ratio of the sprayed water density may be obtained on both sides of an equal point above and below the average heat transfer coefficient.
  • the equal point above and below the average heat transfer coefficient does not necessarily become an equal point above and below the sprayed cooling water density, and therefore the regression formula may be obtained by carrying out tests slightly widely.
  • the value of at least one of the steepness and the sheet-threading speed may change due to a change in the manufacturing conditions.
  • the correlation between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y changes. Therefore, the correlation data are prepared for each of a plurality of conditions having different values of the steepness and the sheet-threading speed, and, in the target ratio-setting process, the target ratio Xt may be set based on a correlation data in accordance with actually measured values of the steepness and the sheet-threading speed during the actual operation of the plurality of correlation data. Thereby, it becomes possible to carry out uniform cooling suitable for the manufacturing conditions during the actual operation.
  • the inventors further obtained the following findings.
  • the temperature of the hot-rolled steel sheet H is controlled at a predetermined target temperature (a temperature suitable for coiling) when coiling the hot-rolled steel sheet H using the coiling apparatus 15.
  • a temperature-measuring process in which the temperature of the hot-rolled steel sheet H on the downstream side of the cooling section (that is, the cooling apparatus 14) is measured in chronological order, an average temperature value-computing process in which a chronological average value of the temperature is computed based on the measurement result of the temperature so that the chronological average value of the temperature matches a predetermined target temperature, and an amount of heat dissipated by cooling-adjusting process in which the total value of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet H in the cooling section is adjusted may be newly added to the above-described target ratio-setting process and cooling control process.
  • thermometer 40 which is disposed between the cooling apparatus 14 and the coiling apparatus 15 as illustrated in FIG. 13 and measures the temperature of the hot-rolled steel sheet H can be used.
  • the temperatures at locations set in the rolling direction of the hot-rolled steel sheet H are measured at certain time intervals (sampling intervals) using the thermometer 40, and chronological data of the temperature measurement results are obtained.
  • the temperature measurement area using the thermometer 40 includes all the area of the hot-rolled steel sheet H in the width direction.
  • the sheet-threading speed (transportation speed) of the hot-rolled steel sheet H is multiplied at the sampling times of the respective temperature measurement results
  • the locations of the hot-rolled steel sheet H in the rolling direction, at which the respective temperature measurement results have been obtained can be computed. That is, when the sampling times of the respective temperature measurement results are multiplied by the sheet-threading speed, it becomes possible to link the chronological data of the temperature measurement results to the locations in the rolling direction.
  • a chronological average value of the temperature measurement results is computed using the chronological data of the temperature measurement results. Specifically, each time when a certain number of the temperature measurement results are obtained, the average value of the certain number of the temperature measurement results may be computed.
  • the total value of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet H in the cooling section is adjusted so that the chronological average value of the temperature measurement results computed as described above matches a predetermined target temperature.
  • the on-off control of cooling headers connected to the cooling apparatus 14 may be carried out on a theoretical value obtained in advance using an experiment theoretical formula represented by, for example, Mitsuzuka's formula based on a learned value set to correct the error with an actual operation achievement.
  • the on-off of the cooling headers may be feedback-controlled or feedforward-controlled based on the temperature actually measured using the thermometer 40.
  • thermometer 40 thermometer 40
  • shape meter 41 that measures the wave shape of the hot-rolled steel sheet H which is disposed between the cooling apparatus 14 and the coiling apparatus 15 as illustrated in FIG. 13 .
  • the shape meter 41 measures the shape of the same measurement location (hereinafter this measurement location will be sometimes referred to as a fixed point) as the thermometer 40 set on the hot-rolled steel sheet H.
  • the shape refers to the steepness obtained through the line integration of the heights or changing components of pitches of the wave using the movement amount of the hot-rolled steel sheet H in the sheet-threading direction as the changing amount of the hot-rolled steel sheet H in the height direction observed in a measurement at the fixed point.
  • the changing amount per unit time that is, the changing speed is also obtained.
  • the shape measurement area includes all the areas of the hot-rolled steel sheet H in the width direction.
  • the sampling times of the respective measurement results are multiplied by the sheet-threading speed, it becomes possible to link the chronological data of the respective measurement results to the locations in the rolling direction.
  • FIG. 5 illustrates the relationship between the temperature change and steepness of the hot-rolled steel sheet H during cooling in ROT of a typical strip in an ordinary operation.
  • the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet H in FIG. 5 is 1.2:1, and the top side cooling capability is superior to the bottom side cooling capability.
  • the top graph in FIG. 5 indicates the temperature change with respect to the distance from a coil tip or a time at which a coil passes the fixed point
  • the bottom graph in FIG. 5 indicates the steepness with respect to the distance from the coil tip or the time at which the coil passes the fixed point.
  • the area A in FIG. 5 is an area before the strip tip portion illustrated in FIG. 13 is bit in a coiler of the coiling apparatus 15 (since there is no tension, the shape is defective in this area).
  • the area B in FIG. 5 is an area after the strip tip portion is bit in the coiler (the area in which the wave shape is changed to be flat by the influence of unit tension).
  • FIG. 6 illustrates the temperature-changing component with respect to the steepness of the same shape during cooling in ROT of the typical strip in the ordinary operation.
  • the temperature-changing component is a residual error obtained by subtracting the actual steel sheet temperature by the chronological average of the temperature (hereinafter sometimes referred to as "average temperature").
  • the average temperature may be the average of the temperature of a range that is a cycle or more of the wave shape of the hot-rolled steel sheet H.
  • the average temperature is, in principle, the average of the temperature of a range of the unit cycle. In addition, it is confirmed from operation data that there is no large difference between the average temperature of a range of a cycle and the average temperature of a range of two or more cycles.
  • the average temperature simply needs to be computed from a range of at least a cycle of the wave shape.
  • the upper limit of the range of the wave shape of the hot-rolled steel sheet H is not particularly limited; however, a sufficiently accurate average temperature can be obtained when the range is preferably set to 5 cycles.
  • a permissible average temperature can be obtained even when the average temperature is computed not from a range of the unit cycle but from a range of 2 to 5 cycles.
  • the upward side of the vertical direction (the direction that intersects the top and bottom surfaces of the hot-rolled steel sheet H) of the hot-rolled steel sheet H is set as positive, in an area with a positive changing speed measured at the fixed point, in a case in which the temperature (the temperature measured at the fixed point) of the hot-rolled steel sheet H is lower than the average temperature of a range of one or more cycles of the wave shape of the hot-rolled steel sheet H, at least one of a direction in which the amount of heat dissipated from the top surface by cooling decreases and a direction in which the amount of heat dissipated from the bottom surface by cooling increases is determined as a control direction, and, in a case in which the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of a direction in which the amount of heat dissipated from the top surface by cooling increases and a direction in which the amount of heat dissipated from the bottom surface by cooling decreases is determined as the control direction.
  • At least one of a direction in which the amount of heat dissipated from the top surface by cooling increases and a direction in which the amount of heat dissipated from the bottom surface by cooling decreases is determined as the control direction, and, in a case in which the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of a direction in which the amount of heat dissipated from the top surface by cooling decreases and a direction in which the amount of heat dissipated from the bottom surface by cooling increases is determined as the control direction.
  • At least one of a direction in which the amount of heat dissipated from the top surface by cooling decreases and a direction in which the amount of heat dissipated from the bottom surface by cooling increases is determined as the control direction
  • at least one of a direction in which the amount of heat dissipated from the top surface by cooling increases and a direction in which the amount of heat dissipated from the bottom surface by cooling decreases is determined as the control direction.
  • the temperature-measuring process in which the temperature (the temperature at the fixed point) of the hot-rolled steel sheet H is measured in chronological order on the downstream side of the cooling section, a changing speed-measuring process in which the changing speed of the hot-rolled steel sheet H in the vertical direction is measured in chronological order at the same place (the fixed point) as the temperature measurement place of the hot-rolled steel sheet H, a control direction-determining process in which the control directions of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling are determined based on the temperature measurement results and the changing speed measurement results, and an amount of heat dissipated by cooling-adjusting process in which at least one of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet H in the cooling section is adjusted based on the determined control directions are defined.
  • control direction-determining process in an area with a positive changing speed measured at the fixed point in the hot-rolled steel sheet H, in a case in which the temperature of the hot-rolled steel sheet H at the fixed point is lower than the average temperature of the hot-rolled steel sheet H at the fixed point, at least one of a direction in which the amount of heat dissipated from the top surface by cooling decreases and a direction in which the amount of heat dissipated from the bottom surface by cooling increases is determined as the control direction, and, in a case in which the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of a direction in which the amount of heat dissipated from the top surface by cooling increases and a direction in which the amount of heat dissipated from the bottom surface by cooling decreases is determined as the control direction.
  • control direction-determining process in an area with a negative changing speed, in a case in which the temperature of the hot-rolled steel sheet H is lower than the average temperature, at least one of a direction in which the amount of heat dissipated from the top surface by cooling increases and a direction in which the amount of heat dissipated from the bottom surface by cooling decreases is determined as the control direction, and, in a case in which the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of a direction in which the amount of heat dissipated from the top surface by cooling decreases and a direction in which the amount of heat dissipated from the bottom surface by cooling increases is determined as the control direction.
  • the cooling headers connected to cooling holes 31 in the top side cooling apparatus 14a and the cooling headers connected to cooling holes 31 in the bottom side cooling apparatus 14b may be on-off controlled respectively.
  • the cooling capabilities of the respective cooling headers in the top side cooling apparatus 14a and the bottom side cooling apparatus 14b may be controlled. That is, at least one of the sprayed water density, pressure and water temperature of cooling water sprayed from the respective cooling holes 31 may be adjusted.
  • the flow rate or pressure of cooling water sprayed from the top side cooling apparatus 14a and the bottom side cooling apparatus 14b may be adjusted by thinning out the cooling headers (cooling holes 31) of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b.
  • the cooling headers that constitute the top side cooling apparatus 14a are preferably thinned out.
  • the hot-rolled steel sheet H is uniformly cooled by spraying cooling water onto the top surface of the hot-rolled steel sheet H from the top side cooling apparatus 14a and spraying cooling water onto the bottom surface of the hot-rolled steel sheet H from the bottom side cooling apparatus 14b using the cooling capabilities adjusted as described above.
  • the cooling of the hot-rolled steel sheet H using the cooling apparatus 14 is preferably carried out in a range of the exit-side temperature of a finishing mill to a temperature of the hot-rolled steel sheet H of 600°C.
  • a temperature range in which the temperature of the hot-rolled steel sheet H is 600°C or higher is a so-called film boiling area. That is, in this case, it is possible to prevent a so-called transition boiling area and to cool the hot-rolled steel sheet H in the film boiling area.
  • the hot-rolled steel sheet H is cooled in a state in which the entire surface of the hot-rolled steel sheet H is covered with a vapor film, it is possible to uniformly cool the hot-rolled steel sheet H. Therefore, it is possible to more uniformly cool the hot-rolled steel sheet H in a range in which the temperature of the hot-rolled steel sheet H is 600°C or higher as in the present embodiment.
  • the steepness of the wave shape of the hot-rolled steel sheet H and the sheet-threading speed of the hot-rolled steel sheet H were set to be constant.
  • the steepness or the sheet-threading speed of the hot-rolled steel sheet H is different in each of the coils.
  • the temperature standard deviation Y of the hot-rolled steel sheet H becomes large. That is, as the top and bottom heat transfer coefficient ratio X is away from "1" as illustrated in FIG. 10 , the temperature standard deviation Y becomes large in accordance with the steepness (the sensitivity of the steepness).
  • the relationship between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y is expressed using a V-shaped regression line for each steepness as described above.
  • the sheet-threading speed of the hot-rolled steel sheet H is constant at 10 m/sec (600 m/min).
  • the temperature standard deviation Y of the hot-rolled steel sheet H becomes large. That is, as the top and bottom heat transfer coefficient ratio X is away from "1" as illustrated in FIG. 12 , the temperature standard deviation Y becomes large in accordance with the sheet-threading speed (the sensitivity of the sheet-threading speed).
  • the relationship between the top and bottom heat transfer coefficient ratio X and the temperature standard deviation Y is expressed using a V-shaped regression line for each sheet-threading speed as described above. Meanwhile, in FIG. 12 , the steepness of the wave shape of the hot-rolled steel sheet H is constant at 2%.
  • the change of the temperature standard deviation Y with respect to the top and bottom heat transfer coefficient ratio X can be qualitatively evaluated, but cannot be accurately quantitatively evaluated.
  • table data indicating the correlation between each steepness and the temperature standard deviation Y of the cooled hot-rolled steel sheet H are obtained by, for example, fixing the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet H in advance, and changing the steepness in a stepwise manner from 3% to 0% as illustrated in FIG. 9 .
  • the temperature standard deviation Y with respect to the actual steepness z% of the hot-rolled steel sheet H is corrected to the temperature standard deviation Y' with respect to a predetermined steepness using an interpolation function.
  • a temperature standard deviation Yz' is computed using the following formula (1) based on the temperature standard deviation Yz at the steepness z%.
  • the temperature standard deviation Yz' may be computed by, for example, computing the gradient ⁇ of the steepness in FIG. 9 using the least squares method or the like and using the gradient ⁇ .
  • Yz ' Yz ⁇ 2 / z
  • the steepness may be corrected to the predetermined steepness, and the temperature standard deviation Y may be derived from the regression formula.
  • Table 3 describes the temperature standard deviations Y of the hot-rolled steel sheet H in a case in which the top and bottom heat transfer coefficient ratio X is changed with respect to the steepness in FIG. 9 as illustrated in FIG.
  • the indication and evaluation standards of the top and bottom heat transfer coefficient ratio X in Table 3 are the same as in the evaluation in Table 1, and thus will not be described.
  • the temperature standard deviation Y of the hot-rolled steel sheet H in accordance with the steepness can be derived using FIG. 10 or Table 3.
  • table data indicating the correlation between the respective sheet-threading speeds and the temperature standard deviation Y of the cooled hot-rolled steel sheet H are obtained by, for example, changing the sheet-threading speed in a stepwise manner from 5 m/sec (300 m/min) to 20 m/sec (1200 m/min) as illustrated in FIG. 11 .
  • the temperature standard deviation Y with respect to the actual sheet-threading speed v (m/sec) of the hot-rolled steel sheet H is corrected to the temperature standard deviation Y' with respect to a predetermined sheet-threading speed using an interpolation function.
  • a temperature standard deviation Yv' is computed using the following formula (2) based on the temperature standard deviation Yv at the sheet-threading speed v (m/sec).
  • the temperature standard deviation Yv' may be computed by, for example, computing the gradient ⁇ of the sheet-threading speed in FIG. 11 using the least squares method or the like and using the gradient ⁇ .
  • Yz ' Yv ⁇ 10 / v
  • the sheet-threading speed may be corrected to the predetermined sheet-threading speed, and the temperature standard deviation Y may be derived from the regression formula.
  • Table 4 describes the temperature standard deviations Y of the hot-rolled steel sheet H in a case in which the top and bottom heat transfer coefficient ratio X is changed with respect to the sheet-threading speed in FIG. 11 as illustrated in FIG.
  • the indication and evaluation standards of the top and bottom heat transfer coefficient ratio X in Table 4 are the same as in the evaluation in Table 1, and thus will not be described.
  • the temperature standard deviation Y of the hot-rolled steel sheet H in accordance with the sheet-threading speed can be derived using FIG. 12 or Table 4.
  • the temperature and wave shape of the hot-rolled steel sheet H cooled using the cooling apparatus 14 may be measured, and the cooling capability of the top side cooling apparatus 14a and the cooling capability of the bottom side cooling apparatus 14b may be adjusted based on the measurement results. That is, the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b may be feedback-controlled.
  • thermometer 40 that measures the temperature of the hot-rolled steel sheet H and the shape meter 41 that measures the wave shape of the hot-rolled steel sheet H are disposed between the cooling apparatus 14 and the coiling apparatus 15 as illustrated in FIG. 13 .
  • the temperature and shape of the hot-rolled steel sheet H in the process of sheet-threading are measured at the same point of the fixed point respectively using the thermometer 40 and the shape meter 41, and the temperature and the shape are measured as chronological data.
  • the temperature measurement area includes all the area of the hot-rolled steel sheet H in the width direction.
  • the shape indicates the changing amount of the hot-rolled steel sheet H in the height direction observed in a measurement at the fixed point.
  • the shape measurement area includes all the area of the hot-rolled steel sheet H in the width direction.
  • the increase and decrease directions (control directions) of the top side cooling capability (amount of heat dissipated from the top surface by cooling) and the bottom side cooling capability (amount of heat dissipated from the bottom surface by cooling) for decreasing the temperature standard deviation Y are determined, and it is possible to adjust the top and bottom heat transfer coefficient ratio X.
  • top and bottom heat transfer coefficient ratio X based on the degree of the temperature standard deviation Y so that the temperature standard deviation Y converges in a permissible range, for example, a range of the minimum value Ymin to the minimum value Ymin+10°C. Since the method for determining the top and bottom heat transfer coefficient ratio X is the same as in the above embodiment described using FIGS. 3 and 4 , the method will not be described in detail.
  • the temperature standard deviation Y is converged in a range of the minimum value Ymin to the minimum value Ymin+10°C, the variations in yield stress, tensile strength and the like are suppressed within the manufacturing permissible ranges, and the hot-rolled steel sheet H can be uniformly cooled.
  • the temperature standard deviation Y can be converged in a range of the minimum value Ymin to the minimum value Ymin+10°C as long as a sprayed cooling water density ratio is ⁇ 5% or less with respect to the sprayed cooling water density ratio at which the temperature standard deviation Y becomes the minimum value Ymin. That is, in a case in which the sprayed cooling water density is used, the top and bottom ratio of the sprayed cooling water density (sprayed cooling water density ratio) is desirably set to ⁇ 5% or less with respect to the sprayed cooling water density ratio at which the temperature standard deviation Y becomes the minimum value Ymin.
  • the permissible range does not always include the top and bottom sprayed water density.
  • the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b can be adjusted to be qualitatively and quantitatively appropriate cooling capabilities through feedback control, it is possible to further improve the uniformity of the hot-rolled steel sheet H which will be cooled afterwards.
  • the cooling section in which the hot-rolled steel sheet H is cooled may be divided into a plurality of sections, for example, two divided cooling sections Z1 and Z2 in the rolling direction as illustrated in FIG. 14 .
  • Each of the divided cooling sections Z1 and Z2 is provided with the cooling apparatus 14.
  • the thermometer 40 and the shape meter 41 are provided respectively at the border between the respective divided cooling sections Z1 and Z2, that is, on the downstream side of the divided cooling sections Z 1 and Z2.
  • the cooling section is divided into two divided cooling sections, but the number of divisions is not limited thereto, and can be arbitrarily set.
  • the cooling section may be divided into 1 to 5 divided cooling sections.
  • the temperature and wave shape of the hot-rolled steel sheet H on the downstream side of the divided cooling sections Z1 and Z2 are respectively measured using the respective thermometers 40 and the respective shape meters 41.
  • the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b at the respective divided cooling sections Z1 and Z2 are controlled based on the measurement results.
  • the cooling capabilities are controlled so that the temperature standard deviation Y of the hot-rolled steel sheet H is converged in the permissible range, for example, a range of the minimum value Ymin to the minimum value Ymin+10°C as described above.
  • At least one of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet H at the respective divided cooling sections Z1 and Z2 is adjusted in the above manner.
  • the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b are feedback-controlled based on the measurement results of the thermometer 40 and the shape meter 41 on the downstream side, thereby at least one of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling is adjusted.
  • the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b may be feedforward-controlled or feedback-controlled based on the measurement results of the thermometer 40 and the shape meter 41 on the downstream side. In any cases, in the divided cooling section Z2, at least one of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling is adjusted.
  • thermometer 40 and the shape meter 41 Since the method for controlling the cooling capabilities of the top side cooling apparatus 14a and the bottom side cooling apparatus 14b based on the measurement results of the thermometer 40 and the shape meter 41 is the same as in the above embodiment described using FIGS. 5 to 8 , the method will not be described in detail.
  • the temperature standard deviation Y of the hot-rolled steel sheet H in accordance with at least the steepness or the sheet-threading speed is corrected using the same method as in the above embodiment described using FIGS. 9 to 12 .
  • At least one of the amount of heat dissipated from the top surface by cooling and the amount of heat dissipated from the bottom surface by cooling of the hot-rolled steel sheet H in the respective divided cooling sections Z1 and Z2 is corrected based on the corrected temperature standard deviation Y (Y'). Thereby, it is possible to more uniformly cool the hot-rolled steel sheet H.
  • FIG. 15 illustrates an example of a pattern in which a wave shape having an amplitude changing in the sheet width direction of the hot-rolled steel sheet H is formed due to center buckle.
  • FIG. 16 schematically illustrates an example of a hot rolling facility 2 in another embodiment.
  • the hot rolling facility 2 is a facility aimed to sandwich the top and bottom of a heated slab S using rolls, continuously roll the slab to make the slab as thin as at least 1.2 mm, and coil the slab.
  • the hot rolling facility 2 has a heating furnace 111 for heating the slab S, a width-direction mill 116 that rolls the slab S heated in the heating furnace 111 in a width direction, a roughing mill 112 that rolls the slab S rolled in the width direction from the vertical direction so as to produce a rough bar, a finishing mill 113 that further continuously hot-finishing-rolls the rough bar to a predetermined thickness, a cooling apparatus 114 that cools the hot-rolled steel sheet H hot-finishing-rolled using the finishing mill 113 using cooling water, and a coiling apparatus 115 that coils the hot-rolled steel sheet H cooled using the cooling apparatus 114 into a coil shape.
  • the heating furnace 111 is provided with a side burner, an axial burner and a roof burner that heat the slab S brought from the outside through a charging hole by blowing flame.
  • the slab S brought into the heating furnace 111 is sequentially heated in respective heating areas formed in respective zones, and, furthermore, a heat-retention treatment for enabling transportation at an optimal temperature is carried out by uniformly heating the slab S using the roof burner in a soaking area formed in a final zone.
  • a heating treatment in the heating furnace 111 completely ends, the slab S is transported to the outside of the heating furnace 111, and moved into a rolling process by the roughing mill 112.
  • the slab S transported from the heating furnace 111 is passed through gaps between columnar rotary rolls provided across a plurality of stands.
  • the roughing mill 112 hot-rolls the slab S only using work rolls 112a provided at the top and bottom of a first stand so as to form a rough bar.
  • the rough bar which has passed through the work rolls 112a is further continuously rolled using a plurality of fourfold mills 112b constituted by a work roll and a back-up roll.
  • the rough bar is rolled into a thickness of approximately 30 mm to 60 mm, and transported to the finishing mill 113.
  • the configuration of the roughing mill 112 is not limited to what has been described in the embodiment, and the number of rolls and the like can be arbitrarily set.
  • the finishing mill 113 finishing-rolls the rough bar transported from the roughing mill 112 until the thickness becomes approximately several millimeters.
  • the finishing mill 113 passes the rough bar through gaps between top and bottom finish rolling rolls 113a linearly arranged across 6 to 7 stands so as to gradually reduce the rough bar.
  • the hot-rolled steel sheet H finishing-rolled using the finishing mill 113 is transported to the cooling apparatus 114 using the transportation rolls 132 (refer to FIG. 17 ). Meanwhile, a mill having the above-described pair of finish rolling rolls 113a linearly arrayed vertically is also referred to as a so-called rolling stand.
  • cooling apparatuses 142 that carry out inter-stand cooling (supplementary cooling) during finish rolling are disposed between the respective rolling rolls 113a arrayed across 6 to 7 stands (that is, between the rolling stands).
  • the details of the apparatus configuration and the like of the cooling apparatus 142 will be described below with reference to FIG. 20 .
  • FIG. 16 illustrates a case in which the cooling apparatuses 142 are disposed at two places in the finishing mill 113, but the cooling apparatuses 142 may be provided between all the rolling rolls 113a, or may be provided between some of the rolling rolls.
  • the cooling apparatus 114 is a facility for carrying out nozzle cooling on the hot-rolled steel sheet H transported from the finishing mill 113 through laminating or spraying. As illustrated in FIG. 17 , the cooling apparatus 114 has a top side cooling apparatus 114a that sprays cooling water from cooling holes 131 on the top side to the top surface of the hot-rolled steel sheet H moving on the transportation rolls 132 in a run-out table, and a bottom side cooling apparatus 114b that sprays cooling water from cooling holes 131 on the bottom side to the bottom surface of the hot-rolled steel sheet H.
  • a plurality of the cooling holes 131 is provided in the top side cooling apparatus 114a and the bottom side cooling apparatus 114b respectively.
  • a cooling header (not illustrated) is connected to the cooling holes 131.
  • the number of the cooling holes 131 determines the cooling capabilities of the top side cooling apparatus 114a and the bottom side cooling apparatus 114b.
  • the cooling apparatus 114 may be constituted by at least one of a top and bottom split laminar, a pipe laminar, spray cooling and the like.
  • the cooling headers connected to cooling holes 131 in the top side cooling apparatus 114a and the cooling headers connected to cooling holes 131 in the bottom side cooling apparatus 114b may be on-off controlled respectively.
  • the operation parameters of the respective cooling headers in the top side cooling apparatus 114a and the bottom side cooling apparatus 114b may be controlled. That is, at least one of the sprayed water density, pressure and water temperature of cooling water sprayed from the respective cooling holes 131 may be adjusted.
  • the flow rate or pressure of cooling water sprayed from the top side cooling apparatus 114a and the bottom side cooling apparatus 114b may be adjusted by thinning out the cooling headers (cooling holes 131) of the top side cooling apparatus 114a and the bottom side cooling apparatus 114b.
  • the cooling headers that constitute the top side cooling apparatus 114a are preferably thinned out.
  • the coiling apparatus 115 coils the hot-rolled steel sheet H cooled using the cooling apparatus 114 at a predetermined coiling temperature as illustrated in FIG. 16 .
  • the hot-rolled steel sheet H coiled into a coil shape using the coiling apparatus 115 is transported to the outside of the hot rolling facility 2.
  • the hot-rolled steel sheet H having a wave shape with a surface height (wave height) changing in the rolling direction is cooled in the cooling apparatus 114 of the hot rolling facility 2 constituted as described above, it is possible to uniformly cool the hot-rolled steel sheet H by appropriately adjusting the water quantity densities, pressures, water temperatures and the like of cooling water sprayed from the top side cooling apparatus 114a and cooling water sprayed from the bottom side cooling apparatus 114b as described above.
  • the hot-rolled steel sheet H As such, in the hot-rolled steel sheet H, portions that locally come into contact with the transportation rolls 132 or the aprons 133 become more easily coolable than other portions due to heat dissipation by contact. Therefore, the hot-rolled steel sheet H is ununiformly cooled.
  • the sheet-threading speed of the hot-rolled steel sheet H is set to a high speed, the contact period of time becomes short. Furthermore, when the sheet-threading speed is increased, the hot-rolled steel sheet H in the process of sheet threading becomes floated from the transportation rolls 132 or the aprons 133 due to repulsion by the contact between the hot-rolled steel sheet H and the transportation rolls 132 or the aprons 133.
  • the hot-rolled steel sheet H does not only become floated from the transportation rolls 132 or the aprons 133 due to repulsion by the contact, but the contact period of time or number of contacts between the hot-rolled steel sheet H and the transportation rolls 132 or the aprons 133 also decreases, and therefore the temperature decrease by the contact becomes negligible.
  • the heat dissipation by contact can be suppressed by increasing the sheet-threading speed, and the hot-rolled steel sheet H can be more uniformly cooled as illustrated in FIG. 19B .
  • the inventors found that the hot-rolled steel sheet H can be sufficiently uniformly cooled by setting the sheet-threading speed to 550 m/min or more.
  • the above finding is about the cooling of the hot-rolled steel sheet H having a wave shape; however, regardless of the height of the wave shape, the lowermost point of the hot-rolled steel sheet H comes into contact with the transportation rolls 132 or the aprons 133, and therefore, regardless of the height of the wave shape, an increase in the sheet-threading speed is effective for uniform cooling.
  • the sheet-threading speed of the hot-rolled steel sheet H is set to 550 m/min or more, since the hot-rolled steel sheet H becomes floated from the transportation rolls 132 or the aprons 133, there is no soaked water on the hot-rolled steel sheet H as in the related art even when cooling water is sprayed onto the hot-rolled steel sheet H in the above state. Therefore, it is possible to prevent the hot-rolled steel sheet H from being ununiformly cooled due to soaked water.
  • the sheet-threading speed of the hot-rolled steel sheet H in the cooling section is set to 550 m/min or more in addition to the above-described control of the amount of heat dissipated from the top and bottom surfaces, it is possible to more uniformly cool the hot-rolled steel sheet H having a wave shape with a height periodically changing in the rolling direction.
  • the sheet-threading speed of the hot-rolled steel sheet H is preferably faster, but it is impossible to exceed the mechanical limit speed (for example, 1550 m/min). Therefore, practically, the sheet-threading speed of the hot-rolled steel sheet H in the cooling section is set in a range of 550 m/min to the mechanical limit speed.
  • the sheet-threading speed of the hot-rolled steel sheet H is preferably set in a range of 550 m/min to the operation upper limit speed (for example, 1200 m/min).
  • the setting of the sheet-threading speed to a high speed may be reliably combined into the method for cooling a hot-rolled steel sheet described using FIGS. 1 to 14 .
  • the hot-rolled steel sheet H having a large tensile strength particularly, a steel sheet or the like called a so-called high tensile strength steel having a tensile strength (TS) of 800 MPa or more and a realistic upper limit of 1400 MPa
  • TS tensile strength
  • the hot-rolled steel sheet H was sufficiently cooled by suppressing the sheet-threading speed of the hot-rolled steel sheet H in the cooling apparatus 114 (that is, the cooling section) to be low.
  • the hot-rolled steel sheet H in the cooling apparatus 114 is suppressed to be low, in a case in which a wave shape is formed in the hot-rolled steel sheet H, the local contacts between the hot-rolled steel sheet H and the transportation rolls 132 or the aprons 133 make the contact portions more easily coolable due to heat dissipation by contact as described above, the hot-rolled steel sheet is ununiformly cooled.
  • the inventors found that, when cooling is carried out between a pair of finish rolling rolls 113a (that is, rolling stands) provided across, for example, 6 to 7 stands in the finishing mill 113 of the hot rolling facility 2 (so-called inter-stand cooling), the heat dissipation by working can be suppressed, and the sheet-threading speed of the hot-rolled steel sheet H in the cooling apparatus 114 can be set to 550 m/min or more.
  • inter-stand cooling will be described with reference to FIG. 20 .
  • FIG. 20 is an explanatory view of the finishing mill 113 that can carry out the inter-stand cooling, in which a part of the finishing mill 113 is enlarged for the description and three rolling stands are illustrated. Meanwhile, in FIG. 20 , the same components as in the above embodiment will be given the same reference numeral.
  • a plurality (three in FIG. 20 ) of rolling stands 140 having a pair of vertically linearly arrayed finish rolling rolls 113a and the like is provided in the finishing mill 113.
  • the cooling apparatuses 142 which are facilities that carry out nozzle cooling through lamination or spraying are provided between the respective rolling stands 140, which make it possible to carry out the inter-stand cooling on the hot-rolled steel sheet H between the rolling stands 140.
  • the cooling apparatus 142 has a top side cooling apparatus 142a that sprays cooling water from the top side through cooling holes 146 onto the hot-rolled steel sheet H transported in the finishing mill 113 and a bottom side cooling apparatus 142b that sprays cooling water from the bottom side onto the hot-rolled steel sheet H as illustrated in FIG. 20 .
  • a plurality of the cooling hole 146 is provided respectively in the top side cooling apparatus 142a and the bottom side cooling apparatus 142b.
  • a cooling header (not illustrated) is connected to the cooling hole 146.
  • the cooling apparatus 142 may be constituted by at least one of a top and bottom split laminar, a pipe laminar, spray cooling and the like.
  • the finishing mill 113 having the configuration illustrated in FIG. 20 , particularly, in a case in which the tensile strength (TS) of the hot-rolled steel sheet H is 800 MPa or more, the heat dissipation by working in the hot-rolled steel sheet H is suppressed by carrying out the inter-stand cooling. Thereby, it becomes possible to maintain the sheet-threading speed of the hot-rolled steel sheet H in the cooling apparatus 114 at 550 m/min or more.
  • TS tensile strength
  • the problem of the related art caused in a case in which cooling was carried out at a slow sheet-threading speed, which was the local contacts between the hot-rolled steel sheet H and the transportation rolls 132 or the aprons 133 and the contact portions becoming more easily coolable due to heat dissipation by contact is solved, and the hot-rolled steel sheet H can be sufficiently uniformly cooled.
  • the cooling of the hot-rolled steel sheet H using the cooling apparatus 114 is preferably carried out in a temperature range of the hot-rolled steel sheet H of 600°C or higher.
  • the temperature range in which the temperature of the hot-rolled steel sheet H becomes 600°C or higher is a so-called film boiling range. That is, in this case, it is possible to avoid the so-called transition boiling area and to cool the hot-rolled steel sheet H in the film boiling area.
  • the transition boiling area when cooling water is sprayed onto the surface of the hot-rolled steel sheet H, portions covered with a vapor film and portions in which the cooling water is directly sprayed onto the hot-rolled steel sheet H are present in a mixed state on the surface of the hot-rolled steel sheet H. Therefore, it is not possible to uniformly cool the hot-rolled steel sheet H.
  • the hot-rolled steel sheet H is cooled in a state in which the entire surface of the hot-rolled steel sheet H is covered with a vapor film, it is possible to uniformly cool the hot-rolled steel sheet H. Therefore, it is possible to more uniformly cool the hot-rolled steel sheet H in a range in which the temperature of the hot-rolled steel sheet H is 600°C or higher as in the embodiment.
  • the inventors carried out cooling tests of a hot-rolled steel sheet as examples in order to verify that the hot-rolled steel sheet could be uniformly cooled by setting the sheet-threading speed of the hot-rolled steel sheet to 550 m/min or more.
  • Hot-rolled steel sheets with a middle wave having a sheet thickness of 2.5 mm, a width of 1200 mm, a tensile strength of 400 MPa and a steepness of 2% were cooled with varying sheet-threading speeds in a cooling apparatus.
  • the sheet-threading speeds were 400 m/min, 450 m/min, 500 m/min, 550 m/min, 600 m/min and 650 m/min, and the hot-rolled steel sheets were cooled at the respective sheet-threading speeds 20 times.
  • CT temperature change amount an average value of the standard deviations of temperature changes was computed using the temperature measurement results.
  • Table 3 The evaluation results of the computed CT temperature change amount are described in Table 3 below. Meanwhile, in terms of the evaluation criteria, a case in which the CT temperature change amount was larger than 25°C was evaluated as ununiform cooling, and a case in which the CT temperature change amount was 25°C or less was evaluated as uniform cooling.
  • the CT temperature change amount is not sufficiently reduced (higher than 25°C), and the hot-rolled steel sheet is not sufficiently uniformly cooled.
  • the sheet-threading speed is 550 m/min or more
  • the CT temperature change amount is suppressed to 25°C or less, and the hot-rolled steel sheet is uniformly cooled.
  • the sheet-threading speed is 600 m/min or more
  • the above condition is more preferable for the uniform cooling of the hot-rolled steel sheet.
  • the inter-stand cooling was carried out on hot-rolled steel sheets with a middle wave having a sheet thickness of 2.5 mm, a width of 1200 mm, a tensile strength of 800 MPa and a steepness of 2% so that the exit-side temperature of finish rolling became 880°C, and cooling was carried out with varying sheet-threading speeds in a cooling apparatus.
  • the sheet-threading speeds were 400 m/min, 450 m/min, 500 m/min, 550 m/min, 600 m/min and 650 m/min, and the hot-rolled steel sheets were cooled at the respective sheet-threading speeds 20 times.
  • the CT temperature change amount was suppressed even in the hot-rolled steel sheets having a relatively high hardness (tensile strength 800 MPa). That is, it was found that it became possible to uniformly cool all steel materials, particularly, steel materials having a high hardness by setting the sheet-threading speed during the cooling of the hot-rolled steel sheet to 550 m/min or more, and, additionally, carrying out the inter-stand cooling in a finishing mill.
  • the present invention is useful when cooling a hot-rolled steel sheet which has been hot-rolled using a finishing mill so as to have a wave shape having a surface height changing in the rolling direction.

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Claims (15)

  1. Verfahren zur Kühlung eines warmgewalzten Stahlblechs, in dem ein warmgewalztes Stahlblech (H), das mit Hilfe einer Fertigwalzstraße (13, 113) warmgewalzt ist, in einer Kühlstrecke gekühlt wird, die auf einem Transportweg vorgesehen ist, dadurch gekennzeichnet, dass das Verfahren aufweist:
    einen Sollverhältnis-Festlegungsvorgang, in dem ein oberes und unteres Wärmeübergangskoeffizientenverhältnis X1,bei dem eine Temperaturstandardabweichung Y einen Minimalwert Ymin annimmt, als Sollverhältnis Xt auf der Grundlage von Korrelationsdaten festgelegt wird, die eine Korrelation zwischen einem oberen und unteren Wärmeübergangskoeffizientenverhältnis X, das ein Verhältnis von Wärmeübergangskoeffizienten einer Ober- und einer Unterseite des warmgewalzten Stahlblechs (H) ist, und der Temperaturstandardabweichung Y während oder nach der Kühlung des warmgewalzten Stahlblechs (H) angeben, die vorab unter Bedingungen experimentell erhalten wurden, unter denen Steilheit und Transportgeschwindigkeit des warmgewalzten Stahlblechs (H) auf Konstantwerte festgelegt sind;
    einen Kühlungssteuervorgang, in dem eine von einer Oberseite durch Kühlung abgeführte Wärmemenge und/oder eine von einer Unterseite durch Kühlung abgeführte Wärmemenge des warmgewalzten Stahlblechs (H) in der Kühlstrecke so gesteuert wird, dass das obere und untere Wärmeübergangskoeffizientenverhältnis X des warmgewalzten Stahlblechs in der Kühlstrecke dem Sollverhältnis Xt entspricht;
    einen Temperaturmessvorgang, in dem eine Temperatur des warmgewalzten Stahlblechs (H) in bestimmten Zeitintervallen gemessen wird und chronologische Daten von Temperaturmessergebnissen auf einer nachgelagerten Seite der Kühlstrecke erhalten werden; einen Änderungsgeschwindigkeits-Messvorgang, in dem eine Änderungsgeschwindigkeit des warmgewalzten Stahlblechs (H) in Vertikalrichtung in chronologischer Reihenfolge an einer selben Stelle wie eine Temperaturmessstelle des warmgewalzten Stahlblechs (H) auf der nachgelagerten Seite der Kühlstrecke gemessen wird;
    einen Steuerrichtungs-Bestimmungsvorgang, in dem bei positiver Festlegung von "aufwärts" der Vertikalrichtung des warmgewalzten Stahlblechs (H) in einem Gebiet mit einer positiven Änderungsgeschwindigkeit in einem Fall, in dem eine Temperatur des warmgewalzten Stahlblechs (H) niedriger als eine mittlere Temperatur in einem Bereich von einem oder mehreren Zyklen einer Wellenform des warmgewalzten Stahlblechs (H) ist, eine Richtung, in der die von der Oberseite durch Kühlung abgeführte Wärmemenge abnimmt, und/oder eine Richtung, in der die von der Unterseite durch Kühlung abgeführte Wärmemenge zunimmt, als Steuerrichtung bestimmt wird, in einem Fall, in dem die Temperatur des warmgewalzten Stahlblechs (H) höher als die mittlere Temperatur ist, eine Richtung, in der die von der Oberseite durch Kühlung abgeführte Wärmemenge zunimmt, und/oder eine Richtung, in der die von der Unterseite durch Kühlung abgeführte Wärmemenge abnimmt, als Steuerrichtung bestimmt wird, in einem Gebiet mit einer negativen Änderungsgeschwindigkeit in einem Fall, in dem die Temperatur des warmgewalzten Stahlblechs (H) niedriger als die mittlere Temperatur ist, eine Richtung, in der die von der Oberseite durch Kühlung abgeführte Wärmemenge zunimmt, und/oder eine Richtung, in der die von der Unterseite durch Kühlung abgeführte Wärmemenge abnimmt, als Steuerrichtung bestimmt wird, und in einem Fall, in dem die Temperatur des warmgewalzten Stahlblechs (H) höher als die mittlere Temperatur ist, eine Richtung, in der die von der Oberseite durch Kühlung abgeführte Wärmemenge abnimmt, und/oder eine Richtung, in der die von der Unterseite durch Kühlung abgeführte Wärmemenge zunimmt, als Steuerrichtung bestimmt wird; und
    einen Einstellvorgang der durch Kühlung abgeführten Wärmemenge, der die von der Oberseite durch Kühlung abgeführte Wärmemenge und/oder die von der Unterseite durch Kühlung abgeführte Wärmemenge des warmgewalzten Stahlblechs in der Kühlstrecke auf der Grundlage der Steuerrichtung einstellt, die im Steuerrichtungs-Bestimmungsvorgang bestimmt wird.
  2. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1,
    wobei im Sollverhältnis-Festlegungsvorgang ein oberes und unteres Wärmeübergangskoeffizientenverhältnis X, bei dem die Temperaturstandardabweichung Y in einem Bereich vom Minimalwert Ymin bis zum Minimalwert Ymin + 10 °C konvergiert, als Sollverhältnis Xt auf der Grundlage der Korrelationsdaten festgelegt wird.
  3. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1 oder 2,
    wobei die Korrelationsdaten jeweils für mehrere Bedingungen aufbereitet sind, unter denen sich Werte der Steilheit und der Transportgeschwindigkeit unterscheiden, und im Sollverhältnis-Festlegungsvorgang das Sollverhältnis Xt auf der Grundlage von Korrelationsdaten festgelegt wird, die aktuellen Ist-Messwerten der Steilheit und der Transportgeschwindigkeit der mehreren Korrelationsdaten entsprechen.
  4. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 3,
    wobei die Korrelationsdaten Daten sind, die eine Korrelation zwischen dem oberen und unteren Wärmeübergangskoeffizientenverhältnis X und der Temperaturstandardabweichung Y mit Hilfe einer Regressionsformel angeben.
  5. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 4,
    wobei die Regressionsformel eine Formel ist, die mit Hilfe von linearer Regression abgeleitet ist.
  6. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 3,
    wobei die Korrelationsdaten Daten sind, die eine Korrelation zwischen dem oberen und unteren Wärmeübergangskoeffizientenverhältnis X und der Temperaturstandardabweichung Y mit Hilfe einer Tabelle angeben.
  7. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1 oder 2,
    wobei die Kühlstrecke in mehrere aufgeteilte Kühlstrecken in Transportrichtung des warmgewalzten Stahlblechs (H) aufgeteilt ist, die Temperatur und Änderungsgeschwindigkeit des warmgewalzten Stahlblechs (H) in chronologischer Reihenfolge an jeder von Grenzen der aufgeteilten Kühlstrecken im Temperaturmessvorgang und im Änderungsgeschwindigkeits-Messvorgang gemessen werden;
    Abnahme- und Zunahmerichtungen der von der Ober- und Unterseite des warmgewalzten Stahlblechs (H) durch Kühlung abgeführten Wärmemengen für die jeweiligen aufgeteilten Kühlstrecken auf der Grundlage von Messergebnissen der Temperatur und Änderungsgeschwindigkeiten des warmgewalzten Stahlblechs (H) an den jeweiligen Grenzen der aufgeteilten Kühlstrecken im Steuerrichtungs-Bestimmungsvorgang bestimmt werden; und
    eine Feedback-Regelung oder Feedforward-Regelung durchgeführt wird, um die von der Oberseite durch Kühlung abgeführte Wärmemenge und/oder die von der Unterseite durch Kühlung abgeführte Wärmemenge des warmgewalzten Stahlblechs (H) an jeder der aufgeteilten Kühlstrecken auf der Grundlage der Steuerrichtung einzustellen, die für jede der aufgeteilten Kühlstrecken im Einstellvorgang der durch Kühlung abgeführten Wärmemenge bestimmt wird.
  8. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 7, wobei das Verfahren ferner aufweist:
    einen Messvorgang, in dem die Steilheit oder Transportgeschwindigkeit des warmgewalzten Stahlblechs (H) an jeder der Grenzen der aufgeteilten Kühlstrecken gemessen wird; und einen Korrekturvorgang der durch Kühlung abgeführten Wärmemenge, in dem die von der Oberseite durch Kühlung abgeführte Wärmemenge und/oder die von der Unterseite durch Kühlung abgeführte Wärmemenge des warmgewalzten Stahlblechs (H) an jeder der aufgeteilten Kühlstrecken auf der Grundlage von Messergebnissen der Steilheit oder der Transportgeschwindigkeiten korrigiert wird.
  9. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1 oder 2,
    wobei das Verfahren ferner aufweist:
    einen Nachkühlvorgang, in dem das warmgewalzte Stahlblech (H) auf einer nachgelagerten Seite der Kühlstrecke weiter gekühlt wird, um die Temperaturstandardabweichung des warmgewalzten Stahlblechs (H) in einen zulässigen Bereich fallen zu lassen.
  10. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1 oder 2,
    wobei die Transportgeschwindigkeit des warmgewalzten Stahlblechs (H) in der Kühlstrecke in einem Bereich von 550 m/min bis zu einer mechanischen Grenzgeschwindigkeit festgelegt ist.
  11. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 10,
    wobei eine Zugfestigkeit des warmgewalzten Stahlblechs (H) mindestens 800 MPa beträgt.
  12. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 10,
    wobei die Fertigwalzstraße (13, 113) durch mehrere Walzgerüste (140) gebildet ist und ferner ein zusätzlicher Kühlvorgang vorgesehen ist, in dem das warmgewalzte Stahlblech (H) zwischen den mehreren Walzgerüsten (140) zusätzlich gekühlt wird.
  13. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1 oder 2,
    wobei eine Oberseiten-Kühlvorrichtung (14a, 114a) mit mehreren Düsenbalken (31, 131), die Kühlwasser auf eine Oberseite des warmgewalzten Stahlblechs (H) abstrahlt, und eine Unterseiten-Kühlvorrichtung (14b, 114b) mit mehreren Düsenbalken (31, 131), die Kühlwasser auf eine Unterseite des warmgewalzten Stahlblechs (H) abstrahlt, in der Kühlstrecke vorgesehen sind und
    die von der Oberseite durch Kühlung abgeführte Wärmemenge und die von der Unterseite durch Kühlung abgeführte Wärmemenge durch Durchführung einer Ein/Aus-Steuerung der jeweiligen Düsenbalken (31, 131) eingestellt werden.
  14. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1 oder 2,
    wobei eine Oberseiten-Kühlvorrichtung (14a, 114a) mit mehreren Düsenbalken (31, 131), die Kühlwasser auf eine Oberseite des warmgewalzten Stahlblechs (H) abstrahlt, und eine Unterseiten-Kühlvorrichtung (14b, 114b) mit mehreren Düsenbalken (31, 131), die Kühlwasser auf eine Unterseite des warmgewalzten Stahlblechs (H) abstrahlt, in der Kühlstrecke vorgesehen sind und
    die von der Oberseite durch Kühlung abgeführte Wärmemenge und die von der Unterseite durch Kühlung abgeführte Wärmemenge durch Steuern von Spritzwasserdichte, Druck und/oder Wassertemperatur jedes der Düsenbalken (31, 131) eingestellt werden.
  15. Verfahren zur Kühlung eines warmgewalzten Stahlblechs nach Anspruch 1 oder 2,
    wobei Kühlung in der Kühlstrecke bei einer Temperatur des warmgewalzten Stahlblechs (H) in einem Bereich von mindestens 600 °C durchgeführt wird.
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BR112013028835B1 (pt) 2022-08-09

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