TWI515054B - Method of cooling hot rolled steel sheet - Google Patents

Description

Hot rolled steel plate cooling method Technical field

The present invention relates to a method for cooling a hot rolled steel sheet for use in cooling hot rolled steel sheets of a hot rolling mill.

Background technique

Hot rolled steel sheets used in automobiles, industrial machines, and the like are generally produced by a rough rolling step and a finishing rolling step. Fig. 21 is a view schematically showing a method of manufacturing a conventional hot-rolled steel sheet. In the manufacturing step of the hot-rolled steel sheet, first, the rough-rolling mill 201 rolls and rolls the molten steel which has been adjusted to a predetermined composition by continuous casting, and then consists of a plurality of rolling stations 202a to 202d. The finishing mill 203 performs hot rolling to form a hot rolled steel sheet H having a predetermined thickness. Next, the hot-rolled steel sheet H is cooled by the cooling water injected from the cooling device 211, and then wound into a coil shape by the coiling device 212.

The cooling device 211 is generally used for performing so-called laminar cooling of the hot-rolled steel sheet H fed from the finishing mill 203. The cooling device 211 can spray cooling water as a jet water through a cooling nozzle from above the vertical direction on the hot-rolled steel sheet H that is moved on the slide table, and spray cooling water on the lower surface of the hot-rolled steel sheet H through the laminar flow tube. Spray water to cool the hot rolled steel sheet H.

Next, heretofore, for example, Patent Document 1 has disclosed a technique for avoiding the shape of the steel sheet by reducing the surface temperature difference between the upper and lower portions of the thick steel plate. According to the technique disclosed in the above Patent Document 1, the water amount ratio of the cooling water supplied to the upper surface and the lower surface of the steel sheet can be adjusted based on the surface temperature difference obtained by simultaneously measuring the surface temperatures of the upper and lower surfaces of the steel sheet by the thermometer while cooling.

Further, for example, Patent Document 2 discloses that a pulverized material is cooled by using a sprayer between two adjacent rolling stands of a finishing mill to start and end the γ-α transformation of the rolled material to avoid rolling. The technology of the deterioration of the board between the stations.

Further, for example, Patent Document 3 discloses that the inclination of the tip end of the steel sheet is measured by an inclination meter provided on the exit side of the rolling mill, and the flow rate of the cooling water is changed and adjusted in the width direction in accordance with the measured inclination. To avoid the technique of perforation of steel plates.

Further, for example, Patent Document 4 discloses a method of eliminating the thickness distribution of the waveform in the width direction of the hot-rolled steel sheet and uniformizing the thickness in the sheet width direction, and the sheet width direction of the hot-rolled steel sheet is The technique in which the difference between the highest thermal conductivity and the lowest thermal conductivity is controlled within a predetermined value range.

Here, the hot-rolled steel sheet H produced by the manufacturing method shown in Fig. 21 may be on the conveying roller 220 of the sliding device (hereinafter also referred to as "ROT") of the cooling device 211 as shown in Fig. 22 A waveform is formed in the rolling direction (arrow direction in Fig. 22). At this time, the cooling of the upper surface and the lower surface of the hot-rolled steel sheet H will fall. That is, the cooling variation caused by the waveform of the hot-rolled steel sheet H itself causes a problem that uniform cooling cannot be performed in the rolling direction.

Therefore, for example, Patent Document 5 discloses a steel sheet having a corrugated shape in the rolling direction, in order to uniformize the cooling of the steel sheet, so that the cooling ability of the upper cooling portion and the lower cooling portion is the same, so that the water in the upper portion of the steel sheet is accumulated. The technique of minimizing the influence of the distance from the lower roller table roller.

[First technical literature] [Patent Literature]

[Patent Document 1]: Japanese Patent Laid-Open Publication No. 2005-74463

[Patent Document 2] Japanese Patent Laid-Open No. Hei 5-337505

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2005-271052

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2003-48003

[Patent Document 5] Japanese Patent Laid-Open No. Hei 6-328117

Summary of invention

However, the cooling method of Patent Document 1 does not consider the case where the hot-rolled steel sheet is formed into a waveform in the rolling direction. The above-described waveform-formed hot-rolled steel sheet H is partially contacted with the conveying roller 220 at the bottom of the waveform as shown in Fig. 22 . Further, the hot-rolled steel sheet H may also be in partial contact with the bottom of the wave and the guard (not shown in FIG. 22) provided as a support for preventing the hot-rolled steel sheet H from falling between the transport rollers 220. In the corrugated hot-rolled steel sheet H, the portion in contact with the conveying roller 220 or the apron is easily cooled by contact with heat and is more easily cooled than other portions. Therefore, there is a problem that the cooling of the hot-rolled steel sheet H is uneven. That is, Patent Document 1 does not consider that the hot-rolled steel sheet has a corrugated shape, and the conveying roller and the apron are partially in contact with the hot-rolled steel sheet, and the contact portion thereof is easily cooled by contact with heat. Therefore However, the hot rolled steel sheet in which the waveform is formed as described above may not be uniformly cooled.

Further, the technique disclosed in Patent Document 2 is to perform γ-α metamorphism between the rolling stands of the finishing mill to make the ultra-low carbon steel having a low hardness (softness), and the purpose is not to perform uniform cooling. Further, the invention of Patent Document 2 is not related to the cooling of the rolled material in the rolling direction, or the related cooling of the so-called high-tensile steel having a tensile strength (TS) of 800 MPa or more. Therefore, when the rolled material is a hot rolled steel sheet having a corrugated shape and a steel having a high hardness, uniform cooling may not be performed.

Further, in the cooling method of Patent Document 3, the inclination of the width direction of the steel sheet is measured, and the flow rate of the cooling water in the portion where the inclination is large is adjusted. However, once the flow rate of the cooling water in the width direction of the steel sheet is changed, it is difficult to make the temperature in the sheet width direction of the steel sheet uniform. Further, Patent Document 3 does not consider the case where the hot-rolled steel sheet is formed into a wave shape in the rolling direction, and it is possible to uniformly cool the hot-rolled steel sheet as described above.

Further, the cooling of Patent Document 4 is cooled by the hot-rolled steel sheet before the finish rolling of the finishing mill, and therefore cannot be applied to a hot-rolled steel sheet which has been subjected to finish rolling to form a predetermined thickness. Further, Patent Document 4 does not consider the case where the hot-rolled steel sheet is formed into a wave shape in the rolling direction, and it is possible to uniformly cool the hot-rolled steel sheet in the rolling direction as described above.

Further, in the cooling method of Patent Document 5, the cooling ability of the upper cooling includes cooling of the cooling water supplied from the upper water injection nozzle to the steel sheet, and also includes cooling by the accumulated water in the upper portion of the steel sheet. The above-mentioned accumulated water is affected by the inclination of the waveform formed on the steel plate and the plate feeding speed of the steel plate, so the cooling ability of the accumulated water to the steel plate cannot be strictly defined. So, it is difficult to control it correctly The cooling capacity of the cooling. Therefore, it is also difficult to make the cooling ability of the upper cooling and the lower cooling the same. Further, when the cooling ability of the upper cooling and the lower cooling is the same, an example of the method for determining the cooling ability is exemplified, but the method for determining the generality is not disclosed. Therefore, the cooling method of Patent Document 5 may fail to uniformly cool the hot rolled steel sheet.

The present invention has been devised in view of the above problems, and its object is to uniformly cool a hot rolled steel sheet which has been hot rolled by a finishing mill.

The present invention adopts the following method in order to solve the above problems in order to achieve the object. which is,

(1) A method for cooling a hot-rolled steel sheet according to an aspect of the present invention is to cool a hot-rolled steel sheet which has been hot-rolled by a finishing mill in a cooling section provided on a conveying path thereof, and is characterized by comprising the following steps: The ratio setting step is based on preliminarily determining the ratio of the thermal conductivity of the hot-rolled steel sheet above and below the ratio of the thermal conductivity of the hot-rolled steel sheet under the condition that the inclination of the hot-rolled steel sheet and the sheet feeding speed are constant. The correlation between X and the temperature standard deviation Y of the hot-rolled steel sheet during cooling or after cooling, and the thermal conductivity coefficient ratio X1 above the minimum temperature Ymin can be set as the target ratio Xt; a cooling control step of controlling at least one of an upper heat removal heat removal amount and a lower heat removal heat removal amount of the hot-rolled steel sheet in the cooling zone so that the thermal conductivity ratio X of the hot-rolled steel sheet in the cooling section is higher than the target ratio Xt is consistent.

(2) The hot-rolled steel sheet cooling method disclosed in the above (1), in the target ratio setting step, may be based on the aforementioned related information The temperature standard deviation Y is controlled to be within the range of the minimum value Ymin to the minimum value Ymin + 10 ° C. The upper and lower thermal conductivity ratio X is set to the aforementioned target ratio Xt.

(3) In the method for cooling a hot-rolled steel sheet disclosed in the above (1) or (2), the related information may be separately prepared for a plurality of conditions in which the values of the inclination and the sheet feeding speed are different, and the target ratio setting step is And setting the target ratio Xt based on the correlation data corresponding to the measured value of the inclination and the plate feeding speed in the correlation data of the plurality of numbers.

(4) In the method for cooling a hot-rolled steel sheet disclosed in the above (3), the related information may be a data showing a correlation between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y by a regression equation.

(5) In the method for cooling a hot-rolled steel sheet disclosed in the above (4), the regression formula may be derived by linear regression.

(6) In the method for cooling a hot-rolled steel sheet disclosed in the above (3), the related information may be a table showing a correlation between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y.

(7) The method for cooling a hot-rolled steel sheet according to the above (1) or (2), further comprising the step of: measuring a temperature of the hot-rolled steel sheet on a downstream side of the cooling section in a time series a temperature average value calculation step of calculating a time-series average value of the temperature based on the measurement result of the temperature; and a cooling heat removal adjustment step of adjusting the upper surface cooling heat removal amount of the hot-rolled steel sheet in the cooling zone and the foregoing The total value of the heat removal is cooled below so that the time-series average of the aforementioned temperatures coincides with the predetermined target temperature.

(8) The method for cooling a hot-rolled steel sheet according to the above (1) or (2), further comprising the step of: measuring a temperature of the hot-rolled steel sheet on a downstream side of the cooling section in a time series; a temperature; a fluctuation speed measuring step of measuring a rate of change in a vertical direction of the hot-rolled steel sheet at a portion identical to a temperature measurement portion of the hot-rolled steel sheet on a downstream side of the cooling section in a time series; a control direction determining step; When the upper side of the hot-rolled steel sheet has a positive value in the vertical direction, the temperature of the hot-rolled steel sheet is averaged over a period of one cycle or longer with respect to the waveform of the hot-rolled steel sheet in a field in which the fluctuation speed is a positive value. When the temperature is low, at least one of the direction in which the cooling and heat removal is reduced and the direction in which the cooling and heat removal in the lower portion are increased is determined as the control direction, and when the temperature of the hot-rolled steel sheet is higher than the average temperature, the foregoing At least one of the direction in which the upper heat removal heat is increased and the direction in which the lower cooling heat removal is reduced is determined as the aforementioned control direction, and In the field where the fluctuation speed is a negative value, when the temperature of the hot-rolled steel sheet is lower than the average temperature, at least one of a direction in which the upper cooling heat removal amount increases and a direction in which the lower surface cooling heat removal amount decreases is determined. In the control direction, when the temperature of the hot-rolled steel sheet is higher than the average temperature, at least one of the direction in which the cooling and heat removal is reduced and the direction in which the cooling and heat removal in the lower surface are increased are determined as the control direction; And a cooling and heat removal adjustment step of adjusting at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet in the cooling section based on the control direction determined in the control direction determining step.

(9) In the method for cooling a hot-rolled steel sheet disclosed in the above (8), the aforementioned The cooling section may be divided into a plurality of divided cooling sections along the sheet feeding direction of the hot-rolled steel sheet, and in the temperature measuring step and the variable speed measuring step, the heat is measured in time series by the boundary of the divided cooling section. The temperature and the fluctuation speed of the rolled steel sheet, in the control direction determining step, the hot-rolled steel sheet is individually determined for the divided cooling section based on the measurement results of the temperature and the fluctuation speed of the hot-rolled steel sheet individually at the boundary of the divided cooling section In the cooling and heat removal adjustment step, the feedback control method or the feedforward control is performed based on the control direction determined by the individual divided cooling sections, respectively, in the cooling and de-heating adjustment step of the upper and lower sides, so as to separate the cooling sections At least one of the aforementioned upper cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet is adjusted.

(10) The method for cooling a hot-rolled steel sheet according to the above (9), further comprising the step of: measuring the inclination of the hot-rolled steel sheet or the sheet feeding speed of the boundary of the divided cooling section; And a cooling and heat removal correction step of correcting at least one of the upper cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet in the divided cooling section based on the measurement result of the inclination or the sheet feeding speed.

(11) The method for cooling a hot-rolled steel sheet according to the above (1) or (2), further comprising a post-cooling step of cooling the hot-rolled steel sheet on a downstream side of the cooling section to obtain the hot-rolled steel sheet The standard deviation of the temperature is within the allowable range.

(12) In the method for cooling a hot-rolled steel sheet according to the above (1) or (2), the sheet feeding speed of the hot-rolled steel sheet in the cooling section may be set at Above 550m/min to below the mechanical limit speed.

(13) The method for cooling a hot-rolled steel sheet according to the above (1) or (2), wherein the hot-rolled steel sheet has a tensile strength of 800 MPa or more.

(14) In the method for cooling a hot-rolled steel sheet as disclosed in the above (12), the finishing mill may be composed of a plurality of rolling stations, and the method may further include an auxiliary cooling step, which is performed between the plurality of rolling stations Auxiliary cooling of the aforementioned hot rolled steel sheet is performed.

(15) The method for cooling a hot-rolled steel sheet according to the above (1) or (2), wherein the cooling section may further include a plurality of header upper side cooling means including a cooling water sprayable on the hot-rolled steel sheet, and The lower header cooling device includes a plurality of headers that can spray cooling water toward the lower surface of the hot-rolled steel sheet, and the upper cooling heat removal and the lower cooling heat removal can be adjusted by opening and closing control of the respective headers.

(16) The method of cooling a hot-rolled steel sheet according to the above (1) or (2), wherein the cooling section may further include a plurality of header upper side cooling means including a cooling water sprayable on the hot-rolled steel sheet, and a plurality of header lower cooling devices capable of injecting cooling water under the hot-rolled steel sheet, wherein the upper cooling heat removal amount and the lower cooling heat removal amount are at least one of a water density, a pressure, and a water temperature of the respective headers. Adjust by control.

(17) In the method of cooling a hot-rolled steel sheet according to the above (1) or (2), the cooling in the cooling zone may be performed in a range in which the temperature of the hot-rolled steel sheet is 600 °C or higher.

The inclination of the inventor of the present invention in the hot rolled steel plate and the plate feeding speed are Under certain conditions, after investigating the relationship between the ratio of the thermal conductivity of the upper and lower thermal conductivity of the hot-rolled steel sheet and the temperature standard deviation Y of the hot-rolled steel sheet during cooling or after cooling, it has been found that The thermal conductivity ratio X is controlled to a specific value to minimize the temperature standard deviation Y (i.e., the hot rolled steel sheet can be uniformly cooled).

Therefore, according to the present invention, it is possible to determine the thermal conductivity coefficient ratio X and the temperature standard deviation Y of the hot-rolled steel sheet which has been experimentally determined in advance, and to make the temperature standard deviation Y be the minimum value Ymin. The coefficient ratio X1 is set to the target ratio Xt, and controls at least one of the upper heat removal heat removal amount and the lower heat removal heat removal amount of the hot-rolled steel sheet so that the upper and lower thermal conductivity ratio X of the hot-rolled steel sheet in the cooling section coincides with the target ratio Xt described above. Therefore, it is possible to uniformly cool the hot-rolled steel sheet which has been subjected to hot rolling by a finishing mill to form a corrugated steel sheet.

1, 2‧‧‧ hot rolling equipment

11, 111‧‧‧ heating furnace

12, 112, 201‧‧‧ rough rolling mill

12a, 112a‧‧‧ work rolls

12b, 112b‧‧‧ quadruple mill

13, 113, 203‧‧‧ finishing mill

13a, 113a‧‧‧ fine rolls

14, 114, 142, 211‧‧‧ □ cooling device

14a, 114a, 142a‧‧‧ upper cooling unit

14b, 114b, 142b‧‧‧ lower cooling unit

15, 115‧‧‧ coiling device

16, 116‧‧‧Width direction rolling mill

31, 131, 146‧‧ ‧ cooling port

32, 132, 220‧‧‧ conveyor rollers

40‧‧‧ thermometer

41‧‧‧ Shape meter

133‧‧‧ Aunt

140, 202a~202d‧‧‧Rolling table

212‧‧‧ coiling device

A, B‧‧‧ fields

H‧‧‧Hot rolled steel plate

S‧‧‧ steel embryo

Z1, Z2‧‧‧ split cooling interval

Fig. 1 is an explanatory view showing a hot rolling apparatus 1 capable of realizing a method of cooling a hot rolled steel sheet according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing an outline of the configuration of the cooling device 14 provided in the hot rolling facility 1.

Fig. 3 is a graph showing the correlation between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y obtained under the condition that the inclination of the hot-rolled steel sheet H and the sheet feeding speed are constant.

Fig. 4 is an explanatory diagram showing a method of obtaining the lowest point (minimum value Ymin) of the temperature standard deviation Y from the correlation shown in Fig. 3.

Fig. 5 is a graph showing the relationship between the temperature variation and the inclination of the hot-rolled steel sheet H in the ROT of the representative steel strip in the usual operation, and the upper graph is shown. Indicates the temperature change corresponding to the distance from the tip of the coil or the elapsed time of the fixed point. The lower graph shows the slope corresponding to the distance from the tip of the coil or the elapsed time of the fixed point.

Fig. 6 is a graph showing the relationship between the temperature fluctuation and the inclination of the hot-rolled steel sheet H cooled in the ROT of the representative steel strip in the normal operation.

Fig. 7 is a view showing that the fluctuating speed of the hot-rolled steel sheet H is lower than the average temperature of the hot-rolled steel sheet H in the positive value field, and the temperature of the hot-rolled steel sheet H is lowered, and the fluctuation speed is in the negative value range and the temperature of the hot-rolled steel sheet H is raised. The graph of the relationship between the temperature change and the inclination of the hot-rolled steel sheet H after cooling and removing heat and increasing the heat removal and heat removal is reduced. Further, the inclination of the waveform of the hot-rolled steel sheet H means a value obtained by dividing the amplitude of the waveform by the length of the rolling direction of one cycle.

8 is a view showing that the fluctuating speed of the hot-rolled steel sheet H is lower than the average temperature of the hot-rolled steel sheet H in the positive value field, and the temperature of the hot-rolled steel sheet H is lowered, and the fluctuation speed is in the negative value range and the temperature of the hot-rolled steel sheet H is raised. A graph showing the relationship between the temperature change and the inclination of the hot-rolled steel sheet H after cooling and removing heat and reducing the heat removal and heat removal.

Fig. 9 is a graph showing the correlation between the inclination of the hot-rolled steel sheet H and the temperature standard deviation Y obtained under the condition that the upper and lower thermal conductivity ratio X and the sheet feeding speed are constant.

Fig. 10 is a graph showing the correlation between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y in terms of a plurality of conditions in which the values of the inclinations are different (but the plate feeding speed is fixed).

Figure 11 shows the standard deviation of the plate feeding speed and temperature of the hot-rolled steel sheet H obtained under the condition that the upper and lower thermal conductivity ratio X and the inclination are constant. A chart of the relationship between Y.

Fig. 12 is a graph showing the correlation between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y in a plurality of conditions (but the inclination is fixed) in which the values of the plate feed speeds are different.

Fig. 13 is an explanatory view showing details of the periphery of the cooling device 14 of the hot rolling facility 1.

FIG. 14 is an explanatory view showing a modification of the cooling device 14.

Fig. 15 is an explanatory view showing a state in which the temperature standard deviation has been formed in the sheet width direction of the hot-rolled steel sheet H.

Fig. 16 is an explanatory view showing a hot rolling facility 2 which can realize a cooling method of the hot rolled steel sheet H according to another embodiment.

Fig. 17 is an explanatory view showing an outline of the configuration of the cooling device 114 provided in the hot rolling facility 2.

Fig. 18A is an explanatory view showing a state in which the lowest point of the hot-rolled steel sheet H contacts the conveying roller 132.

Fig. 18B is an explanatory view showing a state in which the lowest point of the hot-rolled steel sheet H contacts the conveying roller 132 and the protector 133.

Fig. 19A is a graph showing the temporal change of the temperature of the hot-rolled steel sheet H when the sheet feeding speed of the hot-rolled steel sheet H is low.

Fig. 19B is a graph showing the temporal change of the temperature of the hot-rolled steel sheet H when the sheet feeding speed of the hot-rolled steel sheet H is high.

Fig. 20 is an explanatory view of a finishing mill 113 capable of performing inter-rolling cooling.

Fig. 21 is an explanatory view showing a manufacturing method of a conventional hot-rolled steel sheet H.

Fig. 22 is an explanatory view showing a conventional cooling method of the hot-rolled steel sheet H.

Form for implementing the invention

Hereinafter, a method of cooling a hot-rolled steel sheet for cooling a hot-rolled steel sheet, such as an automobile or an industrial machine, will be described as an embodiment of the present invention with reference to the drawings.

Fig. 1 is a view schematically showing an example of a hot rolling facility 1 which can realize a method of cooling a hot rolled steel sheet according to the present embodiment. The hot rolling equipment 1 is intended to be a device in which a heated steel slab S is held up and down by a roll and continuously rolled to a minimum of 1 mm and then coiled.

The hot rolling apparatus 1 includes a heating furnace 11 capable of heating the steel preform S, and a width direction rolling mill 16 capable of rolling the steel slab S which has been heated in the heating furnace 11 in the width direction, and can be rolled from the upper and lower directions. The rough rolling mill 12 for forming a rough-rolled product by rolling the steel slab S in the width direction, and further continuously hot-rolling the rough-rolled material to a finishing mill 13 having a predetermined thickness, which can be cooled by cooling water The cooling device 14 of the hot-rolled steel sheet H that has been hot-rolled by the rolling mill 13 can wind the hot-rolled steel sheet H that has been cooled by the cooling device 14 into a coil-like coiling device 15.

The heating furnace 11 is provided with a side burner, an axial flow burner, and a top burner that can heat the steel slab S by ejecting a flame from a steel slab that is loaded from the outside through the loading port. The steel slabs S that have been moved into the heating furnace 11 are sequentially heated in the respective heating zones formed in the respective zones, and the steel slabs S are uniformly heated by the top burner in the soaking zone formed in the final zone. In order to carry out the heat treatment required for transport at the optimum temperature. Once the entire heat treatment of the heating furnace 11 is completed, the steel slab S is conveyed outside the heating furnace 11, and the rolls of the roughing mill 12 are successively carried out. Rolling process.

The roughing mill 12 will feed the steel slabs S through the gaps of the cylindrical rotating rolls disposed across the plurality of rolling stands. For example, the roughing mill 12 may hot-roll the steel slab S by only the work rolls 12a disposed in the upper and lower stages in the first rolling stand to form a rough rolled material. Next, the quadruple mill 12b composed of the work rolls and the reinforcing rolls is continuously rolled for the rough-rolled material that has passed through the work rolls 12a. As a result, at the end of the rough rolling pass, the rough rolled material is rolled to a thickness of about 30 to 60 mm, and then conveyed to the finishing mill 13.

The finishing mill 13 finish-rolls the rough-rolled material fed from the roughing mill 12 to a thickness of several mm. These finishing mills 13 are configured such that the rough-rolled material is arranged in a gap between the finishing rolls 13a of the upper and lower straight lines across 6 to 7 rolling stands, and is gradually pressurized. The hot-rolled steel sheet H subjected to the finish rolling of the finishing mill 13 is sent to the cooling device 14 by a conveying roller 32 which will be described later.

The cooling device 14 is a device for performing so-called laminar cooling on the hot-rolled steel sheet H fed from the finishing mill 13. As shown in FIG. 2, the cooling device 14 includes a cooling water upper side cooling device 14a for ejecting the upper surface of the hot-rolled steel sheet H on the conveying roller 32 of the sliding table, and a hot-rolled steel sheet. Below the H, the cooling water lower side cooling device 14b is sprayed from the lower side cooling port 31. The upper cooling device 14a and the lower cooling device 14b are individually provided with a plurality of cooling ports 31.

Further, the cooling port 31 is connected to a cooling header (not shown). The number of the cooling ports 31 determines the cooling capacity of the upper cooling device 14a and the lower cooling device 14b. In addition, the cooling device 14 may also constitute an upper and lower split flow (split) At least one of laminar), laminar flow, spray cooling, and the like. Further, the section in which the hot-rolled steel sheet H is cooled by the cooling device 14 corresponds to the cooling section of the present invention.

As shown in Fig. 1, the coiling device 15 can wind the hot-rolled steel sheet H which has been cooled by the cooling device 14 at a predetermined coil temperature. The hot-rolled steel sheet H which has been wound into a coil shape by the coiling device 15 is sent to the outside of the hot rolling apparatus 1.

Hereinafter, a method of cooling a hot-rolled steel sheet according to the present embodiment which can be realized by the hot rolling facility 1 as described above will be described.

In the following description, as shown in Fig. 22, the hot-rolled steel sheet H which has been hot-rolled by the finishing mill 13 has a waveform in which the surface height (wave height) fluctuates in the rolling direction. Further, in the following description, the influence of the accumulated water remaining on the hot-rolled steel sheet H is ignored in the cooling of the hot-rolled steel sheet H. Actually, as a result of investigation by the inventors of the present invention, it is known that the influence of accumulated water remaining on the hot-rolled steel sheet H hardly exists.

The hot-rolled steel sheet cooling method of the present embodiment includes a target ratio setting step and a cooling control step.

The details will be described later, but in the target ratio setting step, the upper portion of the representative hot-rolled steel sheet H is obtained in advance based on the experimentally determined inclination of the hot-rolled steel sheet H and the sheet feeding speed. The ratio of the thermal conductivity coefficient above the thermal conductivity coefficient ratio X to the correlation between the temperature standard deviation Y of the hot-rolled steel sheet H during cooling or after cooling, and the temperature standard deviation Y is the minimum thermal conductivity ratio above the minimum Ymin X1 is set to the target ratio Xt.

And, in the cooling control step, the hot-rolled steel sheet H in the cooling section is controlled. The heat transfer coefficient ratio X of the hot-rolled steel sheet H in the cooling section (the section where the hot-rolled steel sheet H is cooled by the cooling device 14) and the target ratio Xt described above are at least one of the cooling heat removal heat and the lower heat removal heat removal. Consistent.

The relevant data used in the target ratio setting step described above is experimentally determined in advance by the hot rolling facility 1 before actual operation (before actual production of the hot-rolled steel sheet H as a product). Hereinafter, the method of determining the relevant data used in the target ratio setting step will be described in detail.

First, before cooling the hot-rolled steel sheet H by the cooling device 14, the cooling capacity (upper cooling capacity) of the upper side cooling device 14a of the cooling device 14 and the cooling capacity (lower cooling capacity) of the lower side cooling device 14b are adjusted in advance. The upper side cooling capacity and the lower side cooling capacity are adjusted by using the thermal conductivity of the hot-rolled steel sheet H cooled by the upper side cooling device 14a and the thermal conductivity of the hot-rolled steel sheet H cooled by the lower side cooling device 14b. .

Here, a method of calculating the thermal conductivity of the upper surface and the lower surface of the hot-rolled steel sheet H will be described. The thermal conductivity is derived from the cooling and heat removal (thermal energy) per unit time per unit area divided by the temperature difference between the thermal conductor and the heat medium (thermal conductivity = cooling removal heat / temperature difference). The temperature difference is the difference between the temperature of the hot rolled steel sheet H measured by the thermometer on the inlet side of the cooling device 14 and the temperature of the cooling water used by the cooling device 14.

Further, the value of the temperature difference between the cooling and heat removal hot-rolled steel sheets H and the specific heat and mass are individually (cooling heat removal = temperature difference × specific heat × mass). That is, the cooling and heat removal of the hot-rolled steel sheet H in the heat-removing cooling device 14 is cooled, and the difference between the temperature of the hot-rolled steel sheet H measured by the thermometer on the inlet side of the cooling device 14 and the thermometer on the outlet side is hot rolling. The specific heat of the steel plate H, by the cooling device 14 The value obtained by individually multiplying the mass of the cooled hot-rolled steel sheet H.

The thermal conductivity of the hot-rolled steel sheet H calculated as described above is divided into the thermal conductivity of the upper surface and the lower surface of the hot-rolled steel sheet H. These upper and lower thermal conductivity coefficients are calculated by, for example, predetermining the ratios as follows.

In other words, the thermal conductivity of the hot-rolled steel sheet H when the hot-rolled steel sheet H is cooled by the upper cooling device 14a and the thermal conductivity of the hot-rolled steel sheet H when the hot-rolled steel sheet H is cooled by the lower cooling device 14b are measured.

At this time, the amount of cooling water from the upper side cooling device 14a is made equal to the amount of cooling water from the lower side cooling device 14b. The reciprocal of the ratio of the thermal conductivity when the upper side cooling device 14a is used to the thermal conductivity when the lower side cooling device 14b is used is the amount of cooling water of the upper side cooling device 14a when the upper and lower thermal conductivity ratio X is "1". The amount of cooling water of the lower side cooling device 14b is above the ratio.

Then, the upper and lower ratios of the amount of cooling water calculated as described above are multiplied by the amount of cooling water of the upper side cooling device 14a or the amount of cooling water of the lower side cooling device 14b when the hot rolled steel sheet H is cooled, that is, the upper surface and the lower surface of the hot rolled steel sheet H are calculated. The ratio of thermal conductivity (upper and lower thermal conductivity ratio X).

Further, in the above description, the thermal conductivity of the hot-rolled steel sheet H cooled only by the upper side cooling device 14a and the lower side cooling device 14b is used, but cooling by both the upper side cooling device 14a and the lower side cooling device 14b may be employed. The thermal conductivity of the hot rolled steel sheet H. In other words, the thermal conductivity of the hot-rolled steel sheet H after the amount of cooling water of the upper cooling device 14a and the lower cooling device 14b is changed can be measured, and the thermal conductivity of the upper and lower surfaces of the hot-rolled steel sheet H can be calculated by using the ratio of the thermal conductivity. ratio.

As described above, the thermal conductivity of the hot-rolled steel sheet H is calculated, and based on the above ratio of the thermal conductivity of the hot-rolled steel sheet H to the lower surface (the upper and lower thermal conductivity ratio X), the heat conduction between the upper surface and the lower surface of the hot-rolled steel sheet H can be calculated. coefficient.

Next, using the above-described hot-rolled steel sheet H upper and lower thermal conductivity ratio X, the cooling capacities of the upper side cooling device 14a and the lower side cooling device 14b are adjusted based on Fig. 3, respectively. The horizontal axis of Fig. 3 represents the ratio of the average thermal conductivity of the hot-rolled steel sheet H to the average thermal conductivity below (i.e., the same as the upper and lower thermal conductivity ratio X), and the vertical axis represents the maximum rolling direction of the hot-rolled steel sheet H. Standard deviation of temperature from minimum temperature (temperature standard deviation Y.)

Moreover, FIG. 3 shows that the cooling capacity of the upper side cooling device 14a and the lower side cooling device 14b is adjusted to change the hot rolling under the condition that the inclination of the waveform of the hot-rolled steel sheet H and the sheet feeding speed of the hot-rolled steel sheet H are constant. The ratio of the thermal conductivity ratio X above the steel sheet H, and the correlation between the thermal conductivity ratio X of the hot-rolled steel sheet H after cooling and the temperature standard deviation Y (relevant data).

Referring to Fig. 3, it is understood that the correlation between the temperature standard deviation Y and the upper and lower thermal conductivity ratio X is such that the temperature standard deviation Y is a V-shaped relationship of the minimum value Ymin when the upper and lower thermal conductivity ratio X is "1".

Further, the inclination of the waveform of the hot-rolled steel sheet H is the value obtained by dividing the amplitude of the waveform by the length in the rolling direction of one cycle. Fig. 3 shows the correlation between the upper thermal conductivity ratio X and the temperature standard deviation Y under the condition that the inclination of the hot-rolled steel sheet H is set to 2% and the sheet feeding speed is set to 600 m/min (10 m/sac). The temperature standard deviation Y can also be measured in the cooling of hot rolled steel sheet H Determined, or measured after cooling. Further, the target cooling temperature of the hot-rolled steel sheet H in Fig. 3 is a temperature of 600 ° C or higher, such as 800 ° C.

The target ratio setting step is based on the above-described experimentally obtained correlation data, and the temperature standard deviation Y is set to the minimum value Ymin and the thermal conductivity ratio X is set to the target ratio Xt. The above related data may also be prepared to display the correlation between the upper and lower thermal conductivity ratio X and the temperature standard deviation Y in a table (form form) (form table data), or to prepare the upper and lower thermal conductivity by a numerical formula (such as a regression formula). Information on the relationship between the ratio X and the temperature standard deviation Y.

For example, when the relevant data is prepared to display the correlation between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y in a regression formula, the V-shaped line shown in FIG. 3 is sandwiched by the bottom of the valley and is roughly drawn on both sides. It is also possible to derive a regression formula for linear regression of the line. If it is assumed to be a linear distribution, the number of times of confirmation by the material to be tested and the number of calibrations required to calculate the prediction can be reduced.

Therefore, for example, the minimum value Ymin of the temperature standard deviation Y can be obtained by various methods such as the dichotomy of the commonly known search algorithm, the golden section method, and the random search. Thus, based on the related data shown in FIG. 3, the temperature standard deviation Y of the hot-rolled steel sheet H can be derived as the minimum thermal conductivity ratio X1 above the minimum value Ymin. Here, the regression formula of the temperature standard deviation Y of the rolling direction of the hot-rolled steel sheet H corresponding to the upper and lower thermal conductivity ratios X can be obtained in advance on both sides of the point where the average thermal conductivity is equal to the upper and lower sides. .

Hereinafter, the above-described dichotomy is used to describe the hot rolling. The method of the minimum value Ymin of the temperature standard deviation Y of the steel sheet H.

Fig. 4 is a view showing a standard case in which the regression line of the standard deviation Y of the temperature difference Y is different and the difference is different. As shown in FIG. 4, first, the temperature standard deviations Ya, Yb, and Yc of the point c of the point a, the point b, the point a, and the point b are measured. In addition, the point a between point a and point b means the point c having the value of the thermal conductivity ratio Xa above the point a and the ratio of the thermal conductivity coefficient Xb above the point b, the same applies hereinafter. Next, it is judged whether the temperature standard deviation Yc approximates the value of Ya or Yb. In the present embodiment, Yc approximates Ya.

Next, the temperature standard deviation Yd of the point d of the point between the point a and the point c is selected. Then, it is judged whether the temperature standard deviation Yd is approximately the value of Ya or Yc. In the present embodiment, Yd approximates Yc.

Next, the temperature standard deviation Ye of the point e between the point c and the point d is selected. Then, it is judged whether the temperature standard deviation Ye approximates the value of Yc or Yd. In the present embodiment, Ye approximates Yd.

The above calculation is repeated to define the lowest point f (minimum value Ymin) of the temperature standard deviation Y of the hot-rolled steel sheet H. In addition, in order to define the practical minimum point f, the above calculation may be performed for five times. Alternatively, the range of the thermal conductivity ratio X above and below the search object may be divided into 10 parts, and the above calculation may be performed in an individual range to define the lowest point f.

Further, the upper and lower thermal conductivity ratios X can be calibrated by the so-called Newton method. At this time, the regression formula described above may be used, and the ratio of the thermal conductivity ratio X above the value corresponding to the actual temperature standard deviation Y to the thermal conductivity ratio X above the temperature standard deviation Y may be obtained and used. The above-described amount of deviation is used to correct the upper and lower thermal conductivity ratios X when the hot-rolled steel sheet H is cooled.

As described above, the temperature standard deviation Y of the hot-rolled steel sheet H can be derived as the minimum thermal conductivity ratio X1 (Xf in Fig. 4) above the minimum value Ymin. Further, in the relationship between the V-shaped temperature standard deviation Y and the upper and lower thermal conductivity ratio X, the regression function can be easily obtained by the least square method or the like for the two sides.

Next, referring to Fig. 3, the temperature standard deviation Y of the hot-rolled steel sheet H can be set to "1" above and below the minimum value Ymin. Therefore, after obtaining the relevant data shown in FIG. 3, in order to minimize the temperature standard deviation Y, that is, to uniformly cool the hot-rolled steel sheet H, the target ratio Xt is set in the target ratio setting step in actual operation. "1".

Next, in the cooling control step, at least one of the upper surface heat removal heat removal amount and the lower heat removal heat removal amount of the hot-rolled steel sheet H in the cooling section is controlled so that the thermal conductivity ratio X of the hot-rolled steel sheet H in the cooling section is higher than the above The target ratio Xt (ie "1") is consistent.

Specifically, in order to make the upper thermal conductivity ratio X of the hot-rolled steel sheet H in the cooling section coincide with the target ratio Xt (ie, “1”), for example, the cooling capacity of the upper cooling device 14a and the lower cooling device can be used. The cooling capacity of 14b is adjusted to be the same, and the heat removal and heat removal of the hot-rolled steel sheet H is the same as the cooling and heat removal below.

Table 1 shows the relevant data shown in Figure 3 (ie, the correlation between the upper and lower thermal conductivity ratio X and the temperature standard deviation Y) and the value from the temperature standard deviation Y minus the minimum value Ymin (= 2.3 ° C) (and the minimum value) The difference between the standard deviations between the two, and the evaluation of the temperature standard deviation Y.

In Table 1, the thermal conductivity ratio X system molecule is the upper surface of the hot rolled steel sheet H The thermal conductivity and the denominator are the thermal conductivity of the hot rolled steel sheet H. Further, in the evaluation in Table 1 (evaluation of the condition of the upper and lower thermal conductivity ratio X), the condition that the temperature standard deviation Y is the minimum value Ymin is set to "A", and the difference between the standard deviation between the lower and lower values is set as The condition suitable for operation within 10 ° C is "B", and the condition for making an attempt error to obtain the above regression formula is "C". Next, referring to Table 1, the evaluation is also "A", that is, the temperature standard deviation Y of the hot-rolled steel sheet H is the minimum value Ymin and the thermal conductivity ratio X1 is "1".

In addition, if the temperature standard deviation Y of the hot-rolled steel sheet H is controlled within at least the minimum value Ymin to the minimum value Ymin + 10 ° C, the deviation of the relief stress, the tensile strength, and the like can be controlled within the manufacturing tolerance range. It can be said that the hot rolled steel sheet H can be uniformly cooled. That is, in the target ratio setting step described above, the temperature standard deviation Y may be controlled within a range from the minimum value Y to the minimum value Ymin + 10 ° C based on the correlation data experimentally calculated in advance. The ratio X is set to the target ratio Xt.

Further, there are various disturbances in the temperature measurement of the hot-rolled steel sheet H, so strictly speaking, the minimum value Ymin of the hot-rolled steel sheet H may not be zero. Therefore, in order to eliminate the influence of the above interference, the manufacturing allowable range is set within the range of the temperature standard deviation Y of the hot-rolled steel sheet H from the minimum value Ymin to the minimum value Ymin + 10 °C.

In order to control the temperature standard deviation Y within the range from the minimum value Ymin to the minimum value Ymin + 10 ° C, in FIG. 3 or FIG. 4, the point on the vertical axis from the temperature standard deviation Y is the minimum value Ymin + 10 ° C A straight line is drawn in the direction of the horizontal axis, and two intersections of the straight line and the two regression lines on both sides of the V-shaped curve are obtained, and the target ratio Xt is set in the upper thermal conductivity ratio X between the two intersections. In addition, in Table 1, when the thermal conductivity ratio X above the "B" is set as the target ratio Xt, the temperature standard deviation Y can be controlled within the range from the minimum value Ymin to the minimum value Ymin + 10 °C.

Further, in order to match the upper and lower thermal conductivity ratio X with the target ratio Xt, it is most convenient to operate at least one of the upper cooling device 14a and the lower cooling device 14b. Therefore, for example, in FIG. 3 and FIG. 4, the value of the horizontal axis can also be read as the upper and lower water volume density ratio, and the corresponding water amount density can be obtained on both sides of the point where the average thermal conductivity of the sandwich is equal on the upper and lower sides. The regression formula of the temperature standard deviation Y of the ratio of the hot-rolled steel sheet H. However, the point where the average thermal conductivity is equal on both the upper and lower sides is not necessarily the point at which the cooling water density is equal on the upper and lower sides, so that the test can be performed extensively to obtain the regression formula.

Further, at the time of actual operation, the value of at least one of the inclination and the plate feeding speed may be changed due to the change of the manufacturing conditions. Once the value of at least one of the inclination and the feed speed changes, the upper and lower thermal conductivity ratio X and the temperature standard The correlation of the deviation Y will also change. Therefore, the related data may be separately prepared for a plurality of conditions in which the values of the inclination and the plate feeding speed are different, and in the target ratio setting step, the inclination of the actual operation and the feeding plate are based on the relevant data of the plural numbers. The target ratio Xt is set based on the actual measured value of the speed. Thereby, uniform cooling suitable for the manufacturing conditions at the time of actual operation can be performed.

Here, the inventors of the present invention have made an effort to review the cooling of the hot-rolled steel sheet H uniformly, and adjust the cooling capacity of the upper side cooling device 14a and the lower side cooling device 14b (control the heat-removing heat removal of the hot-rolled steel sheet H and the cooling and heat removal below) The results are further found as follows.

The inventors of the present invention have made a review of the characteristics of the temperature standard deviation Y caused by the cooling in the state in which the hot-rolled steel sheet H has been formed into a waveform, and found the following facts.

In general, in actual operation, by coiling the hot-rolled steel sheet H by the coiling device 15, it is necessary to control the temperature of the hot-rolled steel sheet H to a predetermined target temperature (temperature suitable for coiling) to maintain the hot-rolled steel sheet H. Quality.

Therefore, a temperature measurement step of measuring the temperature of the hot-rolled steel sheet H on the downstream side of the cooling section (that is, the cooling device 14) in accordance with the time series may be added to the target ratio setting step and the cooling control step, and the measurement result based on the temperature may be added. And calculating a temperature average value of the time series average value of the temperature, adjusting the total value of the cooling heat removal amount of the hot-rolled steel sheet H in the cooling zone and the cooling and heat removal amount below to make the time-series average value of the aforementioned temperature and the predetermined target A cooling-free heat removal step with consistent temperature.

In order to implement these new processes, it can be configured in the cooling device as shown in FIG. A thermometer 40 for measuring the temperature of the hot rolled steel sheet H between the coil 14 and the coiling device 15 is placed.

In the temperature measuring step, the hot-rolled steel sheet H that has been transported from the cooling device 14 to the coiling device 15 is set at a position in the rolling direction of the hot-rolled steel sheet H by a thermometer 40 at a predetermined time interval (sampling interval). The temperature is measured and the time series data of the temperature measurement results are obtained. Further, the measurement range of the temperature of the thermometer 40 includes the entire width direction of the hot-rolled steel sheet H. Further, when the sampling time of each temperature measurement result is multiplied by the sheet feeding speed (conveying speed) of the hot-rolled steel sheet H, the position in the rolling direction of the hot-rolled steel sheet H in which the respective temperature measurement results are obtained can be calculated. That is, when the time of sampling the temperature measurement results is multiplied by the sheet feeding speed, the time series data of the temperature measurement result can be made to correspond to the position of the rolling direction.

In the temperature average calculation step, the time-series average of the temperature measurement results is calculated using the time series data of the temperature measurement results described above. Specifically, the average value of the constant number of temperature measurement results can be calculated each time a certain number of temperature measurement results are obtained. Next, in the cooling and heat removal step, the total value of the cooling heat removal amount of the hot-rolled steel sheet H in the cooling zone and the cooling and heat removal amount below is adjusted to calculate the time series average value of the temperature measurement result as described above and the predetermined target. The temperature is the same.

Here, it is necessary to achieve a control target in which the thermal conductivity ratio X above the hot-rolled steel sheet H in the cooling zone is equal to the target ratio Xt, and the total value of the upper cooling heat removal amount and the lower cooling heat removal amount is adjusted.

Specifically, when adjusting the total value of the above cooling heat removal amount and the following cooling heat removal amount, the setting may be based on, for example, adopting the three-dimensional equation. The learning value of the error between the theoretical value correction and the actual operational performance obtained in advance by the experimental theoretical expression is performed, and the cooling header opening and closing control connected to the cooling device 14 is performed. Alternatively, feedback control or feedforward control may be performed on the opening and closing of the cooling header based on the temperature actually measured by the thermometer 40.

Next, the cooling control of the conventional ROT will be described using the data obtained from the above-described thermometer 40 and the shape meter 41 for measuring the waveform of the hot-rolled steel sheet H disposed between the cooling device 14 and the coiling device 15 as shown in FIG. .

Further, the shape meter 41 is for measuring the shape of the measurement position (hereinafter also referred to as a fixed point) of the thermometer 40 set on the hot-rolled steel sheet H. In this case, the amount of change in the height direction of the hot-rolled steel sheet H observed at the time of the fixed-point measurement is the amount of movement of the hot-rolled steel sheet H in the sheet-feeding direction, and the line of the distance between the waves or the variation component is obtained. The slope is out. At the same time, the amount of change per unit time, that is, the rate of change, will also be obtained. Further, the field of measurement of the shape and the field of measurement of temperature include the entire width direction of the hot-rolled steel sheet H. Similarly to the temperature measurement result, when the time of each sampled measurement result (inclination, fluctuation speed, etc.) is multiplied by the plate feeding speed, the time series data of each measurement result can be made to correspond to the position of the rolling direction.

Fig. 5 is a graph showing the relationship between the temperature fluctuation and the inclination of the hot-rolled steel sheet H cooled in the ROT of a representative steel strip in the usual operation. The thermal conductivity ratio X of the hot-rolled steel sheet H in Fig. 5 is 1.2:1, and the upper side cooling capacity is higher than the lower side cooling capacity. The upper side graph of Fig. 5 shows the temperature change corresponding to the distance from the tip end of the coil or the elapsed time of the fixed point. The lower graph of Fig. 5 shows the inclination corresponding to the distance from the tip end of the coil or the elapsed time of the fixed point.

Field A of Figure 5 is before the strip end of the strip shown in Figure 13 is bitten into the coiler. The field (the area that is not well shaped due to no tension). The field B in Fig. 5 is the field after the tip end of the strip bites into the coiler (the area in which the waveform is gently changed due to the influence of the unit tension). A large temperature variation (i.e., temperature standard deviation Y) occurring in the field A in which the shape of the hot-rolled steel sheet H described above is not gentle is expected to be improved.

Therefore, the inventors of the present invention made an experiment aiming at suppressing an increase in the temperature standard deviation Y of the ROT, and as a result, found the following.

Fig. 6 is the same as Fig. 5 and shows the temperature fluctuation component corresponding to the inclination of the same shape in the ROT of the representative steel strip in the normal operation. The temperature fluctuation component refers to a residual after subtracting the time series average of the temperature (hereinafter also referred to as "average temperature") from the actual steel sheet temperature. For example, the average temperature may be an average of a range of one cycle or more of the waveform of the hot-rolled steel sheet H.

In addition, the average temperature is in principle the average of the range under the periodic unit. Moreover, the average temperature in the range of one cycle is not significantly different from the average temperature in the range of two cycles or more, and it has been confirmed by the operation data.

Therefore, at least the average temperature of the range of one cycle of the waveform can be calculated. The upper limit of the range of the waveform of the hot-rolled steel sheet H is not particularly limited, but it is preferably set to 5 cycles to obtain an average temperature with sufficient accuracy. Further, even if the average range is not in the range of the period unit, if it is within the range of 2 to 5 cycles, an allowable average temperature can be obtained.

Here, in the field where the vertical direction of the hot-rolled steel sheet H (the direction perpendicular to the upper and lower sides of the hot-rolled steel sheet H) is a positive value, the hot-rolled steel sheet H is in the field where the fluctuation speed measured at the fixed point is a positive value. Temperature (temperature measured at a fixed point) When the temperature is lower than the average temperature of the range of one cycle or more of the waveform of the hot-rolled steel sheet H, at least one of the direction in which the cooling and heat removal is reduced and the direction in which the cooling and heat removal are increased is determined as the control direction, and is in the heat. When the temperature of the rolled steel sheet H is higher than the average temperature described above, at least one of the direction in which the above-described cooling and heat removal increases and the direction in which the cooling and heat removal decreases are determined as the control direction.

Further, in the field where the fluctuation speed measured at the fixed point is a negative value, when the temperature of the hot-rolled steel sheet H is lower than the average temperature described above, the direction in which the above-described cooling and heat removal increases and the direction in which the cooling and heat removal are reduced are reduced. At least one of them is determined as the control direction, and when the temperature of the hot-rolled steel sheet H is higher than the average temperature described above, at least one of the direction in which the cooling and heat removal is reduced and the direction in which the cooling and heat removal is increased is determined as the control. direction.

Next, based on the control direction as described above, at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in the cooling section is adjusted, as shown in Fig. 7, it can be seen that it can be reduced as compared with Fig. 6. The shape of the hot-rolled steel sheet H is not gentle in the temperature fluctuation occurring in the field A.

The case where the operation opposite to the above is performed is disclosed as follows. In the field where the fluctuating speed measured at a fixed point is positive, when the temperature of the hot-rolled steel sheet H is lower than the average temperature of the hot-rolled steel sheet H, the direction of the upper cooling and the removal of heat and the cooling and heat removal are reduced. At least one of the directions is determined as the control direction, and when the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of the direction in which the cooling and heat removal is reduced and the direction in which the cooling and heat removal are increased is determined as the control. direction.

Moreover, in the field where the rate of change measured at a fixed point is negative, the hot rolled steel sheet When H is lower than the average temperature described above, at least one of the direction in which the above-described cooling and heat removal is reduced and the direction in which the cooling and heat removal is increased is determined as the control direction, and the temperature of the hot-rolled steel sheet H is averaged relative to the above. When the temperature is high, at least one of the direction in which the above-described cooling and heat removal is increased and the direction in which the cooling and heat removal are reduced is determined as the control direction.

Next, by adjusting at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in the cooling section based on the above-described control direction, as shown in FIG. 8, it is understood that the hot rolling is expanded as compared with FIG. The shape of the steel sheet H is not gentle in the temperature fluctuation occurring in the field A. In addition, the examples described herein may not be changed before the cooling stop temperature can be changed.

According to the above relationship, it is possible to determine the cooling capacity of the upper side cooling device 14a and the lower side cooling device 14b of the cooling device 14 by reducing the temperature variation, that is, the temperature standard deviation Y. In addition, Table 2 is a summary table of the above relationship.

As described above, the target ratio setting step and the cooling control step may be separately added to the temperature measurement step of measuring the temperature (temperature at the fixed point) of the hot-rolled steel sheet H on the downstream side of the cooling section in time series, and measuring by time series and The measurement procedure of the fluctuation speed of the fluctuation speed of the hot-rolled steel sheet H in the same portion (fixed point) of the hot-rolled steel sheet H at the same portion (fixed point) is determined based on the temperature measurement result and the fluctuation speed measurement result. The control direction determining step of the amount and the control direction of the cooling and heat removal, and the cooling and heat removing step of adjusting at least one of the upper cooling heat removal amount and the lower cooling heat removal amount of the hot rolled steel sheet H in the cooling section based on the determined control direction .

Here, in the control direction determining step, as in the above, in the field where the fluctuation speed of the hot-rolled steel sheet H is positive, the temperature at the fixed point of the hot-rolled steel sheet H is fixed with respect to the fixed point of the hot-rolled steel sheet H. When the average temperature is low, at least one of the direction in which the cooling and heat removal is reduced and the direction in which the cooling and heat removal are increased is determined as the control direction, and when the temperature of the hot-rolled steel sheet H is higher than the average temperature described above, At least one of the direction in which the above-described cooling and heat removal is increased and the direction in which the cooling and heat removal are reduced is determined as the control direction.

Further, in the control direction determining step, in the field where the fluctuation speed is a negative value, when the temperature of the hot-rolled steel sheet H is lower than the average temperature, the direction of the upper cooling and heat removal is lowered and the lower surface is cooled. At least one of the directions in which the heat is reduced is determined as the control direction, and when the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of the direction of cooling and heat removal and the direction of cooling and heat removal are increased. Decided to control the direction.

Further, the above cooling method is also required to achieve a control target in which the thermal conductivity ratio X above the hot-rolled steel sheet H in the cooling section is made to coincide with the target ratio Xt, and the above-described cooling and heat removal and the cooling and heat removal are adjusted.

Further, when the cooling capacity of the upper side cooling device 14a and the cooling capacity of the lower side cooling device 14b are adjusted, for example, the cooling header and the lower side cooling device 14b connected to the cooling port 31 of the upper side cooling device 14a, respectively. The cooling header connected to the cooling port 31 is opened and closed. Alternatively, the cooling capacity of each of the cooling headers of the upper side cooling device 14a and the lower side cooling device 14b may be controlled. That is, at least one of the water amount density, the pressure, and the water temperature of the cooling water sprayed from each of the cooling ports 31 may be adjusted.

Further, the cooling headers (cooling ports 31) of the upper cooling device 14a and the lower cooling device 14b can be reduced to adjust the flow rate and pressure of the cooling water sprayed from the upper cooling device 14a and the lower cooling device 14b. For example, when the cooling capacity of the upper side cooling device 14a before the cooling header is reduced is higher than the cooling capacity of the lower side cooling device 14b, the cooling header constituting the upper side cooling device 14a should be reduced.

By the cooling capacity of the above-described adjustment, the cooling water is sprayed from the upper cooling device 14a onto the hot-rolled steel sheet H, and the cooling water is sprayed from the lower cooling device 14b toward the lower surface of the hot-rolled steel sheet H, whereby the hot-rolled steel sheet H can be uniformly cooled.

In the above embodiment, the case where the sheet feeding speed of the hot-rolled steel sheet H is fixed to 600 m/min and the relevant data shown in Fig. 3 is obtained has been described. Further, although the details are to be described later, the inventors of the present invention have made efforts to review the results. It is known that the cooling of the hot-rolled steel sheet H can be more uniform if the sheet feeding speed is set to 550 m/min or more.

It is known that when the sheet feeding speed of the hot-rolled steel sheet H is set to 550 m/min or more, even if the cooling water is sprayed toward the hot-rolled steel sheet H, the influence of the water accumulated on the hot-rolled steel sheet H can be remarkably reduced. Therefore, it is also possible to avoid uneven cooling of the hot-rolled steel sheet H due to water accumulation.

In the above embodiment, the cooling of the hot-rolled steel sheet H by the cooling device 14 is preferably performed within a range from the temperature at the exit of the finishing mill to the temperature of the hot-rolled steel sheet H of 600 °C. The temperature of hot rolled steel sheet H is 600 ° C or higher The field is the so-called membrane boiling field. That is, at this time, water cooling of the hot-rolled steel sheet H can be performed in the film boiling field in the so-called metamorphic boiling field. In the field of the abnormal boiling, after the cooling water is sprayed onto the surface of the hot-rolled steel sheet H, the surface of the hot-rolled steel sheet H is coexisted as a portion covered with the vapor film and the portion of the cooling water directly sprayed onto the hot-rolled steel sheet H.

Therefore, the hot rolled steel sheet H cannot be uniformly cooled. Further, in the field of film boiling, the hot-rolled steel sheet H is cooled in a state where the entire surface of the hot-rolled steel sheet H is covered with a vapor film, so that the hot-rolled steel sheet H can be uniformly cooled. Therefore, as in the present embodiment, the hot-rolled steel sheet H can be more uniformly cooled in a range in which the temperature of the hot-rolled steel sheet H is 600 ° C or more.

In the above embodiment, when the cooling capacity of the upper side cooling device 14a of the cooling device 14 and the cooling capacity of the lower side cooling device 14b are adjusted using the related data shown in Fig. 3, the inclination of the waveform of the hot rolled steel sheet H is adjusted. The plate feeding speed with the hot-rolled steel sheet H is fixed. However, by way of example, the inclination of the hot-rolled steel sheets H and the sheet feeding speed may also differ for each steel coil.

According to the investigation by the inventors of the present invention, as an example, as shown in Fig. 9, when the inclination of the waveform of the hot-rolled steel sheet H is increased, the temperature standard deviation Y of the hot-rolled steel sheet H is also increased. That is, as shown in FIG. 10, as the upper and lower thermal conductivity ratio X deviates from "1", the temperature standard deviation Y increases in accordance with the inclination (sensitivity of the inclination). In Fig. 10, as described above, the relationship between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y is shown by the regression line of each of the inclinations by the V-shape. Further, in Fig. 10, the sheet feeding speed of the hot-rolled steel sheet H is fixed at 10 m/sec (600 m/min).

Also, by way of example, as shown in FIG. 11, once the hot rolled steel sheet H is When the feed speed is high, the temperature standard deviation Y of the hot-rolled steel sheet H will increase. That is, as shown in FIG. 12, as the upper and lower thermal conductivity ratio X deviates from "1", the temperature standard deviation Y increases in accordance with the plate feeding speed (sensitivity of the plate feeding speed). In Fig. 12, as described above, the relationship between the upper and lower thermal conductivity ratio X and the temperature standard deviation Y has been shown by the regression line of the V word for each of the sheet feeding speeds. Further, in Fig. 12, the inclination of the waveform of the hot-rolled steel sheet H was fixed at 2%.

As described above, when the inclination of the hot-rolled steel sheet H and the sheet feeding speed are not fixed, the temperature standard deviation Y can be qualitatively evaluated corresponding to the change in the upper and lower thermal conductivity ratios X, but it cannot be accurately quantitatively evaluated.

Therefore, the thermal conductivity ratio X of the upper and lower portions of the hot-rolled steel sheet H is fixed in advance, and as shown in FIG. 9, the inclination is changed stepwise from 3% to 0%, and the respective inclinations and the hot-rolled steel sheets are obtained in advance. Table data on the correlation between the temperature standard deviation Y after cooling and H. Next, the temperature standard deviation Y corresponding to the inclination z% of the actual hot-rolled steel sheet H is corrected by the interpolation function to the temperature standard deviation Y' corresponding to the predetermined inclination. Specifically, when the predetermined inclination is set to 2% as the correction condition, the temperature standard deviation Yz' is calculated by the following formula (1) based on the temperature standard deviation Yz at the inclination z%. Alternatively, for example, the slope α of the inclination of Fig. 9 may be calculated by the least square method or the like, and the temperature standard deviation Yz' may be calculated using the slope α.

Yz’=Yz×2/z. . . . (1)

Moreover, the inclination can be corrected to a predetermined inclination by the regression formula of the V-shaped curve shown in FIG. 10, and the temperature standard deviation Y can be derived from the above regression formula. In addition, Table 3 shows the temperature scale of the hot-rolled steel sheet H after the upper and lower thermal conductivity ratio X is changed with respect to the inclination in FIG. 9 as shown in FIG. Quasi-deviation Y, the standard deviation Y of each temperature from the hot-rolled steel sheet H minus the minimum value Ymin (Ymin=1.2°C when the inclination is 1%, Ymin=2.3°C when the inclination is 2%, and the inclination is 3% The value after Ymin = 3.5 ° C) (the difference between the standard deviation from the minimum value) and the evaluation of the temperature standard deviation Y.

The display and evaluation criteria of the upper and lower thermal conductivity ratios X in the above Table 3 are the same as those in Table 1, and the description thereof will be omitted. Using the above FIG. 10 or Table 3, the temperature standard deviation Y of the hot-rolled steel sheet H corresponding to the inclination can be derived. Secondly, for example, when the inclination is corrected to 2%, the evaluation of Table 3 is "B", that is, the difference from the standard deviation of the minimum value of the hot-rolled steel sheet H can be 10 ° C or less. The ratio X is set to 1.1.

Similarly, as shown in FIG. 11, the sheet feeding speed can be changed from 5 m/sec (300 m/min) to 20 m/sec (1200 m/min) in stages, and the respective sheet feeding speeds and hot-rolled steel sheets can be obtained in advance. Table data on the correlation between the temperature standard deviation Y after cooling and H. Next, the temperature standard deviation Y corresponding to the actual sheet feeding speed v (m/sec) of the actual hot-rolled steel sheet H is corrected by the interpolation function to the temperature standard deviation Y' corresponding to the predetermined sheet feeding speed. Specifically, when the predetermined sheet feeding speed is set to 10 (m/sec) as the correction condition, the temperature standard deviation Yv at the sheet feeding speed v (m/sec) is calculated by the following formula (2). Temperature standard deviation Yv'. Alternatively, for example, the slope α of the sheet feeding speed of Fig. 11 may be calculated by the least square method or the like, and the temperature standard deviation Yv' may be calculated using the slope α.

Yz’=Yv×10/v. . . . (2)

Moreover, the plate feed speed can be corrected to a predetermined plate feed speed by the regression formula of the V-shaped curve shown in FIG. 12, and the temperature standard deviation Y can be derived from the above regression formula. Further, in Table 4, the temperature standard deviation Y of the hot-rolled steel sheet H after the upper and lower thermal conductivity ratio X is changed with respect to the sheet feeding speed in Fig. 11 is shown as shown in Fig. 12, and the minimum value is subtracted from each temperature standard deviation Y. Ymin (Ymin=1.2°C when the plate feeding speed is 5m/s, Ymin=2.3°C when the plate feeding speed is 10m/s, Ymin=3.5°C when the plate feeding speed is 15m/s, and the feeding speed is 20m/ In s, the value after Ymin = 4.6 ° C) (the difference between the standard deviation from the minimum value) and the evaluation of the temperature standard deviation Y.

The display and evaluation criteria of the upper and lower thermal conductivity ratios X in the above Table 4 are the same as those in Table 1, and the description thereof will be omitted. Using the above-described Fig. 12 or Table 4, the temperature standard deviation Y of the hot-rolled steel sheet H corresponding to the sheet feeding speed can be derived. Secondly, For example, when the sheet feeding speed is corrected to 10 m/sec, the evaluation of Table 4 is "B", that is, the difference from the standard deviation of the minimum value of the hot-rolled steel sheet H can be 10 ° C or less. The ratio X is set to 1.1.

As described above, even if the inclination of the hot-rolled steel sheet H and the sheet feeding speed are not fixed, the change in the temperature standard deviation Y corresponding to the upper and lower thermal conductivity ratios can be accurately quantitatively evaluated by the corrected temperature standard deviation Y.

In the above embodiment, the temperature and waveform of the hot-rolled steel sheet H cooled by the cooling device 14 can be measured, and the cooling capacity of the upper cooling device 14a and the cooling capacity of the lower cooling device 14b can be adjusted based on the measurement results. That is, the feedback control of the cooling capacities of the upper side cooling device 14a and the lower side cooling device 14b can be performed.

At this time, as shown in FIG. 13, between the cooling device 14 and the coiling device 15, a thermometer 40 for measuring the temperature of the hot-rolled steel sheet H and a shape gauge 41 for measuring the waveform of the hot-rolled steel sheet H are disposed.

Next, the hot-rolled steel sheet H in the feed plate is subjected to fixed-point measurement of temperature and shape at the same point by the thermometer 40 and the shape meter 41, and is measured as time-series data. Further, the measurement range of the temperature includes the entire width direction of the hot-rolled steel sheet H. Further, the shape represents the amount of change in the height direction of the hot-rolled steel sheet H observed at the time of the fixed point measurement. Further, the measurement range of the shape is the same as the measurement range of the temperature, and includes the entire width direction of the hot-rolled steel sheet H. By multiplying the sampling time by the plate feeding speed, the time series data of the measurement results such as the temperature and the fluctuation speed can be correlated with the position of the rolling direction.

As described with reference to FIG. 5, FIG. 6, FIG. 7, and FIG. 8, in the field where the fluctuation speed of the hot-rolled steel sheet H is positive, the temperature at the fixed point of the hot-rolled steel sheet H is relative to the average temperature at the fixed point. At lower times, the upper standard cooling capacity (the above cooling and heat removal) can be reduced to reduce the temperature standard deviation Y. Similarly, by increasing the lower side cooling capacity (cooling heat removal below), the temperature standard deviation Y can be reduced. With the above relationship, that is, it is determined that the temperature standard deviation Y is reduced, the cooling capacity of either the upper side cooling device 14a and the lower side cooling device 14b of the cooling device 14 can be adjusted.

In other words, if the temperature change position corresponding to the waveform of the hot-rolled steel sheet H is grasped, it can be understood that the temperature standard deviation Y that has occurred now occurs due to either the upper side cooling or the lower side cooling. Therefore, it is possible to determine the direction of increase and decrease (control direction) for lowering the cooling capacity (the upper heat removal heat removal) and the lower side cooling capacity (the lower cooling heat removal) of the temperature standard deviation Y, and to adjust the upper and lower thermal conductivity ratio X.

Further, the upper and lower thermal conductivity ratios X may be determined based on the magnitude of the temperature standard deviation Y to control the temperature standard deviation Y within a range from the allowable range such as the minimum value Ymin to the minimum value Ymin + 10 °C. The method of determining the upper and lower thermal conductivity ratios X is the same as that of the above-described embodiment described with reference to FIGS. 3 and 4, and thus detailed description thereof will be omitted. In addition, by controlling the temperature standard deviation Y within the range from the minimum value Ymin to the minimum value Ymin + 10 ° C, the deviation of the relief stress, the tensile strength, and the like can be controlled within the manufacturing tolerance range, and the hot rolling is uniformly cooled. Steel plate H.

Further, although there is no small deviation, if the cooling water amount density ratio is within ±5% with respect to the cooling water amount density ratio which allows the temperature standard deviation Y to be the minimum value Ymin, the temperature standard deviation Y can be controlled to the minimum value. Ymin is within the range of the minimum value Ymin + 10 °C. In other words, when the cooling water amount density is used, it is preferable to set the ratio of the cooling water amount density to the upper (the cooling water amount density ratio) to be within 5% with respect to the cooling water amount density ratio at which the temperature standard deviation Y is the minimum value Ymin. However, the above tolerance range does not necessarily include the same water volume density.

As described above, the feedback control of the cooling capacities of the upper side cooling device 14a and the lower side cooling device 14b can be adjusted to be suitable for setting The cooling capacity of the hot-rolled steel sheet H can be further improved by the cooling capacity of the hot-rolled steel sheet.

In the above embodiment, as shown in FIG. 14, the cooling section for cooling the hot-rolled steel sheet H may be divided into a plurality of divided cooling sections Z1 and Z2 in the rolling direction. Each of the divided cooling sections Z1 and Z2 is provided with a cooling device 14, respectively. Further, a thermometer 40 and a shape meter 41 are provided on the downstream sides of the divided cooling sections Z1 and Z2, which are boundaries of the divided cooling sections Z1 and Z2, respectively. Further, in the present embodiment, the cooling section is divided into two divided cooling sections, but the number of divisions is not limited thereto and can be arbitrarily set. For example, the cooling interval can also be divided into 1 to 5 divided cooling intervals.

At this time, the temperature and waveform of the hot-rolled steel sheet H on the downstream side of the divided cooling sections Z1 and Z2 are measured by the thermometers 40 and the respective shape gauges 41, respectively. Next, the cooling ability of the upper side cooling device 14a and the lower side cooling device 14b of each divided cooling zone Z1, Z2 is controlled based on the measurement result of these. At this time, the cooling ability is controlled to control the temperature standard deviation Y of the hot-rolled steel sheet H within a range of the allowable range such as the minimum value Ymin to the minimum value Ymin + 10 ° C described above. In this way, at least one of the upper surface of the hot-rolled steel sheet H of each of the divided cooling sections Z1 and Z2, and the heat of cooling and the heat of the lower side can be adjusted.

For example, in the divided cooling zone Z1, based on the measurement results of the thermometer 40 and the shape meter 41 on the downstream side thereof, feedback control can be performed on the cooling capacities of the upper side cooling device 14a and the lower side cooling device 14b, and the above cooling can be adjusted. At least one of heat removal and heat removal below.

Further, in the divided cooling zone Z2, the upper side cooling device 14a and the lower side may be based on the measurement results of the thermometer 40 and the shape meter 41 on the downstream side. The cooling capacity of the cooling device 14b is subjected to feedforward control or feedback control. In either case, at least one of the upper cooling heat removal and the lower cooling heat removal may be adjusted in the divided cooling zone Z2.

The method of controlling the cooling ability of the upper side cooling device 14a and the lower side cooling device 14b based on the measurement results of the thermometer 40 and the shape meter 41 is the same as that of the above-described embodiment described with reference to FIGS. 5 to 8, and therefore detailed description thereof will be omitted.

At this time, at least one of the cooling heat removal and the lower cooling and heat removal of the hot-rolled steel sheet H are adjusted in each of the divided cooling zones Z1 and Z2, so that more strict control can be performed. Therefore, the hot rolled steel sheet H can be cooled more uniformly.

In the above embodiment, when at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H is adjusted in each of the divided cooling sections Z1 and Z2, the measurement results of the thermometer 40 and the shape meter 41 are also At least one of the inclination of the waveform of the hot-rolled steel sheet H and the sheet feeding speed can be used. At this time, the temperature standard deviation Y of the hot-rolled steel sheet H corresponding to at least the inclination or the sheet feeding speed is corrected by the same method as the above-described embodiment described with reference to Figs. 9 to 12 . Next, at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in each of the divided cooling sections Z1 and Z2 is corrected based on the corrected temperature standard deviation Y (Y'). Thereby, the hot-rolled steel sheet H can be cooled uniformly.

Further, according to the present embodiment, the plate width direction of the hot-rolled steel sheet H can be precisely rolled into a uniform shape and material. Fig. 15 is a view showing a waveform having a different amplitude in the width direction of the hot-rolled steel sheet H due to the wrinkles in the middle of the surface. One of the states. As described above, when a waveform having a different amplitude is formed in the sheet width direction and a temperature standard deviation is formed in the sheet width direction, the temperature standard deviation in the sheet width direction can be reduced by the above-described embodiment.

Hereinafter, a method of uniformly cooling the hot-rolled steel sheet H in a high-speed setting of the borrowing plate speed will be described in detail.

Fig. 16 is a view schematically showing an example of the hot rolling facility 2 of another embodiment. This hot rolling facility 2 is intended to continuously roll a heated steel slab S up and down by a roll, and to roll it to a minimum of 1.2 mm and then coil it.

The hot rolling facility 2 includes a heating furnace 111 capable of heating the steel preform S, a width direction rolling mill 116 capable of rolling in the width direction and being heated by the heating furnace 111, and rolling from the upper and lower directions to the above width The roughing mill 112 which forms the rough-rolled material by rolling the steel slab S, and the hot-rolling finishing of the rough-rolled material to the predetermined thickness, and the cooling mill The cooling device 114 of the hot-rolled steel sheet H of the hot-rolled steel of the rolling mill 113 can wind the hot-rolled steel sheet H cooled by the cooling device 114 into a coil-like coiling device 115.

The heating furnace 111 is provided with a side burner, an axial flow burner, and a top burner which can heat the steel preform S by ejecting a flame from a steel billet S which is carried in from the outside through the loading port. The steel slabs S carried into the heating furnace 111 are sequentially heated in the respective heating zones formed in the respective zones, and the steel slabs S are uniformly heated by the top burner in the soaking zone formed in the final zone. Perform the insulation treatment required to deliver at the optimum temperature. After the heating treatment of the heating furnace 111 is completed, the steel preform S is conveyed outside the heating furnace 111, and the rolling process of the roughing mill 112 is continued.

In the roughing mill 112, the steel blank S fed from the heating furnace 111 passes through the gap of the cylindrical rotating rolls disposed across the plurality of rolling stands. For example, the roughing mill 112 may hot-roll the steel slab S by only the work rolls 112a disposed in the upper and lower stages of the first rolling stand to form a rough rolled material.

Next, the quadruple rolling mill 112b composed of the work rolls and the reinforcing rolls is continuously rolled by the rough rolled material which has passed through the work rolls 112a. As a result, at the end of the rough rolling pass, the rough rolled material is rolled to a thickness of about 30 to 60 mm, and is again sent to the finishing mill 113. Further, the structure of the roughing mill 112 is not limited to those disclosed in the embodiment, and the number of rolls or the like can be arbitrarily set.

The finishing mill 113 finish-rolls the rough-rolled material fed from the roughing mill 112 until the thickness thereof is several mm. The finishing mills 113 are configured such that the rough-rolled material is arranged in a gap between the finishing rolls 113a of the upper and lower straight lines across 6 to 7 rolling stands, and is gradually pressurized. The hot-rolled steel sheet H subjected to the finish rolling of the finishing mill 113 is sent to the cooling device 114 by the conveying roller 32 (see Fig. 17). Further, the rolling mill provided with the above-described one of the upper and lower straight lines to the finish rolling roll 113a is also referred to as a so-called roll rolling stand.

Further, between each of the finishing rolls 113a arranged between 6 to 7 rolling stands (that is, between the rolling stands), a cooling device 142 (assisted cooling) for performing inter-rolling cooling (auxiliary cooling) during finish rolling is disposed. Device). The detailed description of the device structure and the like of the cooling device 142 will be described later with reference to Fig. 20 . Although FIG. 16 shows a case where the cooling device 142 is disposed in two places of the finishing mill 113, the cooling device 142 may be formed between all the finishing rolls 113a or only in a part thereof.

The cooling device 114 is used for hot rolling of the self-finishing mill 113. The steel plate H is subjected to a laminar or spray nozzle cooling device. As shown in FIG. 17, the cooling device 114 includes a cooling water upper side cooling device 114a for ejecting the upper surface of the hot-rolled steel sheet H on the conveying roller 132 of the sliding table, and a hot-rolled steel plate. Below the H, the cooling water lower side cooling device 114b is sprayed from the lower side cooling port 131.

The upper cooling device 114a and the lower cooling device 114b are individually provided with a plurality of cooling ports 131. Further, the cooling port 131 is connected to a cooling header (not shown). The number of the cooling ports 131 determines the cooling capacity of the upper cooling device 114a and the lower cooling device 114b. Further, the cooling device 114 may constitute at least one of an up-and-down split layer flow, a laminar flow, and spray cooling.

In the cooling device 114, when the cooling capacity of the upper cooling device 114a and the cooling capacity of the lower cooling device 114b are adjusted, for example, the cooling header and the lower side connected to the cooling port 131 of the upper cooling device 114a may be used as an example. The cooling header connected to the cooling port 131 of the cooling device 114b is opened and closed.

Alternatively, the operating parameters of the respective cooling headers of the upper side cooling device 114a and the lower side cooling device 114b may be controlled. In other words, at least one of the water amount density, the pressure, and the water temperature of the cooling water sprayed from each of the cooling ports 131 may be adjusted.

Further, the cooling headers (cooling ports 131) of the upper cooling device 114a and the lower cooling device 114b can be reduced to adjust the flow rate and pressure of the cooling water sprayed from the upper cooling device 114a and the lower cooling device 114b. For example, when the cooling capacity of the upper side cooling device 114a before the cooling header is reduced is higher than the cooling capacity of the lower side cooling device 114b, the cooling header constituting the upper side cooling device 114a should be reduced.

The coiling device 115, as shown in Fig. 16, can wind the hot-rolled steel sheet H which has been cooled by the cooling device 114 at a predetermined coil temperature. The hot-rolled steel sheet H wound into a coil shape by the coiling device 115 is sent to the outside of the hot rolling equipment 2.

In the cooling device 114 of the hot rolling facility 2, when the hot-rolled steel sheet H having the surface height (wave height) varying in the rolling direction is cooled, the upper cooling device 114a can be appropriately adjusted as described above. The hot-rolled steel sheet H is uniformly cooled by the sprayed cooling water and the water density, pressure, water temperature, and the like of the cooling water sprayed from the lower side cooling device 114b. However, especially when the sheet feeding speed of the hot-rolled steel sheet H is slow, the time during which the hot-rolled steel sheet H is in partial contact with the conveying roller 132 and the protective 133 is prolonged, and the hot-rolled steel sheet H is brought into contact with the conveying roller 132 and the protective 133. Some of them are easily cooled by contact with heat, which results in uneven cooling. The reason for the above unevenness of cooling will be described below with reference to the drawings.

As shown in Fig. 18A, when the hot-rolled steel sheet H is formed with a wave shape in the rolling direction, the bottom of the waveform of the hot-rolled steel sheet H may be partially in contact with the conveying roller 132. Further, as shown in Fig. 18B, the adjacent conveying rollers 132 in the rolling direction may be provided with a protector 133 as a support for preventing the hot rolled steel sheet H from falling. At this time, the bottom of the waveform of the hot-rolled steel sheet H may be in partial contact with the conveying roller 132 and the protector 133. As described above, the portion of the hot-rolled steel sheet H which is in partial contact with the conveying roller 132 and the apron 133 is also more easily cooled than other portions by contact with heat. Therefore, the cooling of the hot rolled steel sheet H will be uneven.

In particular, when the sheet feeding speed of the hot-rolled steel sheet H is low, the time during which the hot-rolled steel sheet H is partially in contact with the conveying roller 132 and the apron 133 is prolonged. As a result, as shown in FIG. 19A, the hot-rolled steel sheet H and the conveying roller 132 and the protector 133 The portion of the portion contact (the portion circled by the broken line in Fig. 19A) is more easily cooled than the other portions, and the cooling of the hot-rolled steel sheet H is uneven.

On the other hand, if the sheet feeding speed of the hot-rolled steel sheet H is high, the above contact time will be shortened. Further, once the sheet feeding speed is increased, the reflow force due to the contact between the hot-rolled steel sheet H and the conveying roller 132 and the protector 133 is made, and the hot-rolled steel sheet H in the sheet is formed from the conveying rollers 132 and protected. Tan 133 suspension state.

When the sheet feeding speed of the hot-rolled steel sheet H is increased, the hot-rolled steel sheet H is suspended from the conveying roller 132 and the apron 133 due to the repulsive force caused by the contact, and the hot-rolled steel sheet H and the conveying are reduced. The contact time and the number of contacts of the roller 132 and the protector 133 are reduced, so that the temperature drop caused by the above contact is reduced to such an extent that it can be ignored.

Therefore, the sheet feeding speed can be increased, the contact heat removal can be suppressed, and the hot-rolled steel sheet H can be more uniformly cooled as shown in Fig. 19B. Then, the inventors have found that the hot-rolled steel sheet H can be sufficiently uniformly cooled by setting the sheet feeding speed to 550 m/min or more.

Further, the above findings are obtained by cooling the hot-rolled steel sheet H which forms the waveform, but regardless of the height of the waveform, the lowest point of the hot-rolled steel sheet H will contact the conveying roller 132 and the apron 133, so the plate feeding speed is not limited to the height of the waveform. With high speed, uniform cooling can be effectively performed.

In addition, when the sheet feeding speed of the hot-rolled steel sheet H is set to 550 m/min or more, the hot-rolled steel sheet H is formed in a state in which the conveying roller 132 and the apron 133 are suspended, so that the hot-rolled steel sheet H is ejected even in this state. Cooling water can also prevent the presence of accumulated water on the hot rolled steel sheet H as is conventional. Therefore, it is possible to avoid uneven cooling of the hot-rolled steel sheet H due to the accumulation of water.

As described above, in addition to the above-described upper and lower heat removal control, and the sheet feeding speed of the hot-rolled steel sheet H in the cooling section is set to 550 m/min or more, the cooling can be more uniformly cooled with the wave height in the rolling direction. Hot-rolled steel sheet H of the waveform of the ground change.

In addition, the hot plate steel H has a higher plate speed, but it cannot exceed the mechanical limit speed (such as 1550 m/min). Therefore, in essence, the sheet feeding speed of the hot-rolled steel sheet H in the cooling section is set to be in the range of 550 m/min or more to the mechanical limit speed. Moreover, when the upper limit of the plate feeding speed (operating upper limit speed) in the actual operation is preset, the plate feeding speed of the hot rolled steel sheet H is preferably set to be above 550 m/min to the upper limit operating speed (such as 1200 m/min). Within the scope.

Needless to say, the hot-rolled steel sheet cooling method described with reference to FIGS. 1 to 14 may be added at a high speed setting (provided in a range from 550 m/min or more to a mechanical limit speed).

In addition, it is generally known that the hot-rolled steel sheet H having a large tensile strength (especially a steel sheet having a tensile strength (TS) of 800 MPa or more and actually having an upper limit of 1400 MPa is called a high-strength steel sheet) The high hardness of the hot-rolled steel sheet H causes a large amount of heat generated during the rolling of the hot rolling equipment 2. Therefore, the sheet feeding speed of the hot-rolled steel sheet H in the cooling device 114 (i.e., the cooling zone) has been reduced so far to sufficiently cool.

However, when the sheet feeding speed of the hot-rolled steel sheet H in the cooling device 114 is lowered, when the hot-rolled steel sheet H is formed with a wave shape, the hot-rolled steel sheet H is partially in contact with the conveying roller 132 and the apron 133 as described above, resulting in contact. Part of the cooling is easy due to contact with heat, and uneven cooling occurs.

Therefore, the inventors of the present invention have found that in the finishing mill 113 of the hot rolling facility 2, one pair of finishing rolls 113a (i.e., rolling stations), such as across 6 to 7 rolling stands, are cooled to each other (so-called By cooling between the rolling stands, the above-described processing heat can be suppressed, and the sheet feeding speed of the hot-rolled steel sheet H in the cooling device 114 is set to 550 m/min or more. Hereinafter, the above-described inter-rolling table cooling will be described with reference to Fig. 20 .

Fig. 20 is an explanatory view of a finishing mill 113 capable of performing inter-rolling cooling, and a part of the finishing mill 113 is enlarged for the sake of explanation, and three rolling stands are illustrated. In FIG. 20, the same components as those of the above-described embodiment are denoted by the same reference numerals. As shown in Fig. 20, the finishing mill 113 is provided with a plurality of rolling stands 140 including one of the upper and lower straight lines, the finishing rolls 113a and the like (three in Fig. 20). Each of the rolling stands 140 is provided with a cooling device 142 as a device for performing nozzle cooling of a laminar flow or a spray method, and the hot-rolled steel sheet H can be cooled between the rolling stands 140.

As shown in FIG. 20, the cooling device 142 includes a cooling water upper side cooling device 142a for discharging the hot-rolled steel sheet H conveyed in the finishing mill 113 from the upper side, and a hot-rolled steel sheet H. The lower side discharges the cooling water lower side cooling device 142b. The upper cooling device 142a and the lower cooling device 142b are individually provided with a plurality of cooling ports 146. Further, the cooling port 146 is connected to a cooling header (not shown). Further, the cooling device 142 may constitute at least one of an up-and-down split layer flow, a laminar flow, and spray cooling.

In the finishing mill 113 shown in FIG. 20, in particular, when the tensile strength (TS) of the hot-rolled steel sheet H is 800 MPa or more, it is possible to suppress the heat generation of the hot-rolled steel sheet H by performing cooling between the rolling stands. Thereby, the cooling device 114 can be In the hot-rolled steel sheet H, the sheet feeding speed is maintained at 550 m/min or more. Therefore, it is possible to solve the problem that the contact portion of the hot-rolled steel sheet H which is problematic in cooling at a low-speed sheet feeding speed and the conveying roller 132 and the protector 133 is easily cooled by contact with heat, and can be sufficiently The hot rolled steel sheet H is uniformly cooled.

In the above embodiment, the cooling of the hot-rolled steel sheet H by the cooling device 114 is preferably carried out in a range in which the temperature of the hot-rolled steel sheet H is 600 °C or higher. The temperature range of the hot-rolled steel sheet H is 600 ° C or higher, which is the so-called film boiling field. That is, at this time, the hot-rolled steel sheet H can be cooled in the film-state boiling region while avoiding the so-called metamorphic boiling field. In the field of the abnormal boiling, after the cooling water is sprayed onto the surface of the hot-rolled steel sheet H, the surface of the hot-rolled steel sheet H is coexisted as a portion covered by the vapor film, and a portion where the cooling water is directly sprayed on the hot-rolled steel sheet H. Therefore, the hot rolled steel sheet H cannot be uniformly cooled.

Further, in the field of film boiling, the hot-rolled steel sheet H is cooled in a state where the entire surface of the hot-rolled steel sheet H is covered with a vapor film, so that the hot-rolled steel sheet H can be uniformly cooled. Therefore, as in the present embodiment, the hot-rolled steel sheet H can be more uniformly cooled in the range of the temperature of the hot-rolled steel sheet H of 600 ° C or more.

The preferred embodiments of the present invention have been described above with reference to the drawings, but the present invention is not limited to the embodiments described above. It is to be understood that those skilled in the art can devise various modifications and alterations within the scope of the invention as disclosed in the appended claims.

[Examples]

The inventor of the present invention verified that the plate feeding speed of the hot rolled steel sheet was set. At 550 m/min or more, uniform cooling of the hot-rolled steel sheet can be performed, and a cooling test of the hot-rolled steel sheet is carried out as an example.

(First embodiment)

A hot-rolled steel sheet having a medium wave having a thickness of 2.5 mm, a width of 1200 mm, a tensile strength of 400 MPa, and a slope of 2% has been formed, and the sheet feeding speed in the cooling device is changed to be cooled. Specifically, the sheet feeding speed is changed to 400 m/min, 450 m/min, 500 m/min, 550 m/min, 600 m/min, and 650 m/min, and each of the cooling of the hot-rolled steel sheets at various sheet feeding speeds is performed. 20 times.

Next, the temperature of the hot-rolled steel sheet at the time of coiling was measured, and the average value (CT temperature fluctuation amount) of the standard deviation of the temperature fluctuation was calculated using the temperature measurement result. The results of the evaluation of the CT temperature fluctuation amount calculated above are shown in Table 3 below. In addition, the evaluation criteria were evaluated as having no uniform cooling when the CT temperature variation amount was greater than 25 ° C, and were rated as uniform cooling when the CT temperature fluctuation amount was 25 ° C or less.

As shown in Table 5, when the sheet feeding speed was 500 m/min or less, the amount of change in the CT temperature was not sufficiently reduced (above 25 ° C), and uniform cooling of the hot-rolled steel sheet was not sufficiently performed. However, when the plate feeding speed is 550 m/min or more, the CT temperature changes. The momentum is reduced to below 25 ° C, and it is known that the uniform cooling of the hot rolled steel sheet has been performed. In addition, especially when the sheet feeding speed is 600 m/min or more, the CT temperature is lowered to less than 10 ° C (8 ° C, 6 ° C), so that this condition is more suitable for achieving uniform cooling of the hot rolled steel sheet.

(Second embodiment)

The hot-rolled steel sheet having a medium thickness of 2.5 mm, a width of 1200 mm, a tensile strength of 800 MPa, and a slope of 2% has been subjected to inter-rolling cooling to reduce the outlet side temperature of the finish rolling to 880 ° C, and the cooling device is changed. The board is cooled in speed. Specifically, the sheet feeding speed is changed to 400 m/min, 450 m/min, 500 m/min, 550 m/min, 600 m/min, and 650 m/min, and each of the cooling of the hot-rolled steel sheets at various sheet feeding speeds is performed. 20 times.

Next, the temperature of the hot-rolled steel sheet at the time of coiling was measured, and the average value (CT temperature fluctuation amount) of the standard deviation of the temperature fluctuation was calculated using the temperature measurement result. The results of the evaluation of the CT temperature fluctuation amount calculated above are shown in Table 4 below. Further, the evaluation criteria were the same as in the above-described first embodiment, and cooling between the rolling stands was not performed only at the sheet feeding speed of 400 m/min.

As shown in Table 6, when the sheet feeding speed is 500 m/min or less, the CT temperature fluctuation amount is not sufficiently reduced even if the inter-rolling table cooling is performed (higher than 25 ° C), while the uniform cooling of the hot rolled steel sheet was not carried out. Further, when the sheet feeding speed was 550 m/min or more, the amount of change in the CT temperature was lowered to 25 ° C or less, and it was found that the uniform cooling of the hot-rolled steel sheet was performed.

Further, after cooling between the rolling stands (that is, as shown in Table 6), the hot-rolled steel sheet having a high hardness (tensile strength of 800 MPa) can also reduce the amount of variation in CT temperature. In other words, it is understood that the hot plate rolling speed at the time of cooling of the hot-rolled steel sheet is 550 m/min or more, and rolling between the rolling mills in the finishing mill is performed, so that all the steel materials, particularly those having a high hardness, can be uniformly cooled.

Industrial availability

The present invention is applicable to the hot rolling of a finishing mill and the formation of a hot rolled steel sheet having a waveform whose surface height fluctuates in the rolling direction.

Claims (17)

A method for cooling a hot-rolled steel sheet, wherein a hot-rolled steel sheet which has been hot-rolled by a finishing mill is cooled in a cooling section provided on a feeding path thereof, comprising the following steps: a target ratio setting step based on preliminary experimentally The thermal conductivity ratio X above the ratio of the thermal conductivity of the upper and lower sides of the hot-rolled steel sheet and the cooling of the hot-rolled steel sheet are obtained in advance, under the condition that the inclination of the hot-rolled steel sheet and the sheet feeding speed are constant. The correlation data of the temperature standard deviation Y in the middle or after cooling, and the thermal conductivity coefficient ratio X1 above the minimum temperature Ymin is set as the target ratio Xt; and the cooling control step controls the cooling interval At least one of the upper surface of the hot-rolled steel sheet and the heat-dissipating heat and the heat-removing heat is cooled so that the thermal conductivity ratio X of the hot-rolled steel sheet in the cooling zone is equal to the target ratio Xt. The method for cooling a hot-rolled steel sheet according to claim 1, wherein in the foregoing target ratio setting step, the temperature standard deviation Y is controlled to a minimum value Ymin to a minimum value Ymin+10°C based on the aforementioned related information. The thermal conductivity ratio X above and below the range is set to the aforementioned target ratio Xt. The method for cooling a hot-rolled steel sheet according to claim 1 or 2, wherein the related information is separately prepared for a plurality of conditions in which the values of the inclination and the plate feeding speed are different, In the target ratio setting step, the target ratio Xt is set based on the correlation data corresponding to the measured value of the inclination and the plate feeding speed in the correlation data of the plurality of numbers. The method for cooling a hot-rolled steel sheet according to item 3 of the patent application, wherein the aforementioned related data is a data showing a correlation between the upper and lower thermal conductivity ratio X and the temperature standard deviation Y by a regression formula. For example, in the hot-rolled steel sheet cooling method of claim 4, the foregoing regression formula is derived by linear regression. The method for cooling a hot-rolled steel sheet according to item 3 of the patent application, wherein the related information is a table showing data on the correlation between the upper and lower thermal conductivity ratios X and the temperature standard deviation Y. The hot-rolled steel sheet cooling method according to claim 1 or 2, further comprising the step of: measuring a temperature of the hot-rolled steel sheet on a downstream side of the cooling section in a time series according to a time series; and calculating a temperature average value And calculating a time-series average value of the temperature based on the measurement result of the temperature; and a cooling and heat removal adjustment step of adjusting a total value of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet in the cooling section, The time series average of the aforementioned temperatures is made to coincide with the predetermined target temperature. The hot-rolled steel sheet cooling method according to claim 1 or 2, further comprising the steps of: measuring a temperature, and measuring the cooling interval according to a time series a temperature of the hot-rolled steel sheet on the downstream side; a fluctuation speed measuring step of measuring a vertical direction of the hot-rolled steel sheet at a portion of the same portion as a temperature-measuring portion of the hot-rolled steel sheet on the downstream side of the cooling section in a time series a speed; a control direction determining step, wherein a temperature of the hot-rolled steel sheet is 1 cycle with respect to a waveform of the hot-rolled steel sheet in a field in which the fluctuation speed is a positive value when a positive value is above a vertical direction of the hot-rolled steel sheet When the average temperature of the above range is low, at least one of the direction in which the cooling and heat removal is reduced and the direction in which the cooling and heat removal in the lower surface are increased is determined as the control direction, and the temperature of the hot-rolled steel sheet is relative to the average temperature. When it is high, at least one of the direction in which the above-described cooling and heat removal is increased and the direction in which the cooling and heat removal is reduced is determined as the control direction, and in the field where the fluctuation speed is a negative value, in the hot-rolled steel sheet. When the temperature is lower than the average temperature, the direction of the above cooling and heat removal is increased and the front At least one of the directions of cooling and heat removal reduction is determined as the control direction, and when the temperature of the hot-rolled steel sheet is higher than the average temperature, the direction of the above-described cooling and heat removal is reduced and the heat is removed by the lower surface. At least one of the increasing directions is determined as the control direction; and the cooling and heat removal adjusting step adjusts the aforementioned upper cooling heat removal amount of the hot-rolled steel sheet in the cooling interval based on the control direction determined in the control direction determining step And at least one of the foregoing cooling and heat removal. A method for cooling a hot rolled steel sheet according to item 8 of the patent application, wherein the aforementioned The cooling zone is divided into a plurality of divided cooling sections along the sheet feeding direction of the hot-rolled steel sheet, and in the temperature measuring step and the fluctuation speed measuring step, the hot-rolled steel sheet is individually measured in time series with respect to the boundary of the divided cooling section. The temperature and the fluctuation speed, in the control direction determining step, the measurement result of the temperature and the fluctuation speed of the hot-rolled steel sheet which are individual on the boundary between the divided cooling sections, and the above-mentioned divided cooling section is individually determined on the hot-rolled steel sheet In the cooling and heat removal adjustment step, the cooling and heat removal adjustment step performs feedback control or feedforward control based on the control direction that has been determined for each of the divided cooling sections, and individually adjusts the aforementioned divided cooling sections. At least one of the above-described upper cooling heat removal heat and the lower cooling heat removal heat of the hot-rolled steel sheet. The method for cooling a hot-rolled steel sheet according to claim 9 further comprises the steps of: measuring the aforementioned inclination of the hot-rolled steel sheet or the feeding speed of the hot-rolled steel sheet at a boundary of the divided cooling section; and cooling and removing heat The correction step corrects at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet in the divided cooling section based on the measurement result of the inclination or the sheet feeding speed. The hot-rolled steel sheet cooling method according to claim 1 or 2, further comprising a post-cooling step, which is on the downstream side of the cooling section and then cooled The hot-rolled steel sheet is described such that the temperature standard deviation of the hot-rolled steel sheet is within an allowable range. The hot-rolled steel sheet cooling method according to claim 1 or 2, wherein the sheet feeding speed of the hot-rolled steel sheet in the cooling section is set to be in a range from 550 m/min or more to a mechanical limit speed. The hot-rolled steel sheet cooling method according to claim 12, wherein the hot-rolled steel sheet has a tensile strength of 800 MPa or more. The hot-rolled steel sheet cooling method according to claim 12, wherein the finishing mill is composed of a plurality of rolling stations, and the method further comprises an auxiliary cooling step of performing the aforementioned hot rolling between the plurality of rolling stations. Auxiliary cooling of the steel plate. The hot-rolled steel sheet cooling method according to claim 1 or 2, wherein the cooling section is provided with a plurality of header upper side cooling means capable of injecting cooling water onto the hot-rolled steel sheet, and having a hot rolling direction A lower header cooling device that sprays cooling water under the steel plate, and the above-described upper cooling and heat removal and the lower cooling and heat removal can be adjusted by opening and closing the respective headers. The hot-rolled steel sheet cooling method according to the first or second aspect of the invention, wherein the cooling section is provided with a plurality of header upper side cooling means capable of injecting cooling water onto the hot-rolled steel sheet, and having a heat toward the foregoing The lower side cooling device of the plurality of headers for injecting the cooling water under the rolled steel plate, the above-mentioned upper cooling and heat removal and the lower cooling and heat removal can be adjusted by controlling at least one of the water density, the pressure and the water temperature of the respective headers. The method for cooling a hot-rolled steel sheet according to claim 1 or 2, wherein the cooling in the cooling section is performed in a range in which the temperature of the hot-rolled steel sheet is 600 ° C or more.