JP2003293030A - Steel sheet cooling method - Google Patents

Abstract

(57) [Problem] To provide a cooling method for manufacturing a steel sheet having excellent flatness without a shape defect such as warpage or bending when a steel sheet is controlled and cooled. SOLUTION: While the hot-rolled high-temperature steel sheet has nozzles above and below, the nozzle is conveyed in a cooling device provided with a plurality of cooling zones in the steel sheet advancing direction in which the cooling water amount of the nozzle can be controlled. In the cooling method of cooling the steel sheet by supplying more cooling water, based on the difference between the predicted temperature and the actual temperature of the surface temperature of the rolled steel sheet after the completion of rolling, the water ratio of the cooling zone of the cooling device is set. At the same time, the temperature of the upper and lower surfaces of the steel plate is measured on the entrance side of each cooling zone, and the correction of the water / water ratio in the cooling zone based on the difference between the upper and lower surfaces is sequentially performed for each cooling zone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cooling a hot-rolled steel sheet, and more specifically, it has a plurality of cooling zones having upper and lower nozzles and in which the water injection amount of the nozzles can be controlled in the traveling direction of the steel sheet. While transporting inside the equipped cooling device,
The present invention relates to a method for cooling a steel sheet by supplying cooling water from this nozzle.

[0002]

2. Description of the Related Art A process for continuously cooling a hot steel sheet after hot rolling online to produce a thick steel sheet having high strength and high toughness is widely used. In this manufacturing process,
Since the structure of steel can be controlled by continuous cooling, it is possible to reduce the alloying elements added and to omit the heat treatment process.
Greatly reduces manufacturing costs. In addition, the reduction of alloying elements contributes to a great improvement in welding work efficiency by improving weldability, reducing the amount of preheating, and enabling the application of high heat input welding.

For this cooling, there are many processes in which the cooling water is sprayed onto the upper and lower surfaces of the steel sheet while being conveyed into a cooling device having water cooling nozzles on the upper and lower surfaces of the steel sheet. It is used. However, since cooling water stays on the upper surface of the steel sheet, the cooling behavior on the upper surface and the lower surface is different. Therefore, if the same amount of cooling water is supplied up and down, the cooling capacity of the upper surface becomes larger than that of the lower surface, and asymmetrical temperature distribution occurs on the upper and lower surfaces after completion of cooling, causing the steel plate to warp or bend due to thermal stress. It is deformed, resulting in defective shape.

In order to prevent the occurrence of the defective shape, the lower water amount, that is, the cooling water amount supplied from the lower surface side of the steel plate is taken into consideration in consideration of the cooling ability of the cooling water staying on the upper surface, that is, the water on the plate. , The upper / lower water amount, that is, the cooling water amount supplied from the upper surface side of the steel plate, is set to a lower / upper water amount ratio. This water-to-water ratio is set by empirically finding a value that provides good flatness for each steel plate size, steel plate temperature, and cooling conditions such as the amount of cooling water and the cooling stop temperature.

For example, Japanese Unexamined Patent Publication (Kokai) No. 63-105917 discloses a method for cooling a hot-rolled steel sheet, which is caused by a difference in surface temperature between the upper surface side and the lower surface side of the steel sheet. To prevent this, immediately before cooling, measure the steel plate surface temperature on the upper surface side and the steel plate surface temperature on the lower surface side, and consider the temperature difference and correct the preset upper surface side cooling water flow rate and lower surface side cooling water flow rate. Then, the method of cooling a steel plate is disclosed.

[0006] This method corrects the amount of cooling water so as to absorb the temperature difference between the upper and lower surfaces of the steel sheet before cooling.
For that purpose, it is necessary to accurately predict not only the surface temperature of the upper and lower surfaces of the steel sheet but also the cooling ability of the upper and lower surfaces. This is because if the cooling capacity is different, the amount of temperature drop will be different even if the cooling water amount and the cooling time are the same. However, the cooling capacity of a steel sheet is greatly influenced by its scale properties and surface roughness, etc., and is affected by the operating conditions of the heating process and rolling process, which are the pre-processes of controlled cooling, and varies from sheet to sheet. However, it is very difficult to accurately predict the cooling capacity in the pre-control cooling stage without actually cooling. Therefore, it is difficult to stably reduce the defective shape only by detecting the temperature difference between the upper and lower surfaces of the steel sheet and controlling the cooling water amount immediately before the controlled cooling.

Further, the difference between the prediction and the actual results of the steel sheet temperature at the time of rolling completion has a great influence on the shape after cooling. If this temperature error is not taken into consideration, the correction amount such as the cooling water amount during cooling becomes large and the accuracy is improved. The temperature difference cannot be reduced well.

[0008]

The injection of cooling water in the cooling device is started before the completion of rolling of the steel sheet for the purpose of stabilizing the amount of supplied water. Therefore, the sewage ratio at this time is preset based on the cooling conditions such as the size of the steel plate to be cooled, the steel plate temperature at the end of rolling, the cooling water amount, and the cooling stop temperature.

However, as described above, the steel plate before (control) cooling is affected by the operation of the previous process such as heating and rolling, and even if the steel plate has the same size, the steel plate temperature and scale properties at the time of completion of rolling, The surface roughness is often different from one to another. It is difficult to reduce the temperature difference between the upper and lower surfaces of the steel sheet after the controlled cooling by cooling such a steel sheet with the preset ratio of water flow rate.

According to the present invention, when the thick steel plate is controlled and cooled, the temperature difference between the upper and lower surfaces of the steel plate after cooling is reduced, so that the thick steel plate having no flatness such as warpage and bending and excellent flatness is manufactured. An object of the present invention is to provide a cooling method for this.

[0011]

The present invention has been made to solve the above-mentioned problems, and the gist thereof is as follows. (1) While carrying a hot-rolled high-temperature steel plate through a cooling device having nozzles at the top and bottom and a plurality of cooling zones in which the water injection amount of the nozzles is controllable in the steel plate advancing direction, In a cooling method of supplying cooling water to cool the steel sheet, based on the difference between the predicted temperature and the actual temperature of the surface temperature of the rolled steel sheet after rolling is completed, while setting the water quantity ratio of the cooling zone of the cooling device. Further, the upper and lower surface temperature of the steel sheet is further measured on the inlet side of each cooling zone, and the upper and lower surface temperature of the cooling zone is corrected based on the difference between the upper and lower surface temperatures of the cooling zone. Characteristic steel plate cooling method. (2) The method of cooling a steel sheet according to (1), characterized in that the hot-rolled steel sheet is divided into a plurality of cooling regions in the longitudinal direction, and the ratio of up-and-down water amount of the cooling device is corrected for each divided region. .

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the structure of an example of a cooling device for carrying out the cooling method of the present invention, as will be described in detail later.

The cooling device 2 is provided with a plurality of cooling zones C. Each cooling zone has an upper cooling nozzle 3 and an upper flow rate control valve 5 for controlling the amount of cooling water to the cooling nozzle, and a lower cooling zone. A lower flow rate adjusting valve 6 for adjusting the amount of cooling water to the nozzle 4 and the cooling nozzle is provided.

On the front surface of the rolling mill 1, a rolling completion temperature measuring thermometer 7 for measuring the surface temperature of the steel sheet when rolling is completed.
However, on the inlet side of each cooling zone C of the cooling device, a cooling zone inlet side upper surface thermometer 8 for measuring the upper surface temperature of the steel sheet and a cooling zone inlet side lower surface thermometer 9 for measuring the lower surface temperature of the steel sheet are provided. ing.

Further, an initialization calculator 10 for initially setting cooling conditions, a flow rate correction calculator 11 for calculating a correction amount of the cooling water amount based on the measurement result of the steel plate temperature from the thermometer, and each cooling A flow rate control device 12 is provided to control the flow rate of cooling water in the nozzles of the zone.

In the present invention, the sewage ratio is adjusted by the following two steps.

The sewage ratio is lower water density / upper water density, and the sewage ratio may be corrected by correcting the upper and / or lower water density, but from the viewpoint of control efficiency, It is desirable to fix the water quantity density as a reference and correct the upper water quantity density to correct the ratio of upper and lower water quantity.

Therefore, in the following description, the upper and lower water quantity ratios are corrected by correcting the upper water quantity density.

<Step 1: Correction of water / water ratio based on difference between prediction and actual result of steel plate surface temperature after completion of rolling> This correction is based on the temperature measurement result of the steel plate at the time of completion of rolling.
This is done for all cooling zones.

The upper / lower cooling water amount ratio before the completion of rolling is preset based on the cooling conditions such as the size of the steel plate to be cooled, the rolling completion temperature of the steel plate, the cooling water amount, and the cooling stop temperature. However, if the steel plate temperature at the completion of rolling is different from the predicted temperature, the cooling stop temperature in the subsequent cooling will also differ from the prediction.Therefore, in order to hit the cooling stop temperature, correct the steel plate transport speed in the cooling device. However, it becomes necessary to adjust the cooling time. However, if the setting of the transport speed is changed, the cooling capacity of the plate water on the upper surface of the steel plate changes, so it is necessary to correct the water and water ratio in consideration of the change margin.

For example, when the actual rolling completion temperature becomes lower than the predicted rolling completion temperature, the cooling start temperature also becomes lower than the predicted temperature. Therefore, in order to hit the target cooling stop temperature, the steel plate in the cooling device is set. It is necessary to speed up the transportation and shorten the cooling time. However, when the steel sheet is conveyed at a high speed, the cooling capacity of the water on the sheet becomes small. Therefore, it is necessary to reduce the ratio of sewage water and increase the amount of water injected to the upper surface of the steel sheet.

Where T _{A is the} actual rolling completion temperature (° C.),
T _P : Assuming the rolling completion predicted temperature (° C.), since T _P > T _A (1), 1−T _A / T _P > 0 (2). Therefore, by multiplying the coefficient on the left-hand side of equation (2), if Q '= (1+ (1- T A / T P) × k 1) × Qsetup (3), with respect to water density set, T Water density can be increased by using _A and T _P.

However, Q ': the upper water quantity density (m ³ /
(M ² · min)) Qsetup: upper water density (m ³ / (m ²
· Min)) k _1: a top cooling water density correction coefficient in step 1. Here, k ₁ can be set by simulation or analysis of operation results.

[0024] Similarly, even if the T _A is higher than T _P, (3) to the upper water density is set by using the equation, T _A, to reduce the water density with T _P pressure You can

As described above, in the step 1 of the method of the present invention, the setting of the ratio of the cooling water amount to the water amount is corrected based on the difference between the actual results and the prediction of the steel sheet temperature at the time of completion of rolling, so that the step 2 will be described later. It is possible to reduce the correction amount of the water amount density in.

<Step 2: Correction of upper and lower water temperature ratio of steel plate on the inlet side of each cooling zone based on the temperature difference between steel plates> This correction is performed by measuring the temperature difference between the steel plate upper and lower surfaces on the inlet side of each cooling zone. Based on the above, at least for the cooling zone where the steel sheet enters immediately after the measurement. In step 1 alone, the steel sheet is cooled without considering the temperature difference between the upper and lower surfaces, so that the temperature difference between the upper and lower surfaces similarly occurs after the cooling is completed.
In order to eliminate this, the temperature difference between the upper and lower surfaces of the steel sheet is measured on the inlet side of each cooling zone, and the water / water ratio is corrected based on the temperature difference.

For example, if the upper surface temperature at the start of cooling is kept higher than the lower surface temperature, if the upper surface is not cooled more than the lower surface, the cooling is completed with the upper surface temperature higher than the lower surface temperature. The steel sheet is deformed due to the temperature difference between the upper and lower surfaces. In this case, in order to reduce the temperature difference between the upper and lower surfaces at the end of cooling, it is necessary to reduce the ratio of the amount of water supplied to the upper surface and the amount of water supplied to the upper surface of the steel sheet. Where ΔT _n : nth
If the temperature difference between the upper and lower surfaces on the inlet side of the cooling zone (upper surface temperature-lower surface temperature) (° C.) is ΔT _n > 0 (4), then Q _n = (1 + ΔT _n / k _n ) × Q setup (5 ), The upper water density already corrected in step 1:
With respect to S × Qsetup, ΔT _n can be used to increase the water density.

However, Q _n : upper water density of the nth cooling zone after correction (m ³ /
(M ² · min)) k _n : correction coefficient S for upper water quantity density in the nth cooling zone in step 2 S: correction coefficient for upper and lower water quantity in step 1 (= (1+ (1
−T _A / T _P ) × k ₁ )). Here, k _n can be set by analyzing the simulation or operation results.

Similarly, even when the upper surface temperature becomes lower than the lower surface temperature, by using the equation (5), the water content density can be reduced by using ΔT _n with respect to the set upper water content density.

In step 2, the temperature difference between the upper and lower surfaces is directly reflected in the ratio of the amount of water in the upper and lower surfaces based on the measurement result of the temperature difference between the upper and lower surfaces, so that the effect of reducing the temperature difference between the upper and lower surfaces is higher than that in step 1. In particular, after the second cooling zone in step 2, the water / water ratio will be controlled based on the temperature difference between the upper and lower surfaces during cooling,
Since the control can be performed in consideration of the factors such as the steel plate surface scale and the roughness that become the disturbance of the steel plate cooling ability, a high temperature difference reduction effect can be obtained.

In the above cooling control, the density of the vertical water in the cooling device was adjusted based on the upper and lower surface temperatures of the front surface (front portion) of the steel sheet. However, since the steel sheet is cooled while being conveyed in the longitudinal direction, the air cooling time until the start of cooling differs between the front surface portion (front portion) and the rear surface portion (tail portion) of the steel sheet, and as a result, cooling start The temperature of time will also be different. Therefore, particularly when the temperature difference in the longitudinal direction of the steel sheet is large, for example, in a steel sheet having a long rolling length, a steel sheet having a relatively thin sheet thickness, etc., the cooling region of the steel sheet is divided into a plurality of blocks in the longitudinal direction, It is preferable to perform the cooling control of step 1 and step 2 for each block. FIG. 2 is a diagram showing an example in which the cooling region of the steel sheet P is divided and cooling control is performed for each block in the cooling method of the present invention, as will be described later. As a result, even in a steel sheet having a large temperature difference in the longitudinal direction, it is possible to accurately reduce the temperature difference between the upper and lower surfaces and prevent the occurrence of shape defects.

The present invention will be described in detail below with reference to specific examples.

FIG. 1 is a schematic view showing one structural example of a cooling device for carrying out the cooling method of the present invention.

The steel sheet P finish-rolled by the rolling mill 1 is
It is cooled by the control cooling device 2. In the cooling device 2,
From the inlet side of the controlled cooling device, the cooling zone C (C₁, C₂,
..Cn) are arranged, and each cooling zone has its own
Upper cooling nozzle 3 (3₁Three₂... 3_n) And this
Upper flow rate control valve 5 that controls the amount of cooling water to the cooling nozzle
(5₁5,₂・ ・ ・ 5_n) And the lower cooling nozzle 4
(4₁Four₂・ ・ ・ 4_n) And cooling to this cooling nozzle
Lower flow control valve 6 (6₁, 6₂・ ・ ・ 6
_n) Is provided.

On the front surface of the rolling mill, a thermometer 7 for measuring the rolling completion temperature for measuring the surface temperature of the steel sheet when the rolling is completed.
But the entry side of the cooling zone of the controlled cooling apparatus, the cooling zone entry side upper surface thermometer 8 (8 ₁ to measure the upper surface temperature of the steel sheet,
8 ₂ , ... 8 _n ) and a cooling zone entrance side lower surface thermometer 9 (9 ₁ , 9 ₂ , ... 9 _n ) for measuring the lower surface temperature of the steel sheet.

Further, an initialization calculator 10 for initially setting cooling conditions, a flow rate correction calculator 11 for calculating a correction amount of the cooling water amount based on the measurement result of the steel plate temperature from the thermometer, and an initialization calculation. A flow rate control device 12 for controlling the flow rate of the nozzles in each cooling zone is provided in accordance with commands from the cooling device and the flow rate correction calculator.

In the method for cooling a steel sheet according to the present invention, the ratio of the amount of water supplied to each cooling zone of the cooling device is determined based on the size of the steel sheet to be cooled, the temperature of the steel sheet after rolling, the water density, the cooling stop temperature, etc. It is preset by the setting calculator 10.

First, in step 1, after the rolling is completed by the rolling mill 1, the temperature of the steel sheet P is measured by the rolling completion temperature measuring thermometer 7. The steel plate temperature at this time is preferably an average temperature over the entire length of the steel plate P, but is not limited to this as long as it is a temperature representative of the entire steel plate. The measured steel plate temperature is sent to the flow rate correction calculator 11, and based on the difference between the actual value of the steel plate temperature and the preset steel plate predicted temperature, the calculator 11 calculates the flow rate correction value, and this is calculated. Through the flow rate adjusting device 12, a command is sent to the flow rate adjusting valves 5 _{1 to} 5n and / or 6 _{1 to} 6n in each cooling zone. This corrects the ratio of the amount of water supplied to the entire cooling zone.

The method of calculating the correction amount of the cooling water is as described above.

Next, FIG. 3 is a schematic diagram showing a control flow after step 2 in one specific example of the cooling method of the present invention. The details of the device configuration are the same as in FIG.

In step 2, as shown in FIG. 3A, when the steel sheet P enters the inlet side of the inlet side cooling zone (hereinafter referred to as the first cooling zone) C ₁ of the cooling device 2, the first side Measurement of the upper and lower surface temperatures of the steel sheet is started by the upper surface thermometer 8 ₁ and the lower surface thermometer 9 ₁ on the cooling zone entrance side provided on the entrance side of the cooling zone. The measured steel plate temperature is sent to the flow rate correction calculator 11, and the flow rate correction amount in the first cooling zone is calculated based on the upper and lower surface temperature difference of the steel plate temperature. Next, FIG. 3B
As shown in the flow amount of correction through flow control device 12, flow control valve of the first cooling zone C ₁ 5 ₁ and / or,
6 ₁ is commanded to change the amount of cooling water of the upper cooling nozzle 3 ₁ and / or the lower cooling nozzle 4 ₁ to correct the ratio of upper and lower water amounts and perform cooling. The method for calculating the correction amount of the cooling water is as described above.

Next, as shown in FIG. 3 (c), when the steel plate enters the entrance side of the second cooling zone C ₂ , the upper surface thermometer 8 ₂ provided on the entrance side of the second cooling zone and the bottom surface thermometer. The upper and lower surface temperatures are measured by 9 ₂ , and the measured steel plate temperature is sent to the flow rate correction calculator 11, and the flow rate correction amount in the second cooling zone C ₂ is calculated based on the upper and lower surface temperature difference of the steel plate temperature. It Next, as shown in FIG. 3D, the flow rate correction amount is commanded to the flow rate adjusting valves 5 ₂ and / or 6 ₂ in the second cooling zone C ₂ through the flow rate adjusting device 12, and the upper cooling nozzle 3 ₂ and / or the cooling water amount of the lower cooling nozzle 4 ₂ is changed to correct the ratio of upper and lower water amounts, and cooling is performed.

Thereafter, as shown in FIG. 3 (e) and thereafter, the upper surface thermometers 8 ₃ to 8 _n on the inlet side of each cooling zone C _{3 to} C _n are also the same as in the case of C ₂ . Bottom thermometer 9 ₃
The temperature of the upper and lower surfaces is measured when the steel plate reaches the entrance side of each cooling zone by ~ 9 _n , and the measured steel plate temperature is sent to the flow rate correction calculator 11 and based on the difference between the upper and lower surface temperatures of the steel plate. The flow rate correction amount of each cooling zone after the third cooling zone, that is, the cooling zone that enters after the measurement of the steel plate temperature is calculated. The flow rate correction amount is commanded through the flow rate adjusting device 12 to the flow rate adjusting valves 5 _{3 to} 5 _n and / or 6 _{3 to} 6 _n of the respective cooling zones C _{3 to} C _n , and the upper cooling nozzles 3 _{3 to} 3 _n.
And / or the cooling water amount of the lower cooling nozzles 4 ₃ to 4 _n is corrected to correct the ratio of upper and lower water amounts in each cooling zone to perform cooling. The method for calculating the correction amount of the cooling water is as described above.

As a result, it is possible to suppress the defective shape due to the temperature difference between the upper and lower surfaces at the end of cooling.

FIG. 4 illustrates an example in which the cooling method of the present invention is applied to a steel sheet having a large temperature difference in the longitudinal direction. The details of the device configuration are the same as in FIG. That is, as shown in FIG. 2, the cooling region of the steel plate P is divided into a plurality of blocks (first block P ₁ , second block P ₂ , third block P ₃ , ..., Nth block P _{n) in the} longitudinal direction. ) And, for each block, step 2 above.
Is applied.

The application of Step 1 is the same as in the above case, and after the rolling is completed by the rolling mill 1, the temperature of the steel sheet P is measured by the thermometer 7 for measuring the completion temperature of rolling.
The steel plate temperature at this time is preferably an average temperature over the entire length of the steel plate P, but is not limited to this as long as it is a temperature representative of the entire steel plate. The measured steel plate temperature is sent to the flow rate correction calculator 11, and based on the error between the actual value of this steel plate temperature and the preset steel plate temperature, this calculator 11
In the flow rate correction value calculated by the flow control device 12 so that each cooling zone of the flow control valve 5 ₁ to 5 _n and / or,
Send commands to 6 _{1 to} 6 _n .

Next, in step 2, as shown in FIG. 4A, the front surface block P ₁ of the steel plate P is
Inlet side cooling zone of the cooling device 2 (hereinafter referred to as the first cooling zone C
₁ ) when entering the inlet side, the upper and lower surfaces of the first block P ₁ are controlled by the cooling zone inlet side upper surface thermometer 8 ₁ and the lower surface thermometer 9 ₁ provided on the inlet side of the first cooling zone C ₁ of the cooling device. The temperature measurement is started, and the measured steel plate temperature is sent to the flow rate correction calculator 11. The flow rate correction calculator 11 calculates the flow rate correction amount in the first cooling zone C ₁ during cooling of the first block P ₁ based on the difference between the upper and lower surface temperatures of the steel plate. Next, as shown in (b) of FIG. 4, the first cooling zone C ₁ at the time of the first block P ₁ cooling
The flow rate correction amount is commanded to the flow rate adjusting valves 5 ₁ and / or 6 ₁ in the first cooling zone C ₁ through the flow rate adjusting device 12 to change the cooling water amount of the upper cooling nozzle 3 ₁ and / or the lower cooling nozzle 4 _1. By changing the ratio, the ratio of the amount of water supplied to the water is corrected, and the block P ₁ is cooled at C ₁ .

At this time, the second block P ₂ following the block P ₁ has entered the entrance side of the first cooling zone C ₁ .
Measurement of the upper and lower surface temperatures of P ₂ is started by the upper surface thermometer 8 ₁ and the lower surface thermometer 9 ₁ on the cooling zone entrance side provided on the entrance side of the first cooling zone C ₁ , and the measured steel plate temperature is corrected by the flow rate. Send to the arithmetic unit 11. In the flow rate correction calculator 11, the second block P
Based on the temperature difference between the upper and lower surfaces of ₂ , the flow rate correction amount of the first cooling zone C ₁ during the cooling of P ₂ is calculated.

Next, as shown in FIG. 4 (c), the block P ₁ has entered the entrance side of the second cooling zone C ₂ and the cooling zone entrance provided on the entrance side of the cooling zone C _2. Measurement of the upper and lower surface temperatures of the block P ₁ is started by the side upper surface thermometer 8 ₂ and the lower surface thermometer 9 ₂ , and the measured steel plate temperature is sent to the flow rate correction calculator 11. The flow rate correction calculator 11 calculates the flow rate correction amount of C ₂ when P _{1 is} cooled, based on the upper and lower surface temperature difference of the steel plate temperature of the block P ₁ .

Next, as shown in FIG. 4D, the flow rate correction amount of the first cooling zone C ₁ during the cooling of the block P ₂ calculated by the flow rate correction arithmetic unit 11 in FIG. 4B. through flow control device 12, flow control valve of C ₁ 5 ₁ and /
Alternatively, in response to 6 ₁ , the cooling water amount of the upper cooling nozzle 3 ₁ and / or the lower cooling nozzle 4 ₁ is changed to correct the ratio of the upper and lower water amounts of C ₁ to cool P ₂ . At this time, block P ₃
Has entered the inlet side of the first cooling zone C ₁ , and the upper and lower surface temperatures of P ₃ are measured by the inlet side upper surface thermometer 8 ₁ and the lower surface thermometer 9 ₁ provided on the inlet side of C _1. And sends the measured steel plate temperature to the flow rate correction calculator 11. The flow rate correction calculator 11 calculates the flow rate correction amount of C ₁ when cooling P ₃ based on the difference between the upper and lower surface temperatures of the steel plate.

Next, as shown in FIG. 4 (e), the block P ₁ is in the second cooling zone C ₂ and is calculated by the flow rate correction calculator 11 in FIG. 4 (c). P ₁
The C ₂ flow rate correction amount during cooling is commanded to the C ₂ flow rate adjusting valve 5 ₂ and / or 6 ₂ through the flow rate adjusting device 12,
The amount of cooling water of the upper cooling nozzle 3 ₂ and / or the lower cooling nozzle 4 ₂ is changed to correct the ratio of upper and lower water amounts of C ₂ to cool P ₁ .

Further, as shown in (f) of FIG. 4, the first block P ₁ has entered the cooling zone C _{3 on} the inlet side, and C
₃ of the cooling zone entry side upper surface thermometer 8 ₃ provided entry side, the lower surface thermometer 9 _3, to start the measurement of the upper and lower surfaces a temperature of P _1.

Thereafter, the same steps as described above are repeated for each block of the steel sheet and each cooling zone of the cooling device to cool the steel sheet.

In the above steps, the method for setting the correction amount of each water amount ratio is as described above. As a result, even in a steel sheet having a large temperature difference in the longitudinal direction, it is possible to accurately reduce the temperature difference between the upper and lower surfaces and prevent the occurrence of shape defects.

[0055]

EXAMPLE 1 As shown in FIG. 1, a cooling device having nozzles arranged at the top and bottom and having five cooling zones capable of controlling the water injection amount of the nozzles was used, and the size was 20 mm × 4000 mm × 20.
Cooling was performed while transporting a 000 mm thick steel plate. The cooling stop temperature was 500 ° C. When cooling,
Cooled by applying the cooling method of the present invention and, for comparison, cooled by two methods of cooling without modifying the initially set cooling conditions, and the amount of shape deformation after cooling was measured. .

The predicted rolling completion temperature was 820 ° C., but the actual rolling completion temperature was 800 ° C. In the method of the present invention, based on the difference between the predicted temperature and the actual temperature, step 1 is corrected for all cooling zones, and then step 2 is corrected for each cooling zone to complete the cooling. The correction was controlled by setting the entire steel plate as one block.

On the other hand, in the comparative example, the cooling was completed without modifying the initially set initial value. Table 1 shows the measurement results of the water / sewage ratio in the correction (step 1) for all cooling zones after completion of rolling, the water / sewage ratio in the correction (step 2) for each cooling zone during cooling, and the variable measurement after cooling. Shown in 1.

[0058]

[Table 1]

As shown in Table 1, in the conventional cooling method,
While 120 mm of deformation was generated after the completion of cooling, when the method of the present invention was applied for cooling, a steel plate having an extremely good shape with no deformation was obtained. Example 2 The same cooling device as in Example 1 was used, and the size was 20 mm ×
Cooling was performed while transporting a thick steel plate of 4000 mm × 45000 mm. The cooling stop temperature was 500 ° C. Incidentally, in cooling, cooling was performed by applying the cooling method of the present invention, and for comparison, cooling was performed by two methods, namely, cooling without modifying the initially set cooling conditions, and after cooling, The amount of shape deformation was measured.

The predicted rolling completion temperature was 820 ° C., but the actual rolling completion temperature was 800 ° C. In the method of the present invention, based on the difference between the predicted temperature and the actual temperature, step 1 is corrected for all cooling zones, and then the cooling area of the steel plate is set to 3 blocks with one block having a length of 15000 mm. It was divided into equal parts, and the correction of step 2 was carried out for each block and each zone to complete the cooling.

On the other hand, in the comparative example, the cooling was completed without modifying the initially set initial value. Table 2 shows the ratio of water and sewage in the correction (step 1) to all cooling zones after the completion of rolling, each block during cooling, the ratio of water and sewage in the correction (step 2) for each cooling zone, and the variable measurement after cooling. The measurement results are shown in Table 2. The temperature difference between the upper and lower surfaces of each block on the inlet side of the first cooling zone C ₁ was 15 ° C. for the first block P ₁ , 20 ° C. for the second block P ₂ , and 25 ° C. for the third block P ₃ . .

[0062]

[Table 2]

As shown in Table 2, in the conventional cooling method,
While the deformation of 150 mm was generated after the completion of cooling, when the method of the present invention was applied for cooling, a steel plate having an extremely good shape with no deformation was obtained.

[0064]

According to the method of the present invention, when the thick steel plate is controlled and cooled, it is possible to obtain a thick steel plate having no shape defect such as warpage and bending, and it is possible to reduce the cost of straightening.
It is possible to stably manufacture a steel sheet having no variation in material.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of a cooling device for carrying out a cooling method of the present invention.

FIG. 2 is a diagram showing an example in which a cooling area of a steel sheet is divided and controlled in the cooling method of the present invention.

FIG. 3 is a diagram showing a cooling control flow in one embodiment of the cooling method of the present invention.

FIG. 4 is a diagram showing a cooling control flow in another embodiment of the cooling method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Rolling mill 2 ... Cooling device 3, 3 ₁ , 3 _{2 to} 3 _n ... Upper cooling nozzle 4, 4 ₁ , 4 ₂ to 4 _n ... Lower cooling nozzle 5, 5 ₁ , 5 _{2 to} 5 _n ... Upper flow rate adjustment Valves 6, 6 ₁ , 6 _{2 to} 6 _n ... Lower flow rate adjusting valve 7 ... Rolling completion temperature measuring thermometers 8, 8 ₁ , 8 ₂ to 8 _n ... Cooling zone inlet side upper surface thermometers 9, 9 ₁ , 9 ₂ to 9 _n ... cooling zone entry side lower surface thermometer 10 ... initialization calculator 11 ... flow modification calculator 12 ... flow control device _{C, C 1, C 2 ~Cn} ... cooling zone _{P, P 1, P 2 ~P} n …steel sheet

Continued front page    (72) Inventor Sudo             No. 1 Nishinosu, Oita City, Oita Prefecture Made in New Japan             Oita Steel Works, Ltd. F-term (reference) 4K034 AA02 BA05 CA01 DA06 DB03                       FA05 FB01                 4K043 AA01 BA03 CB04 EA02 FA03                       FA13 GA10

Claims (2)

[Claims] 1. A hot-rolled high-temperature steel plate is conveyed in a cooling device having nozzles at the top and bottom and a plurality of cooling zones in which the water injection amount of the nozzles is controllable in the steel plate advancing direction, In a cooling method of supplying cooling water from a nozzle to cool a steel sheet, based on the difference between the predicted temperature and the actual temperature of the surface temperature of the rolled steel sheet after rolling is completed, the water supply / sewer ratio of the cooling zone of the cooling device is set. In addition, the upper and lower surface temperatures of the steel sheet are further measured on the inlet side of each cooling zone, and the upper and lower surface temperature ratios of the cooling zones are corrected based on the difference between the upper and lower surface temperatures, which are sequentially performed for each cooling zone. A method for cooling a steel sheet, which is characterized in that 2. The steel sheet according to claim 1, wherein the hot-rolled steel sheet is divided into a plurality of cooling regions in the longitudinal direction, and the water-to-water ratio of the cooling device is corrected for each divided region. Cooling method.