JP2017170488A - Method and apparatus for cooling thick steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cooling a thick steel plate, in which occurrence of warpage due to thermal stress is sufficiently suppressed so that post-cooling quality is adequately improved.SOLUTION: There is provided a method for cooling a thick steel plate of the present invention in which a thick steel plate after hot rolling is cooled by a cooling apparatus, that includes the steps of: including at least one cooling zone in the cooling apparatus along a conveyance direction, and extracting a point which is positioned above a thickness direction center and at which a distance to the thickness direction center is the largest, and a point which is positioned below the thickness direction center and at which a distance to the thickness direction center is the largest, among multiple points in the thickness direction of the thick steel plate at which a standard deviation ratio relative to an average cooling rate in the cooling zone is a prescribed threshold or less; forming a pair of determination points obtained by combining a point at which the distance to the thickness direction center is shorter out of the extracted pair of points with a point that is symmetrical to this point and to the thickness direction center; and adjusting an upper and lower water amount ratio so that a temperature difference of a pair of determination points is a prescribed value or less at a final point of the cooling zone.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a thick steel plate cooling method and a thick steel plate cooling device.

  In the manufacture of thick steel plates, the hot-rolled thick steel plates may be rapidly cooled with cooling water in order to obtain a quenching effect or the like. As a device for performing such processing, a thick steel plate cooling device configured to spray cooling water from a cooling device onto a transported thick steel plate is known.

  However, when the cooling water is sprayed on the thick steel plate by this thick steel plate cooling device, an asymmetric temperature distribution is easily generated in the vertical direction with respect to the thickness direction center of the thick steel plate. As a result, the thick steel plate may be warped due to thermal stress, and a satisfactory plate shape may not be obtained.

  In view of such circumstances, a “cooling control method, a cooling control device, and a cooling water amount calculation device” (see JP 2007-190597 A) has been proposed today. The cooling control method described in the above publication is based on the temperature in the scheduled cooling schedule that defines the conditions for cooling the thick steel plate to a predetermined temperature, and the heat transfer coefficient from the first cooling water density in the cooling water that cools one side of the thick steel plate. The amount of water sprayed on the upper and lower surfaces of the thick steel plate is defined based on this heat transfer coefficient. According to this cooling control method, the shape deterioration of the thick steel plate due to the difference in the cooling rate between the upper and lower surfaces can be suppressed. It is said that.

  However, the cooling control method described in this publication determines the amount of water sprayed on the upper and lower surfaces based on the heat transfer coefficient obtained from the first cooling water density in the cooling water for cooling one side of the steel plate, The asymmetry of the temperature distribution in is not fully considered. Therefore, this cooling control method may not be able to sufficiently suppress warpage of the steel sheet due to thermal stress.

JP 2007-190597 A

  The present invention has been made in view of such circumstances, and the steel plate cooling capable of sufficiently suppressing the occurrence of warpage of the steel plate due to thermal stress and sufficiently improving the quality of the steel plate after cooling. An object is to provide a method and a steel plate cooling device.

  This invention made in order to solve the said subject is a thick steel plate cooling method which cools the thick steel plate after hot rolling using the cooling device provided in the conveyance direction of the thick steel plate after hot rolling, A cooling device having at least one cooling zone along the conveying direction, a step of measuring the temperature of the upper and lower surfaces of the thick steel plate that is put into the cooling device, the measurement temperature measured in the measurement step, and the cooling Based on the water density distribution in the zone, the width of the thick steel plate, the transport speed of the thick steel plate and the heat transfer coefficient set using the correction coefficient, the cooling zone at a plurality of points in the thickness direction of the thick steel plate A step of predicting a temperature for every time from the start to the end of cooling, a step of calculating an average cooling rate from the start to the end of cooling in the cooling zone at the plurality of points, and a time for each time of the cooling zone The step of calculating the cooling rate at multiple points and calculating the standard deviation of the cooling rate for each time, and the thickness of the thick steel plate in which the ratio of the standard deviation to the average cooling rate in the cooling zone is a predetermined threshold or less Among the plurality of points in the direction, it is located above the center in the thickness direction, the point where the distance from the center in the thickness direction is the maximum, and located below the center in the thickness direction, A step of extracting the point having the maximum distance, a point having a shorter distance from the center in the thickness direction of the pair of points extracted in the extraction step, and a point symmetrical to the center in the thickness direction. And a step of adjusting the water / water ratio so that the temperature difference between the pair of determination points is equal to or less than a predetermined value at the end point of the cooling zone.

  In general, in the cooling zone, the ratio of the standard deviation of the cooling rate per hour of the plurality of points to the average cooling rate of the plurality of points in the thickness direction of the thick steel plate increases as the distance from the center in the thickness direction increases. There is a tendency. Further, these ratios are different in the vertical direction with respect to the center in the thickness direction. In this regard, the method of manufacturing the thick steel plate is more than the center in the thickness direction among the plurality of points in the thickness direction of the thick steel plate in which the ratio of the standard deviation to the average cooling rate is equal to or less than a predetermined threshold in the cooling zone. The point that is located above and has the maximum distance from the center in the thickness direction, and the point that is located below the center in the thickness direction and has the maximum distance from the center in the thickness direction are extracted and extracted. A point having a shorter distance from the center in the thickness direction of the pair of points and a point symmetric with respect to the center in the thickness direction are defined as a pair of determination points, and a temperature difference between the pair of determination points is a predetermined value or less. Adjust the water and water ratio so that Therefore, the manufacturing method of the thick steel plate can maintain the cooling rate of the portion existing between the pair of determination points in the thickness direction substantially evenly, and the portion positioned on the outer side in the thickness direction than the pair of determination points. The vertical symmetry of the cooling rate can be promoted. Therefore, the manufacturing method of the said thick steel plate can fully suppress generation | occurrence | production of the warp of the thick steel plate by a thermal stress, and can fully improve the quality of the thick steel plate after cooling.

  The steel plate cooling method may further include a step of determining a water / water ratio when the temperature difference between the pair of determination points is equal to or less than the predetermined value. Thus, by further providing a step of determining the water / water ratio when the temperature difference between the pair of determination points is equal to or less than the predetermined value, occurrence of warpage is sufficiently suppressed, and the thickness is sufficiently high. A steel plate can be manufactured easily and reliably.

  The thick steel plate cooling device of the present invention made to solve the above-described problems is a transport device for transporting a thick steel plate, at least one cooling zone provided in the transport direction of the thick steel plate, and upstream of the cooling zone. A temperature measuring device for measuring the temperature of the upper and lower surfaces of the thick steel plate, and a control device for adjusting a water / water ratio in the cooling zone based on a measurement result of the temperature measuring device, wherein the control device is the temperature measuring device. The thickness of the thick steel plate based on the measured temperature measured by the water temperature density distribution in the cooling zone, the width of the thick steel plate, the transport speed of the thick steel plate and the heat transfer coefficient set using the correction coefficient A control element that predicts the temperature for each time from the start to the end of cooling in the cooling zone at a plurality of points in the direction; A control element for calculating the cooling rate, a control element for calculating the cooling rate at the plurality of points for each time of the cooling zone, and calculating a standard deviation of the cooling rate for each time, and the average cooling rate for the cooling zone Of the plurality of points in the thickness direction of the thick steel plate where the ratio of the standard deviation to the predetermined threshold or less, the point located above the center in the thickness direction and the distance from the center in the thickness direction is the maximum, and The distance between the control element that extracts the point that is located below the center in the thickness direction and has the maximum distance from the center in the thickness direction and the center in the thickness direction among the pair of points extracted in the extraction process is short. And a control element having a pair of determination points that are symmetrical with respect to this point and the center in the thickness direction, and at the end point of the cooling zone, the temperature difference between the pair of determination points is equal to or less than a predetermined value. Adjust the water / water ratio And a control element.

  The steel plate cooling device is configured such that the ratio of the standard deviation of the cooling rate for each hour to the average cooling rate of the plurality of points in the thickness direction of the thick steel plate in the cooling zone is the thickness among the plurality of points where the ratio is equal to or less than a predetermined threshold. The point that is located above the center of the direction and has the maximum distance from the center in the thickness direction, and the point that is located below the center of the thickness direction and has the maximum distance from the center in the thickness direction, are extracted. Among the extracted pair of points, a point having a shorter distance from the center in the thickness direction and a point symmetric with respect to this point and the center in the thickness direction are set as a pair of determination points, and at the end point of the cooling zone, Since the water / water ratio can be adjusted so that the temperature difference between the pair of judgment points is less than or equal to a predetermined value, the occurrence of warpage due to thermal stress is sufficiently suppressed as described above, and the quality after cooling is sufficiently improved. Can be manufactured.

  As described above, the thick steel plate cooling method and the thick steel plate cooling apparatus of the present invention can sufficiently suppress the occurrence of warpage of the thick steel plate due to thermal stress, and can sufficiently improve the quality of the thick steel plate after cooling. .

It is a schematic diagram which shows the structure of the steel plate processing equipment provided with the steel plate cooling device which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the thick steel plate cooling device of FIG. It is a flowchart of the thick steel plate cooling method which concerns on one Embodiment of this invention using the thick steel plate cooling device of FIG. It is a graph which shows the estimated temperature from the cooling start in each cooling zone in an Example to an end. It is a graph which shows the relationship between the average cooling rate of the intermediate point of the thickness direction center of a thick steel plate in a 3rd cooling zone from a 1st cooling zone of an Example, and the lower surface, and the cooling rate for every time. It is a graph which shows the amount of up-and-down water amount in each cooling zone of an Example. It is a graph which shows the cooling rate ratio of a vertically symmetrical position from the thickness direction center of the thick steel plate in each cooling zone of an Example. It is a graph which shows the amount of upper and lower water volume in each cooling zone of a comparative example. It is a graph which shows the cooling rate ratio of a vertically symmetrical position from the thickness direction center of the thick steel plate in each cooling zone of a comparative example.

  Hereinafter, embodiments of the present invention will be described in detail.

[Thick steel plate processing equipment]
The thick steel plate processing facility of FIG. 1 was rolled by a heating furnace 1 for heating a raw material thick steel plate (slab) P, a rough rolling machine 2 for hot rolling the heated raw material thick steel plate P, and a rough rolling mill 2. A finishing mill 3 for further hot rolling the thick steel plate P, a thick steel plate cooling device 4 according to an embodiment of the present invention for cooling the thick steel plate P hot-rolled by the finishing mill 3, and the cooled thickness And a leveler 5 for correcting the steel plate P.

  About the heating furnace 1, the roughing mill 2, the finishing mill 3, and the leveler 5, since it can be set as a well-known structure, detailed description is abbreviate | omitted.

[Thick steel plate cooling device]
As shown in FIG. 2, the thick steel plate cooling device 4 conveys the hot steel plate P after hot rolling in the direction of arrow D while sprinkling cooling water on the upper and lower surfaces of the thick steel plate P. This is also called an accelerated cooling device. In the thick steel plate cooling device 4, the thick steel plate P is rapidly cooled to a preset cooling stop temperature. The cooling stop temperature is determined according to the target product (use of the thick steel plate P), and is, for example, 200 ° C. or higher and 650 ° C. or lower.

  Although it does not specifically limit as average thickness of the thick steel plate P cooled with the said thick steel plate cooling device 4, For example, it can be 12 mm or more and 100 mm or less. In addition, the average width B (average length in the transverse direction perpendicular to the conveyance direction D) of the thick steel plate P is not particularly limited, but may be, for example, 1500 mm or more and 5000 mm or less.

  As shown in FIG. 2, the thick steel plate cooling device 4 includes a transport device 10 for transporting the thick steel plate P, a plurality of cooling zones 20 a to 20 d provided in the transport direction of the thick steel plate P, and a plurality of cooling zones 20 a to 20. A temperature measuring device 30 that measures the temperature of the upper and lower surfaces of the thick steel plate P on the upstream side in the conveying direction of 20d, and a control device that adjusts the water / water ratio in the plurality of cooling zones 20a to 20d based on the measurement results of the temperature measuring device 30 40.

<Conveyor>
The conveyance apparatus 10 can be made into the roller conveyor comprised by the some roller 11, as illustrated in FIG.

<Temperature measuring device>
Any temperature measuring device 30 may be used as long as the temperature of the upper and lower surfaces of the thick steel plate P can be measured on the upstream side of the first cooling zone 20a located at the most upstream among the plurality of cooling zones 20a to 20d. A thermometer can be used.

<Cooling zone>
The plurality of cooling zones 20 a to 20 d are provided along the transport direction D. The plurality of cooling zones 20a to 20d are each provided with a plurality of cooling headers (not shown). Specifically, each of the cooling zones 20a to 20d is provided with one or more upper surface cooling headers for cooling the upper surface of the thick steel plate P and one or more lower surface cooling headers for cooling the lower surface of the thick steel plate P. . Although it does not specifically limit as a specific structure of the said upper surface cooling header and a lower surface cooling header, For example, it is a rectangular parallelepiped shape long in a cross direction (horizontal direction perpendicular | vertical to the conveyance direction D), respectively, and the side facing the thick steel plate P It can be set as the structure which has a some nozzle in the surface. When the upper surface cooling header and the lower surface cooling header have a plurality of nozzles, the plurality of nozzles are configured to be supplied with cooling water via a flow rate adjustment valve. Each of the upper surface cooling header and the lower surface cooling header is configured such that cooling water can be sprinkled from the plurality of nozzles to the thick steel plate P. In addition, when a plurality of cooling headers are provided in each of the cooling zones 20a to 20d, it is preferable that a plurality of pairs of cooling headers each including a top cooling header and a bottom cooling header are provided.

<Control device>
For example, the control device 40 controls the opening / closing amount of the cooling water sprayed from the cooling zones 20a to 20d by controlling the opening degree of the flow rate adjusting valve. The control device 40 can be configured by, for example, a personal computer or a programmable controller. The control device 40 measures the measured temperature measured by the temperature measuring device 30, the water density distribution W (x) in the transport direction D in the cooling zones 20a to 20d, the width B of the thick steel plate P, the transport speed v of the thick steel plate P, and the correction. Control for predicting the temperature for each time from the start to the end of cooling in the cooling zones 20a to 20d at a plurality of points in the thickness direction of the thick steel plate P based on the heat transfer coefficient α (x) set using the coefficient. And the average cooling rate CR _avg (i, k) from the start to the end of cooling in the cooling zones 20a to 20d at the plurality of points i (where k is the kth cooling zone from the upstream side). The control elements to be calculated and the cooling speeds CR (i, j, k) at the plurality of points for each time j in the cooling zones 20a to 20d are calculated, and the cooling speed CR (i, j, k) for each time is calculated. The ratio of the standard deviation σ (i, k) to the average cooling rate CR _avg (i, k) in the cooling zones 20a to 20d is equal to or less than a predetermined threshold in the control element for calculating the quasi-deviation σ (i, k). Of the plurality of points in the thickness direction of the thick steel plate P, located above the center in the thickness direction, located at the point where the distance from the center in the thickness direction is the maximum, and below the center in the thickness direction, A control element that extracts a point having the maximum distance from the center in the thickness direction, a point having a shorter distance from the center in the thickness direction among the pair of points extracted in the extraction step, and this point and the center in the thickness direction Control element having a pair of determination points that are symmetrical to each other, and a control element that adjusts the water / water ratio so that the temperature difference between the pair of determination points is equal to or less than a predetermined value at the end points of the cooling zones 20a to 20d. And the temperature difference between the pair of determination points is equal to or less than the predetermined value. When Tsu and a control element for determining the vertical water volume ratio, and controls the operation of the steel plate cooling device 4.

[Thick steel plate cooling method]
Next, a thick steel plate cooling method according to an embodiment of the present invention for cooling the thick steel plate P after hot rolling using the thick steel plate cooling device 4 provided in the transport direction D after hot rolling will be described. As shown in FIG. 3, the steel plate cooling method includes an initial condition setting step (S01), a temperature measurement step (S02), a temperature prediction step (S03), an average cooling rate calculation step (S04), and a standard. Deviation calculation step (S05), extraction step (S06), determination point determination step (S07), temperature difference convergence determination step (S08), determination step (S09), and water amount ratio adjustment step (S10) Is provided. In the thick steel plate cooling method, the temperature measuring step (S02) is performed by the temperature measuring device 30, and the other steps are performed by the control device 40. Moreover, in the said steel plate cooling method, it is performed for each cooling zone 20a-20d from the said temperature estimation process (S03) to a water-and-water ratio adjustment process (S10).

<Initial condition setting process>
In the initial condition setting step (S01), the initial value of the water density distribution W (x) in the transport direction D and other operating conditions are set. Other operating conditions set in step S01 include physical properties such as plate thickness, width, specific heat, thermal conductivity, transformation calorific value, thickness of cooling water, cooling stop temperature, cooling rate control width, thickness of thick steel plate P. The conveyance speed of the steel plate P, the actual temperature of the thick steel plate P before cooling, and the like are set. These initial conditions can be set, for example, by reading from a storage device such as a hard disk drive or a memory, communicating with an external control device, etc., or manually input by a user.

<Temperature measurement process>
In the temperature measurement step (S02), the temperature Ts ₁ [K] of the upper surface and the temperature Ts ₂ [K] of the lower surface of the thick steel plate P charged into the thick steel plate cooling device 4 are measured. In step S02, the temperature measuring device 30 measures the temperature of the upper and lower surfaces of the thick steel plate P before the cooling water sprinkling (immediately before entering the first cooling zone 20a) on the upstream side of the first cooling zone 20a. Although it does not specifically limit as a measurement position of the temperature of the upper and lower surfaces of the thick steel plate P in step S02, The center part of the width direction is preferable. Note that the temperatures Ts ₁ and Ts _{2 on} the upper and lower surfaces of the thick steel plate P vary depending on the specifications of the thick steel plate P, etc. It is not constant due to the influence of

<Temperature prediction process>
In the temperature prediction step (S03), the cooling zones 20a to 20a when the cooling water is sprayed on the upper and lower surfaces of the thick steel plate P based on the measured temperature measured in step S02 with a preset water density distribution W (x). A temperature for each time from the start to the end of cooling at a plurality of points in the thickness direction of the thick steel plate P at 20d is predicted. In step S03, in order to estimate the temperature based on the measurement temperature measured in step S02, when the temperature of the central portion in the width direction of the thick steel plate P is measured in step S02, the thickness direction of the central portion in the width direction of the thick steel plate P is measured. Predict the temperature at multiple points at. The plurality of points are set symmetrically from the center in the thickness direction of the thick steel plate P. As a minimum of the number of measurement points of the thickness direction of thick steel plate P in Step S03, 5 is preferred and 9 is more preferred. On the other hand, as an upper limit of the number of measurement points in the thickness direction of the thick steel plate P in step S03, 31 is preferable and 21 is more preferable. If the number of measurement points in the thickness direction of the steel plate P is less than the lower limit, the number of measurement points may be insufficient, and the adjustment of the water / water ratio may be insufficient. Conversely, if the number of measurement points in the thickness direction of the steel plate P exceeds the above upper limit, the number of measurement points will increase unnecessarily, and the amount of calculation required to adjust the water and water ratio will become enormous and the water and water ratio will be adjusted quickly. May be difficult. In addition, although it is preferable that all the space | intervals of said several point are equal, the distance between adjacent points may differ as long as it sets up and down symmetrically from the thickness direction center of the thick steel plate P.

Specifically, in step S03, the measured temperatures Ts ₁ and Ts _{2 on} the upper and lower surfaces of the thick steel plate P measured in step S02, the water density distribution W (x) in each of the cooling zones 20a to 20d, and the thick steel plate P Based on the width B [mm], the conveying speed v [m / s] of the thick steel plate P, and the heat transfer coefficient α set by using the correction coefficient ε, each cooling of a plurality of points in the thickness direction of the thick steel plate P is performed. The temperature for each time from the start to the end of cooling in the zones 20a to 20d is predicted. In step S03, the predicted temperatures at a plurality of points in the thickness direction of the thick steel plate P are calculated by calculating the heat conduction in the thickness direction of the thick steel plate P using a one-dimensional heat conduction equation in the thickness direction.

<Average cooling rate calculation step>
In the average cooling rate calculation step (S04), an average cooling temperature from the start to the end of cooling in each of the cooling zones 20a to 20d at the plurality of points is calculated. In step S04, for example, the temperature drop {T _jin (k) −T _Zout (k)} from the entrance to the exit of each point in each cooling zone 20a to 20d is passed through each cooling zone 20a to 20d at each point. time using a _{{t zout (k) -t zin} (k)}, the average cooling temperature _{CR avg} [℃ / sec] in each cooling zone 20a~20d is calculated by the following equation (1).
CR _avg (i, k) = {T _zin (k) −T _Zout (k)} / {t _zout (k) −t _zin (k)} (1)

<Standard deviation calculation process>
In the standard deviation calculation step (S05), the cooling rates CR (i, j, k) at the plurality of points for each time of each of the cooling zones 20a to 20d are calculated, and the cooling rates CR (i, j, k) for each time are calculated. The standard deviation σ (i, k) of k) is calculated. In S05, the passage times of the plurality of points in each of the cooling zones 20a to 20d are separated by a constant calculation step j, and the cooling rate CR (i, j, k) for each calculation step j is decreased for each calculation step j. The standard deviation σ (i, k) is calculated by the following equation (2) using the temperature {T _jin (k) −T _jout (k)} and the time {t _jout (k) −t _jin (k)}. ) Is calculated by the following equation (3).
CR (i, j, k) = {T _jin (k) −T _jout (k)} / {t _jout (k) −t _jin (k)} (2)

<Extraction process>
In the extraction step (S06), the thickness of the thick steel plate P in which the ratio of the standard deviation σ (i, k) to the average cooling rate CR _avg (i, k) is equal to or less than a predetermined threshold in each of the cooling zones 20a to 20d. Among the plurality of points in the direction, it is located above the center in the thickness direction, the point where the distance from the center in the thickness direction is the maximum, and located below the center in the thickness direction, The point with the maximum distance is extracted. This threshold value is determined based on, for example, the management width of the cooling rate required for building the thick steel plate P in order to keep the quality constant.

<Decision point determination process>
In the determination point determination step (S07), a pair of determinations is made of a point having a shorter distance from the center in the thickness direction and a point symmetrical to the center in the thickness direction among the pair of points extracted in step S06. Let it be a point.

<Temperature difference convergence determination process>
In the temperature difference convergence determination step (S08), it is determined whether the temperature difference between the pair of determination points determined in step S07 is within a predetermined range at the end points of the cooling zones 20a to 20d. When the temperature difference between the pair of determination points becomes equal to or less than the predetermined value in step S08, the process proceeds to step S09 to determine the amount of water and sewage. On the other hand, when the temperature difference between the pair of determination points exceeds a predetermined value in step S08, the process proceeds to step S10 to adjust the water / water ratio. The predetermined value can be set, for example, in the range of 0.05 ° C. or more and 5 ° C. or less, and preferably 0.1 ° C.

<Decision process>
In the determination step (S09), when the temperature difference between the pair of determination points becomes equal to or less than the predetermined value, the water flow ratio is determined on the assumption that the temperature difference in the vertical direction has converged.

<Water and sewage adjustment process>
In the water / water amount adjustment step (S10), the water / water ratio is adjusted so that the temperature difference between the pair of determination points is equal to or less than a predetermined value at the end points of the cooling zones 20a to 20d. In step S10, the water / water ratio is adjusted using convergence calculation so that the temperature difference between the pair of determination points at the end points of the cooling zones 20a to 20d is equal to or less than a predetermined value. In step S10, the water / water ratio between the cooling zones 20a to 20d is sequentially adjusted from the upstream first cooling zone 20a.

  When the water / water ratio is adjusted in step S10, the thickness when the cooling water is sprayed on the upper and lower surfaces of the thick steel plate P using the water density distribution W (x) based on the adjusted water / water ratio again after returning to step S03. The temperature for each time from the start to the end of cooling in each of the cooling zones 20a to 20d at a plurality of points in the thickness direction of the steel sheet P is predicted.

  Then, the adjustment of the water density distribution W (x) is repeated by the above procedure until the temperature difference between the pair of determination points becomes equal to or less than a predetermined value.

<Advantages>
In the manufacturing method of the thick steel plate, the thickness direction of the thick steel plate P in which the ratio of the standard deviation σ (i, k) to the average cooling rate CR _avg (i, k) is equal to or less than a predetermined threshold in the cooling zones 20a to 20d. Among the plurality of points, the point located above the center in the thickness direction and having the maximum distance from the center in the thickness direction, and the distance from the center in the thickness direction located below the center in the thickness direction Of the pair of extracted points, the point having the shorter distance from the center in the thickness direction and the point symmetrical to the center in the thickness direction as a pair of determination points. The water / water ratio is adjusted so that the temperature difference between the pair of determination points is equal to or less than a predetermined value. Therefore, the manufacturing method of the thick steel plate can maintain the cooling rate of the portion existing between the pair of determination points in the thickness direction substantially evenly, and the portion positioned on the outer side in the thickness direction than the pair of determination points. The vertical symmetry of the cooling rate can be promoted. Therefore, the manufacturing method of the said thick steel plate can fully suppress generation | occurrence | production of the curvature of the thick steel plate P by a thermal stress, and can fully improve the quality of the thick steel plate P after cooling.

The steel plate cooling device 4 has a standard deviation σ (i, k) of the cooling rate per time with respect to the average cooling rate CR _avg (i, k) at a plurality of points in the thickness direction of the thick steel plate P in the cooling zones 20a to 20d. ) Of the plurality of points whose ratio is equal to or less than a predetermined threshold value, located above the center in the thickness direction, located at the maximum distance from the center in the thickness direction, and located below the center in the thickness direction Then, the point having the maximum distance from the thickness direction center is extracted, and the point having the shorter distance from the thickness direction center of the pair of extracted points and the point and the thickness direction center are symmetric. As described above, the water / water ratio can be adjusted so that the temperature difference between the pair of determination points is equal to or less than a predetermined value at the end points of the cooling zones 20a to 20d. Warpage due to thermal stress is sufficiently suppressed, and after cooling It is possible to manufacture a thick steel plate P whose quality is sufficiently improved.

[Other Embodiments]
In addition, the thick steel plate cooling method and the thick steel plate cooling apparatus according to the present invention can be implemented in various modified and modified modes in addition to the above mode. For example, the steel plate cooling device preferably includes a plurality of cooling zones in order to more accurately suppress warpage of the thick steel plate after cooling, but may include only one cooling zone. One cooling zone does not necessarily have to have a plurality of pairs of cooling headers, and may have only a pair of upper and lower cooling headers, for example, or may have a different number of upper and lower cooling headers. Further, the cooling header may be configured to adjust the water density distribution in the transverse direction.

  The said steel plate cooling device may be provided with the draining header which pushes a stagnant water in the cross direction by the injection of a cooling water between several upper surface cooling headers (it makes a stagnant water height 0). When such a draining header is used, it is preferable to set in advance a heat transfer coefficient calculation formula based on an optimal cooling model for each layout pattern of the draining header to be used.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

(sample)
A thick steel plate having an average thickness of 20 mm, an average width of 3000 mm, and a steel type of 0.06% C steel was prepared. As the thick steel plate cooling device, there are four cooling zones (first cooling zone (1Z), second cooling zone (2Z), third cooling zone (3Z), fourth cooling zone (4Z )) Was used, and the cooling stop temperature of the thick steel plate was 500 ° C. The temperature of the upper and lower surfaces of the thick steel plate immediately before entering the first cooling zone measured by the temperature measuring device was 800 ° C.

[Example]
21 measurement points that are equal in the thickness direction are set at the center in the width direction of the thick steel plate, and the temperature for each time from the start to the end of the cooling in the four cooling zones at each measurement point is the procedure of the above temperature prediction process. Predicted according to. In addition, the estimated temperature of the cooling zones 1Z-4Z in each measurement point divided into 4 from the upper surface to the lower surface is shown in FIG.

  Subsequently, the average cooling rate from the start to the end of cooling in each of the cooling zones 1Z to 4Z was calculated according to the procedure of the above-described average cooling rate calculation step. Moreover, the standard deviation of the cooling rate for each time of each cooling zone 1Z-4Z was calculated according to the procedure of the above-mentioned standard deviation calculation process. In addition, the relationship of the average cooling rate in the intermediate point of the thickness direction center in cooling zone 1Z-3Z and a lower surface, and the cooling rate for every time is shown in FIG.

  Next, among the plurality of points at which the ratio of the standard deviation to the average cooling rate is equal to or less than the threshold value in each of the cooling zones 1Z to 4Z, the distance from the center in the thickness direction is the maximum. And a point located below the center in the thickness direction and having the maximum distance from the center in the thickness direction were extracted. Furthermore, a point having a shorter distance from the center in the thickness direction out of each pair of points extracted in each of the cooling zones 1Z to 4Z and a point symmetrical to the center in the thickness direction are set as a pair of determination points. . Then, at the end points of the respective cooling zones 1Z to 4Z, the water ratio between the upper and lower water was adjusted so that the temperature difference between the pair of determination points was 0.1 ° C. or less, and the thick steel plate was cooled at the adjusted water ratio. The determination points in the cooling zones 1Z and 2Z were x / t = 0.30, and the determination points in the cooling zones 3Z and 4Z were x / t = 0.25. In addition, t means the average thickness of a thick steel plate, and x means the distance from the center in the thickness direction to the determination point. FIG. 6 shows the water / water ratio in the embodiment, and the cooling rate ratios at the end points of the cooling zones 1Z to 4Z calculated according to the procedure of the temperature prediction step above and below the center in the thickness direction at the center in the width direction of the thick steel plate. Is shown in FIG.

[Comparative example]
The determination point in each of the cooling zones 1Z to 4Z is fixed at x / t = 0.25, and the water amount ratio is adjusted so that the temperature difference between the determination points is 0.1 ° C. or less. The thick steel plate was cooled at a ratio. FIG. 8 shows the water / water ratio in the comparative example, and the cooling rate ratios at the end points of the respective cooling zones 1Z to 4Z calculated in accordance with the above-described temperature prediction process procedure in the vertically symmetrical position from the center in the thickness direction at the center in the width direction of the steel plate. Is shown in FIG.

[Evaluation results]
As shown in FIGS. 7 and 9, compared to the comparative example, the embodiment is designed to make the cooling rate uniform in the vertical symmetry position with respect to the center in the thickness direction, and in particular, the uniform cooling rate on the upper and lower surface sides. It can be seen that conversion is promoted. Specifically, in the comparative example, the cooling rate at the pair of determination points can be made uniform, but a relatively large variation occurs in the cooling rate at the vertically symmetrical position at a point away from the determination point toward the upper and lower surfaces. On the other hand, in the example, it is understood that the variation in the cooling rate at the symmetrical position in the vertical direction is suppressed even at a point away from the pair of determination points on the upper and lower surface side.

  As described above, the thick steel plate cooling method and the thick steel plate cooling apparatus according to the present invention can sufficiently suppress the occurrence of warpage of the thick steel plate due to thermal stress, and thus are suitable for manufacturing high-quality thick steel plates. .

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Coarse rolling mill 3 Finish rolling mill 4 Thick steel plate cooling device 5 Leveler 10 Conveying device 11 Roller 20a-20d Cooling zone 30 Temperature measuring device 40 Control device P Thick steel plate D Conveying direction

Claims (3)

Using a cooling device provided in the conveying direction of the thick steel plate after hot rolling, a thick steel plate cooling method for cooling the thick steel plate after hot rolling,
The cooling device has at least one cooling zone along the conveying direction;
Measuring the temperature of the upper and lower surfaces of the thick steel plate to be charged into the cooling device;
Based on the measurement temperature measured in the measurement step, the water density density distribution in the cooling zone, the width of the thick steel plate, the conveyance speed of the thick steel plate and the heat transfer coefficient set using the correction coefficient, the thick steel plate Predicting the temperature for each time from the start to the end of cooling in the cooling zone at a plurality of points in the thickness direction,
Calculating an average cooling rate from the start to the end of cooling in the cooling zones of the plurality of points;
Calculating a cooling rate of the plurality of points at each time of the cooling zone, and calculating a standard deviation of the cooling rate at each time;
Among the plurality of points in the thickness direction of the thick steel plate in which the ratio of the standard deviation to the average cooling rate is equal to or less than a predetermined threshold in the cooling zone, it is located above the center in the thickness direction, Extracting a point where the distance is maximum and a point located below the center in the thickness direction and having the maximum distance from the center in the thickness direction;
A step of using a point having a shorter distance from the center in the thickness direction of the pair of points extracted in the extraction step and a point symmetrical to the center in the thickness direction as a pair of determination points;
Adjusting the water / water ratio so that the temperature difference between the pair of determination points is a predetermined value or less at the end point of the cooling zone.   The thick steel plate cooling method according to claim 1, further comprising a step of determining a water / water ratio when the temperature difference between the pair of determination points is equal to or less than the predetermined value. A transport device for transporting thick steel plates;
At least one cooling zone provided in the conveying direction of the thick steel plate;
A temperature measuring device for measuring the temperature of the upper and lower surfaces of the thick steel plate upstream of the cooling zone;
A control device that adjusts the water / water ratio in the cooling zone based on the measurement result of the temperature measuring device,
The control device is
Based on the measured temperature measured by the temperature measuring device, the water density density distribution in the cooling zone, the width of the thick steel plate, the transport speed of the thick steel plate and the heat transfer coefficient set using the correction coefficient, the thickness A control element that predicts the temperature for each time from the start to the end of cooling in the cooling zone at a plurality of points in the thickness direction of the steel sheet;
A control element for calculating an average cooling rate from the start to the end of cooling in the cooling zones of the plurality of points;
A control element that calculates the cooling rate of the plurality of points at each time of the cooling zone, and calculates a standard deviation of the cooling rate at each time;
Among the plurality of points in the thickness direction of the thick steel plate in which the ratio of the standard deviation to the average cooling rate is equal to or less than a predetermined threshold in the cooling zone, it is located above the center in the thickness direction, A control element for extracting a point where the distance is maximum and a point located below the center in the thickness direction and having the maximum distance from the center in the thickness direction;
A control element having a pair of determination points, which is a point having a shorter distance from the center in the thickness direction among the pair of points extracted in the extraction step, and a point symmetric with respect to the center in the thickness direction;
A steel plate cooling apparatus comprising: a control element that adjusts a water / water ratio so that a temperature difference between the pair of determination points is equal to or less than a predetermined value at an end point of the cooling zone.

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