JP5239887B2 - Hot rolled steel sheet manufacturing apparatus and manufacturing method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an apparatus and a method for manufacturing a hot-rolled steel sheet. Specifically, the hot-rolled steel sheet is water-cooled by injecting cooling water onto a high-temperature steel sheet immediately after being hot-rolled by a hot rolling mill. When manufacturing this, it is related with the manufacturing apparatus and manufacturing method of a hot-rolled steel plate which can control accurately the temperature of the steel plate at the time of stopping this cooling.

  In a hot rolling facility equipped with a finish rolling mill and a transfer table (runout table) installed on the downstream side of the finish rolling mill, a high temperature steel plate finish-rolled by the finish rolling mill is transferred to the surface of the steel plate. Water cooling is performed by spraying cooling water from a water cooling device disposed in the coil, and then the coil is wound by a winding device to form a coil. In order to produce a hot-rolled steel sheet having the desired mechanical properties, the temperature drop history of the steel sheet on the transfer table from the finish rolling by the finish rolling mill to the winding of the coil is controlled with high precision, and precipitation is performed. It is necessary to actively control the metal structure.

  FIG. 11 is a graph showing the relationship between the descent history of the steel sheet that has finished finish rolling and the metal structure that precipitates. As shown in the graph of FIG. 1, since the metal structure deposited by changing the temperature of the steel sheet immediately after stopping the water cooling (hereinafter referred to as “quenching stop temperature”) to a, b, and c also changes, the quench stop temperature The metallographic structure of the hot-rolled steel sheet can be controlled by appropriately controlling. Thus, in order to produce a hot-rolled steel sheet having excellent mechanical properties, it is necessary to accurately control the quenching stop temperature to a predetermined temperature and to stop quenching accurately at a temperature at which the necessary metal structure is deposited. There is. For this reason, it is required to appropriately control the water cooling device so that the rapid cooling stop temperature becomes a predetermined temperature accurately in accordance with the speed of the finish-rolled steel sheet and the fluctuation of the rolling temperature.

Several inventions for controlling the temperature drop history of a steel sheet after hot finish rolling, including the control of the quenching stop temperature, have been proposed so far.
For example, Patent Document 1 affects the change in the speed of the steel sheet by accelerated rolling by controlling the water cooling device so that both the target water cooling time and the target air cooling time can be secured for the steel sheet after finish rolling. An invention is disclosed in which the temperature drop history is kept constant and the winding temperature is controlled to a predetermined temperature.

  Further, Patent Document 2 uses a steel plate temperature detection means and cooling water control means arranged for each of a large number of cooling zones, and gives a target value for obtaining a necessary temperature drop history for each cooling zone. An invention for obtaining a desired temperature drop history in the entire cooling process is disclosed.

Japanese Patent Laid-Open No. 6-238312 JP-A-6-246331

However, the rapid cooling stop temperature of the steel sheet cannot be accurately controlled based on any of the inventions disclosed in Patent Documents 1 and 2.
That is, as shown in the graph of FIG. 11 described above, it is necessary to control the quenching stop temperature to the target temperature in order to precipitate a desired metal structure. However, the invention disclosed in Patent Document 1 discloses a steel sheet after finish rolling. Since the water cooling time at the time of rapid cooling is controlled and the rapid cooling stop temperature is not controlled to the target temperature, the invention disclosed in Patent Document 1 cannot accurately control the rapid cooling stop temperature.

  Further, in the invention disclosed in Patent Document 2, the cooling capacity of the water cooling device is adjusted so that the difference between the detection value by the temperature detecting means arranged in large numbers and the target value becomes small. However, the temperature detected by this temperature detection means is the surface temperature of the steel sheet during water cooling.

FIG. 12 is a graph showing the results of calculating the surface temperature of the steel sheet and the average temperature in the plate thickness direction when the steel sheet is rapidly cooled by spraying cooling water onto the steel sheet with a water cooling device.
Here, the “thickness direction average temperature” will be described. As shown in the graph of FIG. 12, at the time of rapid cooling, since the heat is taken away from the steel plate surface, the surface temperature is the lowest and has a temperature distribution in the plate thickness direction. Therefore, multiple temperature calculation points are set in the plate thickness direction, the temperature at each temperature calculation point is calculated in consideration of the heat flux from the steel plate surface, the heat conduction inside the steel plate, etc., and the temperature at each point is averaged. The thing is called the “thickness direction average temperature”.

  Assuming that there is no heat outflow from the steel sheet surface after quenching the steel sheet, the temperature distribution in the sheet thickness direction becomes smaller due to thermal diffusion and eventually becomes the same as the “average temperature in the sheet thickness direction”. The “thickness direction average temperature” is the control target value.

  As shown in the graph of FIG. 12, when the cooling water is injected in the cooling zone of the water cooling device to rapidly cool the steel sheet and then the cooling water injection is stopped, the surface temperature of the steel sheet is in the thickness direction when the cooling water is injected. The temperature is significantly lower than the average temperature, and the difference between the two is not stable. Then, the surface temperature immediately after the cooling water injection is stopped and the air cooling is started is, for a while after that (region A in the graph of FIG. 12), the heat inside the steel plate moves to the surface side (this specification). In the book, such heat transfer is called “recuperation”), the surface temperature of the steel sheet is rising and in a transitional state, but the difference between the two rapidly decreases, and when this excessive state is passed The surface temperature of the steel sheet decreases stably in the same way as the average thickness direction temperature.

  In this way, there is a large difference between the surface temperature of the steel sheet during rapid cooling and the average temperature in the thickness direction, so even if you directly measure the surface temperature of the steel sheet during rapid cooling stop, you can accurately measure the rapid cooling stop temperature of the steel sheet. However, it is necessary to obtain the quenching stop temperature of the steel sheet as the average thickness direction temperature. Since the invention disclosed by Patent Document 2 is based on the surface temperature of the steel sheet detected by the temperature detecting means, even the invention disclosed by Patent Document 2 cannot accurately control the rapid cooling stop temperature.

  Temporarily, in the invention disclosed by patent document 2, the case where the surface temperature is measured after waiting until the difference between the surface temperature after stopping the water cooling and the average thickness direction temperature becomes small is examined. For example, when a steel sheet having a plate thickness of 4.0 mm and an initial temperature of 900 ° C. is rapidly cooled at a cooling rate of 100 ° C./second until the average temperature in the plate thickness direction becomes 700 ° C., The surface temperature is 678 ° C., which is 22 ° C. lower than the average thickness direction temperature, and it takes 0.40 seconds for the surface temperature to stabilize and the surface temperature to change from rising to falling. In the case of 10 m / sec, which is the finish rolling speed (steel plate transport speed) of a general finish rolling apparatus, a distance of 4.0 m is required.

  In this way, if the distance from the end of the cooling zone to the temperature detecting means is set long in order to obtain a time for the surface temperature of the steel plate to stabilize during air cooling after the rapid cooling stop, the time from the rapid cooling stop to the detection of the surface temperature is increased. In short, since the temperature of the steel sheet decreases during this period, the rapid cooling stop temperature cannot be controlled. This also increases the length of one cooling zone, and the temperature drop history cannot be accurately controlled.

  For this reason, in the invention disclosed in Patent Document 2, even if the surface temperature is measured while waiting for the difference between the surface temperature after the rapid cooling stop and the average temperature in the thickness direction to become small, the rapid cooling stop temperature is accurately determined. In addition to being unable to control, it is difficult to increase the cooling rate during rapid cooling because cooling water cannot be injected in the section from the end of the cooling zone to the temperature detection position. Furthermore, in the present invention, it is necessary to use a separate control computer, feed forward controller, feedback controller, thermometer, and flow rate adjusting valve for each cooling zone, and there is also a problem that equipment costs increase.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a hot-rolled steel sheet manufacturing apparatus and a manufacturing method capable of controlling the quenching stop temperature with high accuracy. To do.

  The present invention stabilizes the temperature of the cooled steel sheet when the steel sheet is hot-rolled and sprayed with cooling water to cool the steel sheet and then the cooling water injection is stopped and the steel sheet is subsequently air-cooled. The difference between the estimated calculation value and the measured value of the surface temperature of the steel sheet at a predetermined time after stopping the cooling water injection is calculated, and this difference and the estimation calculation of the average temperature in the thickness direction when the cooling water injection stops If the average temperature in the thickness direction at the time of rapid cooling stop is estimated and calculated based on the value, the rapid cooling stop temperature can be estimated with high accuracy, and if the injection of cooling water by the water cooling device is controlled using this estimated calculated value, the rapid cooling stop temperature This is based on the technical idea that can be controlled with high accuracy.

  Here, “the temperature of the cooled steel plate is stabilized” will be described. During cooling water injection, the surface of the steel plate is directly exposed to the cooling water, so the steel plate surface temperature is lower than the internal temperature in the steel plate thickness direction, and the steel plate surface temperature and the internal temperature in the steel plate thickness direction. A temperature difference in various ranges such as a large temperature difference and a small temperature difference occurs between the two and the temperature of the steel sheet is in a transient state, which can be said to be an unstable state. Moreover, since it receives the influence of the disturbance by the injected cooling water, it cannot be said that the measured value of the steel sheet surface temperature is stable. That is, the temperature difference increases or decreases, and is not stable. On the other hand, after the cooling water injection is stopped, as shown in the graph of FIG. 12, the surface calculated temperature rises once, and then draws a temperature curve that turns downward and begins to turn downward. Indicates a temperature drop tendency when air-cooled on the apparatus, and indicates a state substantially parallel to the temperature gradient of the plate thickness direction average calculated temperature. Therefore, after the disturbance of water cooling is stopped, the influence of water cooling that has affected the temperature change is eliminated, so that the temperature of the steel sheet to be cooled is stabilized. In the present invention, the control is performed using a region where the steel plate temperature is stable.

The present invention includes a hot rolling mill, a water cooling device that is installed on the outlet side of the hot rolling mill and that is cooled by spraying cooling water onto a steel sheet that is rolled and conveyed by the hot rolling mill. A cooling control device for controlling the steel sheet to a predetermined temperature by stopping cooling water injection and subsequently air-cooling the steel sheet, and a surface temperature of the steel sheet at a predetermined time after the cooling water injection is stopped. A surface temperature measuring means for measuring, the cooling control device is a measured value of the surface temperature of the steel sheet by the surface temperature measuring means, and an estimated calculation value of the surface temperature of the steel sheet at a predetermined time using a heat transfer model of the steel sheet, Based on the deviation of the cooling water, the average temperature in the plate thickness direction when the cooling water injection is stopped is calculated, and the cooling water injection by the water cooling device is made so that the calculated value of the average thickness direction temperature becomes the target value. controlling the, and The predetermined time, the estimated value of the surface temperature of the steel sheet is estimated using the heat transfer model of the steel sheet, characterized in that the injection of the cooling water from rising even after stopping it is time after time to turn the lowered heat It is a manufacturing apparatus of a rolled steel sheet.

From another point of view, the present invention is such that after cooling water is sprayed onto the steel sheet that is hot-rolled and conveyed, the steel sheet is water-cooled, and then the cooling water injection is stopped to subsequently air-cool the steel sheet. A method of manufacturing a hot-rolled steel sheet including a step of controlling the steel sheet to a predetermined temperature, using a measured value of the surface temperature of the steel sheet at a predetermined time after stopping the cooling water injection and a heat transfer model of the steel sheet. Based on the deviation from the estimated calculation value of the surface temperature of the steel sheet at a predetermined time, the thickness direction average temperature of the steel sheet when the cooling water injection is stopped is calculated, and the calculated value of the thickness direction average temperature is Controlling the injection of cooling water so that it becomes the target value , and the predetermined time is after the estimated value of the surface temperature of the steel sheet estimated using the heat transfer model of the steel sheet has stopped the injection of cooling water It is the time after the time when it goes from rising to falling Is a hot rolled steel sheet manufacturing method characterized by and.

  In these present inventions, a plurality of surface temperature measuring means are arranged in the conveying direction of the steel sheet, and the cooling control device of the steel sheet estimated by using the heat transfer model of the steel sheet among the plurality of surface temperature measuring means. It is desirable that the surface temperature measuring means is disposed at a position closest to the downstream side rather than a position where the estimated value of the surface temperature turns from rising to falling after the cooling water injection is stopped.

  Further, in these inventions, the surface temperature measuring means is a radiation thermometer arranged at a position facing the steel plate, and a water column forming means for forming a water column as an optical waveguide between the steel plate and the radiation thermometer. It is desirable to measure the surface temperature of the steel sheet by detecting radiation light from the surface of the steel sheet through this water column with a radiation thermometer.

  According to the present invention, the average temperature in the thickness direction at the quenching stop position of the steel sheet, which changes every moment due to the change in the finishing mill exit temperature, the change in the steel sheet speed, etc., is measured by the surface temperature measuring means installed downstream of the quenching stop position. It can be estimated with high accuracy based on the measured value. Therefore, the estimated value of the quenching stop temperature is obtained by sequentially correcting the open / close state of the valve of the water cooling device according to the difference between the estimated value of the quenching stop temperature estimated in this way and the target value of the quenching stop temperature. It can be accurately controlled to match the target value.

  During air cooling immediately after the rapid cooling stop when cooling water injection is stopped, the surface temperature of the steel sheet is significantly lower than the average temperature in the thickness direction, so the surface temperature is reduced by reheating from the inside to the surface of the steel sheet. Rises. For this reason, in this invention, it is desirable to estimate the plate | board thickness direction average temperature of the steel plate in a rapid cooling stop position using the measured value by the surface temperature measuring means installed behind a recuperation completion position.

  On the other hand, the shorter the elapsed time from the rapid cooling stop to the surface temperature measurement, the better the control performance. Therefore, it is desirable to install a plurality of surface temperature measuring means and to estimate the average temperature in the thickness direction of the steel sheet at the time of rapid cooling stop using the surface temperature measuring means located behind and closest to the recuperation completion position. .

  According to the present invention, when the cooling water is sprayed onto the steel sheet that is hot-rolled and conveyed to cool the steel sheet, the cooling water injection is stopped and the steel sheet is subsequently cooled by air. The plate thickness direction average temperature of the steel sheet at the rapid cooling stop position where the injection is stopped can be estimated with high accuracy, and by using this estimated calculation value, the cooling water injection by the water cooling device is controlled, and the rapid cooling stop temperature of the steel plate is highly accurate. Can be controlled.

FIG. 1 is an explanatory view schematically showing a configuration of an example of a hot-rolled steel sheet manufacturing apparatus according to the present invention. FIG. 2 is a graph showing that an error in the estimated value of the rapid cooling stop temperature occurs. FIG. 3 is a graph showing that the estimated value of the rapid cooling stop temperature is controlled to the target value according to the present invention. FIG. 4 is a graph showing the influence of the plate thickness or the cooling rate on the recuperation time. FIG. 5 is a graph showing that the estimated quenching stop temperature is controlled by the present invention. FIG. 6 is a graph showing the temperature in the longitudinal direction of the steel plate when controlled according to the conventional example. FIG. 7 is a graph showing the longitudinal temperature of the steel plate when the first example of the present invention is implemented. FIG. 8 is an explanatory diagram showing an overall configuration of a hot-rolled steel sheet manufacturing apparatus according to an example. FIG. 9 is a graph showing the temperature in the longitudinal direction of the steel plate when controlled by a conventional example. FIG. 10 is a graph showing the temperature in the longitudinal direction of the steel sheet when the embodiment of the present invention is implemented. FIG. 11 is a graph showing the relationship between the descent history of the steel sheet that has finished finish rolling and the metal structure that precipitates. FIG. 12 is a graph showing the results of calculating the surface temperature of the steel sheet and the average temperature in the plate thickness direction when the steel sheet is rapidly cooled by spraying cooling water onto the steel sheet with a water cooling device.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is an explanatory view schematically showing a configuration of an example of a hot-rolled steel sheet manufacturing apparatus 0 according to the present invention. In FIG. 1, the code | symbol 1 shows the steel plate by which hot rolling was performed, the code | symbol 2 shows a finishing mill, the code | symbol 3 shows a conveyance table (runout table), the code | symbol 4 shows a winding device, the code | symbol 5 Indicates a water cooling device comprising n controllable water cooling headers for injecting cooling water onto the upper surface of the steel plate 1 and quenching, and a valve for adjusting the amount of water supplied to each water cooling header. A water cooling device having m controllable water cooling headers for injecting cooling water onto the bottom surface and quenching and a valve for adjusting the amount of water supplied to each water cooling header is shown. Reference numeral 7 denotes a water cooling device inlet side thermometer. 8 indicates an intermediate thermometer, 9 indicates a steel plate thickness measuring device, 10 indicates a steel plate speed measuring device, 11 indicates a quenching steel plate temperature prediction device, and 12 indicates a quenching stop temperature. Shows the control device, and further Reference numeral 13 denotes a quench stop temperature estimation device.

  As shown in FIG. 1, the manufacturing apparatus 0 includes a hot finish rolling mill 2, water cooling apparatuses 5 and 6, a runout table 3, a surface temperature measuring means 8, a rapid cooling steel plate temperature prediction apparatus 11, and a rapid cooling stop. Since the cooling control device 14 including the temperature control device 12 and the rapid cooling stop temperature estimation device 13 is provided, these components will be sequentially described.

[Hot finish rolling mill 2]
The hot finish rolling mill 2 performs hot finish rolling on the steel sheet 1 and may be any well-known and commonly used finish rolling mill of this type.

[Water cooling devices 5 and 6 and runout table 3]
The water-cooling device 5 has n controllable water-cooling headers arranged in parallel to the delivery direction of the steel plate 1 above the steel plate 1 on the exit side of the hot finish rolling mill 2, and for each water-cooling header. And a valve for adjusting the amount of water to be provided. In accordance with a valve operation command output from a rapid cooling stop temperature control device 12 to be described later, cooling water is sprayed onto the upper surface of the steel plate 1 that is rolled and conveyed by the hot finish rolling mill 2 to rapidly cool the steel plate 1. The water cooling device 5 may be any well-known and commonly used water cooling device of this type.

  On the other hand, the water-cooling device 6 includes m controllable water-cooling headers arranged in parallel to the delivery side of the steel plate 1 below the steel plate 1 on the exit side of the hot finish rolling mill 2, and each water-cooling header. And a valve for adjusting the amount of water to be disposed and supplied. In accordance with a valve operation command output from a rapid cooling stop temperature control device 12 to be described later, cooling water is sprayed onto the lower surface of the steel plate 1 that is rolled and conveyed by the hot finishing mill 2 to rapidly cool the steel plate 1. The water cooling device 6 may be any well-known and commonly used water cooling device of this type.

  The run-out table 3 includes a plurality of conveyance rolls arranged in parallel, and conveys the steel plate 1 that has been hot-rolled to the winding device 4. Further, since the run-out table 3 continues to transport the steel plate 1 from which the cooling water injection by the water cooling devices 5 and 6 has been stopped, the steel plate 1 transported by the run-out table 3 continues to be air-cooled after the cooling water injection is stopped. Is done. The runout table 3 may be any well-known and commonly used type of runout table.

[Surface temperature measuring means 8]
The surface temperature measuring means 8 measures the surface temperature of the steel sheet 1 at a predetermined time after the cooling water jetting by the water cooling devices 5 and 6 is stopped. In the manufacturing apparatus 0 shown in FIG. 6, an intermediate thermometer 8 disposed at a predetermined position in the middle in the longitudinal direction and above the steel plate 1 was used.

  The example shown in FIG. 1 is a case where two intermediate thermometers 8-1 and 8-2 are arranged side by side in the conveying direction of the steel plate 1, but one may be installed or Three or more may be juxtaposed in the transport direction. Further, the intermediate thermometer 8 may be disposed below the steel plate 1.

  The intermediate thermometer 8 may be any thermometer as long as it can measure the surface temperature of the steel sheet 1, and need not be limited to a specific type. In the present embodiment, a so-called water column thermometer is used in order to reduce a measurement error caused by the injected cooling water. The water column thermometer is a radiation thermometer arranged at a position facing the steel plate 1 and a water column as an optical waveguide between the steel plate 1 and the radiation thermometer, as is well known from Japanese Patent No. 3818501. A thermometer comprising a water column forming means for forming the surface of the steel sheet 1, and the surface temperature of the steel sheet 1 is measured with high accuracy by detecting radiation light from the surface of the steel sheet 1 through the water column with a radiation thermometer. Is something that can be done.

The measured value of the surface temperature of the steel plate 1 by the intermediate thermometer 8 is input to a rapid cooling stop temperature estimation device 13 described later.
[Cooling control device 14]
The cooling control device 14 includes a rapid cooling steel plate temperature prediction device 11, a rapid cooling stop temperature control device 12, and a rapid cooling stop temperature estimation device 13.

  The steel plate temperature prediction device 11 at the time of rapid cooling is a measurement value of the surface temperature of the steel plate 1 on the water cooling device inlet side input from the water cooling device inlet side thermometer 7, and the plate thickness of the steel plate 1 input from the steel plate thickness measuring device 9. Based on the measured value and the measured value of the conveying speed of the steel plate 1 input from the steel plate speed measuring device 10, prediction is performed by estimating the surface temperature of the steel plate 1 during rapid cooling using the heat transfer model of the steel plate 1. Details of calculation contents by the rapid cooling steel plate temperature prediction device 11 will be described later.

  The rapid cooling stop temperature estimation device 13 uses the measured value of the surface temperature of the steel sheet 1 by the surface temperature measuring means 8 and the heat transfer model of the steel sheet 1 and the surface of the steel sheet 1 at the same timing as the measurement by the surface temperature measuring means 8. Based on the deviation from the estimated calculation value of the temperature, an average temperature in the plate thickness direction of the steel plate 1 when the cooling of the cooling water by the water cooling devices 5 and 6 is stopped is calculated. Details of the calculation contents by the rapid cooling stop temperature estimation device 13 will be described later.

  Further, the rapid cooling stop temperature control device 12 performs the water cooling so that the calculated value of the plate thickness direction average temperature of the steel plate 1 input from the rapid cooling stop temperature estimation device 13 when the cooling water injection stops is the target value. By outputting a command to sequentially correct the open / closed state of the valves of the devices 5 and 6 and controlling the injection of the cooling water by the water cooling devices 5 and 6, the estimated value of the rapid cooling stop temperature is accurately matched with the target value. To control.

  In this way, the cooling control device 14 stops the jetting of the cooling water by the water cooling devices 5 and 6 and subsequently cools the steel plate 1 conveyed on the runout table 3 while cooling the plate of the steel plate 1 at the time of rapid cooling stop. The cooling water injection by the water cooling devices 5 and 6 is controlled so that the calculated value of the thickness direction average temperature becomes the target value.

The manufacturing apparatus 0 shown in FIG. 1 is configured as described above.
Next, the 1st example of the method of manufacturing a hot rolled sheet steel using this manufacturing apparatus 0 is demonstrated. In this first example, the cooling rate of the steel sheet 1 that is rapidly cooled by being injected with cooling water is controlled to a predetermined rate, and the rapid cooling stop temperature is controlled to a target value.

  When the steel plate 1 finish-rolled by the hot finish rolling mill 2 passes through the water-cooling device inlet side thermometer 7, the surface temperature of the steel plate 1 is measured by the water cooling device inlet-side thermometer 7, and the steel plate thickness is measured. The thickness of the steel plate 1 is measured by the device 9.

  The steel plate temperature prediction device 11 at the time of rapid cooling is the measured surface temperature and plate thickness, the speed of passing through the water cooling devices 5 and 6, and the specific heat, density, water temperature and temperature data of the steel plate 1 necessary for the temperature prediction calculation, Is used to perform temperature prediction calculation using a heat transfer model of the steel sheet 1 when passing through the water-cooling devices 5 and 6, and estimate and predict the surface temperature of the steel sheet 1 during rapid cooling.

  In addition, when the water-cooling apparatus entrance side thermometer 7 is not installed, you may substitute with the predicted value of the exit temperature of the hot finishing rolling mill 2. FIG. Moreover, when the steel plate thickness measuring apparatus 9 is not installed, you may substitute with the predicted value of the outlet plate thickness of the hot finishing mill 2.

  Moreover, in order to perform this temperature prediction calculation, it is necessary to set the amount of cooling water per one water cooling header of the water cooling devices 5 and 6, and the following procedure is performed. First, assuming that the amount of water in the water-cooling headers of all the water-cooling devices 5 and 6 is the maximum water amount of the device, the temperature prediction of the steel sheet from the outlet of the hot finish rolling mill 2 until it passes through the water-cooling devices 5 and 6 Perform the calculation. Then, the cooling rate of the steel sheet 1 from the start of rapid cooling until reaching the target quenching stop temperature is calculated, and the amount of cooling water whose cooling rate calculated using a convergence calculation means such as a bisection method matches a predetermined cooling rate is obtained. Is the set cooling water amount.

In the case of the water cooling devices 5 and 6 that are not provided with a water amount adjusting valve, the maximum water amount of the water cooling devices 5 and 6 (simply the amount of outflow water when the valve is opened) is set as the set cooling water amount.
Next, the steel plate temperature prediction device 11 at the time of quenching is assumed that the water cooling header water amount of all the water cooling devices 5 and 6 is the set water amount obtained by the above method, from the outlet of the hot finish rolling mill 2 to the water cooling device 5, The temperature prediction calculation until passing through 6 is performed, and the calculation result is transmitted to the rapid cooling stop temperature control device 12.

In addition, the temperature prediction calculation result to be transmitted is the plate thickness direction average temperature and the surface temperature and the plate thickness direction temperature distribution at each water cooling header position.
The quenching stop temperature control device 12 obtains a position (quenching stop position) at which the calculated plate thickness direction average temperature reaches the target quenching stop temperature (quenching stop position), and from the water cooling header closest to the hot finish rolling mill 2 to this quenching stop position. A valve operation command is sent to the water cooling devices 5 and 6 so that the determined set amount of water flows out to the water cooling header disposed between them.

FIG. 2 is a graph showing that an error in the estimated value of the rapid cooling stop temperature occurs.
When the water cooling devices 5 and 6 are operated as described above, the plate thickness direction average calculated temperature predicted by the rapid cooling steel plate temperature prediction device 11 is controlled to the target rapid cooling stop temperature as shown in the graph of FIG. . However, since the plate thickness direction average calculation temperature includes a temperature prediction error caused by the estimation error of the cooling capacity of the water cooling devices 5 and 6, the actual plate thickness direction average temperature is always controlled to the target temperature. Do not mean. Further, when the predicted value is used for the surface temperature of the steel sheet 1 finish-rolled by the hot finish rolling mill 2, the predicted error is added to the plate thickness direction average calculated temperature, and the predicted value is similarly added to the plate thickness of the steel sheet 1. When is used, the prediction error is also added.

Therefore, in the present invention, the rapid cooling stop temperature is controlled with high accuracy by using the measured value of the surface temperature of the steel sheet 1 by the intermediate thermometer 8 installed downstream of the rapid cooling stop position.
As shown in the graph in FIG. 2, the rapid cooling steel plate temperature prediction device 11 performs the temperature prediction calculation of the air cooling section from the rapid cooling stop position to the measurement position by the intermediate thermometer 8, thereby Calculate the calculated surface temperature. Then, the quenching stop temperature estimating device 13 calculates the difference between the calculated value of the surface temperature calculated by the steel plate temperature predicting device 11 at the time of quenching and the measured value of the surface temperature of the steel plate 1 by the intermediate thermometer 8. By adding the difference to the plate thickness direction average calculated temperature at the quenching stop position calculated by the quenching steel plate temperature prediction device 11, the quenching stop temperature estimated value is calculated.

  The estimated value of the quenching stop temperature obtained by the quenching stop temperature estimating device 13 includes a temperature prediction calculation error of the air cooling part from the quenching stop position to the measurement position by the intermediate thermometer 8, but this air cooling part is a water cooling part to be rapidly cooled. In comparison, since the cooling capacity is small, the temperature drop amount is small, and the phenomenon that the cooling ability is suddenly changed due to the change in the boiling state peculiar to water cooling does not occur. It is much more accurate and less error-prone than the predicted value calculated from the measured side temperature through the water cooling section.

FIG. 3 is a graph showing that the estimated value of the rapid cooling stop temperature is controlled to the target value according to the present invention.
In the present invention, using the estimated quenching stop temperature with a small error, the water cooling devices 5 and 6 are fed back so that the estimated quenching stop temperature matches the target quenching stop temperature as shown in the graph of FIG. Thus, the sheet thickness direction average temperature immediately after the rapid cooling stop can be controlled with high accuracy.

  In the example shown in FIG. 3, since the cooling rate of the steel sheet 1 at the time of rapid cooling is a constant value, in order to make the estimated rapid cooling stop temperature coincide with the target rapid cooling stop temperature, the rapid cooling stop position must be corrected. I must. The rapid cooling stop position to be corrected is easily calculated from the difference between the estimated rapid cooling stop temperature, the target rapid cooling stop temperature, and the cooling rate, and is used for the water cooling header from the rapid cooling stop position before correction to the corrected rapid cooling stop position. Command the set water volume valve (close if the valve is open, open if the valve is closed).

  Furthermore, the longitudinal direction of the steel plate 1 can be controlled by periodically performing the series of calculations and settings described so far in a cycle of 0.4 seconds to 2.0 seconds, and the steel plate 1 can be conveyed by accelerated rolling. Even when the speed continuously changes, the rapid cooling stop temperature can be controlled to the target value.

In the present invention, in order to control the quenching stop temperature with high accuracy, it is effective to appropriately set the measurement position of the intermediate thermometer 8.
That is, the surface temperature of the steel sheet 1 at the quenching stop position is lower than the average temperature in the plate thickness direction. Immediately after the quenching stop position, reheating occurs inside the steel sheet 1 and the heat moves to the surface so that the surface temperature rapidly increases. Since it is in a rising transient state, it is desirable not to use the measured value of the intermediate thermometer in such a state for calculating the estimated value of the rapid cooling stop temperature. Specifically, the measurement position of the intermediate thermometer 8 is a position where the rapid change of the surface temperature of the steel plate 1 is finished, the difference between the surface temperature and the plate thickness direction average temperature is small, and the surface temperature turns from rising to falling. In other words, in other words, when the estimated value of the surface temperature of the steel plate 1 estimated using the heat transfer model of the steel plate 1 changes from rising to falling after stopping the injection of the cooling water (the transfer of the steel plate). It is desirable to measure the surface temperature of the steel sheet with the intermediate thermometer 8 at a predetermined time after the differential value of the estimated curve of the surface temperature of the steel sheet estimated using a thermal model becomes zero.

FIG. 4 is a graph showing the influence of the plate thickness or cooling rate on the time (hereinafter referred to as “recovery time”) when the surface temperature changes from rising to falling immediately after the rapid cooling stop.
The recuperation time can be obtained by temperature calculation, and can be arranged by the plate thickness and the cooling rate as shown in the graph of FIG.

  For this reason, the installation position of the intermediate thermometer 8 has an optimum position according to the rapid cooling stop position, the steel plate speed, the plate thickness, and the cooling rate. When only one intermediate thermometer 8 is installed, it may be installed at a position farthest from the hot finish rolling mill 2 among the various operating conditions.

  On the other hand, since the present invention estimates the rapid cooling stop temperature from the measured value of the intermediate thermometer 8, the longer the distance from the rapid cooling stop position to the installation position of the intermediate thermometer 8, the longer the dead time. As a result, the control performance of the feedback control deteriorates, and the error in the temperature prediction calculation of the air cooling section increases, leading to a decrease in control accuracy. Therefore, the installation position of the intermediate thermometer 8 is within the possible range of the rapid cooling stop position. It is desirable to approach.

  For this reason, a plurality of intermediate thermometers 8 are arranged side by side in the conveying direction of the steel sheet 1, and the measured value of the intermediate thermometer 8 present at the closest position after the required recuperation time from the rapid cooling stop position is controlled. By using it, it is possible to suppress a decrease in control accuracy. In addition, when the conveyance speed of the steel sheet 1 is continuously changed by accelerated rolling and the rapid cooling stop position is also continuously changed accordingly, the intermediate thermometer 8 used for the control is restored from the rapid cooling stop position. By continuously switching to the nearest intermediate thermometer 8 after passing the heat time, it is possible to suppress a decrease in control accuracy.

  Next, the 2nd example of the method of manufacturing a hot-rolled steel plate using the manufacturing apparatus 0 shown in FIG. 1 is demonstrated. In this second example, the rapid cooling stop temperature is controlled to the target value by changing the cooling rate during rapid cooling while keeping the rapid cooling stop position constant.

  When the steel plate 1 finish-rolled by the hot finish rolling mill 2 passes through the water-cooling device inlet side thermometer 7, the surface temperature of the steel plate 1 is measured by the water cooling device inlet-side thermometer 7, and the steel plate thickness is measured. The thickness of the steel plate 1 is measured by the device 9.

  The steel plate temperature prediction device 11 at the time of rapid cooling is the measured surface temperature and plate thickness, the speed of passing through the water cooling devices 5 and 6, and the specific heat, density, water temperature and temperature data of the steel plate 1 necessary for the temperature prediction calculation, Is used to perform temperature prediction calculation using a heat transfer model of the steel sheet 1 when passing through the water-cooling devices 5 and 6, and estimate and predict the surface temperature of the steel sheet 1 during rapid cooling. At this time, the rapid cooling stop position is set in advance, and a temperature prediction calculation up to the rapid cooling stop position is performed.

  In addition, when the water-cooling apparatus entrance side thermometer 7 is not installed, you may substitute with the predicted value of the exit temperature of the hot finishing rolling mill 2. FIG. Moreover, when the steel plate thickness measuring apparatus 9 is not installed, you may substitute with the predicted value of the outlet plate thickness of the hot finishing mill 2.

  Moreover, in order to perform this temperature prediction calculation, it is necessary to set the amount of cooling water per one water cooling header of the water cooling devices 5 and 6, and the following procedure is performed. First, assuming that the amount of water in the water-cooling headers of all the water-cooling devices 5 and 6 is the maximum water amount of the device, the temperature prediction of the steel sheet from the outlet of the hot finish rolling mill 2 until it passes through the water-cooling devices 5 and 6 Perform the calculation. Then, the thickness direction average temperature calculation value at the rapid cooling stop position is calculated, and a cooling water amount is calculated by using a convergence calculation means such as a bisection method so that the thickness direction average temperature calculation value matches the target quenching stop temperature. Is the set cooling water amount.

  Next, the steel plate temperature prediction device 11 at the time of quenching quenches from the outlet of the hot finish rolling mill 2 on the assumption that the water cooling header water amount of the water cooling devices 5 and 6 up to the rapid cooling stop position is the set water amount obtained by the above method. A temperature prediction calculation up to the stop position is performed, and the calculation result is transmitted to the rapid cooling stop temperature control device 12. The temperature prediction calculation result to be transmitted is the average temperature and surface temperature in the plate thickness direction and the temperature distribution in the plate thickness direction at the rapid cooling stop position.

  The rapid cooling stop temperature control device 12 sends a valve operation command to the water cooling devices 5 and 6 so that the determined set amount of water flows out to the water cooling header from the water cooling header closest to the hot finish rolling mill 2 to the rapid cooling stop position. Send.

  When the water cooling devices 5 and 6 are operated by the above method, as shown in the graph of FIG. 2, the plate thickness direction average calculated temperature predicted by the rapid cooling steel plate temperature prediction device 11 is controlled to the target rapid cooling stop temperature. However, since the plate thickness direction average calculation temperature includes a temperature prediction error caused by an estimation error of the cooling capacity of the water cooling devices 5 and 6, the actual temperature is not necessarily controlled to the target temperature. . Further, when the predicted value is used for the surface temperature of the steel sheet 1 finish-rolled by the hot finish rolling mill 2, the predicted error is added to the plate thickness direction average calculated temperature, and the predicted value is similarly added to the plate thickness of the steel sheet 1. When is used, the prediction error is also added.

Therefore, in the present invention, the rapid cooling stop temperature is controlled with high accuracy by using the measured value of the intermediate thermometer 8 installed behind the rapid cooling stop position.
As shown in the graph of FIG. 2, the steel plate temperature prediction device 11 at the time of quenching performs temperature prediction calculation of the air cooling part from the quenching stop position to the measurement position of the intermediate thermometer 8, and the thermometer measurement value and the surface temperature calculation value are calculated. The error is calculated. Then, this error is added to the plate thickness direction average calculated temperature at the rapid cooling stop position to calculate the rapid cooling stop temperature estimated value.

  Although the estimated value of the rapid cooling stop includes an error in predicting the temperature of the air cooling section from the rapid cooling stop position to the measurement position by the intermediate thermometer 8, the cooling capacity of the air cooling section is smaller than that of the water cooling section. Since there is no phenomenon that is difficult to predict and the cooling capacity is suddenly changed due to a change in the boiling state peculiar to water cooling, than the value calculated through the water cooling section from the measured value by the water cooling device inlet side thermometer 7, Accurate and small error.

FIG. 5 is a graph showing that the estimated quenching stop temperature is controlled by the present invention.
If the estimated quenching stop temperature value with a small error is used and the water cooling devices 5 and 6 are feedback-controlled so that the estimated quenching stop temperature value matches the target quenching stop temperature as shown in the graph of FIG. The sheet thickness direction average temperature immediately after can be controlled with high accuracy.

  In this second example, since the rapid cooling stop position is determined in advance, in order to make the estimated rapid cooling stop temperature coincide with the target rapid cooling stop temperature, the set water amount of the water cooling devices 5 and 6 must be corrected. I must. Calculate the set amount of water to be corrected using a convergence calculation means such as a bisection method so that the estimated quenching stop temperature matches the target quenching stop temperature. Command to set water volume valve.

  Furthermore, by performing the series of calculations and settings described so far periodically at a period of 0.4 second to 2.0 seconds, the longitudinal direction of the steel plate 1 can be controlled, and the steel plate 1 can be controlled by accelerated rolling. Even in the case where the transfer speed continuously changes, the quenching stop temperature can be controlled to the target value.

  In the second embodiment, as in the first embodiment, it is necessary to appropriately set the measurement position of the intermediate thermometer 8. However, since the rapid cooling stop position is a predetermined position, the change in the rapid cooling stop position is performed. Therefore, the optimum installation range of the intermediate thermometer 8 is narrower than that of the first embodiment.

  As described above, according to the present invention, when cooling water is sprayed on the steel sheet 1 that is hot-rolled and conveyed to cool the steel sheet 1, the cooling water injection is stopped and the steel sheet is subsequently air-cooled. Furthermore, with a simple configuration, it is possible to accurately estimate the sheet thickness direction average temperature of the steel sheet at the rapid cooling stop position where the cooling water injection is stopped, and to control the cooling water injection by the water cooling device using this estimated calculation value. Thus, the rapid cooling stop temperature of the steel sheet can be controlled with high accuracy.

Furthermore, the present invention will be described more specifically with reference to examples.
A hot-rolled steel sheet was manufactured under the conditions listed below using the hot-rolled steel sheet manufacturing apparatus 0 shown in FIG. In this embodiment, water cooling devices 5 and 6 having a plurality of water cooling headers having an on / off valve without a water amount adjusting function are installed at the outlet of the hot finish rolling mill 2, and the water cooling devices 5 and 6 are connected to the outlets of the water cooling devices 5 and 6. The first intermediate thermometer 8-1 was installed 24m behind, and the second intermediate thermometer 8-2 was installed 30m behind.
Steel type of steel plate 1 440 MPa class high-strength hot-rolled steel plate 1 Thickness of about 3.7 mm (measured value)
Water cooling device inlet side temperature about 860 ℃ (measured value)
Target quench stop temperature 800 ℃
Speed of steel plate 1 640 mpm → 920 mpm (accelerated rolling)
Water-cooled header valve type On / off valve (no set water volume adjustment function)
Length of water cooling device 5 (upper surface) 36.0m
Length of water cooling device 6 (bottom surface) 36.0m
Number of valves of the water cooling device 5 (upper surface) 48 Number of valves of the water cooling device 6 (lower surface) 30 Water density of the water cooling device 5 (upper surface) 1.1 m ³ / m ² hr (when the valve is on)
Water density of water cooling device 6 (bottom surface) 0.8 m ³ / m ² hr (when valve is on)
Position of the intermediate thermometer 8-1 Position 24.0m backward from the inlet of the water cooling devices 5 and 6 Position of the intermediate thermometer 8-2 Position 30.0m backward from the inlet of the water cooling devices 5 and 6 FIG. FIG. 7 is a graph showing the longitudinal temperature of the steel plate 1 when the above-described first example of the present invention is implemented.

  In the graph of the quenching stop temperature control results shown in FIGS. 6 and 7, in the upper row, the water cooling device inlet side (finishing outlet) temperature measurement value in the longitudinal direction of the steel sheet, the thickness direction average calculated temperature at the quenching stop position, and quenching in the order from the top. The estimated stop temperature, the measured value of the intermediate thermometer 8-1 and the measured value of the intermediate thermometer 8-2 are shown, the speed of the steel plate 1 is shown in the middle, and the quenching position is shown in the lower. When the rapid cooling stop position is less than 15 m, the rapid cooling stop temperature estimated value is calculated based on the measured value of the intermediate thermometer 8-1, and when it exceeds 15 m, the intermediate thermometer 8-2 is switched to.

  In the conventional example shown in FIG. 6, without using the measured values of the intermediate thermometers 8-1 and 8-2, the water cooling devices 5 and 6 are adjusted so that the average calculated temperature in the thickness direction at the rapid cooling stop position becomes the target 800 ° C. This is the result of control.

  The water cooling header valves of the water cooling devices 5 and 6 do not have a set water amount adjustment function, and if the cooling capacity is insufficient, it is necessary to move the rapid cooling stop position backward to increase the total amount of cooling water. In this embodiment, since the accelerated rolling is performed, the speed of the steel sheet 1 is increased to the maximum speed of 920 mpm, but the average temperature in the thickness direction at the quenching stop position is controlled to the target temperature, so that it corresponds to the speed increase. The rapid cooling stop position is moved backward.

  As shown in the graph of FIG. 6, in the conventional example, the estimated quenching stop temperature calculated using the measured value of the intermediate thermometer 8 is about 20 ° C. lower than the target 800 ° C., and this control method has sufficient accuracy. Cannot be obtained.

  On the other hand, as shown in the graph of FIG. 7, in the present invention example, the measured value of the surface temperature of the steel sheet 1 by the intermediate thermometers 8-1 and 8-2 is used, and the estimated quenching stop temperature at the quenching stop position is Since the water cooling devices 5 and 6 were controlled to reach the target 800 ° C., the estimated value of the quenching stop temperature was lower than the target at the tip of the steel plate 1, but the error between the estimated quenching temperature and the target temperature was reduced. It can be seen that the feedback control function is performed so that the estimated quenching stop temperature is accurately controlled to the target temperature.

Next, Example 2 will be described.
FIG. 8 is an explanatory diagram illustrating the overall configuration of the hot rolled steel sheet manufacturing apparatus 0-1 according to the second embodiment. In the following description, portions different from the hot rolled steel sheet manufacturing apparatus 0 shown in FIG. 1 will be described, and the same portions will be denoted by the same reference numerals, and redundant description will be omitted.

  The manufacturing apparatus 8-1 shown in FIG. 8 is different from the manufacturing apparatus shown in FIG. 1 in that water cooling devices 5 and 6 capable of adjusting the water density are arranged at the outlet of the hot finish rolling mill 2, and the water cooling device The intermediate thermometer 8-1 is installed 1m behind the 5 and 6 outlets, and the intermediate thermometer 8-2 is installed 3m behind.

  This intermediate thermometer 8-1 is for reproducing a part of the technique described in Patent Document 2. This technology aims to finely control the cooling rate in the longitudinal direction of the steel plate from finish rolling to winding, and in order to achieve this, a number of water-cooling devices on the run-out table and each outlet side are provided. A temperature detection device is provided, a target temperature is set for each temperature detection device, and a number of water cooling devices are feedback-controlled so that each temperature detection value matches the target. As described above, since a large number of water cooling devices and temperature detection devices are required, the distance from the water cooling device to the temperature detection device is inevitably shortened, and it is difficult to ensure the necessary recuperation time.

  Here, in order to reproduce a part of the prior art, paying attention to one water cooling device and a temperature detection device, the intermediate thermometer 8-1 is disposed close to the water cooling devices 5 and 6, and the measurement of the intermediate thermometer 8-1 is performed. Feedback control is performed using the value directly.

A hot-rolled steel sheet was manufactured under the following conditions using the manufacturing apparatus of FIG. In addition, since the recuperation completion time on this condition is 0.3 second in calculation, and it is 2.4 m in terms of distance, the measurement of the surface temperature of the steel sheet 1 by the intermediate thermometer 8-1 is in the middle of recuperation. Done.
Steel type of steel plate 1 440 MPa class high-strength hot-rolled steel plate 1 Thickness of about 3.0 mm (measured value)
Entry temperature of water cooling devices 5 and 6 Approx. 860 ° C (measured value)
Target quench stop speed 60 ℃ / sec Target quench stop temperature 740 ℃
Speed of steel plate 1 480 mpm (no accelerated rolling)
Length of water cooling device 5, 6 16.0m
Water-cooled header valve type Water volume density (upper surface) of the water-cooling devices 5 and 6 with a set water amount adjusting function 0.0 to 1.1 m ³ / m ² hr (valve opening 0 to 10
0%)
Water density of water cooling devices 5 and 6 (lower surface) 0.0 to 0.8 m ³ / m ² hr (valve opening 0 to 10
0%)
Position of the intermediate thermometer 8-1 1.0m position behind the outlets of the water cooling devices 5 and 6 Position of the intermediate thermometer 8-2 3.0m position behind the outlets of the water cooling devices 5 and 6 FIG. 10 is a graph showing the temperature in the longitudinal direction of the steel plate when the embodiment of the present invention is carried out.

  The graph of the quenching stop temperature control result shown in FIGS. 9 and 10 shows the quenching stop temperature estimation calculated based on the measured value of the surface temperature of the steel sheet 1 by the intermediate thermometer 8-2 in the longitudinal direction of the steel sheet in order from the top. The measured value of the surface temperature of the steel sheet 1 with the intermediate thermometer 8-1 and the measured value of the surface temperature of the steel sheet 1 with the intermediate thermometer 8-2 are shown. Same water density). Note that accelerated rolling is not performed, the steel plate speed is constant, and there is no change in the rapid cooling stop position.

  FIG. 9 is based on the invention described in Japanese Patent Application Laid-Open No. 6-246331, and is a result of a rapid cooling control experiment simulating one cooling zone. The measured value of the intermediate thermometer 8-1 is controlled to the target quenching stop temperature of 740 ° C., but the installation position of the intermediate thermometer 8-1 has not passed the recuperation time, and the steel plate surface temperature has increased. Therefore, the measured value of the intermediate thermometer 8-21 is lower than the measured value of the intermediate thermometer 8-2 after the recuperation time.

The estimated quenching stop temperature estimated based on the measured value of the intermediate thermometer 8-2 is about 10 ° C. higher than the target, and the control accuracy of the quenching stop temperature is poor in this control method.
On the other hand, FIG. 10 uses the measured value of the surface temperature of the steel sheet 1 by the intermediate thermometer 2 to control the water cooling devices 5 and 6 so that the estimated quenching stop temperature at the quenching stop position becomes the target 740 ° C. It is the control result performed.

  Although the estimated value of the quenching stop temperature exceeds the target at the tip of the steel plate 1, a feedback control function that reduces the error between the estimated value of the quenching stop temperature and the target temperature works, and the estimated value of the quenching stop temperature becomes the target temperature. It can be seen that it is accurately controlled.

0, 0-1 Hot rolled steel plate manufacturing equipment 1 Steel plate 2 Hot finish rolling mill 3 Transport table (runout table)
4 Winding device 5, 6 Water cooling device 7 Water cooling device inlet side thermometer 8, 8-1, 8-2 Surface temperature measuring means (intermediate thermometer)
9 Steel plate thickness measurement device 10 Steel plate speed measurement device 11 Rapid cooling steel plate temperature prediction device 12 Rapid cooling stop temperature control device 13 Rapid cooling stop temperature estimation device 14 Cooling control device

Claims (5)

A hot rolling mill, a water cooling device that is installed on the outlet side of the hot rolling mill and that is cooled by spraying cooling water onto a steel sheet that is rolled and conveyed by the hot rolling mill, and injection of the cooling water A cooling control device for controlling the steel plate to a predetermined temperature by air-cooling the steel plate and measuring the surface temperature of the steel plate at a predetermined time after stopping the cooling water injection And a surface temperature measuring means for
The cooling control device is based on a difference between a measured value of the surface temperature of the steel sheet by the surface temperature measuring means and an estimated value of the surface temperature of the steel sheet at the predetermined time using a heat transfer model of the steel sheet. Calculating the average thickness direction temperature of the steel sheet when the cooling water injection is stopped, and injecting the cooling water by the water cooling device so that the calculated value of the average thickness direction temperature becomes the target value. Controlling , and
The predetermined time is a time after the estimated value of the surface temperature of the steel sheet estimated using the heat transfer model of the steel sheet turns from rising to falling after stopping the injection of the cooling water. An apparatus for producing a hot-rolled steel sheet characterized by the following. A plurality of the surface temperature measuring means are arranged in the conveying direction of the steel sheet, and the cooling control device is configured to estimate the steel sheet using a heat transfer model of the steel sheet among the plurality of surface temperature measuring means. 2. The hot rolling according to claim 1, wherein the surface temperature measuring means is disposed at a position closest to the downstream side of the position where the estimated value of the surface temperature changes from rising to falling after the cooling water injection is stopped. Steel plate manufacturing equipment. The surface temperature measuring means includes a radiation thermometer disposed at a position facing the steel plate, and a water column forming means for forming a water column as an optical waveguide between the steel plate and the radiation thermometer, The apparatus for producing a hot-rolled steel sheet according to claim 1 or 2 , wherein the surface temperature of the steel sheet is measured by detecting radiation light from the surface of the steel sheet through the water column with the radiation thermometer. After the cooling water is sprayed onto the steel sheet that is hot-rolled and conveyed, the steel sheet is water-cooled, and then the cooling water injection is stopped and the steel sheet is subsequently air-cooled to control the steel sheet to a predetermined temperature. A method for producing a hot-rolled steel sheet including a process,
The difference between the measured value of the surface temperature of the steel plate at a predetermined time after stopping the injection of the cooling water and the estimated calculation value of the surface temperature of the steel plate at the predetermined time using the heat transfer model of the steel plate The cooling water injection is controlled so that the average thickness direction temperature of the steel sheet when the cooling water injection is stopped is calculated and the calculated value of the average thickness direction temperature becomes the target value. It is, and
The predetermined time is a time after the estimated value of the surface temperature of the steel sheet estimated using the heat transfer model of the steel sheet turns from rising to falling after stopping the injection of the cooling water. A method for producing a hot-rolled steel sheet characterized by the following. The surface temperature of the steel plate includes a radiation thermometer disposed at a position facing the steel plate, and a water column forming means for forming a water column as an optical waveguide between the steel plate and the radiation thermometer, The method for manufacturing a hot-rolled steel sheet according to claim 4 , wherein the measurement is performed using an apparatus for measuring the surface temperature of the steel sheet by detecting radiation light from the surface of the steel sheet with a radiation thermometer through a water column.

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