JPWO2014087520A1 - Hot-rolled steel sheet cooling device - Google Patents

Abstract

The hot-rolled steel sheet cooling device of the present invention includes a thermometer that measures the temperature of the hot-rolled steel sheet; a shape meter that measures the shape of the hot-rolled steel sheet; and an upper cooling device that cools the upper surface of the hot-rolled steel sheet in a cooling section. A lower cooling device for cooling the lower surface of the hot-rolled steel sheet in the cooling section; and the cooling by controlling the upper cooling device and the lower cooling device based on the temperature measurement result and the shape measurement result And a control device that controls at least one of an upper surface cooling heat removal amount and a lower surface cooling heat removal amount of the hot-rolled steel sheet in the section.

Description

  The present invention relates to a hot-rolled steel sheet cooling device for cooling a hot-rolled steel sheet hot-rolled by a finish rolling mill.

For example, hot-rolled steel sheets used for automobiles and industrial machines are generally manufactured through a rough rolling process and a finish rolling process. FIG. 18 is a diagram schematically showing a conventional method for producing a hot-rolled steel sheet. In the manufacturing process of a hot-rolled steel sheet, first, a slab S obtained by continuously casting molten steel adjusted to a predetermined composition is rolled by a roughing mill 201, and then finished by a plurality of rolling stands 202a to 202d. Hot-rolled steel sheet H having a predetermined thickness is formed by hot rolling with a rolling mill 203. And after this hot-rolled steel sheet H is cooled by the cooling water poured from the cooling device 211, it is wound up by the winding device 212 in a coil shape.

  The cooling device 211 is a facility for performing so-called laminar cooling on the hot-rolled steel sheet H that is generally conveyed from the finish rolling mill 203. The cooling device 211 injects cooling water as jet water from above in the vertical direction to the upper surface of the hot-rolled steel sheet H moving on the run-out table, and also against the lower surface of the hot-rolled steel sheet H. Then, the hot-rolled steel sheet H is cooled by injecting cooling water as jet water through the pipe laminator.

  Conventionally, for example, Patent Document 1 discloses a technique for preventing a shape defect of a steel sheet by reducing the surface temperature difference between the upper and lower surfaces of the thick steel sheet. According to the technique disclosed in Patent Document 1, based on the surface temperature difference obtained by simultaneously measuring the surface temperature of the upper and lower surfaces of the steel sheet with a thermometer during cooling by the cooling device, the upper and lower surfaces of the steel sheet Adjust the ratio of the amount of cooling water supplied to the.

  Further, for example, in Patent Document 2, the material to be rolled is cooled by using spray spray between two adjacent stands of the finish rolling mill to start and complete the γ-α transformation of the material to be rolled. A technique for preventing deterioration of the sheet-passability between the two is disclosed.

  Also, for example, in Patent Document 3, the steepness meter installed on the exit side of the rolling mill is used to measure the steepness at the tip of the steel sheet, and the cooling water flow rate is changed in the width direction according to the measured steepness. Thus, a technique for preventing perforation of a steel sheet is disclosed.

  Furthermore, for example, Patent Document 4 aims at eliminating the wavy plate thickness distribution in the plate width direction of the hot-rolled steel plate and uniforming the plate thickness in the plate width direction, and in the plate width direction of the hot-rolled steel plate. A technique for controlling the difference between the maximum heat transfer coefficient and the minimum heat transfer coefficient to fall within a predetermined value range is disclosed.

  Here, the hot-rolled steel sheet H manufactured by the manufacturing method shown in FIG. 18 is, for example, as shown in FIG. 19, a transport roll of a run-out table (hereinafter sometimes referred to as “ROT”) in the cooling device 211. On 220, a wave shape may be generated in the rolling direction (the arrow direction in FIG. 19). In that case, variation occurs in cooling of the upper surface and the lower surface of the hot-rolled steel sheet H. That is, there is a problem that uniform cooling cannot be performed in the rolling direction due to a cooling deviation caused by the wave shape of the hot-rolled steel sheet H itself.

  Thus, for example, in Patent Document 5, in a steel plate having a corrugated shape in the rolling direction, in order to uniformize the cooling of the steel plate, the influence of the distance between the upper landing water of the steel plate and the lower table roller is described. A technique for making the cooling capacity of the upper cooling and the lower cooling the same so as to minimize is disclosed.

Japanese Unexamined Patent Publication No. 2005-74463 Japanese Laid-Open Patent Publication No. 5-337505 Japanese Patent Laid-Open No. 2005-271052 Japanese Unexamined Patent Publication No. 2003-48003 Japanese Unexamined Patent Publication No. 6-328117

  However, the cooling method of Patent Document 1 does not consider the case where the hot-rolled steel sheet has a wave shape in the rolling direction. In the hot-rolled steel sheet H having the above-described corrugated shape, as shown in FIG. Further, the hot-rolled steel sheet H is also in local contact with an apron (not shown in FIG. 19) provided as a support for preventing the hot-rolled steel sheet H from falling between the conveying rolls 220 at the corrugated bottom. There is a case. In the corrugated hot-rolled steel sheet H, a portion that is locally in contact with the transport roll 220 and the apron is more easily cooled than other portions by contact heat removal. For this reason, there existed a problem that the hot-rolled steel plate H was cooled unevenly. That is, Patent Document 1 considers that the hot-rolled steel sheet is corrugated so that the transport roll or apron and the hot-rolled steel sheet are in local contact, and the contact portion is easily cooled by contact heat removal. Absent. Therefore, there are cases where the hot-rolled steel sheet having the corrugated shape cannot be cooled uniformly.

  Further, the technique described in Patent Document 2 is intended to perform uniform cooling by subjecting an extremely low carbon steel having a relatively low hardness (soft) to a γ-α transformation between the stands of a finishing mill. It is not a thing. Further, the invention of Patent Document 2 does not relate to cooling when the material to be rolled has a wave shape in the pressure direction or when the material to be rolled is a steel material called so-called high tensile steel having a tensile strength (TS) of 800 MPa or more. Therefore, when the material to be rolled is a hot-rolled steel plate having a corrugated shape or a steel material having a relatively high hardness, there is a possibility that uniform cooling may not be performed.

  Moreover, in the cooling method of patent document 3, the steepness of the width direction of a steel plate is measured, and the cooling water flow rate of the part with the high steepness is adjusted. However, if the cooling water flow rate in the plate width direction of the steel plate is changed, it becomes difficult to make the temperature in the plate width direction of the steel plate uniform. Furthermore, Patent Document 3 does not consider the case where the hot-rolled steel sheet has a wave shape in the rolling direction, and as described above, the hot-rolled steel sheet may not be uniformly cooled.

  Moreover, since the cooling of patent document 4 is cooling of the hot-rolled steel plate immediately before a finish rolling mill roll bite, it cannot be applied to the hot-rolled steel plate that has been finish-rolled to a predetermined thickness. Furthermore, Patent Document 4 does not consider the case where a wave shape is formed in the rolling direction of the hot-rolled steel sheet, and as described above, the hot-rolled steel sheet cannot be uniformly cooled in the rolling direction. There is a case.

  Further, in the cooling method of Patent Document 5, the cooling capacity of the upper cooling includes cooling by riding water on the upper part of the steel sheet in addition to cooling by the cooling water supplied to the steel sheet from the upper water injection nozzle. Since this boarding water is influenced by the steepness of the wave shape formed on the steel plate and the plate passing speed of the steel plate, the cooling ability of the steel plate by the boarding water cannot be specified strictly. Then, it is difficult to accurately control the cooling capacity of the upper cooling. For this reason, it is difficult to make the cooling capacity of the upper cooling and the lower cooling the same. Moreover, when the cooling capacity of the upper cooling and the lower cooling is made the same, an example of a method for determining the cooling capacity is illustrated, but a universal determination method is not disclosed. Therefore, the cooling method of patent document 5 may not cool a hot-rolled steel plate uniformly.

The present invention has been made in view of the above-described problems, and an object thereof is to uniformly cool a hot-rolled steel sheet that has been hot-rolled by a finish rolling mill.

The present invention employs the following means in order to solve the above problems and achieve the object.
That is,

(1) A hot-rolled steel sheet cooling device according to an aspect of the present invention is a hot-rolled steel sheet cooling device that cools a hot-rolled steel sheet hot-rolled by a finish rolling mill in a cooling section provided on the passage plate path. A thermometer for measuring the temperature of the hot-rolled steel sheet downstream of the cooling section; a shape-meter for measuring the shape of the hot-rolled steel sheet downstream of the cooling section; and the heat in the cooling section. An upper cooling device for cooling the upper surface of the rolled steel sheet; a lower cooling device for cooling the lower surface of the hot rolled steel sheet in the cooling section; a temperature measurement result of the hot rolled steel sheet obtained from the thermometer and the shape meter Based on the obtained shape measurement result of the hot-rolled steel sheet, by controlling the upper cooling device and the lower cooling device, the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot rolled steel plate in the cooling section, At least An average temperature calculation for calculating, as an average temperature, a time-series average value of the temperature of the hot-rolled steel sheet on the downstream side of the cooling section based on the temperature measurement result. A fluctuation rate calculation unit that calculates a fluctuation rate of the hot-rolled steel sheet on the downstream side of the cooling section based on the shape measurement result; and when the upward direction in the vertical direction of the hot-rolled steel sheet is positive, When the temperature of the hot-rolled steel sheet is lower than the average temperature in the range of one cycle or more of the wave shape of the hot-rolled steel sheet in a region where the fluctuation speed is positive, the lower surface cooling heat removal amount and the lower surface are reduced. When the temperature of the hot-rolled steel sheet is determined to be at least one of the directions in which the cooling heat removal amount increases as the control direction and the temperature of the hot-rolled steel sheet is higher than the average temperature, the direction in which the upper surface cooling heat removal amount increases and the lower surface cooling heat removal Is determined as the control direction, and when the temperature of the hot-rolled steel sheet is lower than the average temperature in a region where the fluctuation speed is negative, the amount of heat removal from the upper surface is increased. And at least one of the directions in which the lower surface cooling heat removal amount decreases as the control direction, and when the temperature of the hot-rolled steel sheet is higher than the average temperature, the upper surface cooling heat removal amount decreases and the lower surface A control direction determining unit that determines at least one of the directions in which the amount of heat removal from cooling increases as the control direction; and based on the control direction determined by the control direction determining unit, the hot rolled steel sheet in the cooling section A cooling heat removal amount total value adjustment unit for adjusting a total value of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount.

(2) In the hot-rolled steel sheet cooling device according to the above (1), it is preferable that a positional deviation between the temperature measurement part of the thermometer and the shape measurement part of the shape meter on the hot-rolled steel sheet is within 50 mm. .

(3) In the hot-rolled steel sheet cooling device according to (1) or (2) above, the sheet-passing speed of the hot-rolled steel sheet in the cooling section is within a range of 550 m / min or more to a mechanical limit speed or less. It is preferable that it is set.

(4) In the hot-rolled steel sheet cooling device according to (3) above, the hot-rolled steel sheet preferably has a tensile strength of 800 MPa or more.

(5) In the hot-rolled steel sheet cooling device according to (3), the finish rolling mill is composed of a plurality of rolling stands, and auxiliary cooling of the hot-rolled steel sheets is performed between the rolling stands adjacent to each other. It is preferable to further include an auxiliary cooling device for performing.

According to the above aspect of the present invention, the upper cooling capacity and the lower cooling capacity can be adjusted by detecting the phase of the temperature of the hot-rolled steel sheet and comparing it with the wave shape of the hot-rolled steel sheet. The upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the steel sheet can be adjusted. Therefore, after that, the hot-rolled steel sheet can be uniformly cooled by cooling the hot-rolled steel sheet with the adjusted cooling capacity.

It is explanatory drawing which shows the hot rolling equipment 1 provided with the hot-rolled steel plate cooling device in one Embodiment of this invention. It is explanatory drawing which shows the outline of a structure of the cooling device 14 in this embodiment. It is explanatory drawing which shows the outline of a structure of the cooling device 14 vicinity in the hot rolling equipment 1. FIG. A graph showing the relationship between the temperature fluctuation and steepness of a hot-rolled steel sheet H in the ROT cooling of a typical strip in a normal operation, and the upper graph shows the temperature fluctuation with respect to the distance from the coil tip or the fixed point elapsed time. The lower graph shows the steepness with respect to the distance from the coil tip or the fixed point elapsed time. It is a graph which shows the relationship between the temperature fluctuation and the steepness of the hot-rolled steel sheet H in the ROT cooling of a typical strip in a normal operation. The temperature of the hot-rolled steel sheet H is lower than the average temperature of the hot-rolled steel sheet H when the fluctuation speed H degree of the hot-rolled steel sheet is positive, and the temperature of the hot-rolled steel sheet H is higher when the fluctuation speed is negative. In this case, it is a graph showing the relationship between the temperature fluctuation and the steepness of the hot-rolled steel sheet H when the upper surface cooling heat removal amount is decreased and the lower surface cooling heat removal amount is increased. The steepness of the wave shape of the hot-rolled steel sheet H is a value obtained by dividing the amplitude of the wave shape by the length in the rolling direction for one cycle. When the temperature of the hot-rolled steel sheet H is lower than the average temperature of the hot-rolled steel sheet H when the fluctuation speed of the hot-rolled steel sheet H is positive, and the temperature of the hot-rolled steel sheet H is higher when the fluctuation speed is negative. FIG. 6 is a graph showing the relationship between the temperature fluctuation and steepness of the hot-rolled steel sheet H when the upper surface cooling heat removal amount is increased and the lower surface cooling heat removal amount is decreased. It is explanatory drawing which shows arrangement | positioning of the thermometer 40 and the shape meter 41 in the hot rolling equipment 1. FIG. It is explanatory drawing which shows the modification of the cooling device 14 in the hot rolling equipment 1. FIG. It is a graph which shows the relationship between the steepness of a hot-rolled steel sheet H, and a temperature standard deviation. It is a graph which shows the relationship between the plate-feeding speed of a hot-rolled steel plate H, and a temperature standard deviation. It is explanatory drawing which shows a mode that the temperature standard deviation was formed in the plate width direction of the hot-rolled steel plate H. It is explanatory drawing which shows the hot rolling equipment 2 for implement | achieving the cooling method of the hot-rolled steel plate H in other embodiment. It is explanatory drawing which shows the outline of a structure of the cooling device 114 arrange | positioned in the hot rolling equipment 2. FIG. It is explanatory drawing which shows a mode that the lowest point of the hot-rolled steel plate H contacts the conveyance roll 132. FIG. It is explanatory drawing which shows a mode that the lowest point of the hot-rolled steel plate H contacts with the conveyance roll 132 and the apron 133. FIG. It is a graph which shows the time-dependent change of the temperature of the hot-rolled steel sheet H when the plate-feeding speed of the hot-rolled steel sheet H is low. It is a graph which shows the time-dependent change of the temperature of the hot-rolled steel sheet H when the plate-feeding speed of the hot-rolled steel sheet H is high. It is explanatory drawing of the finishing mill 113 which can perform cooling between stands. It is explanatory drawing which shows the manufacturing method of the conventional hot-rolled steel plate H. It is explanatory drawing which shows the cooling method of the conventional hot-rolled steel plate H.

  Hereinafter, as an embodiment of the present invention, for example, a hot-rolled steel sheet cooling device for cooling a hot-rolled steel sheet used for automobiles and industrial machines will be described in detail with reference to the drawings.

FIG. 1 schematically shows an example of a hot rolling facility 1 equipped with a hot-rolled steel sheet cooling device in the present embodiment. This hot rolling facility 1 is a facility intended to continuously roll a heated slab S sandwiched between rolls up and down, thin it to a minimum of 1 mm, and wind it up.
This hot rolling equipment 1 is rolled in the width direction, a heating furnace 11 for heating the slab S, a width-direction rolling mill 16 that rolls the slab S heated in the heating furnace 11 in the width direction, and the width direction. A roughing mill 12 that rolls the slab S from the upper and lower directions to form a rough bar, a finishing mill 13 that continuously hot-rolls the rough bar to a predetermined thickness, and a hot rolling by the finishing mill 13. A cooling device 14 that cools the hot-rolled steel plate H that has been finish-rolled with cooling water, and a winding device 15 that winds the hot-rolled steel plate H cooled by the cooling device 14 into a coil shape are provided.

  The heating furnace 11 is provided with a side burner, an axial flow burner, and a roof burner for heating the slab S by blowing out flames with respect to the slab S carried in from the outside through the loading port. The slab S carried into the heating furnace 11 is sequentially heated in each heating zone formed in each zone, and further in the soaking zone formed in the final zone, the slab S is evenly heated using a roof burner, A coercive heat treatment is performed to enable conveyance at the optimum temperature. When all the heat treatments in the heating furnace 11 are completed, the slab S is transferred to the outside of the heating furnace 11 and moves to a rolling process by the roughing mill 12.

  The roughing mill 12 allows the slab S that has been conveyed to pass through the gap between the cylindrical rotating rolls that are disposed across a plurality of stands. For example, this roughing mill 12 hot-rolls the slab S only by the work rolls 12a arranged up and down in the first stand to form a rough bar. Next, the rough bar that has passed through the work roll 12a is further continuously rolled by a plurality of quadruple rolling mills 12b constituted by the work roll and the backup roll. As a result, at the end of this rough rolling step, the rough bar is rolled to a thickness of about 30 to 60 mm and conveyed to the finishing mill 13.

  The finish rolling mill 13 finish-rolls the coarse bar conveyed from the rough rolling mill 12 until its thickness reaches about several millimeters. These finish rolling mills 13 allow the coarse bars to pass through the gaps between the finish rolling rolls 13a arranged in a straight line over 6 to 7 stands, and gradually reduce them. The hot-rolled steel sheet H finish-rolled by the finish rolling mill 13 is conveyed to the cooling device 14 by a conveyance roll 32 described later.

The cooling device 14 is equipment for applying so-called laminar cooling to the hot-rolled steel sheet H conveyed from the finish rolling mill 13. As shown in FIG. 2, the cooling device 14 has an upper cooling device 14 a that jets cooling water from the upper cooling port 31 to the upper surface of the hot-rolled steel sheet H that moves on the transport roll 32 of the run-out table, The lower side cooling device 14b which injects a cooling water from the lower side cooling port 31 with respect to the lower surface of the hot-rolled steel plate H is provided. A plurality of cooling ports 31 are provided for each of the upper cooling device 14a and the lower cooling device 14b.
A cooling header (not shown) is connected to the cooling port 31. The cooling capacity of the upper cooling device 14a and the lower cooling device 14b is determined by the number of the cooling ports 31. The cooling device 14 may be composed of at least one of an upper / lower split laminar, a pipe laminar, spray cooling, and the like. Further, a section in which the hot-rolled steel sheet H is cooled by the cooling device 14 corresponds to a cooling section in the present invention.

Further, as shown in FIG. 3, on the downstream side of the cooling section (that is, the cooling device 14), a thermometer 40 that measures the temperature at a measurement position determined in the rolling direction of the hot-rolled steel sheet H, A shape meter 41 for measuring the wave shape of the hot-rolled steel sheet H at the same measurement position is arranged.
The thermometer 40 and the shape meter 41 are electrically connected to the control device 50 via a cable or the like. The control device 50 is electrically connected to the upper cooling device 14a and the lower cooling device 14b via a cable or the like.
The thermometer 40 outputs the temperature measurement result of the hot-rolled steel sheet H to the control device 50. The shape meter 41 outputs the shape measurement result of the hot-rolled steel sheet H to the control device 50.
The control device 50 controls the upper cooling device 14a and the lower cooling device 14b on the basis of the temperature measurement result obtained from the thermometer 40 and the shape measurement result obtained from the shape meter 41, thereby performing hot rolling in the cooling section. At least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the steel sheet H is controlled.
The control device 50 includes an average temperature calculation unit 51, a fluctuation speed calculation unit 52, a control direction determination unit 53, and a cooling heat removal total value adjustment unit 54 as functions realized by executing the program. The role of each functional unit will be described later.

As shown in FIG. 1, the winding device 15 winds the hot rolled steel sheet H cooled by the cooling device 14 at a predetermined winding temperature. The hot-rolled steel sheet H wound up in a coil shape by the winding device 15 is conveyed outside the hot rolling facility 1.
In the hot rolling facility 1 configured as described above, the upper cooling device 14a, the lower cooling device 14b, the thermometer 40, the shape meter 41, and the control device 50 are the hot-rolled steel sheet cooling device in the present embodiment. It is composed.

Next, the cooling method of the hot-rolled steel sheet H realized by the hot rolling facility 1 configured as described above will be described.
In the following description, as shown in FIG. 19, a corrugated shape whose surface height (wave height) fluctuates in the rolling direction is formed on the hot-rolled steel sheet H that has been hot-rolled by the finish mill 13. ing. Moreover, in the following description, the influence of the running water which accumulates on the hot-rolled steel sheet H when the hot-rolled steel sheet H is cooled is ignored. Actually, as a result of the investigation by the inventor of the present application, it has been found that there is almost no influence of the running water accumulated on the hot-rolled steel sheet H.

  First, before cooling the hot-rolled steel sheet H with the cooling device 14, the cooling capacity (upper cooling capacity) of the upper cooling device 14a of the cooling apparatus 14 and the cooling capacity (lower cooling capacity) of the lower cooling device 14b are previously set. adjust. The upper cooling capacity and the lower cooling capacity are respectively the heat transfer coefficient of the upper surface of the hot rolled steel sheet H cooled by the upper cooling device 14a and the heat transfer of the lower surface of the hot rolled steel sheet H cooled by the lower cooling device 14b. Adjust using the coefficient.

Here, the calculation method of the heat transfer coefficient of the upper surface and the lower surface of the hot-rolled steel sheet H will be described. The heat transfer coefficient is a value obtained by dividing the amount of heat removed from cooling (heat energy) per unit time from the unit area by the temperature difference between the heat transfer medium and the heat medium (heat transfer coefficient = cooled heat removal / temperature difference). ). The temperature difference here is a difference between the temperature of the hot-rolled steel sheet H measured by the thermometer on the inlet side of the cooling device 14 and the temperature of the cooling water used in the cooling device 14.
The cooling heat removal amount is a value obtained by multiplying the temperature difference, specific heat, and mass of the hot-rolled steel sheet H (cooling heat removal amount = temperature difference × specific heat × mass). That is, the amount of heat removed from cooling is the amount of heat removed from the hot-rolled steel sheet H in the cooling device 14, and the difference in temperature between the hot-rolled steel plates H measured by the thermometer on the inlet side and the thermometer on the outlet side of the cooling device 14. And the specific heat of the hot-rolled steel sheet H and the mass of the hot-rolled steel sheet H cooled by the cooling device 14, respectively.

The heat transfer coefficient of the hot-rolled steel sheet H calculated as described above is divided into the heat transfer coefficients of the upper surface and the lower surface of the hot-rolled steel sheet H. These heat transfer coefficients of the upper surface and the lower surface are calculated using, for example, a ratio obtained in advance as follows.
That is, the heat transfer coefficient of the hot-rolled steel sheet H when the hot-rolled steel sheet H is cooled only by the upper cooling device 14a and the heat transfer of the hot-rolled steel plate H when the hot-rolled steel plate H is cooled only by the lower cooling device 14b. Measure the coefficient.
At this time, the cooling water amount from the upper cooling device 14a and the cooling water amount from the lower cooling device 14b are the same. The reciprocal of the ratio of the measured heat transfer coefficient when using the upper cooling device 14a and the heat transfer coefficient when using the lower cooling device 14b is the upper side when the upper and lower heat transfer coefficient ratio is “1”. This is the vertical ratio between the amount of cooling water from the cooling device 14a and the amount of cooling water from the lower cooling device 14b.
Then, the above-described heat ratio is obtained by multiplying the vertical ratio of the cooling water amount thus obtained by the cooling water amount from the upper cooling device 14a when cooling the hot-rolled steel sheet H or the cooling water amount from the lower cooling device 14b. The ratio of the heat transfer coefficient between the upper surface and the lower surface of the rolled steel sheet H is calculated.
In the above description, the heat transfer coefficient of the hot-rolled steel sheet H that is cooled only by the upper cooling device 14a and the lower cooling device 14b is used. However, it is cooled by both the upper cooling device 14a and the lower cooling device 14b. The heat transfer coefficient of the hot-rolled steel sheet H may be used. That is, the heat transfer coefficient of the hot-rolled steel sheet H when the amount of cooling water of the upper cooling device 14a and the lower cooling device 14b is changed is measured, and the ratio of the heat transfer coefficient is used to determine the upper and lower surfaces of the hot-rolled steel sheet H. The ratio of the heat transfer coefficient may be calculated.

  As described above, the heat transfer coefficient of the hot-rolled steel sheet H is calculated, and the upper surface of the hot-rolled steel sheet H is calculated based on the above ratio (upper and lower heat transfer coefficient ratio) of the heat transfer coefficients of the upper and lower surfaces of the hot-rolled steel sheet H. The heat transfer coefficient of the lower surface is calculated.

  Here, in order to uniformly cool the hot-rolled steel sheet H, the cooling capacity of the upper cooling device 14a and the lower cooling device 14b is adjusted (the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot rolled steel plate H are controlled. As a result of intensive studies by the inventors of the present invention, the following knowledge has been obtained.

  The inventors of the present application have intensively studied the characteristics of the temperature standard deviation generated by cooling in the state where the wave shape of the hot-rolled steel sheet H is generated, and as a result, have clarified the following.

Temperature measurement at a measurement position (hereinafter, this measurement position may be referred to as a fixed point) determined in the rolling direction of the hot-rolled steel sheet H by the thermometer 40 and the shape meter 41 with respect to the hot-rolled steel sheet H in the plate. The shape measurement is performed at a constant time interval (sampling interval), and the temperature measurement result and the time series data of the shape measurement result are acquired.
Note that the temperature measurement region by the thermometer 40 includes the entire width direction of the hot-rolled steel sheet H. In addition, the shape refers to the height or fluctuation component of the wave pitch by using the amount of movement in the sheet passing direction of the hot-rolled steel sheet H as the amount of fluctuation in the height direction of the hot-rolled steel sheet H observed by fixed point measurement. This is the steepness obtained by line integration. At the same time, the fluctuation amount per unit time, that is, the fluctuation speed is also obtained. Furthermore, the shape measurement region includes the entire region in the width direction of the hot-rolled steel sheet H, similarly to the temperature measurement region. Moreover, when the sampling time of each measurement result is multiplied by the sheet feeding speed (conveying speed) of the hot-rolled steel sheet H, the position in the rolling direction of the hot-rolled steel sheet H from which each measurement result is obtained can be calculated. That is, when the time at which the time series data of each measurement result is sampled is multiplied by the sheet feeding speed, the time series data of each measurement result can be linked to the position in the rolling direction.

Using this time series data, first, the total value of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H is adjusted. Specifically, the total value of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H is adjusted so that the time-series average value of the temperature measured by the thermometer 40 matches a predetermined target value. .
And when adjusting the total value of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount, for example, with respect to the theoretical value obtained in advance using an experimental theoretical formula typified by Mitsuka's formula, On / off control of the cooling header connected to the cooling device 14 may be performed based on a learning value set so as to correct the error. Alternatively, on / off of the cooling header may be feedback-controlled or feed-forward controlled based on the temperature actually measured by the thermometer 40.

Next, conventional cooling control of the ROT will be described using data obtained from the thermometer 40 and the shape meter 41 described above. FIG. 4 shows the relationship between the temperature fluctuation and steepness of the hot-rolled steel sheet H that is cooled in the ROT of a typical strip in a normal operation. The upper and lower heat transfer coefficient ratio of the hot-rolled steel sheet H in FIG. 4 is 1.2: 1, and the upper cooling capacity is higher than the lower cooling capacity. The upper graph in FIG. 4 shows the temperature variation with respect to the distance from the coil tip or the fixed point elapsed time, and the lower graph in FIG. 4 shows the distance from the coil tip or the steepness with respect to the fixed point elapsed time.
A region A in FIG. 4 is a region before the strip front end portion shown in FIG. 3 is bitten by the coiler of the winding device 15 (a region having a bad shape because there is no tension). A region B in FIG. 4 is a region after the strip tip portion is bitten by the coiler (a region where the wave shape is changed flat due to the influence of the unit tension). It is desired to improve a large temperature fluctuation (that is, temperature standard deviation) generated in a region where the shape of the hot-rolled steel sheet H is not flat.

  Accordingly, the inventors of the present application have conducted intensive experiments with the goal of suppressing an increase in temperature standard deviation in the ROT, and as a result, have obtained the following knowledge.

FIG. 5 shows the temperature fluctuation component with respect to the same shape steepness of cooling in the ROT of a typical strip in a normal operation as in FIG. This temperature fluctuation component is a residual obtained by subtracting a time-series average of temperature (hereinafter sometimes referred to as “average temperature”) from the actual steel plate temperature. For example, the average temperature may be averaged over a range of one or more wave shapes of the hot-rolled steel sheet H.
The average temperature is in principle the average of the range in units of cycles. In addition, it has been confirmed by the operation data that the average temperature in the range of one cycle is not significantly different from the average temperature in the range of two cycles or more.
Therefore, it is only necessary to calculate an average temperature in a range of at least one waveform. The upper limit of the corrugated range of the hot-rolled steel sheet H is not particularly limited, but preferably an average temperature with sufficient accuracy can be obtained if it is set to 5 cycles. Moreover, even if the range to average is not the range of a period unit, if it is the range of 2 to 5 periods, the acceptable average temperature can be obtained.

Here, when the upward direction in the vertical direction of the hot-rolled steel sheet H (direction perpendicular to the upper and lower surfaces of the hot-rolled steel sheet H) is positive, the wave shape of the hot-rolled steel sheet H is a region where the fluctuation rate measured at a fixed point is positive. When the temperature of the hot-rolled steel sheet H (temperature measured at a fixed point) is lower than the average temperature in the range of one cycle or more, at least one of the direction in which the upper surface cooling heat removal amount decreases and the direction in which the lower surface cooling heat removal amount increases. Is determined as the control direction, and when the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of the direction in which the upper surface cooling heat removal amount increases and the direction in which the lower surface cooling heat removal amount decreases is determined as the control direction. To do.
Further, when the temperature of the hot-rolled steel sheet H is lower than the above average temperature in the region where the fluctuation rate measured at a fixed point is negative, the direction in which the upper surface cooling heat removal amount increases and the direction in which the lower surface cooling heat removal amount decreases. Is determined as a control direction, and when the temperature of the hot-rolled steel sheet H is higher than the above average temperature, at least one of the direction in which the upper surface cooling heat removal amount decreases and the direction in which the lower surface cooling heat removal amount increases is controlled. Determine as direction.
Then, when at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in the cooling section is adjusted based on the control direction determined as described above, as shown in FIG. And it turned out that the temperature fluctuation generate | occur | produced in the area | region A where the shape of the hot-rolled steel plate H is not flat can be reduced.

The case where the reverse operation is performed will be described below. When the temperature of the hot-rolled steel sheet H is lower than the average temperature of the hot-rolled steel sheet H in a region where the fluctuation rate measured at a fixed point is positive, the direction in which the upper surface cooling heat removal amount increases and the lower surface cooling heat removal amount decreases. When at least one of the directions is determined as the control direction and the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of the direction in which the upper surface cooling heat removal amount decreases and the direction in which the lower surface cooling heat removal amount increases is determined. Determine as the control direction.
Further, when the temperature of the hot-rolled steel sheet H is lower than the above average temperature in a region where the fluctuation rate measured at a fixed point is negative, the direction in which the upper surface cooling heat removal amount decreases and the direction in which the lower surface cooling heat removal amount increases. Is determined as a control direction, and when the temperature of the hot-rolled steel sheet H is higher than the above average temperature, at least one of the direction in which the upper surface cooling heat removal amount increases and the direction in which the lower surface cooling heat removal amount decreases is controlled. Determine as direction.
Then, when at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in the cooling section is adjusted based on the control direction determined as described above, as shown in FIG. And it turned out that the temperature fluctuation which generate | occur | produces in the area | region A where the shape of the hot-rolled steel plate H is not flat expands. In the example described here, it is not assumed that the cooling stop temperature may be changed.

  By utilizing this relationship, it becomes clear which cooling capacity of the upper cooling device 14a or the lower cooling device 14b of the cooling device 14 should be adjusted in order to reduce the temperature fluctuation, that is, the temperature standard deviation. Table 1 summarizes the above relationships.

The hot-rolled steel sheet cooling device of the present embodiment realizes the cooling method described above. That is, the average temperature calculation unit 51 of the control device 50 calculates the time series average value of the temperature measurement results obtained from the thermometer 40 in time series as the average temperature. Further, the fluctuation speed calculation unit 52 calculates the fluctuation speed of the hot-rolled steel sheet H based on the shape measurement results obtained from the shape meter 41 in time series.
If the upward direction in the vertical direction of the hot-rolled steel sheet H is positive, the control direction determining unit 53 is an area where the fluctuation rate measured at a fixed point is positive, and the average temperature in the range of one or more wave shapes of the hot-rolled steel sheet H is obtained. On the other hand, when the temperature of the hot-rolled steel sheet H (temperature measured at a fixed point) is low, at least one of the direction in which the upper surface cooling heat removal amount decreases and the direction in which the lower surface cooling heat removal amount increases is determined as the control direction. When the temperature of the hot-rolled steel sheet H is higher than the average temperature, at least one of the direction in which the upper surface cooling heat removal amount increases and the direction in which the lower surface cooling heat removal amount decreases is determined as the control direction.
In addition, the control direction determination unit 53 is a region where the fluctuation rate measured at a fixed point is negative, and when the temperature of the hot-rolled steel sheet H is lower than the above average temperature, the upper surface cooling heat removal amount increases and the lower surface. When the temperature of the hot-rolled steel sheet H is determined to be at least one of the directions in which the cooling heat removal amount decreases as the control direction and the above-mentioned average temperature is higher, the upper surface cooling heat removal amount decreases and the lower surface cooling heat removal amount increases. At least one of the directions to be determined is determined as the control direction.
And the cooling heat removal amount total value adjustment part 54 adjusts the total value of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in a cooling area based on the control direction determined as mentioned above.

When adjusting the cooling capacity of the upper cooling device 14a and the cooling capacity of the lower cooling device 14b, for example, the cooling header connected to the cooling port 31 of the upper cooling device 14a and the cooling port 31 of the lower cooling device 14b. Each of the cooling headers connected to may be controlled on and off. Or you may control the cooling capacity of each cooling header in the upper side cooling device 14a and the lower side cooling device 14b. That is, you may adjust at least one of the water quantity density of the cooling water injected from each cooling port 31, a pressure, and water temperature.
In addition, the cooling headers (cooling ports 31) of the upper cooling device 14a and the lower cooling device 14b may be thinned out to adjust the flow rate and pressure of the cooling water injected from the upper cooling device 14a and the lower cooling device 14b. . For example, when the cooling capacity of the upper cooling device 14a before thinning out the cooling header is higher than the cooling capacity of the lower cooling device 14b, it is preferable to thin out the cooling header constituting the upper cooling device 14a.

  The cooling capacity thus adjusted is used to inject cooling water onto the upper surface of the hot-rolled steel sheet H from the upper cooling device 14a, and to inject cooling water onto the lower surface of the hot-rolled steel plate H from the lower cooling device 14b. The steel plate H is uniformly cooled.

  Thereafter, the hot-rolled steel sheet H cooled by the cooling device 14 is subjected to fixed point measurement at the same point by the thermometer 40 and the shape meter 41, and measured as time series data. The temperature measurement region includes the entire region in the width direction of the hot-rolled steel sheet H. Further, the shape indicates the amount of fluctuation in the height direction of the hot-rolled steel sheet H observed by fixed point measurement. Furthermore, the shape measurement region includes the entire region in the width direction of the hot-rolled steel sheet H, similarly to the temperature measurement region. By multiplying these sampled times by the sheet feeding speed, it becomes possible to link time-series data of measurement results such as temperature and fluctuation speed to the position in the rolling direction.

  As described with reference to FIGS. 4, 5, 6, and 7, the fluctuation rate at the fixed point of the hot-rolled steel sheet H is a positive region, and the fixed point of the hot-rolled steel sheet H with respect to the average temperature at the fixed point. When the temperature is low, the temperature standard deviation can be reduced by decreasing the upper cooling capacity (upper surface cooling heat removal amount). Similarly, the temperature standard deviation can be reduced by increasing the lower cooling capacity (lower surface cooling heat removal amount). If this relationship is utilized, in order to reduce the temperature standard deviation, it becomes clear which of the upper cooling device 14a and the lower cooling device 14b of the cooling device 14 should be adjusted.

That is, by grasping the temperature fluctuation position associated with the wave shape of these hot-rolled steel sheets H, it is clear whether the temperature standard deviation currently generated is generated by the upper cooling or the lower cooling. It becomes possible to do. Therefore, the increase / decrease direction (control direction) of the upper cooling capacity (upper surface cooling heat removal amount) and lower cooling capacity (lower surface cooling heat removal amount) to reduce the temperature standard deviation is determined, and the vertical heat transfer coefficient ratio is adjusted. Can do.
Further, based on the magnitude of the temperature standard deviation, the upper and lower heat transfer coefficient ratio can be determined so that the temperature standard deviation falls within an allowable range, for example, a range from the minimum value to the minimum value + 10 ° C. In addition, by keeping this temperature standard deviation within the range from the minimum value to the minimum value + 10 ° C., variations in yield stress, tensile strength, and the like can be suppressed within manufacturing tolerances, and the hot-rolled steel sheet H can be cooled uniformly. In addition, although there is considerable variation, if the cooling water volume density ratio is within ± 5% of the cooling water volume density ratio at which the temperature standard deviation is the minimum value, the temperature standard deviation is within the minimum value + 10 ° C from the minimum value. Within the range of. That is, when using the cooling water amount density, it is desirable to set the vertical ratio of the cooling water amount density (cooling water amount density ratio) within ± 5% with respect to the cooling water amount density ratio at which the temperature standard deviation is the minimum value. However, this allowable range does not necessarily include the same upper and lower water density.

  According to the above embodiment, after adjusting the cooling capacity of the upper cooling device 14a and the lower cooling device 14b in advance to cool the hot-rolled steel sheet H, the temperature and wave shape of the further cooled hot-rolled steel sheet H are changed. Based on the measurement result, the cooling capacity of the upper cooling device 14a and the cooling capacity of the lower cooling device 14b are adjusted. In this way, the cooling capacity of the upper cooling device 14a and the lower cooling device 14b can be feedback-controlled to adjust the cooling capacity to an appropriate cooling capacity qualitatively and quantitatively, so that the uniformity of the hot-rolled steel sheet H that is subsequently cooled is further improved. Can be made.

  As described above, according to the present embodiment, the hot-rolled steel sheet H can be uniformly cooled with the temperature standard deviation of the hot-rolled steel sheet H being minimized.

In the above embodiment, the temperature and shape of the hot-rolled steel sheet H were measured at the same measurement position by the thermometer 40 and the shape meter 41. However, when the inventors of the present application examined, the thermometer 40 and the shape meter were measured. It has been found that the measurement positions of 41 need not be exactly the same. Specifically, as shown in FIG. 8, the displacement (distance) L between the temperature measurement point P1 of the thermometer 40 and the shape measurement point P2 of the shape meter 41 on the hot-rolled steel sheet H is more preferably within 50 mm. It was found that the temperature and shape of the hot-rolled steel sheet H can be properly grasped within 30 mm.
The direction of the positional deviation L between the measurement points of the thermometer 40 and the shape meter 41 may be the sheet passing direction of the hot-rolled steel sheet H as shown in FIG. It may be any direction. In the example of FIG. 8, the thermometer 40 is disposed on the upstream side of the shape meter 41, but conversely, the shape meter 41 may be disposed on the upstream side of the thermometer 40.

Here, the reason why it is preferable to set the positional deviation L between the measurement points of the thermometer 40 and the shape meter 41 within 50 mm will be described. Table 2 shows the positional deviation L between the measurement points of the thermometer 40 and the shape meter 41 under the conditions of the same vertical heat transfer coefficient ratio, steepness, and plate passing speed when the present invention is applied to an actual machine. The temperature standard deviation of the hot-rolled steel sheet H and the difference between each temperature standard deviation and the minimum value (minimum value = 10.0 in Table 2) when changed in the range of −200 to +200 mm with respect to the rolling direction. It shows the relationship with (difference of standard deviation from minimum value).
In Table 2, with reference to the temperature measurement point P1 of the thermometer 40, the positional deviation L when the shape measurement point P2 of the shape meter 41 is set on the downstream side is shown as a positive value. The position deviation L when the shape measuring point P2 of the shape meter 41 is set is indicated by a negative value. Further, when the temperature measurement point P1 of the thermometer 40 and the shape measurement point P2 of the shape meter 41 are set to be the same, the positional deviation L becomes zero.
As shown in Table 2, the difference in the standard deviation from the minimum value can be reduced to + 10 ° C. or less as long as the positional deviation L between the measurement points of the thermometer 40 and the shape meter 41 is within 50 mm regardless of positive or negative. I understand.

  Therefore, if the positional deviation L between the measurement points of the thermometer 40 and the shape meter 41 is within 50 mm, the increase and decrease directions of the upper cooling capacity and the lower cooling capacity for reducing the temperature standard deviation are the same as in the above embodiment. (Control direction) can be determined, and feedback control of the cooling capacity of the upper cooling device 14a and the lower cooling device 14b can be performed.

  In the above embodiment, as shown in FIG. 9, the cooling section in which the hot-rolled steel sheet H is cooled may be divided into a plurality of, for example, two divided cooling sections Z1 and Z2 in the rolling direction. A cooling device 14 is provided in each of the divided cooling zones Z1 and Z2. In addition, a thermometer 40 and a shape meter 41 are provided at the boundary between the divided cooling zones Z1 and Z2, that is, downstream of the divided cooling zones Z1 and Z2. In the present embodiment, the cooling section is divided into two divided cooling sections, but the number of divisions is not limited to this and can be arbitrarily set. For example, the cooling section may be divided into 1 to 5 divided cooling sections.

  In this case, the temperature and the wave shape of the hot-rolled steel sheet H on the downstream side of the divided cooling zones Z1 and Z2 are measured by the thermometers 40 and the shape meters 41, respectively. And based on these measurement results, the cooling capacity of the upper side cooling device 14a and the lower side cooling device 14b in each division | segmentation cooling zone Z1, Z2 is controlled. At this time, the cooling capacity is controlled so that the temperature standard deviation of the hot-rolled steel sheet H falls within an allowable range, for example, within the range from the minimum value to the minimum value + 10 ° C. as described above. Accordingly, at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in each of the divided cooling zones Z1 and Z2 is adjusted.

For example, in the divided cooling zone Z1, the cooling capacity of the upper cooling device 14a and the lower cooling device 14b is feedback-controlled based on the measurement results of the thermometer 40 and the shape meter 41 on the downstream side, and the upper surface cooling heat removal amount and At least one of the bottom surface cooling heat removal amount is adjusted.
In the divided cooling zone Z2, the cooling capacity of the upper cooling device 14a and the lower cooling device 14b may be feedforward controlled based on the measurement results of the thermometer 40 and the shape meter 41 on the downstream side, Alternatively, feedback control may be performed. In any case, at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount is adjusted in the divided cooling zone Z2.

  The method for controlling the cooling capacity of the upper cooling device 14a and the lower cooling device 14b based on the measurement results of the thermometer 40 and the shape meter 41 is the same as in the above-described embodiment described with reference to FIGS. Therefore, detailed description is omitted.

  In this case, in each of the divided cooling zones Z1 and Z2, at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H is adjusted, so that finer control is possible. Therefore, the hot-rolled steel sheet H can be cooled more uniformly.

  In the above embodiment, when adjusting at least one of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H in each of the divided cooling zones Z1 and Z2, the measurement results of the thermometer 40 and the shape meter 41 are used. In addition, at least one of the wave shape steepness of the hot-rolled steel sheet H and the sheet passing speed of the hot-rolled steel sheet H may be used. For example, since the steepness and the sheet passing speed of the hot-rolled steel sheet H may not be constant for each coil, the steepness and the sheet passing speed are also considered.

  As a result of investigation by the inventors of the present application, for example, as shown in FIG. 10, if the steepness of the wave shape of the hot-rolled steel sheet H increases, the temperature standard deviation of the hot-rolled steel sheet H increases. For example, as shown in FIG. 11, when the sheet passing speed of the hot-rolled steel sheet H becomes high, the temperature standard deviation of the hot-rolled steel sheet H increases.

  As described above, when the steepness and the sheet passing speed of the hot-rolled steel sheet H are not constant, the change of the temperature standard deviation with respect to the ratio of the vertical heat transfer coefficient can be qualitatively evaluated but cannot be quantitatively and accurately evaluated. Therefore, for example, a temperature standard deviation corresponding to the steepness or sheet passing speed of the hot-rolled steel sheet H is obtained in advance, and at least the steepness or sheet passing speed of the hot-rolled steel sheet H is measured to correct the temperature standard deviation. And based on this correct | amended temperature standard deviation, the upper surface cooling heat removal amount and lower surface cooling heat removal amount of the hot-rolled steel sheet H in each division | segmentation cooling zone Z1, Z2 are correct | amended. Thereby, the hot-rolled steel sheet H can be cooled more uniformly.

  Moreover, according to this embodiment, it can be finished so that it may become a uniform shape and material also in the plate width direction of the hot-rolled steel plate H. FIG. 12 shows an example of a wave shape in which different amplitudes are generated in the plate width direction due to middle elongation. As described above, even if the temperature standard deviation occurs due to the wave shapes having different amplitudes generated in the plate width direction, the temperature standard deviation in the plate width direction is reduced according to the above-described embodiment. It becomes possible.

  Here, as a result of intensive studies by the present inventors, the hot-rolled steel sheet H is made more uniform by setting the sheet-passing speed of the hot-rolled steel sheet H within a range from 550 m / min or more to a mechanical limit speed or less. I understood that I can do it.

  It has been found that when the sheet passing speed of the hot-rolled steel sheet H is set to 550 m / min or more, even if the cooling water is injected onto the hot-rolled steel sheet H, the influence of the water on the hot-rolled steel sheet H is remarkably reduced. For this reason, the non-uniform cooling of the hot-rolled steel sheet H by the riding water can be avoided.

FIG. 13 schematically shows an example of the hot rolling facility 2 in another embodiment. This hot rolling facility 2 is a facility intended to continuously roll a heated slab S sandwiched between rolls and to roll it down to a minimum thickness of 1.2 mm.
This hot rolling facility 2 is rolled in the width direction, a heating furnace 111 for heating the slab S, a width-direction rolling mill 116 that rolls the slab S heated in the heating furnace 111 in the width direction, and the width direction. A roughing mill 112 that rolls the slab S from above and below to form a rough bar, a finishing mill 113 that continuously hot-rolls the rough bar to a predetermined thickness, and a hot rolling by the finishing mill 113. A cooling device 114 that cools the hot-rolled steel sheet H that has been finish-rolled with cooling water, and a winding device 115 that winds the hot-rolled steel plate H cooled by the cooling device 114 into a coil shape.

  The heating furnace 111 is provided with a side burner, an axial flow burner, and a roof burner for heating the slab S by blowing out flames with respect to the slab S carried in from the outside through the loading port. The slab S carried into the heating furnace 111 is sequentially heated in each heating zone formed in each zone, and further, in the soaking zone formed in the final zone, by heating the slab S evenly using a roof burner, A coercive heat treatment is performed to enable conveyance at the optimum temperature. When all the heat treatments in the heating furnace 111 are completed, the slab S is transferred to the outside of the heating furnace 111 and moves to a rolling process by the rough rolling mill 112.

In the rough rolling mill 112, the slab S conveyed from the heating furnace 111 passes through a gap between cylindrical rotary rolls arranged over a plurality of stands. For example, the rough rolling mill 112 hot-rolls the slab S with only the work rolls 112a disposed up and down in the first stand to form a rough bar.
Next, the coarse bar that has passed through the work roll 112a is further continuously rolled by a plurality of quadruple rolling mills 112b each composed of a work roll and a backup roll. As a result, at the end of this rough rolling step, the rough bar is rolled to a thickness of about 30 to 60 mm and conveyed to the finishing mill 113. In addition, the structure of the rough rolling mill 112 is not limited to what was described in this embodiment, The number of rolls etc. can be set arbitrarily.

The finish rolling mill 113 finish-rolls the rough bar conveyed from the rough rolling mill 112 until the thickness becomes about several mm. These finish rolling mills 113 allow the coarse bars to pass through the gaps between the finish rolling rolls 113a arranged in a straight line over 6 to 7 stands, and gradually reduce them. The hot-rolled steel sheet H finish-rolled by the finish rolling mill 113 is transported to the cooling device 114 by a transport roll 132 (see FIG. 14). In addition, the rolling mill provided with the above-described pair of finish rolling rolls 113a arranged in a straight line is also referred to as a so-called rolling stand.

Moreover, between each rolling roll 113a arranged over 6-7 stands (namely, between rolling stands), the cooling device 142 (auxiliary cooling device) which performs cooling between stands (auxiliary cooling) in finish rolling is carried out. Has been placed. A detailed description of the configuration of the cooling device 142 will be described later with reference to FIG. FIG. 13 shows a case where the cooling devices 142 are arranged at two locations in the finishing mill 113, but this cooling device 142 may be provided between all the rolling rolls 113a. The structure provided only in a part may be sufficient.

The cooling device 114 is a facility for cooling the hot-rolled steel sheet H conveyed from the finish rolling mill 113 by nozzle laminator or spray. As shown in FIG. 14, the cooling device 114 has an upper cooling device 114a for injecting cooling water from the upper cooling port 131 to the upper surface of the hot-rolled steel sheet H moving on the transport roll 132 of the run-out table, On the lower surface of the hot-rolled steel sheet H, a lower cooling device 114b for injecting cooling water from the lower cooling port 131 is provided.
A plurality of cooling ports 131 are provided for each of the upper cooling device 114a and the lower cooling device 114b. A cooling header (not shown) is connected to the cooling port 131. The cooling capacity of the upper cooling device 114a and the lower cooling device 114b is determined by the number of the cooling ports 131. The cooling device 114 may be composed of at least one of upper and lower split laminar, pipe laminar, spray cooling, and the like.

In this cooling device 114, when adjusting the cooling capacity of the upper cooling device 114a and the cooling capacity of the lower cooling device 114b, for example, the cooling header connected to the cooling port 131 of the upper cooling device 114a and the lower cooling device 114b The cooling headers connected to the cooling ports 131 may be on / off controlled respectively.
Or you may control the operation parameter of each cooling header in the upper side cooling device 114a and the lower side cooling device 114b. That is, at least one of the water density, pressure, and water temperature of the cooling water ejected from each cooling port 131 may be adjusted.
Further, the cooling headers (cooling ports 131) of the upper cooling device 114a and the lower cooling device 114b may be thinned out to adjust the flow rate and pressure of the cooling water injected from the upper cooling device 114a and the lower cooling device 114b. . For example, when the cooling capacity of the upper cooling device 114a before thinning out the cooling header is higher than the cooling capacity of the lower cooling device 114b, it is preferable to thin out the cooling header constituting the upper cooling device 114a.

  As shown in FIG. 13, the winding device 115 winds the hot-rolled steel sheet H cooled by the cooling device 114 at a predetermined winding temperature. The hot-rolled steel sheet H wound in a coil shape by the winding device 115 is transported outside the hot rolling facility 2.

  In the cooling device 114 of the hot rolling facility 2 configured as described above, when the hot-rolled steel sheet H in which a corrugated shape whose surface height (wave height) fluctuates in the rolling direction is formed is performed, As described above, the hot-rolled steel sheet H is made uniform by appropriately adjusting the water density, pressure, water temperature, etc. of the cooling water injected from the upper cooling device 114a and the cooling water injected from the lower cooling device 114b. Can be cooled. However, especially when the sheet passing speed of the hot-rolled steel sheet H is slow, the time for which the hot-rolled steel sheet H and the transport roll 132 and the apron 133 are in contact with each other is long, and the transport roll 132 and apron of the hot-rolled steel sheet H are increased. Since the contact portion with 133 is easily cooled by contact heat removal, the cooling becomes uneven. The cause of this non-uniform cooling will be described below with reference to the drawings.

  As shown in FIG. 15A, when the hot-rolled steel sheet H has a corrugated shape in the rolling direction, the corrugated bottom of the hot-rolled steel sheet H may locally contact the transport roll 132. Moreover, as shown to FIG. 15B, the apron 133 may be provided as a support for preventing that the hot-rolled steel plate H falls between the conveyance rolls 132 adjacent along a rolling direction. In this case, there is a possibility that the corrugated bottom portion of the hot-rolled steel sheet H locally contacts the transport roll 132 and the apron 133. As described above, in the hot-rolled steel sheet H, the part that locally contacts the transport roll 132 and the apron 133 is more easily cooled than the other part due to contact heat removal. For this reason, the hot-rolled steel sheet H is cooled unevenly.

In particular, when the sheet passing speed of the hot-rolled steel sheet H is low, the time during which the hot-rolled steel sheet H locally contacts the transport roll 132 and the apron 133 becomes longer. As a result, as shown in FIG. 16A, the portion where the hot-rolled steel sheet H is locally in contact with the transport roll 132 and the apron 133 (portion surrounded by the dotted line in FIG. 16A) is more easily cooled than the other portions. The rolled steel sheet H is cooled unevenly.
On the other hand, when the sheet passing speed of the hot-rolled steel sheet H is increased, the contact time is shortened. In addition, when the sheet passing speed is increased, the hot rolled sheet steel H in the sheet passing plate is lifted from the sheet conveying roll 132 and the apron 133 due to repulsion due to contact between the hot rolled sheet steel H and the conveying roll 132 and the apron 133. Become.
Further, when the sheet passing speed of the hot-rolled steel sheet H is increased, the hot-rolled steel sheet H is lifted from the transport roll 132 and the apron 133 due to the repulsion due to the contact, and the hot-rolled steel sheet H and the transport roll 132 Since the contact time and the number of times of contact with the apron 133 are reduced, the temperature drop due to the contact becomes negligibly small.
Therefore, contact heat removal can be suppressed by increasing the sheet passing speed, and the hot-rolled steel sheet H can be cooled more uniformly as shown in FIG. 16B. The inventors have found that the hot-rolled steel sheet H can be cooled sufficiently uniformly by setting the sheet passing speed to 550 m / min or more in addition to the above-described heat removal control on the upper and lower surfaces.
In addition, although such knowledge is obtained about the cooling in the hot-rolled steel sheet H in which the corrugated shape was formed, the lowest point of the hot-rolled steel sheet H is conveyed regardless of the height of the corrugated shape. Since it comes in contact with the roll 132 and the apron 133, increasing the sheet passing speed regardless of the height of the wave shape is effective for uniform cooling.

  Moreover, since the hot-rolled steel sheet H will be in the state which floated from the conveyance roll 132 or the apron 133 if the plate-feeding speed of the hot-rolled steel sheet H is set to 550 m / min or more, cooling water is supplied to the hot-rolled steel sheet H in this state. Even if it injects, there is no boarding water on the hot-rolled steel sheet H as in the prior art. Therefore, it is possible to avoid the hot-rolled steel sheet H from being unevenly cooled due to the riding water.

As described above, when the sheet passing speed of the hot-rolled steel sheet H in the cooling section is set to 550 m / min or more, the hot-rolled steel sheet H having a wave shape whose wave height periodically varies in the rolling direction is more uniformly cooled. it can.
In addition, although the plate-passing speed of the hot-rolled steel sheet H is better as it is higher, it is impossible to exceed the mechanical limit speed (for example, 1550 m / min). Therefore, the sheet feeding speed of the hot-rolled steel sheet H in the cooling section is substantially set within a range from 550 m / min or more to a mechanical limit speed or less. Moreover, when the upper limit (operation upper limit speed) of the sheeting speed at the time of an actual operation is predetermined, the operation upper limit speed (for example, 1200 m / min) is set from 550 m / min or more. min) is preferably set within a range up to or below.
Of course, the hot-rolled steel sheet cooling device described with reference to FIG. 3 is applied to the hot rolling facility 2 to control the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet H, and to set a high plate feed speed. (Set within a range from 550 m / min or more to a mechanical limit speed or less) may be combined.

  In general, when the steel sheet is a hot-rolled steel sheet H having a high tensile strength (particularly a steel sheet called so-called high tensile steel having a tensile strength (TS) of 800 MPa or more and a practical upper limit of 1400 MPa). It is known that due to the high hardness of the hot-rolled steel sheet H, processing heat generated during rolling in the hot rolling equipment 2 is increased. Therefore, conventionally, cooling is sufficiently performed by suppressing the sheet passing speed of the hot-rolled steel sheet H in the cooling device 114 (that is, the cooling section).

However, if the sheet passing speed of the hot-rolled steel sheet H in the cooling device 114 is kept low, when the corrugated shape is formed on the hot-rolled steel sheet H, as described above, the hot-rolled steel sheet H, the transport roll 132, the apron 133, Due to the local contact, the contact portion is easily cooled by contact heat removal, and uneven cooling is performed.

Therefore, the inventors of the present invention, in the finishing mill 113 of the hot rolling facility 2, for example, cooled between a pair of finish rolling rolls 113a (that is, rolling stands) provided over 6 to 7 stands (so-called rolling stands). It was found that by performing (cooling between stands), the processing heat generation can be suppressed, and the sheet feeding speed of the hot-rolled steel sheet H in the cooling device 114 can be set to 550 m / min or more. Hereinafter, the inter-stand cooling will be described with reference to FIG.

FIG. 17 is an explanatory diagram of the finishing mill 113 capable of performing inter-stand cooling. For the sake of explanation, a part of the finishing mill 113 is enlarged to illustrate three rolling stands. In FIG. 17, the same components as those in the above embodiment are given the same reference numerals. As shown in FIG. 17, the finish rolling mill 113 is provided with a plurality of rolling stands 140 (three in FIG. 17) including a pair of finish rolling rolls 113a and the like arranged in a straight line. Between each rolling stand 140, the cooling device 142 which is the equipment which performs nozzle cooling by a laminar or a spray is provided, and inter-stand cooling is performed with respect to the hot-rolled steel sheet H between the rolling stands 140. It is possible.

As shown in FIG. 17, the cooling device 142 includes an upper cooling device 142 a that ejects cooling water from the upper side through a cooling port 146 to the hot rolled steel plate H conveyed in the finish rolling mill 113, and a lower surface of the hot rolled steel plate H. And a lower cooling device 142b for ejecting cooling water from the lower side. A plurality of cooling ports 146 are provided for each of the upper cooling device 142a and the lower cooling device 142b. In addition, a cooling header (not shown) is connected to the cooling port 146. The cooling device 142 may be composed of at least one of upper and lower split laminar, pipe laminar, spray cooling, and the like.

In the finish rolling mill 113 having the configuration shown in FIG. 17, particularly when the tensile strength (TS) of the hot-rolled steel sheet H is 800 MPa or more, processing heat generation of the hot-rolled steel sheet H is suppressed by performing inter-stand cooling. . Thereby, it is possible to keep the sheet passing speed of the hot-rolled steel sheet H in the cooling device 114 at 550 m / min or more. Therefore, the contact portion is easily cooled by contact heat removal due to local contact between the hot-rolled steel sheet H and the transport roll 132 or the apron 133, which has been a problem when cooling is performed at a conventional low plate speed. Therefore, the hot-rolled steel sheet H can be cooled sufficiently uniformly.

In the above embodiment, the cooling of the hot-rolled steel sheet H by the cooling device 114 is preferably performed in the range from the finish rolling mill outlet temperature to the temperature of the hot-rolled steel sheet H up to 600 ° C. The temperature region where the temperature of the hot-rolled steel sheet H is 600 ° C. or higher is a so-called film boiling region. That is, in this case, the so-called transition boiling region can be avoided and the hot-rolled steel sheet H can be water-cooled in the film boiling region. In the transition boiling region, when the cooling water is sprayed on the surface of the hot-rolled steel sheet H, the surface covered with the vapor film on the surface of the hot-rolled steel sheet H, the part where the cooling water is directly sprayed on the hot-rolled steel sheet H, Are mixed. For this reason, the hot-rolled steel sheet H cannot be cooled uniformly.
On the other hand, in the film boiling region, since the hot-rolled steel sheet H is cooled in a state where the entire surface of the hot-rolled steel sheet H is covered with the vapor film, the hot-rolled steel sheet H can be uniformly cooled. Therefore, the hot-rolled steel sheet H can be cooled more uniformly in the range where the temperature of the hot-rolled steel sheet H is 600 ° C. or more as in this embodiment.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to the said embodiment. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the idea described in the claims, and these naturally belong to the technical scope of the present invention. It is understood.

  In order to demonstrate that the hot-rolled steel sheet is uniformly cooled by setting the sheet-passing speed of the hot-rolled steel sheet to 550 m / min or more, the present inventor conducted a cooling experiment on the hot-rolled steel sheet as an example. It was.

Example 1
The hot-rolled steel sheet on which a plate thickness of 2.5 mm, a width of 1200 mm, a tensile strength of 400 MPa, and a steepness of 2% was formed was cooled by changing the sheet passing speed in the cooling device. Specifically, the sheeting speed is changed to 400 m / min, 450 m / min, 500 m / min, 550 m / min, 600 m / min, and 650 m / min, and the hot-rolled steel sheet is cooled 20 times at each sheeting speed. I went one by one.
And the temperature of the hot-rolled steel plate at the time of winding was measured, and the average value (CT temperature fluctuation amount) of the standard deviation of temperature fluctuation was computed using the temperature measurement result. The results of evaluating the calculated CT temperature fluctuation amount are shown in Table 3 below. As an evaluation standard, when the CT temperature fluctuation amount is larger than 25 ° C., it is evaluated that it is not uniformly cooled, and when the CT temperature fluctuation amount is 25 ° C. or less, it is uniformly cooled. evaluated.

As shown in Table 3, when the sheet feeding speed is 500 m / min or less, the CT temperature fluctuation amount is not sufficiently reduced (higher than 25 ° C.), and the hot-rolled steel sheet is sufficiently cooled uniformly. I have not been told. On the other hand, when the sheet feeding speed was 550 m / min or more, the CT temperature fluctuation amount was suppressed to 25 ° C. or less, and it was found that the hot-rolled steel sheet was uniformly cooled. In particular, when the sheet feeding speed is 600 m / min or more, the CT temperature is suppressed to less than 10 ° C. (8 ° C., 6 ° C.), so this condition realizes uniform cooling of the hot-rolled steel plate. It was found that this is more preferable.

(Example 2)
A hot-rolled steel sheet having a plate thickness of 2.5 mm, a width of 1200 mm, a tensile strength of 800 MPa and a steepness of 2% is cooled between stands so that the exit side temperature of finish rolling is 880 ° C. Cooling was carried out by changing the plate feeding speed. Specifically, the sheeting speed is changed to 400 m / min, 450 m / min, 500 m / min, 550 m / min, 600 m / min, and 650 m / min, and the hot-rolled steel sheet is cooled 20 times at each sheeting speed. I went one by one.
And the temperature of the hot-rolled steel plate at the time of winding was measured, and the average value (CT temperature fluctuation amount) of the standard deviation of temperature fluctuation was computed using the temperature measurement result. The results of evaluating the calculated CT temperature fluctuation amount are shown in Table 4 below. Note that the evaluation criteria are the same as in the case of Example 1, and cooling between stands is not performed only when the plate passing speed is 400 m / min.

  As shown in Table 4, when the sheet passing speed is 500 m / min or less, the CT temperature fluctuation amount is not sufficiently reduced (higher than 25 ° C.) even when the cooling between the stands is performed, and the hot-rolled steel sheet The uniform cooling is not sufficiently performed. On the other hand, when the sheet feeding speed was 550 m / min or more, the CT temperature fluctuation amount was suppressed to 25 ° C. or less, and it was found that the hot-rolled steel sheet was uniformly cooled.

  In addition, when inter-stand cooling is performed (that is, as shown in Table 4), the CT temperature fluctuation amount is suppressed even for hot-rolled steel sheets having relatively high hardness (tensile strength of 800 MPa). That is, in addition to setting the sheeting speed during cooling of the hot-rolled steel sheet to 550 m / min or more, it is uniform for all steel materials, particularly steel materials with high hardness, by carrying out inter-stand rolling with a finish rolling mill. It was found that it was possible to cool down.

  INDUSTRIAL APPLICABILITY The present invention is useful when cooling a hot-rolled steel sheet that has been hot-rolled by a finish rolling mill and has a corrugated shape whose surface height varies in the rolling direction.

1, 2, Hot rolling equipment 11, 111 Heating furnace 12, 112 Rough rolling mill 12a, 112a Work roll 12b, 112b Quadruple rolling mill 13, 113 Finishing rolling mill 13a, 113a Finishing rolling roll 14, 114 Cooling device 14a, 114a Upper cooling device 14b, 114b Lower cooling device 15, 115 Winding device 16, 116 Width rolling mill 31, 131 Cooling port 32, 132 Conveying roll 40 Thermometer 41 Shape meter 50 Controller 51 Average temperature calculation unit 52 Fluctuating speed Calculation part 53 Control direction determination part 54 Cooling heat removal amount total value adjustment part H Hot-rolled steel sheet S Slab Z1, Z2 Division | segmentation cooling area

Claims (5)

A hot-rolled steel sheet cooling device that cools a hot-rolled steel sheet hot-rolled by a finish rolling mill in a cooling section provided on the sheet-passing path,
A thermometer for measuring the temperature of the hot-rolled steel sheet on the downstream side of the cooling section;
A shape meter for measuring the shape of the hot-rolled steel sheet on the downstream side of the cooling section;
An upper cooling device for cooling the upper surface of the hot-rolled steel sheet in the cooling section;
A lower cooling device for cooling the lower surface of the hot-rolled steel sheet in the cooling section;
By controlling the upper cooling device and the lower cooling device based on the temperature measurement result of the hot-rolled steel plate obtained from the thermometer and the shape measurement result of the hot-rolled steel plate obtained from the shape meter, A control device for controlling at least one of an upper surface cooling heat removal amount and a lower surface cooling heat removal amount of the hot-rolled steel sheet in the cooling section;
With
The controller is
An average temperature calculation unit that calculates, as an average temperature, a time-series average value of the temperature of the hot-rolled steel sheet on the downstream side of the cooling section based on the temperature measurement result;
A fluctuation speed calculation unit that calculates a fluctuation speed of the hot-rolled steel sheet on the downstream side of the cooling section based on the shape measurement result; and when the upward direction in the vertical direction of the hot-rolled steel sheet is positive, the fluctuation speed is In the positive region, when the temperature of the hot-rolled steel sheet is lower than the average temperature in the range of one or more wave shapes of the hot-rolled steel sheet, the direction of decreasing the upper surface cooling heat removal amount and the lower surface cooling heat removal amount Is determined as a control direction, and when the temperature of the hot-rolled steel sheet is higher than the average temperature, the upper surface cooling heat removal amount increases and the lower surface cooling heat removal amount decreases. Is determined as the control direction,

When the temperature of the hot-rolled steel sheet is lower than the average temperature in a region where the fluctuation speed is negative, at least one of the direction in which the upper surface cooling heat removal amount increases and the direction in which the lower surface cooling heat removal amount decreases is When the temperature of the hot-rolled steel sheet is determined as a control direction and the average temperature is higher, at least one of the direction in which the upper surface cooling heat removal amount decreases and the direction in which the lower surface cooling heat removal amount increases is set as the control direction. A control direction determining unit to determine;
Cooling heat removal total value adjustment for adjusting the total value of the upper surface cooling heat removal amount and the lower surface cooling heat removal amount of the hot-rolled steel sheet in the cooling section based on the control direction determined by the control direction determination unit A hot-rolled steel sheet cooling device. The hot-rolled steel sheet cooling apparatus according to claim 1, wherein a positional deviation between a temperature measurement location of the thermometer and a shape measurement location of the shape meter on the hot-rolled steel plate is within 50 mm.
The hot-rolled steel sheet cooling according to claim 1 or 2, wherein the sheet-passing speed of the hot-rolled steel sheet in the cooling section is set within a range of 550 m / min or more to a mechanical limit speed or less. apparatus. The hot-rolled steel sheet cooling device according to claim 3, wherein the hot-rolled steel sheet has a tensile strength of 800 MPa or more. The said finishing mill is comprised from the some rolling stand, and is further provided with the auxiliary | assistant cooling device which performs auxiliary | assistant cooling of the said hot-rolled steel plate between the said rolling stands adjacent to each other. Hot rolled steel sheet cooling device.