JP2011073054A - Method and apparatus for cooling hot-rolled steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a hot-rolled steel sheet the variation of quality of which is small as compared with a conventional sheet by making the temperature deviation of the hot-rolled steel sheet after cooling less than the conventional temperature deviation and cooling the hot-rolled steel sheet uniformly in the cooling of the hot-rolled steel sheet, which is performed after finish rolling of the hot-rolled steel sheet. <P>SOLUTION: In the method and the apparatus for cooling, by which the hot-rolled steel sheet after the finish rolling in a hot rolling process is cooled while passing the sheet at the passing speed of ≥3 m/s on the downstream side of the finish rolling, when the temperature of the upper surface of the hot-rolled steel sheet between 850°C and 650°C, the hot-rolled steel sheet is held by imparting the tension of not less than 0.4 kgf/mm<SP>2</SP>(3.92 MPa) on the side of the finishing mill by using rolled shape straightening pinch rolls. When cooling the hot-rolled steel sheet within the range where the temperature of the upper surface of the hot-rolled steel sheet is 650-350°C, cooling is performed by using the cooling water of the flow rate of water per unit area of >3.5 m<SP>3</SP>/m<SP>2</SP>/min onto the upper surface of the hot-rolled steel sheet. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and a cooling device for cooling a hot-rolled steel sheet after finish rolling in a hot rolling process while passing it on a run-out table.

  The steel material discharged from the heating furnace is sent to a finishing mill through a roughing mill. FIG. 11 is an example of a layout of hot rolling equipment for performing a hot rolling process after the finish rolling mill 2. As shown in FIG. 11, a steel sheet 3 continuously rolled by a finish rolling mill 2 including a plurality of stands F1 to F7 and hot-rolled to a desired thickness and width at a final stand is converted into a number of conveying rolls 4a. It is conveyed by a runout table 4 consisting of The runout table 4 is installed in a cooling device 5 disposed on the downstream side of the finish rolling mill 2, and cools the steel plate 3 with various coolers 6 provided above. Thereafter, the steel plate 3 is wound around the coiler 8 via the pinch roll 7 just before the coiler. The pinch roll 7 just before the coiler plays a role of guiding the steel plate 3 to the coiler 8 and holding the back tension after the tail end of the steel plate 3 has passed through the final stand F7 of the finish rolling mill 2.

  Using such hot-rolling equipment, hot-rolled steel sheets (hereinafter referred to as “hot-rolled steel sheets” or simply “steel sheets”) after hot rolling are transported from the finish rolling mill to the coiler by a run-out table. In the meantime, after being cooled to a predetermined temperature by a cooling device (cooler) provided above and below the runout table, it is wound around a coiler. In hot rolling of steel plates, the cooling mode after finish rolling is an important factor for determining the mechanical properties of the steel plates, and it is important to cool the steel plates uniformly to a predetermined temperature. .

  In the cooling step after the finish rolling, the steel sheet is often cooled using, for example, water (hereinafter referred to as “cooling water”) as a cooling medium. In such a case, for example, cooling water is sprayed onto the upper surface of the steel plate to cool the steel plate, but the boiling form of the cooling water on the steel plate varies depending on the upper surface temperature of the steel plate. In generally used laminar cooling, as shown in FIG. 12, when the upper surface temperature T of the steel plate is a high temperature of about 600 ° C. or higher, the region becomes a film boiling region A. When the upper surface temperature T is a low temperature of 350 ° C. or lower, the region is a nucleate boiling region B. Furthermore, between the film boiling region A and the nucleate boiling region B, the region becomes a transition boiling region C.

  Here, in FIG. 13 showing the relationship between the upper surface temperature T of the steel sheet and the heat flux Q at the time of cooling, the inclination of the relationship between the heat flux Q and the upper surface temperature T of the steel sheet becomes a large reverse gradient from the start of cooling. The previous temperature region is referred to as a film boiling region A, the region having a large reverse gradient is referred to as a transition boiling region C, and the region having a positive gradient in a temperature region lower than the large reverse gradient is referred to as a nucleate boiling region B.

In the film boiling region A, when the cooling water is jetted onto the upper surface of the steel plate, the laminar flow reaches the steel plate, but then evaporates immediately, and the upper surface of the steel plate is covered with the vapor film. In this cooling, since the vapor film on the upper surface of the steel plate hinders heat transfer, the heat transfer coefficient (cooling capacity) h of the steel plate is lowered as shown in FIG. However, when the upper surface temperature T of the steel plate is about 600 ° C. or higher, the heat transfer coefficient h is substantially constant, and the heat flux Q decreases as the upper surface temperature T decreases as shown in FIG. Therefore, even if local variation occurs in the upper surface temperature T of the steel sheet, the portion where the upper surface temperature T is high is easy to cool, but the portion where the upper surface temperature T is low is difficult to cool. Then, even if a temperature deviation in the steel sheet (hereinafter referred to as “temperature deviation”) occurs before passing through the film boiling region A, the temperature deviation after passing through the film boiling region A is expressed as the temperature of the steel plate before passing through. It can be made smaller than the deviation. The heat flux Q is calculated by the following equation (2) using the heat transfer coefficient h, the upper surface temperature T of the steel plate, and the temperature W of the cooling water injected onto the steel plate.
Q = h × (T−W) (2)

  In the nucleate boiling region B, when cooling water is sprayed on the upper surface of the steel plate, no vapor film is generated on the upper surface of the steel plate, and the cooling water directly contacts the upper surface of the steel plate. For this reason, in the nucleate boiling area | region B, as shown in FIG. 12, compared with the cooling of the steel plate in the film boiling area | region A, the heat transfer coefficient h of a steel plate becomes high. Further, as shown in FIG. 13, the heat flux Q decreases as the upper surface temperature T of the steel sheet decreases. Therefore, when the temperature deviation of the steel plate occurs before passing through the nucleate boiling region B, the temperature deviation after passing through the nucleate boiling region B can be made smaller than the temperature deviation of the steel plate before passing through.

  However, in the transition boiling region C, when the cooling water is sprayed on the upper surface of the steel sheet, a place where the vapor film and the cooling water directly contact the upper surface of the steel sheet is mixed on the upper surface of the steel sheet. In this transition boiling region C, the heat transfer coefficient h and the heat flux Q rise as the upper surface temperature T of the steel sheet decreases. This is because the contact area between the cooling water and the steel sheet increases as the temperature of the steel sheet decreases. For this reason, as shown in FIG. 13, when the upper surface temperature T of the steel sheet is high, it is difficult to cool, and when the upper surface temperature T is low, it rapidly cools. Therefore, if local variation occurs in the upper surface temperature T of the steel sheet, this temperature variation Grows divergently. That is, the temperature deviation of the steel plate after passing through the transition boiling region C is larger than the temperature deviation of the steel plate before passing through the transition boiling region C. And when a temperature deviation becomes large in this way, a steel plate cannot be cooled uniformly.

  Therefore, a method has been proposed in which cooling is stopped at a temperature higher than the transition boiling start temperature, and then the steel sheet is cooled with cooling water having a water density that causes nucleate boiling (Patent Document 1). This cooling method pays attention to the fact that the transition boiling start temperature and the nucleate boiling start temperature shift to a higher temperature side as the density of the cooling water sprayed onto the steel sheet is higher, and then continues after cooling the steel sheet in the film boiling region. Thus, by increasing the water density of the cooling water and cooling the steel plate in the nucleate boiling region, the steel plate is prevented from passing through the transition boiling region.

However, in the method shown in Patent Document 1, cooling water having a water density of 3 m ³ / m ² / min or less is sprayed on a steel plate in a rod shape. It has been found that passing through the transition boiling region cannot be avoided.

  As described above, the temperature deviation of the steel sheet is small in the film boiling region and the nucleate boiling region. Then, when the steel plate is cooled only in the film boiling region and the nucleate boiling region while avoiding the transition boiling region, the temperature deviation of the steel plate after cooling in the nucleate boiling region is the temperature deviation of the steel plate after cooling in the film boiling region. Should be smaller than.

  However, referring to Table 1 and Table 2 described in Patent Document 1, the temperature deviation of the steel plate on the outlet side of the latter runout (nucleate boiling region) is the temperature deviation of the steel plate on the outlet side of the former runout (film boiling region). Is bigger than. This indicates that when the cooling method of Patent Document 1 is used, the steel plate passes through the transition boiling region, and the temperature deviation of the steel plate is increased by cooling in the transition boiling region. Therefore, in this case, the steel sheet cannot be cooled uniformly.

  On the other hand, when cooling water is sprayed in a state where the plate shape is not flat or in a state where the steel plate is vibrating, the manner in which the cooling water is applied varies depending on the position of the steel plate, resulting in a temperature difference. Therefore, it becomes impossible to manufacture a steel plate with stable quality.

  In particular, in a state where no tension is applied to the steel sheet, if there is an elongation difference distribution in the width direction of the steel sheet that passes through the finish rolling mill, a portion having a large elongation buckles and swells and the plate shape is maintained flat. It may not be possible. Further, regarding the vibration of the steel plate, the steel plate may vibrate when the plate is passed even if tension is applied to the steel plate. When the steel plate that is not flat or vibrates in this way is cooled, the cooling state varies depending on the position of the steel plate, and the quality variation further increases.

There are three possible states (swells) where the plate shape is not flat. 1) Looseness caused by the absence of tension. 2) Warpage of the steel sheet. 3) A so-called plate shape such as end elongation or middle elongation caused by a difference in elongation in the rolling direction.
When these undulations are present, the cooling water hits strongly on the slope that becomes the front surface in the traveling direction, and the cooling water hits weakly on the slope that becomes the rear face, resulting in strong and weak cooling. In addition, cooling water accumulates in the undulation valley portion and is cooled more strongly than the mountain portion. Therefore, it is easy to cool uniformly without undulation, and temperature deviation is less likely to occur. This is especially true in the film boiling region and the nucleate boiling stage. However, if there is a swell, the expansion of the temperature deviation in the transition boiling region is promoted.

In the patent document 2, the present applicant has proposed a rolling facility in which one or more sets of pinch rolls are installed on a runout table.
Patent Document 2 discloses that the purpose is to reduce necking in the plate width direction, and the installation of the pinch roll is at least one set or more, and the temperature of the steel plate is disclosed as a position at 650 ° C. or less. However, normally, the temperature of the steel sheet immediately after passing through the finish rolling mill is about 840 ° C. or higher and 1000 ° C. or lower, and the cooling process after passing through the finish rolling mill until reaching 650 ° C. disclosed in Patent Document 2 above. It takes a lot of distance. Therefore, the tip of the steel plate is not sandwiched until the tip of the steel plate reaches the pinch roll at a position away from the finish rolling mill. Moreover, it does not describe about the tension | tensile_strength applied to a steel plate, and there is no reference regarding the improvement possibility of the plate | board shape of the tip end part of the steel plate which is the said problem. Furthermore, there is no mention regarding suppression of vibration of the steel sheet.

JP 2008-110353 A JP 2001-321816 A

  The present invention has been made in view of such points, and in the cooling of a hot-rolled steel sheet performed after finish rolling of hot rolling, the temperature deviation of the hot-rolled steel sheet after cooling is made less than the conventional temperature deviation, An object of the present invention is to uniformly cool a rolled steel sheet and obtain a hot-rolled steel sheet having a small variation in quality as compared with a conventional steel sheet.

In order to achieve the above-mentioned object, the inventors have conducted intensive research. As a result, even when the hot-rolled steel sheet including the transition boiling region is cooled, the amount of water on the upper surface when strongly cooled is 3.5 m ² / m. It has been found that when it exceeds ² / min, the temperature deviation of the hot-rolled steel sheet after the entire cooling process can be made equal to or less than the temperature deviation before the entire cooling process. This means that if the strong cooling is performed, the temperature deviation generated before the entire cooling process can be made smaller after the entire cooling process than before the cooling process.

  FIG. 14 is a schematic diagram of a temperature drop curve of a conventional hot-rolled steel sheet. In this figure, the solid line is the temperature-decreasing curve of the part being referred to, and the broken line is the temperature-decreasing curve when there is an initial temperature deviation. In FIG. 14, the portion A is a film boiling region, the portion B is a nucleate boiling region, and the portion C is a transition boiling region. The curves A and B are convex downward, but the area C is convex upward. Even if there is an initial temperature deviation in the downwardly convex area, this deviation is reduced, but in the upwardly convex area, the temperature deviation is increased.

Is 3.5m ² / ^{m 2} / min from greater than around 600 ° C. in ^15, at 6m ² / m ² / min, showing the cooling curve when cooling the hot rolled steel sheet of 3mm thick. The actual temperature drop curve albeit convex downward from the figure reduction of temperature deviation even if the cooling in the nucleate boiling region near 3.5m ² / m 2 / ^min than in a straight line it is seen that not very large. Therefore, if the temperature deviation at the end of the film boiling region can be reduced, the temperature deviation at the end of the entire cooling process can be achieved by performing cooling with a water amount exceeding 3.5 m ² / m ² / min that does not increase the temperature deviation of the transition boiling region. Can be reduced.

On the other hand, as described above, during cooling, the temperature deviation is likely to occur even in the film boiling region and the nucleate boiling region due to the waviness shape and the vibration of the steel plate. The inventors have found that it is effective to apply tension immediately after the finish rolling mill in order to eliminate the waviness shape. Moreover, it discovered that it was effective to suppress the steel plate vibration in a transition boiling area | region by installation of a pinch roll as a method for suppressing the vibration of the steel plate which affects the temperature deviation at the time of cooling effectively. Therefore, in order to reduce the temperature deviation at the end of the entire cooling process, the tension is applied before the strong cooling exceeding 3.5 m ² / m ² / min is performed to eliminate the wavy shape, and the vibration of the steel plate is reduced. It is only necessary to suppress the temperature deviation by suppressing the entire cooling region.

The present invention has been made on the basis of the above findings, and the gist thereof is as follows.
(1) A cooling method for cooling a hot-rolled steel sheet after finish rolling in a hot rolling process while passing it at a downstream speed of 3 m / sec or more,
When the upper surface temperature of the hot-rolled steel sheet is from 850 ° C. to 650 ° C., a tension of 0.4 kgf / mm ² (3.92 MPa) or more is applied to the finish rolling mill side using a pinch roll for rolling shape correction. Sandwich the hot rolled steel sheet,
When cooling the hot-rolled steel sheet within the range of the upper surface temperature of the hot-rolled steel sheet from 650 ° C. to 350 ° C., the water density is over 3.5 m ³ / m ² / min with respect to the upper surface of the hot-rolled steel sheet. A method for cooling a hot-rolled steel sheet, characterized in that cooling is performed using a cooling water.

  (2) The collision speed of the cooling water against the upper surface of the hot-rolled steel sheet is set to 20 m / sec or more, and the cooling water covers an area of 80% or more of the upper surface of the hot-rolled steel sheet. The method for cooling a hot-rolled steel sheet according to 1.

  (3) The collision pressure of the cooling water against the upper surface of the hot-rolled steel sheet is 2 kPa or more, and the cooling water covers an area of 80% or more of the upper surface of the hot-rolled steel sheet. The cooling method of the hot-rolled steel sheet as described.

  (4) The flow of the cooling water is conical, and the collision angle of the cooling water with respect to the upper surface of the hot-rolled steel sheet is 75 degrees or more from the horizontal direction, (1) to (3) The method for cooling a hot-rolled steel sheet according to any one of the above.

(5) The first intermediate pinch roll is disposed at a position where the upper surface temperature of the hot-rolled steel sheet is from 650 ° C. to 550 ° C., and the second intermediate pinch roll is disposed at a position from 450 ° C. to 350 ° C. (1) to (4), wherein a tension of 0.4 kgf / mm ² (3.92 MPa) or more is applied to the hot-rolled steel sheet between the first and second intermediate pinch rolls. The method for cooling a hot-rolled steel sheet according to any one of the above.

  (6) The water draining which suppresses that the cooling water sprayed on the upper surface of the hot-rolled steel sheet flows into the hot-rolled steel sheet before and after the start of the cooling step is performed. The method for cooling a hot-rolled steel sheet according to any one of (5).

  (7) The method for cooling a hot-rolled steel sheet according to any one of (1) to (6), wherein only the upper surface of the hot-rolled steel sheet is cooled.

(8) defines the cooling capacity d by the following formula (1), is cooled as less 1.2 times 0.8 times or more than the cooling capacity d _u of the hot-rolled steel sheet upper surface to the lower surface of the cooling capacity d _l The method for cooling a hot-rolled steel sheet according to any one of (1) to (6), wherein:
d = f (q, p, _tw ) (1)
d: cooling capacity, u: an upper surface side, l: lower surface q: cooling water ^{[m 3 / m 2 / min} ], p: the collision pressure [kPa], _{t w:} water temperature

(9) A cooling device that cools the hot-rolled steel sheet after finish rolling in the hot rolling process while passing it at a downstream speed of 3 m / sec or more,
Rolling shape correction that sandwiches the hot-rolled steel sheet by applying a tension of 0.4 kgf / mm ² (3.92 MPa) or more to the finish rolling mill at a position where the upper surface temperature of the hot-rolled steel sheet is 650 ° C. or higher and 850 ° C. or lower. For pinch rolls,
Within the range of 650 ° C. to 350 ° C., using the cooling water having a water density of more than 3.5 m ³ / m ² / min with respect to the upper surface of the hot rolled steel plate, A cooling device for a hot-rolled steel sheet, comprising a cooler for cooling.

  (10) The cooler has a plurality of nozzles, and the cooling water sprayed from the plurality of nozzles has a collision speed of 20 m / sec or more against the upper surface of the hot-rolled steel sheet, and the plurality of nozzles The apparatus for cooling a hot-rolled steel sheet according to (9) above, wherein the cooling water is sprayed so as to cover an area of 80% or more of the upper surface of the rolled steel sheet.

  (11) The cooler has a plurality of nozzles, and the plurality of nozzles covers an area of 80% or more of the upper surface of the hot-rolled steel sheet with cooling water having a collision pressure against the upper surface of the hot-rolled steel sheet of 2 kPa or more. The apparatus for cooling a hot-rolled steel sheet according to (9) above, which has the ability to inject cooling water.

  (12) The plurality of nozzles of the cooler jets cooling water in a conical water flow, and the collision angle of the cooling water with respect to the upper surface of the hot-rolled steel sheet is 75 degrees or more from the horizontal direction, The cooling apparatus for hot-rolled steel sheets according to (10) or (11).

(13) First and second intermediate pinch rolls are respectively disposed at a position where the upper surface temperature of the hot-rolled steel sheet is from 650 ° C. to 550 ° C. and a position where the upper surface temperature is from 450 ° C. to 350 ° C. And the hot-rolled steel sheet between the second intermediate pinch rolls has a tension imparting function of 0.4 kgf / mm ² (3.92 MPa) or more, in any one of (9) to (12) above The cooling apparatus for hot-rolled steel sheets as described.

  (14) The hot-rolled steel sheet cooling apparatus according to any one of (9) to (13), wherein a drainer is provided on an upstream side and a downstream side of the cooler.

  (15) The apparatus for cooling a hot-rolled steel sheet according to (14), wherein the drainer has a nozzle that injects water-draining water onto the hot-rolled steel sheet.

  (16) The cooling device for a hot-rolled steel sheet according to (15), wherein the drainer further includes a draining roll provided so as to be in contact with the hot-rolled steel sheet.

  (17) The cooling device for a hot-rolled steel sheet according to any one of (9) to (16), wherein the cooler cools only an upper surface of the hot-rolled steel sheet.

(18) the cooling machine uses a cooling capacity d defined by the following formula (1), the hot-rolled steel sheet upper surface of the cooling capacity d _u a lower surface of the cooling capacity d _l in comparison with 0.8 times 1 The apparatus for cooling a hot-rolled steel sheet according to any one of (9) to (16), wherein the cooling apparatus has a capability of cooling as less than 2 times.
d = f (q, p, _tw ) (1)
d: cooling capacity, u: an upper surface side, l: lower surface q: cooling water ^{[m 3 / m 2 / min} ], p: the collision pressure [kPa], _{t w:} water temperature

  According to the present invention, in the cooling of hot-rolled steel sheet performed after finish rolling of hot rolling, the temperature deviation of the hot-rolled steel sheet after cooling is made less than the conventional temperature deviation, and the hot-rolled steel sheet is uniformly cooled, As a result, it is possible to obtain a hot-rolled steel sheet having a small variation in quality.

It is a perspective view which shows the outline | summary of the hot rolling equipment provided with the cooling device of this invention. It is explanatory drawing which shows the presence or absence of the pinch roll for rolling shape correction concerning this invention, and the wave | undulation of the steel plate by tension | tensile_strength, (A) is a graph which shows the relationship between a tension | tensile_strength and a wave | undulation ratio, (B) is a pinch roll for rolling shape correction | amendment. (C) is a schematic diagram when a pinch roll for rolling shape correction is provided. It is a graph which shows the relationship between the magnitude | size of a wave | undulation and temperature variation. It is a side view which shows the outline of a structure of a finish rolling mill, a cooler, and another drainer. It is a side view which shows the outline of structures, such as a cooler. It is explanatory drawing which showed the jet collision surface in the upper surface of the steel plate of the cooling water injected by the cooler. It is the graph which showed the relationship between the steel plate upper surface temperature concerning this Embodiment, and a heat transfer coefficient. It is the graph which showed the relationship between the steel plate upper surface temperature concerning this Embodiment, and a heat flow rate. It is the graph which showed the relationship between the cooling time at the time of cooling using this invention, and a heat flux. It is a perspective view which shows the outline | summary of different embodiment of the hot rolling equipment provided with the cooling device of this invention. It is a perspective view which shows the outline | summary of the conventional hot rolling equipment. It is the graph which showed the relationship between the conventional steel plate upper surface temperature and a heat transfer coefficient. It is the graph which showed the relationship between the conventional steel plate upper surface temperature and a heat flux. It is a schematic diagram of the temperature fall curve of the conventional hot-rolled steel plate. It is a cooling curve when hot-rolled steel plate is strongly cooled from around 600 ° C.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

The steel material discharged from the heating furnace is rolled to a thickness of about 40 mm by a roughing mill, then continuously rolled by a finish rolling mill, and rolled to a thickness of about 1 to 4 mm. FIG. 1: shows the outline | summary of a structure after the finish rolling mill 2 in the hot rolling equipment which has the cooling device 5 concerning this invention. The finish rolling mill 2 includes a plurality of, for example, seven stands F1 to F7 as shown in the figure, and is hot-rolled to a steel plate 3 having a desired plate thickness and plate width at the final stand. The temperature of the steel plate 3 immediately after passing through the finishing mill 2 is 840 ° C. or higher and 1000 ° C. or lower. The steel plate 3 is conveyed at a plate speed of 3 m / sec or more in the cooling device 5 having the run-out table 4 composed of a plurality of conveying rolls 4a. Various coolers 6 are arranged on the runout table 4, and the steel plate 3 is cooled by water or the like when being conveyed on the runout table 4, thereby forming a metal structure of a desired material. The cooler 6 is divided into, for example, four zones, and each is controlled by the control unit 30. Of the coolers 6, 6 c has the ability to inject a cooling water amount exceeding 3.5 m ² / m ² / min. The steel plate 3 cooled to a predetermined temperature, for example, 350 ° C. is wound around the coiler 8. On the upstream side of the coiler 8, there is provided a pinch roll 7 just before the coiler composed of a pair of upper and lower rolls. The steel plate 3 is guided to the pinch roll 7 just before the coiler, and is wound around the coiler 8 while adjusting the winding shape in a state where the coiler 8 is appropriately tensioned.

A pinch roll 10 for correcting the rolling shape is formed of a pair of upper and lower rolls and can correct the waviness in the width direction at a position where the upper surface temperature of the steel plate 3 is 650 ° C. or higher and 850 ° C. or lower, downstream of the final stand of the finish rolling mill 2. Has been placed. The rolling shape correcting pinch roll 10 rotates while sandwiching the steel plate 3 by applying a tension of 0.4 kgf / mm ² (3.92 MPa) or more between the finishing mill 2 and the rolling shape correcting pinch roll 10. , Transport downstream. The installation position of the rolling shape correcting pinch roll 10 is preferably as close as possible from the final stand F7. However, at the position where the temperature of the steel plate 3 exceeds 850 ° C., the thickness of the steel plate 3 is changed by the rolling shape correcting pinch roll. This is not preferable because of concern. Therefore, the rolling shape correcting pinch roll 10 is disposed immediately after the upper surface of the steel sheet becomes 850 ° C. or lower, or at least at a position where it becomes 650 ° C. or higher before entering the transition boiling region. Further, the pinch roll diameter, the rolling force, and the like are determined so that the plate thickness of the steel plate 3 does not change. When the immediately quenching zone 6a is provided adjacent to the downstream side of the finish rolling mill 2, a rolling shape correcting pinch roll 10 may be provided on the rear surface of the immediately following quenching zone 6a. Immediately after that, by providing the quenching zone 6a, the position where the upper surface temperature of the steel plate 3 becomes 850 ° C. or less is close to the finishing mill 2, and the distance between the rolling shape straightening pinch roll 10 and the finishing mill 2 can be shortened. it can.

When the tip of the steel plate 3 passes through the final stand of the finish rolling mill 2 and reaches the position of the rolling shape correcting pinch roll 10, the steel plate 3 is sandwiched by the rolling shape correcting pinch roll 10. Since the tail end side of the steel plate 3 is supported by each stand of the finish rolling mill 2, the tip end is sandwiched by applying a tension of 0.4 fkg / mm ² (3.92 MPa) or more from the pinch roll 10 for correcting the rolling shape. Thus, the steel plate 3 is conveyed while maintaining a flat plate shape from the conventional one while eliminating the undulation.

FIG. 2 shows how the sine wave undulation due to the presence or absence of tension is reduced in the steel plate 3 passing through the final stand of the finish rolling mill 2. (A) is a graph showing the ratio of waviness due to tension, where waviness when there is no tension is 1, (B) and (C) are schematic diagrams showing the state of waviness of the steel sheet 3, and (B) is rolling. When the shape correcting pinch roll is not provided, (C) is a case where the rolled shape correcting pinch roll 10 of the present invention is provided and tension is applied. When the thickness of the steel plate 3 before rolling of the final stand is 3.3 mm, the thickness after rolling is 3 mm, and the simulation calculation results, the undulation height after rolling is 30 mm. 10 and a tension of 0.4 kgf / mm ² (3.92 MPa) is applied toward the final stand, the height of the undulation after rolling is about 1 as shown in FIG. / 3. Furthermore, as shown in FIG. 2 (C), when the tension was released, that is, after passing through the pinch roll 10 for correcting the rolling shape, the undulation remained reduced. Accordingly, it has been found that when finish rolling is performed with tension, the sheet is conveyed without undulation even after passing through the pinch roll 10 for correcting the rolling shape. That is, if the tension is 0.4 kgf / mm ² (3.92 MPa) or more, the swell, warpage, and swell including all plate shapes such as end elongation or medium elongation described above become 1/3 or less.
Further, when the tension was 1.5 kgf / mm ² (14.7 MPa), the amount of reduction in swell was about 1/8 as shown in FIG. In the region where the tension is 0.4 kgf / mm ² (3.92 MPa) or more, as shown in FIG. The applied tension is at most about 2 kgf / mm 2 (19.6 MPa).

In this way, the rolling shape correcting pinch roll 10 can flatten the plate shape even if undulation occurs in the steel plate 3 passing through the finishing mill 2. When the steel plate 3 passes through the cooling device 5 while maintaining a flat plate shape, the cooling water sprayed from the cooler 6 is uniformly applied to the upper surface of the steel plate 3 and is cooled under uniform conditions, and various metal structures are formed. It is formed stably. Note that there is a good correlation between the size of the undulation and the temperature variation, as shown in FIG. 3, and by setting the undulation to 1/3 or less, the temperature variation can be reduced to 1/2 to 1/3.
If the tension is 0.4 kgf / mm ² (3.92 MPa) or more, the effect of reducing the undulation is great. However, the undulation can be further reduced by increasing the tension to 0.5 kgf / mm ² (4.90 MPa) or more. In this case, the material uniformity is further improved.

On the most upstream side in the cooling device 5, that is, immediately downstream of the finishing mill 2, a cooling machine 6 a and a cooling machine 6 b for cooling the steel plate 3 immediately after passing through the finishing mill 2 are provided with a pinch roll 10 for correcting the rolling shape. Is provided. As shown in FIG. 4, the cooler 6 a and the cooler 6 b have, for example, a plurality of laminar nozzles 11 that inject cooling water onto the upper surface of the steel plate 3. A plurality of laminar nozzles 11 are provided in alignment with each other in the width direction and the conveyance direction of the steel plate 3. The density of the amount of cooling water sprayed from the laminar nozzle 11 onto the upper surface of the steel plate 3 is, for example, about 1 m ³ / m ² / min. And the steel plate 3 whose upper surface temperature is 840-1000 degreeC immediately after passing the finishing mill 2 is cooled by the cooling water sprayed from the laminar nozzle 11 until the upper surface temperature becomes 650 degrees C or less. . The upper surface temperature of 650 ° C. is higher than the temperature at which cooling by the laminar nozzle 11 starts transition boiling. That is, the present invention is not limited to this embodiment, and may be any temperature range that starts transition boiling of the applied cooler. For example, when the water density at the time of laminar cooling is less than the above 1 m ³ / m ² / min, it is possible to cool 650 ° C. to a low temperature range of 600 ° C.
In addition, it is necessary to consider the arrangement so that a temperature deviation is not caused by cooling with the laminar nozzle 11, and a spray nozzle may be substituted if necessary. Further, the cooling by the cooler is not limited to cooling water, and gas cooling or air / water mixing cooling (mist cooling) may be mixed.

  As shown in FIG. 1, a cooler 6c for cooling the steel plate 3 cooled by the cooler 6a and the cooler 6b is provided on the downstream side of the cooler 6a and the cooler 6b. As shown in FIG. 5, the cooler 6 c has a plurality of spray nozzles 21 that spray cooling water in a conical shape on the upper surface of the steel plate 3, for example, on the upper surface of the steel plate 3. The spray nozzle 21 is disposed at a position where the height E from the tip and the upper surface of the steel plate 3 is 700 mm or more. Thus, the reason why the distance from the upper surface of the steel plate 3 is set to 700 mm or more is to prevent the tip of the steel plate 3 being conveyed from hitting equipment such as the spray nozzle 21. This has two meanings: protection of the equipment such as the spray nozzle 21 and prevention of defects such as wrinkles when the steel plate 3 hits the equipment. Therefore, for example, without increasing the tip position of the spray nozzle 21, it is possible to provide a device that suppresses the plate height by pinching the steel plate 3 to the upstream side of the facility and pinching the steel plate 3, for example. It is difficult to completely eliminate the possibility of wrinkling of the steel plate 3 by this pinch device. Here, the height E is set to 700 mm or more, for example, 1000 mm, in order to reduce the possibility of wrinkling of the steel plate 3 as much as possible.

  As shown in FIG. 6, the spray nozzle 21 is arranged so that the jet collision surface 21 a on the upper surface of the steel plate 3 of the cooling water sprayed from the spray nozzle 21 covers an area of 80% or more of the steel plate 3. When the steel plate 3 is cooled, the cooling capacity differs greatly between the collision portion and the non-collision portion of the cooling water jet. For this reason, when a jet collision part with a large cooling capacity and a jet non-collision part with a small cooling capacity coexist, even if the upper surface temperature of the steel plate 3 is lowered in the jet collision part, the cooling capacity is reduced at the jet non-impact part. Due to the recuperation from the inside of the steel plate 3, the decrease in the upper surface temperature of the steel plate 3 is stagnant. In the film boiling region or the nucleate boiling region in which the relationship between the upper surface temperature of the steel plate 3 and the heat flux is a positive gradient, a large difference does not occur with respect to the reduction of the temperature deviation of the steel plate 3, but in the transition boiling region, Due to the stagnation of the lowering of the upper surface temperature of the steel plate 3, the stay time in the transition boiling region is increased, and the temperature deviation is increased. Therefore, it is desirable that the jet collision surface 21a covers 100% of the steel plate 3. If the jet collision part is not continuous, the jet collision surface 21a covers an area of 80% or more of the upper surface of the steel plate 3, and if there is a sufficient amount of water, the time during the strong cooling process by the cooler 6c is reduced. 80% can be in the nucleate boiling region. Moreover, it is desirable that the jet collision surface 21a from each spray nozzle 21 does not interfere too much with the adjacent jet collision surface 21a.

The water amount density of the cooling water sprayed from the spray nozzle 21 onto the upper surface of the steel plate 3 is 4 m ³ / m ² / min or more and 10 m ³ / m ² / min or less. By setting the water density to 4 m ³ / m ² / min or more, 80% of the time during the strong cooling step can be made the nucleate boiling region. The water density of 10 m ³ / m ² / min is the upper limit of the water density during normal operation. That is, the water density of the cooling water sprayed on the upper surface of the steel plate 3 is desirably 4 m ³ / m ² / min or more and 10 m ³ / m ² / min or less.
Further, as shown in FIG. 5, the cooling water injection angle α is, for example, 3 degrees or more and 30 degrees or less, and the collision angle β with respect to the upper surface of the cooling water steel sheet 3 is 75 degrees or more from the horizontal direction. It is desirable to be. The collision angle β of the cooling water is nearer to the steel plate 3 because it is easy to increase the collision pressure, and the uniformity in the injection range is improved. This is desirable because it increases the effect. However, if it is completely vertical, it is not desirable because it is difficult on the equipment layout to cover an area of 80% or more of the steel sheet with the jet collision surface. Furthermore, it is desirable that the collision speed of the cooling water against the upper surface of the steel plate 3 is 20 m / sec or more and the collision pressure is 2 kPa or more. With such a collision speed or collision pressure, the cooling water jet can reach the upper surface of the steel plate 3 when cooling with a large volume of water density. If the cooling water jet does not reach the upper surface of the steel plate 3, the vapor film on the upper surface of the steel plate 3 cannot be sufficiently removed, and the time of the transition boiling region becomes longer.

  Further, as shown in FIG. 5, the cooler 6 c may include a plurality of spray nozzles 22 that inject cooling water onto the lower surface of the steel plate 3, for example, below the lower surface of the steel plate 3. The water density, the collision speed, or the collision pressure of the cooling water sprayed from the spray nozzle 22 to the lower surface of the steel plate 3 is substantially the same as the spray nozzle 21. That is, the cooling capacity of the spray nozzle 22 on the lower surface side of the steel plate 3 is equivalent to the cooling capacity of the spray nozzle 21 on the upper surface side, excluding the influence of water on the plate and gravity. Further, the water amount density, the collision speed, or the collision pressure of the cooling water sprayed on the lower surface of the steel plate 3 may be adjusted in consideration of the influence of water on the plate and gravity. Then, the steel sheet 3 cooled to the upper surface temperature of 650 ° C. or lower by the cooler 6a and the cooler 6b is cooled by the cooling water sprayed from the spray nozzles 21 and 22 until the upper surface temperature becomes about 350 ° C., for example. The In addition, since cooling from the lower surface is not essential, the cooler 6c may be provided with only the spray nozzle 21 on the upper surface side, but the steel plate 3 is cooled as quickly as possible, and the cooling time in the transition boiling region is Is preferably provided on the lower surface side of the steel plate 3 as in the present embodiment.

  Although omitted in FIG. 1 on the downstream side closest to the cooler 6c, a drainer for preventing the coolant injected onto the upper surface of the steel plate 3 by the cooler 6c from flowing to the downstream side of the cooler 6c. It is desirable that 23 is provided. As shown in FIG. 5, the drainer 23 has a spray nozzle 25 that injects drain water onto the upper surface of the steel plate 3. Furthermore, a draining roll 24 may be installed on the upper surface of the steel plate 3. The draining roll 24 is for reliably preventing the cooling water from flowing downstream. In this way, the cooling water flowing on the upper surface of the steel plate 3 is drained. If the draining is not performed properly, a non-uniform water flow is generated on the steel plate 3, which may cause a temperature variation.

  Although not shown in FIG. 1, another drainer 26 for preventing the coolant from flowing to the cooler 6b side is also provided on the upstream side immediately downstream of the cooler 6c (downstream side of the cooler 6b). It is desirable. As shown in FIG. 5, the other drainer 26 has the same configuration as the drainer 23 and has a spray nozzle 28. In addition, you may install the draining roll 27 similarly to the downstream side. Then, the water draining machine 26 drains the cooling water flowing on the upper surface of the steel plate 3. If the draining is not performed properly, a non-uniform water flow is generated on the steel plate 3, which causes a temperature variation.

  As shown in FIG. 1, the cooling device 5 includes the density of the cooling water sprayed from the laminar nozzle 11 of the cooler 6 a and the cooler 6 b and the spray nozzles 21 and 22 of the cooler 6 c, and the spray time. The control part 30 which controls etc. and controls the temperature of the steel plate 3 is provided. In addition, you may control the injection time of a cooling water by adjusting the length of the conveyance direction of the steel plate 3 of the cooler 6a, the cooler 6b, and the cooler 6c. At this time, it is preferable to change the length of each cooler in units of the table roll 4a.

  The cooling device 5 according to the present embodiment is configured as described above. Next, the cooling method of the steel plate 3 using this cooling device 5 is demonstrated based on FIG.7 and FIG.8. FIG. 7 is a graph showing the relationship between the upper surface temperature T of the steel plate 3 and the heat transfer coefficient (cooling capacity) h, and FIG. 8 is a graph showing the relationship between the upper surface temperature T of the steel plate 3 and the heat flux Q. .

The steel plate 3 continuously rolled by the finish rolling mill 2 and having an upper surface temperature T of about 940 ° C. is conveyed to the cooler 6a and the cooler 6b. In the cooler 6 a and the cooler 6 b, cooling water having a water density of about 1 m ³ / m ² / min controlled by the control unit 30 is injected onto the upper surface of the steel plate 3. With this level of cooling water, the steel plate 3 is cooled in the film boiling region A. The cooling in the cooler 6a and the cooler 6b is not limited to cooling water, and may be gas cooling or air-water mixed cooling. And as shown in FIG. 7, the steel plate 3 is cooled by the cooler 6a and the cooler 6b until the upper surface temperature T becomes about 650 degreeC. This 650 ° C. is a temperature equal to or higher than the temperature at which the upper surface of the steel plate 3 is changed from the film boiling region A to the transition boiling region C when the steel plate 3 is cooled at a water density of about 1 m ³ / m ² / min or less. . That is, the steel plate 3 is cooled in a film boiling state with a constant low heat transfer coefficient h by the cooler 6a and the cooler 6b. Further, as shown in FIG. 8, the heat flux Q decreases as the upper surface temperature T of the steel plate 3 decreases. Therefore, the temperature deviation of the steel plate 3 after passing through the film boiling region A can be made smaller than the temperature deviation of the steel plate 3 before passing through the film boiling region A.

Next, the steel plate 3 cooled to the upper surface temperature T of 650 degrees C or less is conveyed by the cooler 6c. In the cooler 6c, cooling water having a water density of 4 m ³ / m ² / min or more and 10 m ³ / m ² / min or less controlled by the control unit 30 is sprayed on the upper surface of the steel plate 3 and is shown in FIG. Thus, the steel plate 3 is cooled until the upper surface temperature T reaches 350 ° C. at the minimum. Hereinafter, an example in which cooling is performed from 650 ° C. to 350 ° C. by the cooler 6c will be described.

  In the cooling by the cooler 6c, the water density of the cooling water injected to the steel plate 3 is larger than the water density of the cooling water in the cooler 6a and the cooler 6b. It moves to the higher temperature side than the transition boiling region C ′ of the steel plate 3 being cooled by the machine 6a and the cooler 6b. In the cooling by the cooler 6c, the steel plate 3 is initially cooled until the upper surface temperature T reaches 590 ° C. in the transition boiling region C. Thereafter, the cooling of the steel sheet 3 enters the nucleate boiling region B, and is cooled until the upper surface temperature T of the steel sheet 3 reaches 350 ° C. Since the water density in the cooler 6c is large, the cooling time in the transition boiling region C of the steel plate 3 is less than 20% of the cooling time of the steel plate 3 by the cooler 6c. In the nucleate boiling region B, the steel plate 3 is cooled in a nucleate boiling state with a constant high heat transfer coefficient h.

  As shown in FIG. 8, in the nucleate boiling region B, as in the film boiling region A, the heat flux Q decreases as the upper surface temperature T decreases, and the temperature deviation of the steel plate 3 decreases. In the transition boiling region C, the heat flux Q increases as the upper surface temperature T of the steel plate 3 decreases. As described above, the cooling time of the transition boiling region C is 20% of the cooling time of the steel plate 3 by the cooler 6c. Therefore, even if the temperature deviation of the steel plate 3 increases in the transition boiling region C, the influence of the cooling device 5 on the cooling of the steel plate 3 is small. Therefore, the temperature deviation of the steel plate 3 before being cooled by the cooling device 5 can be made equal to or less than the temperature deviation of the steel plate 3 after being cooled by the cooling device 5.

FIG. 9 shows the relationship between the cooling time and the heat flux. As shown in FIG. 9, the time region in which the heat flux increases is cooling by the transition boiling region C, and the region in which the heat flux decreases is cooling by the nucleate boiling region B.
According to the above embodiment, in the cooler 6c, cooling water having a water amount density of 4 m ³ / m ² / min or more is sprayed onto the upper surface of the steel plate 3, and cooling of the steel plate 3 in the transition boiling region C is performed by the cooler. It was possible to suppress the cooling time of the steel sheet in the nucleate boiling region B to 80% or more of the cooling time by suppressing the cooling time by 6c to less than 20%. In such a case, according to the knowledge of the inventors, the temperature deviation of the steel plate 3 before cooling in the cooling device 5 can be made equal to or less than the temperature deviation of the steel plate 3 after cooling in the cooling device 5. Therefore, even if local variations occur in the temperature of the steel plate 3, it is easy to cool at a high temperature, but it is difficult to cool at a low temperature, and the temperature distribution of the steel plate 3 becomes uniform. 3 can be cooled uniformly. That is, in the strong cooling step, it is desirable to cool the steel plate 3 in the nucleate boiling region B for a time that is 80% or more of the cooling time of the strong cooling step.

Further, in the cooler 6c, the water density of the cooling water is increased to more than 3.5 m ³ / m ² / min, preferably 4 m ³ / m ² / min or more, so that the steel plate 3 in the nucleate boiling region B The cooling time can be shortened. Accordingly, the cooling device 5 can be downsized.

  Moreover, since the cooling water is injected by the cooler 6c so that the collision pressure against the upper surface of the steel plate 3 is 2 kPa or more and covers the area of 80% or more of the upper surface of the steel plate 3, the cooling on the steel plate 3 is performed. Water distribution and flow can be controlled uniformly on the upper surface of the steel plate 3, and cooling water can be directly collided with the steel plate 3 to eliminate the vapor film on the upper surface of the steel plate 3, thereby cooling the steel plate 3 more uniformly. Can do.

  Further, many of the causes of shape deterioration are often due to local variations in temperature (temperature deviation), and the temperature deviation can be suppressed by suppressing the cooling time in the transition boiling region C as in the present invention. In addition, shape deterioration is also suppressed.

  Further, in the cooler 6c, when the collision angle β of the cooling water sprayed on the upper surface of the steel plate 3 is 75 degrees or more from the horizontal direction, the cooling water jet collision surface 21a on the upper surface of the steel plate 3 has a relatively small area. Thus, the cooling water collision pressure in the jet collision surface 21a can be made uniform, and the vertical velocity component at the time of the cooling water collision can be increased. Thereby, the collision pressure of the whole upper surface of the steel plate 3 can be made uniform and large, and the steel plate 3 can be uniformly and strongly cooled.

  Further, when the spray nozzle 22 having the same cooling capacity as the upper surface spray nozzle 21 is provided on the lower surface side of the cooler 6c, that is, the water density, the collision speed or the collision pressure of the cooling water is substantially the same as the spray nozzle 21. When the spray nozzle 22 is provided, the lower surface can be cooled simultaneously with the upper surface of the steel plate 3. Thereby, the steel plate 3 can be cooled efficiently in a short time. Moreover, the temperature difference of the upper surface and lower surface of the steel plate 3 can be made small, and the deformation | transformation of the steel plate 3 by a thermal stress can be suppressed. When the temperature difference between the upper surface and the lower surface of the steel plate 3 is large, warping due to thermal stress or the like occurs depending on the steel type, which becomes a factor that hinders the sheet passing property. Here, if the cooling capacity of the upper surface is 0.8 times or more and 1.2 times or less as compared with the cooling capacity of the lower surface, even if it is a steel type that is likely to warp, uniform cooling is not caused. Can be realized. In order to adjust the cooling capacity, the supply amount of the cooling water can be adjusted by the control unit 30. In addition, when only the upper surface is cooled, there is an advantage that it is possible to eliminate the scattering of the cooling water on the lower surface side due to the cooling water blowing from the lower surface, and the countermeasure for preventing the scattering of the cooling water to the electric system or the like becomes unnecessary.

  Further, since the drainer 23 and the other drainer 26 are respectively provided on the downstream side and the upstream side of the cooler 6c, the coolant sprayed onto the upper surface of the steel plate 3 by the cooler 6c is upstream of the cooler 6c. And it does not flow downstream. Thereby, the on-plate water flow that may flow non-uniformly on the steel plate 3 can be suppressed, and cooling can be made uniform. Moreover, since the drainer 23 and the other drainer 26 have the draining rolls 24 and 27 in addition to the spray nozzles 25 and 28, the draining rolls 24 and 27 can perform draining more reliably.

  Thereafter, the steel plate 3 that has been uniformly cooled to a predetermined temperature is wound around a coiler 8. In FIG. 1, the cooler 6 d is provided on the rear surface of the cooler 6 c so that the cooler 6 d can be cooled before being wound by the coiler 8, but whether or not to use this is arbitrary.

In the above embodiment, the cooler 6a and the cooler 6b have the laminar nozzle 11, but may have a spray nozzle (not shown) instead. Such spray nozzles are provided at wider intervals than the spray nozzle 21 of the cooler 6c. The water density of the cooling water sprayed from the spray nozzles of the cooler 6a and the cooler 6b is smaller than the water density of the cooling water from the spray nozzle 21 of the cooler 6c.
The cooler 6d may have a laminar nozzle 11 similarly to the cooler 6a and the cooler 6b, and may have a spray nozzle (not shown) instead.

In the above embodiment, in the cooler 6a and the cooler 6b, the cooling water is injected to the steel plate 3, but instead of this or in combination with this, a gas, for example, air is injected to the steel plate 3. The steel plate 3 may be cooled. Furthermore, you may cool the steel plate 3 without using cooling water.
Similarly to the cooler 6a and the cooler 6b, the cooler 6d may be a gas or cooling water, and an appropriate cooling medium may be used as necessary.

FIG. 10 shows a different embodiment of the present invention, in which first and second intermediate pinch rolls 27 and 24 are provided in the cooling device 5 in addition to the configuration of the embodiment of FIG. . The first intermediate pinch roll 27 is disposed at a position where the upper surface temperature of the steel plate 3 is 650 to 550 ° C., and the second intermediate pinch roll 24 is disposed at a position where the upper surface temperature is 450 to 350 ° C. In the present embodiment, the first and second pinch rolls 27 and 24 are also arranged to serve as the draining rolls 27 and 24 in the above embodiment. Each of the first and second intermediate pinch rolls 27 and 24 is composed of a pair of upper and lower rolls, and is sandwiched between the position of the steel plate 3 sandwiched by the first intermediate pinch roll 27 and the second intermediate pinch roll 24. The position is sandwiched by applying a tension of 0.4 kgf / mm ² (3.92 MPa) or more.

  The first and second intermediate pinch rolls 27 and 24 are arranged at positions where the steel plate 3 is located at the boundary between the strong cooling and the cooling shown in FIG. 7 and at the end of the strong cooling. The steel plate 3 in the region is sandwiched while being appropriately tensioned to keep the plate shape of the steel plate 3 flat and suppress plate vibration during plate passing. Therefore, by arranging the first and second intermediate pinch rolls 27 and 24 in addition to the rolling shape correcting pinch roll 10, cooling can be performed under more uniform conditions in the transition boiling region C. A higher quality steel plate can be obtained without the occurrence.

As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.
For example, the rolling shape correcting pinch roll 10 may be provided at a position where the upper surface temperature of the steel plate is 650 ° C., and the first intermediate pinch roll 27 may also be used. However, at this time, the tension on both sides of the pinch roll must be controlled, and the control becomes complicated. Furthermore, since the 1st and 2nd pinch rolls 27 and 24 perform the role of a draining roll effectively, there exists an effect also in the operation | movement which does not provide tension | tensile_strength.

  Hereinafter, Examples 1 to 7 and Comparative Examples 1 to 7 in the case where the cooling device 5 illustrated in FIG. 1 includes the coolers 6a to 6d and the drainers before and after the cooler 6c will be described. In these Examples 1-7 and Comparative Examples 1-7, the finish rolling mill 2, the cooling device 5, and the coiler 8 are provided in order, and the cooling device 5 cools the steel plate H after finish rolling to a predetermined temperature. Went.

In Examples 1-7 and Comparative Examples 1-7, conditions common to the finish rolling mill 2 and the cooling device 5 are as shown in Tables 1 to 3. Moreover, in Examples 1-7 and Comparative Examples 1-7, as shown in Table 4, it experimented on various conditions. As evaluation of the cooling effect of the steel plate 3, the temperature deviation before cooling of the steel plate 3 in the cooler 6c to be strongly cooled was compared with the temperature deviation after cooling. The evaluation criterion is that the temperature deviation after cooling of the cooler 6d is less than 10 ° C. ◎: very good 10 ° C. or more and less than 15 ° C. ○: good, 15 ° C. or more and less than 30 ° C. Δ: acceptable, 30 ° C. or more is × : Bad.
Since the temperature drop in the cooler 6d is small, the temperature deviation on the outlet side of the cooler 6c is almost equal. In addition, the cooling water density in Table 4 is that of the upper surface, and those that cool the upper and lower surfaces are injected with substantially the same amount of water from the upper and lower sides. Have been supplied.

In Table 4, Examples 1-7 are based on this invention, when the upper surface temperature of a hot-rolled steel sheet is 850 degreeC to 650 degreeC, it uses 0.4 kgf / mm < ² > (3 .92 MPa) or higher tension is applied to the finish rolling mill to sandwich the hot-rolled steel sheet, and the hot-rolled steel sheet is cooled within a range of the upper surface temperature of the hot-rolled steel sheet from 650 ° C. to 350 ° C. In addition, the hot-rolled steel sheet is cooled using cooling water having a water density of more than 3.5 m ³ / m ² / min with respect to the upper surface of the hot-rolled steel sheet. In all of these Examples 1 to 7, the temperature deviation after cooling could be suppressed to less than 15 ° C.

  When Example 1 and 2 are compared, it turns out that the reduction | decrease of the temperature deviation by an intermediate pinch roll is seen. By comparing Examples 1 and 3 or Example 4 and Example 5, it can be seen that the temperature deviation is reduced by increasing the amount of cooling water. By comparing Examples 1 and 4 or 3 and 5, it can be seen that the temperature deviation is reduced by increasing the tension with the pinch roll for correcting the rolling shape. Comparing Example 4 and Example 7, it can be seen that even single-sided cooling of only the upper surface can be suppressed to a temperature deviation close to double-sided cooling.

  In Comparative Examples 1 to 3, the application of tension by the pinch roll for correcting the rolling shape is omitted from Examples 1 to 3. In Comparative Examples 1 to 3, the temperature deviation could be suppressed within 30 ° C, but could not be suppressed below 15 ° C.

  In Comparative Examples 4 to 6, the cooling water density in the cooler 6c is reduced as compared with Examples 1 to 3. In Comparative Examples 4 to 6, the temperature deviation could be suppressed within 30 ° C, but could not be suppressed below 15 ° C.

  The comparative example 7 omits the tension | tensile_strength provision by the pinch roll for rolling shape correction | amendment with respect to Example 1, and drops the cooling water amount density in the cooler 6c. Under such conditions, the temperature deviation could no longer be within 30 ° C., which was much higher than that and the material was not homogeneous.

  In the said Examples 1-7, there exists draining of the cooling water of the cooler 6c.

  The embodiments and forms described above are merely examples of embodiments for carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. It is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  The present invention is useful for a method and a cooling apparatus for cooling a hot-rolled steel sheet after finish rolling in a hot rolling process.

2 Finishing rolling mill 3 Steel plate 4 Run-out table 4a Conveying roll 5 Cooling device 6 Cooling machine 6a Finishing rolling mill exit side cooling machine (upstream side of rolling shape correcting pinch roll)
6b Finishing mill exit side cooler (downstream of pinch roll for rolling shape correction)
6c Cooler with jetting capacity exceeding 3.5m ³ / m ² / min 6d Cooler in front of coiler 7 Pinch roll immediately before coiler 8 Coiler 10 Pinch roll 11 for rolling shape correction Laminar nozzle 21 (upper side) spray nozzle 21a Jet collision surface 22 (lower surface side) spray nozzle 23 drainer 24 drainer roll (second intermediate pinch roll)
25 Spray nozzle 26 Other drainer 27 Drainer roll (first intermediate pinch roll)
28 Spray nozzle 30 Control part A Film boiling area B Nucleate boiling area C Transition boiling area α Cooling water injection angle β Cooling water collision angle E Spray nozzle height

Claims (18)

A cooling method for cooling a hot-rolled steel sheet after finish rolling in a hot rolling process while passing it at a downstream speed of 3 m / sec or more,
When the upper surface temperature of the hot-rolled steel sheet is from 850 ° C. to 650 ° C., a tension of 0.4 kgf / mm ² (3.92 MPa) or more is applied to the finish rolling mill side using a pinch roll for rolling shape correction. Sandwich the hot rolled steel sheet,
When cooling the hot-rolled steel sheet within the range of the upper surface temperature of the hot-rolled steel sheet from 650 ° C. to 350 ° C., the water density is over 3.5 m ³ / m ² / min with respect to the upper surface of the hot-rolled steel sheet. A method for cooling a hot-rolled steel sheet, characterized in that cooling is performed using a cooling water. 2. The heat according to claim 1, wherein a collision speed of the cooling water against the upper surface of the hot-rolled steel sheet is set to 20 m / sec or more, and the cooling water covers an area of 80% or more of the upper surface of the hot-rolled steel sheet. Cooling method for rolled steel sheet. 2. The hot rolling according to claim 1, wherein the cooling pressure of the cooling water against the upper surface of the hot-rolled steel sheet is 2 kPa or more, and the cooling water covers an area of 80% or more of the upper surface of the hot-rolled steel sheet. A method for cooling steel sheets. The water flow of the cooling water is conical, and the collision angle of the cooling water with respect to the upper surface of the hot-rolled steel sheet is 75 degrees or more from the horizontal direction. A method for cooling a hot-rolled steel sheet. A first intermediate pinch roll is disposed at a position where the upper surface temperature of the hot-rolled steel sheet is from 650 ° C. to 550 ° C., and a second intermediate pinch roll is disposed at a position from 450 ° C. to 350 ° C. A tension of 0.4 kgf / mm ² (3.92 MPa) or more is applied to the hot-rolled steel sheet between the first and second intermediate pinch rolls. A method for cooling hot-rolled steel sheets. The draining which suppresses that the cooling water sprayed on the upper surface of the said hot-rolled steel plate flows into the hot-rolled steel plate before the start of the said cooling process and after completion | finish is performed. The method for cooling a hot-rolled steel sheet according to 1. The method for cooling a hot-rolled steel sheet according to any one of claims 1 to 6, wherein only the upper surface of the hot-rolled steel sheet is cooled. Define the cooling capacity d by the following formula (1), characterized by cooling the cooling capacity d _u of the hot-rolled steel sheet upper surface as follows 1.2 times 0.8 times or more than the lower surface of the cooling capacity d _l The method for cooling a hot-rolled steel sheet according to any one of claims 1 to 6.
d = f (q, p, _tw ) (1)
d: cooling capacity, u: an upper surface side, l: lower surface q: cooling water ^{[m 3 / m 2 / min} ], p: the collision pressure [kPa], _{t w:} water temperature A cooling device that cools a hot-rolled steel sheet after finish rolling in a hot rolling process while passing it at a downstream speed of 3 m / sec or more,
Rolling shape correction that sandwiches the hot-rolled steel sheet by applying a tension of 0.4 kgf / mm ² (3.92 MPa) or more to the finish rolling mill at a position where the upper surface temperature of the hot-rolled steel sheet is 650 ° C. or higher and 850 ° C. or lower. For pinch rolls,
Within the range of 650 ° C. to 350 ° C., using the cooling water having a water density of more than 3.5 m ³ / m ² / min with respect to the upper surface of the hot rolled steel plate, A cooling device for a hot-rolled steel sheet, comprising a cooler for cooling. The cooler has a plurality of nozzles, and the cooling water sprayed from the plurality of nozzles has a collision speed with respect to the upper surface of the hot-rolled steel sheet of 20 m / sec or more, and the plurality of nozzles The apparatus for cooling a hot-rolled steel sheet according to claim 9, wherein the cooling water is sprayed so as to cover an area of 80% or more of the upper surface. The cooler has a plurality of nozzles, and the plurality of nozzles are cooled so as to cover an area of 80% or more of the upper surface of the hot-rolled steel sheet with cooling water having a collision pressure against the upper surface of the hot-rolled steel sheet of 2 kPa or more. The apparatus for cooling a hot-rolled steel sheet according to claim 9, wherein the apparatus has a capability of jetting water. The plurality of nozzles of the cooler inject cooling water having a conical water flow, and the collision angle of the cooling water with respect to the upper surface of the hot-rolled steel sheet is 75 degrees or more from the horizontal direction. Or the cooling apparatus of the hot-rolled steel plate of 11. First and second intermediate pinch rolls are disposed at positions where the upper surface temperature of the hot-rolled steel sheet is from 650 ° C. to 550 ° C. and from 450 ° C. to 350 ° C., respectively. The hot-rolled steel sheet according to any one of claims 9 to 12, wherein the hot-rolled steel sheet between the intermediate pinch rolls has a tension imparting function of 0.4 kgf / mm ² (3.92 MPa) or more. Cooling system. The apparatus for cooling a hot-rolled steel sheet according to any one of claims 9 to 13, wherein a drainer is provided on an upstream side and a downstream side of the cooler. The said drainer has a nozzle which injects drain water with respect to the said hot-rolled steel plate, The cooling apparatus of the hot-rolled steel plate of Claim 14 characterized by the above-mentioned. Furthermore, the said drainer has a draining roll provided so that the said hot-rolled steel plate may be contact | connected, The cooling apparatus of the hot-rolled steel plate of Claim 15 characterized by the above-mentioned. The said cooling machine cools only the upper surface of a hot-rolled steel plate, The cooling apparatus of the hot-rolled steel plate in any one of Claims 9-16 characterized by the above-mentioned. The chiller, 1.2 times using a defined cooling capacity d, a cooling capacity d _u of the hot-rolled steel sheet upper surface than the lower surface of the cooling capacity d _l 0.8 times or more by the following formula (1) The apparatus for cooling a hot-rolled steel sheet according to any one of claims 9 to 16, which has the ability to cool as follows.
d = f (q, p, _tw ) (1)
d: cooling capacity, u: an upper surface side, l: lower surface q: cooling water ^{[m 3 / m 2 / min} ], p: the collision pressure [kPa], _{t w:} water temperature

Images