JP3282713B2 - Cooling method for hot steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling method for a hot-rolled high-temperature steel sheet cooling apparatus, which removes accumulated water of cooling water at the outlet of the cooling apparatus and enables uniform cooling of the high-temperature steel sheet. It is.

[0002]

2. Description of the Related Art Generally, hot-rolled hot steel sheets are
Cooling unevenness easily occurs during water cooling immediately after rolling. This cooling unevenness is caused by the deformation and residual stress of the steel sheet,
It is easy to cause operational trouble due to deformation of the steel plate.
Further, the deformed steel plate requires a refining step by a press or a straightening machine, which increases the cost.

[0003] In order to eliminate uneven cooling, various so-called uniform cooling methods have been proposed.

[0004] When cooling a rolled high-temperature steel sheet while passing it on-line, cooling is generally performed by pouring cooling water from above and below in a horizontal state. In particular, in recent years, in controlled rolling in which cooling and rolling are combined or controlled cooling in which steel sheets are cooled online, high-precision temperature control, particularly cooling stop temperature control, is important along with the improvement in product quality.

[0005] For thick steel plates, the product size is large and the width is 5 m.
Due to the large thickness of the plate, a large amount of water is used for cooling.Whether the cooling water is blocked at the outlet side of the cooling device, how much water should be drained, and how quickly the blocked water can be removed It is important that the water is discharged from the end of the plate.

[0006] On the other hand, when the steel sheet is strongly cooled, warpage deformation is likely to occur. The amount of warping and the direction of the warping are determined by the sheet width, the sheet thickness, the temperature difference between the upper and lower surfaces, the temperature gradient in the plate longitudinal direction, the difference in the temperature history between the upper and lower surfaces, and the like. Easily caused by

FIG. 2 schematically shows the form of warpage that occurs during cooling of a steel sheet. It can be roughly divided into (1) and (2), an upwardly convex and downwardly convex C-warp generated in the width direction of the plate, and (3) and (4) an upwardly convex and downwardly generated plate warp generated in the plate longitudinal direction. Has a convex L warp. The direction of these warpages is determined by the temperature difference between the upper and lower surfaces and the initial deflection unavoidably present in the steel sheet, but especially when there is a large temperature gradient in the longitudinal direction of the sheet, C warpage called cooling warpage, L-warping or a combination of both occurs.

As described above, when cooling a steel sheet in an on-line passage type, the steel sheet is passed through a plurality of pairs of rolls serving also as draining rolls for damping the cooling water, and the cooling water is passed between the rolls. Is generally used to cool the steel sheet by injecting water. In the online cooling, when the above-described cooling warpage occurs, a gap is generated between the confined drainer roll and the steel plate, and the cooling water leaks from the gap to supercool the non-cooled portion. In particular, when a downwardly convex C-warp occurs, the cooling water leaks from the gap between the steel plate and the draining roll at the center of the steel sheet, so that the cooling water stays in the center of the sheet width, causing overcooling, and Non-uniform cooling in the direction is inevitable. Furthermore, the accumulated cooling water causes the upper surface of the steel plate in the vicinity of the central portion in the width direction of the steel plate to be supercooled as compared with the lower surface, and thus there is a problem that the C warpage in the width direction of the steel plate is promoted.

On the other hand, various techniques have been studied for a steel plate draining apparatus, and for example, the following techniques have been proposed. (1) Japanese Laid-Open Utility Model Publication No. 53-39508 A method in which an air nozzle is vertically arranged toward the upper surface of a steel sheet to drain water by jetted air. (2) Japanese Patent Laid-Open No. 7-9023 A high-pressure spray water is sprayed in the width direction of the steel sheet from an injection nozzle provided on one side of the steel sheet transferred on the table roller, and the cooling water stays on the steel sheet. A method of removing water from the other end of the steel plate. (3) Japanese Utility Model Application Laid-Open No. 58-125611 and Japanese Utility Model Application Laid-Open No. 59-161062 A method of draining water by pressing a steel plate with rubber lining rolls provided above and below with a steel plate interposed therebetween. (4) JP-A-60-206516;
No. 406 discloses a drainer roll, and sprays water from a spray nozzle provided downstream in the width direction of the steel sheet toward both ends from the center in the width direction of the steel sheet and toward the drainer roll. How to drain.

[0010]

[Problems to be solved by the invention]
A method of arranging an air nozzle vertically on the upper surface of a steel plate to drain water with blast air as in the technique described in Japanese Patent Application Laid-Open No. 3-39508, and a method of draining water using a technique described in Japanese Patent Laid-Open No. 7-9023. In any of the draining methods, in which high-pressure spray water is sprayed from to remove the remaining cooling water from the end of the plate width, a large amount of cooling water flows on a wide plate such as a thick steel plate. Because of the flow, it is difficult to stop and push the cooling water to the end of the plate in a non-contact state.

As described in Japanese Utility Model Laid-Open No. 58-125611 and Japanese Utility Model Laid-Open No. 59-161062, a rubber lining roll is pressed against a steel plate to drain water. , Actual Kaihei 7-33
In a cooling device in which a draining roll is arranged as described in Japanese Patent Publication No. 406, and further from the center of the plate toward the end of the plate, and water is jetted toward the draining roll, cooling water that leaks out is eliminated. Is effective to some extent,
Due to the cooling warpage, a gap is formed between the drain roll and the steel plate, and it is difficult to remove the cooling water flowing out of the gap.

As described above, these conventional draining methods are effective when the draining roll can be pressed against a flat plate or when the amount of cooling water leaking from the draining roll is small. There is a problem that it is not effective when a gap is formed between the drain roll and the steel plate.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is intended to minimize the cooling warpage generated during cooling, suppress the deformation of the plate, and restrain the draining roll and the steel plate. It is an object of the present invention to provide a cooling method for securely draining the water by minimizing a gap generated between the cooling water and the water.

An object of the present invention is to provide a method for cooling a high-temperature steel sheet in which cooling is performed on-line while passing between a plurality of pairs of constraint rolls, wherein the constraint force per constraint roll is not less than a constraint force P represented by the following equation (1). The problem is solved by a method for cooling a high-temperature steel sheet in which cooling is performed by adding a binding force. The task is
A method for cooling a high-temperature steel sheet in which cooling is performed online while passing between a plurality of pairs of constraining rolls, wherein the cooling is performed by adding a constraining force equal to or more than a constraining force P expressed by the following equation (1) per constraining roll. This is solved by a method for cooling a high-temperature steel sheet (claim 1). P = CD _cv t ² L ^0.65 (W / 4000) ² (t) (1) where C: constant = 5 × 10 ⁻⁵ D _cv : temperature gradient (° _C./m ) t: plate thickness ( mm) L: Distance between constraining rolls (m) W: Sheet width (mm).

[0015] By doing so, the gap between the constraining roll and the steel plate can be made 2.0 mm or less, so that even if the cooling water leaks from the gap, it can be made into a range that can be eliminated by a draining nozzle or the like.

In order to investigate the influence of the temperature gradient on the warpage generated during cooling, the inventors obtained the restraining force necessary to suppress the cooling warp generated during cooling by computer simulation of FEM. In this calculation, the plate thickness is 8 to 80 mm, and the temperature gradient in the plate longitudinal direction during cooling is 10 to
300 ° C., the distance between the restraining rolls was calculated in the range of 0.6 to 2.0 m. From the results, the following equation was derived by multiple regression analysis.

As a result, the restraining force P (t) required to suppress cooling warpage per restraining roll is: P = CD _cv t ² L ^0.65 (W / 4000) ² (t) 1) Here, C: constant = 5 × 10 ⁻⁵ _Dcv : temperature gradient (° _C./m ) t: plate thickness (mm) L: distance between constrained rolls (m) W: plate width (mm)

In calculation, the gap between the roll and the steel plate is set to 0.
Although it is possible to determine the restraining force to hold down to mm, it is not realistic because a very large restraining force is required to make the gap 0 mm. It is sufficient that the C warpage is suppressed to a gap allowable value or less, which is a leakage water amount that can be easily removed by providing.
The restraining force P obtained here is a restraining force required to restrain the gap to 2.0 mm, which is an allowable clearance that can be eliminated.

In order to verify the equation (1), the drainage property was experimentally examined by changing the restraining force in an actual machine.
The test result, that is, the variously changed binding force was defined as P ′, and the quality of drainage at that time was good (○: good drainage, that is, leak cooling water can be easily removed by providing a drain nozzle, ×: poor drainage In other words, leakage cooling water cannot be easily removed even if a draining nozzle is provided). As shown in Table 1, when a restraining force was applied to P or more determined by the equation (1), the water drainage property was good.

[0020]

[Table 1]

Further, in some cases, the constraint force required for one constraint roll, which is represented by the above formula (1), exceeds the constraint force that can be added by the equipment. In such a case, the cooling condition is changed so that the restraining force P per restraining roll represented by the formula (1) becomes equal to or less than the restraining force that can be added by the equipment (claim 2). The gap between the constraining roll and the steel plate can be set to 2.0 mm or less, so that even if cooling water leaks from the gap, it can be set to a range that can be eliminated by a drain nozzle or the like. Changes in operating conditions
This refers to a change in the transport speed, a change in the pitch of the constraining rolls, and the like.

Actually, it is not realistic to change the distance L between the constraining rolls because the equipment is remodeled, and the operation is performed by changing the conveying speed of the steel sheet to reduce the temperature gradient _Dcv .
That is, by changing the transport speed of the steel sheet according to the temperature gradient of the steel sheet in the transport direction required during cooling (claim 3), the above expression (1) can be satisfied.

[0023]

【Example】

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an example of an outline of equipment for carrying out the present invention. In FIG. 1, 1 is a thick steel plate, 2
Is an upper constraining roll, 3 is a lower constraining roll, 4 is a slit nozzle, 5 is a circular nozzle, 6 is a hydraulic cylinder, and 7 is a drainer spray nozzle.

The cooling device in this embodiment is a cooling device that cools the steel plate 1 immediately after rolling between the 20 sets of the upper constraining rolls 2 and the lower constraining rolls 3 online while being conveyed. The pitch is 1.0 m. On the upper surface side from the slit nozzle 4 provided immediately above constraining rolls 2 on the upstream side of the plate conveyance direction in the traveling direction of the plate toward the restraining roll on the downstream side between the rolls, plate width 1m per 3m ³ /
Min water is flowing along the board. On the other hand, the lower surface is provided at a pitch of 100 mm, water is jetted from a circular tube nozzle 5 submerged in water, and cooling is performed by a liquid flow generated by the accompanying flow.

In this embodiment, the cooling time is changed by changing the conveying speed of the steel sheet and by setting the number of zones through which the cooling water flows to 1 to 20.
It is possible to change almost continuously by changing up to. In this case, if the cooling water leaks from each zone to the zone downstream of the zone, supercooling occurs at the center of the plate as described above, so the zone where the adjacent cooling water is turned off from the zone where the cooling water is turned on Each of the upper constraining rolls 2 reliably blocks and drains the cooling water so that the cooling water does not flow into the water. On the downstream side of each upper constraining roll 2, a drainer spray nozzle 7 for removing cooling water leaking from a gap between the upper constraining roll 2 and the steel plate 1 from a plate end is provided in each cooling zone. .
Even if the cooling is terminated in an arbitrary zone by this contrivance, even if the cooling water leaks to the downstream side, the device configuration can be eliminated.

Of the 20 sets of constraining rolls, the lower constraining roll 3 also serves as a transport roll and is of a fixed type, but the upper constraining roll 2 can be moved up and down and the gap can be controlled at a pitch of 0.5 mm. is there. When a steel sheet having a thickness equal to or larger than the set gap passes, a restraining force is applied to the steel sheet from the upper restraining roll 2 via the hydraulic cylinder 6 so that cooling warpage generated during cooling is suppressed. Has become. In this embodiment, a binding force of 1 to 5 t can be applied to each roll.

In this embodiment, the board width is 4000 mm, the length is 30 m,
Cooling was performed by passing a high temperature of 25 mm after rolling at a conveying speed of 40 mpm. Using equation (1), the required restraining force was found to be 1.41 t. Therefore, cooling was performed while restraining with a restraining force of 1.50 t. The gap between the rolls is the sheet thickness-1.
It was set to 5 mm, that is, 23.5 mm.

Downstream of each roll in the plate conveying direction, one draining spray nozzle 7 is provided at an angle of 45 degrees with respect to the traveling direction of the steel plate in the sheet conveying direction and from the plate end to the other end. From 100L / min. As a result, the leaked cooling water was quickly removed from the steel plate by the water sprayed from the drainer spray nozzle 7.

At this time, when the temperature distribution of the steel sheet on the entry side was measured by a scanning radiation thermometer, it was 850 ° C. ± 15 ° C.
When the temperature distribution was measured at the same scanning radiation temperature at a position 20 m downstream of the cooling device, the temperature distribution was 530 ° C. ± 10 ° C.
Thus, there was no occurrence of cooling unevenness. At this time, there was no large C-warp deformation in the width direction of the plate, and there was no particularly large deformation even after cooling on the cooling floor, and the product was obtained without refinement. Also,
When the hardness distribution in the sheet width direction was examined after cooling, there was no particularly large difference in hardness distribution. From this, it is determined that there was no large cooling unevenness.

(Embodiment 2) A second embodiment of the present invention uses the same equipment as that of the first embodiment and uses a plate width of 4000 mm and a length of 2 mm.
This is an example in which a rolled high-temperature steel sheet having a thickness of 0 mm and a thickness of 40 mm is cooled.

At a transport speed of 10 mpm, the temperature gradient is
It is 84 ° C./m under the cooling conditions of Example 1, and at this time (1)
The required binding force was determined to be 6.7 t using the equations. This exceeds the capacity of the facility because the range of the binding force is up to 5t in the present facility. Then, when the conveyance speed at which P becomes 5t was obtained, it was 13.4 mpm. Therefore, in this embodiment, the steel sheet is conveyed at 20 mpm, that is, the temperature gradient is set at 4 mpm.
Cooling was performed at 2 ° C / m. The gap between the rolls is
It was set to 1.5 mm, ie 38.5 mm.

In the same manner as in the first embodiment, on the downstream side of each roll in the sheet conveying direction, in the direction opposite to the sheet conveying direction at an angle of 45 degrees with respect to the traveling direction of the steel sheet, and from the plate end to the other end. 100 L / min of draining water is sprayed from one draining spray nozzle 7. As a result, the leaked cooling water was quickly removed from the steel plate by the water sprayed from the drainer spray nozzle 7.

At this time, when the temperature distribution of the steel sheet on the entry side was measured by a scanning radiation thermometer, it was 820 ° C. ± 15 ° C.
When the temperature distribution was measured at the same scanning radiation temperature at a position 20 m downstream of this cooling device, the temperature distribution was 500 ° C. ± 10 ° C.
Thus, there was no occurrence of cooling unevenness. At this time, there was no large C-warp deformation in the width direction of the plate, and there was no particularly large deformation even after cooling on the cooling floor, and the product was obtained without refinement. Also,
When the hardness distribution in the sheet width direction was examined after cooling, there was no particularly large difference in hardness distribution. From this, it is determined that there was no large cooling unevenness.

Example 3 Using the same equipment as used in Example 1, a steel plate having a width of 5000 mm was cooled. Board width
The temperature gradient is 42 ° C./s from 5000 mm, thickness 40 mm, and conveying speed 20 mpm from the calculation of the second embodiment. Exceeds the range 5t of the binding force. So P
Is 5t, and finally the transport speed is 21m
pm or more.

Therefore, in this embodiment, the steel sheet was conveyed at 25 mpm, that is, cooled at a temperature gradient of 34 ° C./m.
The gap between the rolls is -1.5mm, i.e. 38.5mm
Set to.

On the downstream side of the rolls in the plate transport direction, as in the first embodiment, facing the plate transport direction at an angle of 45 degrees with respect to the traveling direction of the steel sheet and from the plate end to the other end. 100 L / min of draining water is sprayed from one draining spray nozzle 7. As a result, the leaked cooling water was quickly removed from the steel plate by the water sprayed from the drainer spray nozzle 7.

At this time, the temperature distribution of the steel sheet on the entry side was measured to be 830 ° C. ± 15 ° C. by a scanning radiation thermometer.
When the temperature distribution was measured at a position 20 m downstream of the cooling device at the same scanning radiation temperature, the temperature distribution was 520 ° C. ± 10 ° C.
Thus, there was no occurrence of cooling unevenness. At this time, there was no large C-warp deformation in the plate width direction, and there was no particularly large deformation even after cooling on the cooling floor, and a product was obtained without any refinement. Also,
When the hardness distribution in the sheet width direction was examined after cooling, there was no particularly large difference in hardness distribution. From this, it is determined that there was no large cooling unevenness.

Comparative Example As a comparative example, cooling was performed in the same cooling device as in Example 1. In this cooling apparatus, cooling was performed by passing a rolled high temperature having a sheet width of 4 m, a length of 30 m and a thickness of 40 mm at a conveying speed of 5 mpm. At this time, the temperature gradient was 84 ° C./m. The gap between the rolls was set to a plate thickness of -1.5 mm, that is, 23.5 mm. Here, 5t, which is the maximum binding force of the equipment, was added as the binding force. At this time,
The required restraining force P obtained from the equation (1) was 6.7 t.

Downstream of each roll in the plate conveying direction, a header is passed in the plate width direction, and 100 L / min of draining water is jetted from one draining spray nozzle 7.

In this cooling device, the cooling water leaks from the gap between the upper constraining roll 2 and the steel plate 1 at the center in the width direction of the plate,
Flows from the final cooling zone to an adjacent zone downstream,
This leaked cooling water could not be completely removed from the end of the plate by the cooling water from the drainer spray nozzle 7 placed on the downstream side of the roll. Since this cooling water was always present, the central portion of the steel sheet was selectively supercooled.

In this situation, the temperature distribution of the steel sheet on the entry side was measured at 850 ° C. ± 15 ° C. by a scanning radiation thermometer. The steel sheet was cooled by this cooling device, and the temperature distribution after cooling was measured at the same scanning radiation temperature at a position 20 m downstream, and found to be 400 ° C. to 510 ° C., and large cooling unevenness occurred. At this time, C warpage deformation was observed in the plate width direction. The plate was conveyed to a cooling floor and cooled to room temperature by air. Therefore, a refining process for removing this deformation with a leveler and a press straightening machine was required. When the hardness distribution in the width direction of the sheet was examined after cooling, high hardness, that is, so-called uneven burning was observed at the center of the sheet.

[0043]

As described above, in the present invention, since the steel sheet is cooled while being restrained by a restraining force equal to or greater than the restraining force given by a predetermined equation, cooling water is supplied from between the steel sheet and the restraining roll. No leakage, no uneven cooling and no C warpage. Therefore, it is possible to stably produce a uniform steel plate with little variation in the material inside the plate. Further, there is no large deformation of the plate during and after cooling, and there is no trouble in passing the plate and continuous operation is not hindered. Furthermore, since there is no large thermal distortion even after cooling, a refining step by a leveler or a press is not required, and a low-cost thick steel plate can be manufactured.

According to the present invention, the cooling conditions are changed so that the required binding force does not exceed the equipment specifications.
The constraint roll load and pitch can be designed economically, and equipment costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of equipment used for implementing the present invention.

FIG. 2 shows C warp and L generated in the width direction of the steel sheet during cooling of the steel sheet.
It is a figure which shows a warpage typically.

[Explanation of symbols]

 Reference Signs List 1 thick steel plate 2 upper constraining roll 3 lower constraining roll 4 slit nozzle 5 circular pipe nozzle 6 hydraulic cylinder 7 drainer spray nozzle

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Makoto Medieval Kobe 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) References JP-A-63-10019 (JP, A) JP-A-6 JP-A-128122 (JP, A) JP-A-62-199723 (JP, A) JP-A-1-205581 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 45/02 320

Claims (3)

(57) [Claims] 1. A method for cooling a high-temperature steel sheet in which cooling is performed online while passing between a plurality of pairs of restraining rolls, wherein a restraining force per restraining roll is not less than a restraining force P represented by the following equation (1). A method for cooling a high-temperature steel sheet in which cooling is performed by adding heat. P = CD _cv t ² L ^0.65 (W / 4000) ² (t) (1) where C: constant = 5 × 10 ⁻⁵ D _cv : temperature gradient (° _C./m ) t: plate thickness ( mm) L: Distance between constraining rolls (m) W: Sheet width (mm) 2. A method for cooling a high-temperature steel sheet in which cooling is performed online while passing between a plurality of pairs of restraining rolls, wherein a restraining force P expressed by the following equation (1) is applied to each restraining roll by equipment. A method for cooling a high-temperature steel sheet, wherein the cooling condition is changed so as to be less than a possible binding force. P = CD _cv t ² L ^0.65 (W / 4000) ² (t) (1) where C: constant = 5 × 10 ⁻⁵ D _cv : temperature gradient (° _C./m ) t: plate thickness ( mm) L: Distance between constraining rolls (m) W: Sheet width (mm) 3. The method for cooling a high-temperature steel sheet according to claim 2.
A method for cooling a high-temperature steel sheet, comprising changing a conveying speed of the steel sheet according to a temperature gradient of the steel sheet in a conveying direction required during cooling.