JP2003334605A - Cooling method for hot steel plate, cooling apparatus for hot steel plate, and production method for steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling method for a thick steel plate which prevents the buckling of the steel plate and destruction of equipment and produces a flat steel plate continuously and stably without C or L shaped curling. <P>SOLUTION: A gap between an upper restraining roll 2 and a lower restraining roll 3 is set below the thickness of the steel plate 1. When the steel plate 1 is passed, the upper restraining roll 2 is raised against pressing force of a hydraulic cylinder 6 and reaction force thereof is applied to the steel plate 1, thus the steel plate 1 is restrained. This restraining force is measured with a sensor, and when the value of the restraining force exceeds a predetermined value, the pressure of the hydraulic cylinder 6 of the upper restraining roll 2 can be adjusted. When the pressure of the hydraulic cylinder 6 is adjusted, restraining-force corresponding to the pressure is applied to the steel plate 1, the upper restraining roll 2 can vertically be moved in accordance with the steel plate 1 corresponding to the reaction force of the steel plate 1. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a cooling device for continuously rolling and cooling a hot-rolled high temperature steel sheet, which prevents C warpage of the steel sheet during cooling and uniformly cools the high temperature steel sheet. And a method for manufacturing a thick steel plate using this cooling method.

[0002]

2. Description of the Related Art Generally, hot-rolled hot steel sheets are
Uneven cooling tends to occur during water cooling immediately after rolling. This cooling unevenness causes deformation and residual stress of the steel sheet and variations in the material after cooling, and also deforms the steel sheet, which easily causes operational troubles. Further, the deformed steel plate requires a refinement process for removing the deformation by a press or a straightening machine later, resulting in high cost. Therefore, various uniform cooling methods have been conventionally proposed in order to eliminate uneven cooling.

[0003] When the hot rolled steel sheet after rolling is cooled online, it is generally performed by pouring cooling water from above and below in a horizontal state. Particularly in recent years, controlled rolling and controlled cooling (TMC) that combines rolling and cooling
P) requires high-precision temperature control, and
At the same time, there is an increasing need to continuously manufacture flat plates with little distortion.

In particular, when manufacturing a thick steel plate having a large plate thickness, the plate width may reach 5 m, and since the plate thickness is thick, a large amount of cooling water is required for cooling, and the cooling device is discharged. At the moment, how to stop the cooling water and stop the outflow of the cooling water to the non-cooling area was an issue. Further, in order to obtain a flat plate after cooling, how to reduce the strain generated in the series of processes of rolling, cooling and straightening is important together with uniform cooling.

In order to solve these problems, conventionally,
Many techniques have been proposed for draining water when cooling a steel sheet.

In Japanese Utility Model Application Laid-Open No. 53-39508, there is disclosed a technology in which an air nozzle is arranged so as to be vertically movable toward the upper surface of a steel plate, and water is drained by jetting air.
No. 125611 discloses a method in which a steel plate is sandwiched between rubber rolls and pressed to drain water. In Japanese Laid-Open Patent Publication No. 60-206516, a drainer roll is arranged, and an injection nozzle is provided in the plate width direction on the downstream side thereof. A technique is disclosed in which water is sprayed from the central portion of the steel sheet in the plate width direction toward both ends and toward the draining roll to drain water.

However, in any of these methods, any of the water draining methods was incomplete in cooling the high-temperature thick steel plate. That is, when a steel sheet is rapidly cooled like a thick steel sheet, the upper surface and the lower surface of the steel sheet do not necessarily have the same cooling, so that deformations called C warp in the plate width direction and L warp in the plate longitudinal direction occur. It is easy to occur.

The amount of warp and the direction of warp of the C warp are determined by the width of the plate, the thickness of the plate, the temperature difference between the upper and lower surfaces, and the difference in the temperature history between the upper and lower surfaces. When this C-warp occurs, a gap is created between the steel plate and the draining roll, and a large amount of cooling water flows out, which makes draining difficult. Such outflow of cooling water causes uneven temperature in the plate.

The L warp determines the amount of warp and the direction of the warp in addition to the plate width, the plate thickness, the temperature difference between the upper and lower surfaces, the difference in the temperature history between the upper and lower surfaces, and the passing speed of the steel plate. When this L-warp occurs, stable passing of the steel plate is hindered, and the steel plate may be stuck in the cooling device. Further, the steel plate may be largely L-warped after passing through the cooling device. If the L-warp is large, the steel plate may not be flattened in the subsequent straightening and may not be a product.

[0010]

On the other hand, there is disclosed a technique for cooling while restraining a steel sheet being cooled so that the C warp does not occur (Japanese Patent Laid-Open No. 10-263670). According to this method, the high-temperature steel plate is passed through the steel plate while the high-strength steel plate is restrained with a restraining force equal to or more than a certain force, and the steel plate is cooled.
However, if the steel plate is restrained with a certain constraint force or more, the steel plate itself will buckle when stress is applied to the steel plate during operation, and the plate will be greatly deformed in the cooling device or after passing through the cooling device, resulting in continuous production. There may be problems that prevent

The present invention has been made to solve the above problems, and in a cooling device for a high temperature steel plate, prevents the steel plate from buckling and damages the equipment, and continuously and stably forms a flat steel plate. It is an object of the present invention to provide a method for cooling a thick steel sheet and a cooling equipment capable of manufacturing the steel sheet without causing C warping or L warping, and a method for manufacturing a thick steel sheet using this cooling method.

[0012]

[Means for Solving the Problems] A first means for solving the above problems is to convey a high temperature steel plate while constraining it by a plurality of sets of upper and lower restraining rolls, and injecting cooling water from above and below the steel plate during the conveyance. Then, when cooling the high temperature steel plate, when the distance between the pair of upper and lower restraint rolls adjacent to each other is L (mm) and the thickness of the steel plate is s (mm), one pair of upper and lower restraint rolls has the following formula (1). Roll constraint force P1 (t) or more P2 (t)
A high-temperature steel sheet cooling method (claim 1) is characterized in that cooling is performed while restraining the steel sheet with a restraining force of less than 1. P1 = 6.85 × 10 ⁻⁷ s ³ L ^0.65 … (1) P2 ＝ 1.2 × 10 ⁻⁶ s ³ L ^0.65 … (2)

Usually, even with a steel plate straightened by a straightening machine before cooling, the cooling start temperature is unbalanced at the upper and lower sides in the cooling stage, or there is a local temperature difference between the upper and lower sides of the steel sheet during cooling for a short time. In such a case, the steel plate warps and a reaction force is generated on the constraining roll.

With a constraining force of P1 or less, the constraining roll floats due to C warpage, leakage of cooling water causes uneven cooling, and thermal strain occurs after cooling. On the other hand, if the steel plate is constrained with a constraining force of P2 or more, the force causes the plate to buckle, and at that stage the plate is kept flat, but when the water cooling is stopped after that, the flat steel plate warps and the inside of the cooling device Therefore, it becomes impossible to carry the sheet, or the apparatus is damaged, or after the apparatus has passed through the cooling apparatus, a great distortion occurs in a step after cooling, for example, when cooling in a cooling bed. If restrained at P1 or more and less than P2, the temperature will diffuse and the temperature deviation will disappear after cooling, and will return to a substantially flat state without restraint.

According to this solving means, C warpage does not occur,
Even if it occurs, it is extremely small, so it is possible to surely drain water, and uneven temperature is unlikely to occur.

A second means for solving the above-mentioned problems is as follows.
When a high temperature steel plate is conveyed while being constrained by a plurality of pairs of upper and lower restraint rolls, and cooling water is poured from above and below the steel plate during the conveyance to cool the high temperature steel plate, the distance between a pair of adjacent upper and lower restraint rolls is L. (Mm) and the thickness of the steel plate is s (mm), the steel plate is constrained with a constraining force of not less than P1 (t) and less than P2 (t) per roll restraining force obtained from the following equation (1) per pair of upper and lower restraining rolls. While cooling, the high-temperature steel plate is characterized in that when the restraint force exceeds P2 (t), the restraint roll is pressed with a force less than P2 and moved up and down following the warp of the plate. It is a method (claim 2). P1 = 6.85 × 10 ⁻⁷ s ³ L ^0.65 … (1) P2 ＝ 1.2 × 10 ⁻⁶ s ³ L ^0.65 … (2)

As described above, when a steel plate is constrained with a constraining force of P2 or more, the force causes the plate to buckle, and the plate is kept flat at that stage. On the other hand, it becomes impossible to convey in the cooling device, the device is damaged, or a great distortion occurs after cooling through the cooling device, for example, during cooling in a cooling bed.

In this means, when a force of P2 or more is generated from the steel sheet, the force applied to the restraining roll is adjusted so that the restraining force is less than P2. As a result, the constraining roll moves up and down while following the steel plate in accordance with the warp of the steel plate to pass the steel plate. Therefore, it becomes possible to prevent the device from being conveyed inside the cooling device and damage the device. Furthermore, after passing through the cooling device, a large strain is prevented during a step after cooling, for example, during cooling in a cooling bed.

Further, since the constraining roll moves up and down following the L warp, the steel sheet passes stably. For example, if cooling is unbalanced and the plate is about to warp, if the plate is pressed with a large restraining force, reverse warpage will occur in the cooling device, or deformation more than expected at the stage of exiting the cooling device To do. In such a case, troubles such as equipment damage and clogging can be prevented, which can be prevented.

A third means for solving the above problems is
When a high temperature steel plate is conveyed while being constrained by a plurality of pairs of upper and lower restraint rolls, and cooling water is poured from above and below the steel plate during the conveyance to cool the high temperature steel plate, the distance between a pair of adjacent upper and lower restraint rolls is L. (Mm) and the thickness of the steel plate is s (mm), the steel plate is constrained with a constraining force of P1 (t) or more and less than P2 (t) that is obtained from the following formula (1) per pair of upper and lower restraining rolls. Cooling is performed while the restraining force becomes P2 (t) or more, the restraining roll is pressed with a force less than P2 and moved up and down following the warp of the plate, and the movement amount is a predetermined limit value. When the temperature exceeds the limit, the restraint roll is retracted to release the restraint force (claim 3). P1 = 6.85 × 10 ⁻⁷ s ³ L ^0.65 … (1) P2 ＝ 1.2 × 10 ⁻⁶ s ³ L ^0.65 … (2)

In the present means, like the second means, the restraining roll is made to follow so that the restraining force does not exceed P2. As a result, when the restraining roll position exceeds the limit value of the predetermined position, the restraining roll is moved. Therefore, even if a steel plate with a very large distortion is put in, it becomes impossible to convey the steel plate inside the cooling device or damage the device.

A fourth means for solving the above problems is
A high-temperature steel plate cooling device that cools a high-temperature steel plate by transporting it while restraining the high-temperature steel plate with a plurality of sets of upper and lower restraining rolls and cooling water from above and below the steel plate during transportation. A high-temperature steel plate cooling device (claim 4) having a function of moving the position of the constraining roll so that the constraining force becomes less than the predetermined value when the value becomes equal to or more than the value.

According to this means, the second means can be easily implemented. At this time, it is preferable to select the “predetermined value” of the binding force as the P2.

A fifth means for solving the above-mentioned problems is the third means, which has a function of expanding the opening degree of the restraint roll and releasing the restraint when the movement amount of the restraint roll exceeds a predetermined value. It is characterized by having (Claim 5).

According to this means, the third means can be easily implemented.

A sixth means for solving the above-mentioned problems is as follows.
A method for manufacturing a thick steel plate, comprising the steps of rolling a slab with a rolling mill, straightening it with a first straightening machine, cooling it with a cooling device, and further straightening it with a second straightening device, wherein cooling by a cooling device is performed. A method for manufacturing a thick steel plate (claim 6), which is the method for cooling a high-temperature steel plate according to any one of claims 1 to 3.

In this means, since any one of the first means to the third means is used in the process of cooling the thick steel plate, C warpage does not occur in the process of cooling and is generated. Since it is also very small, it is possible to surely drain water,
Temperature unevenness is unlikely to occur. Also, after water cooling, the flat steel plate warps, making it impossible to convey in the cooling device,
After damaging the device or exiting the cooling system,
Steps after cooling It is possible to prevent a large strain during cooling in a cooling bed, for example.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an example of a cooling device for a high-temperature steel plate according to an embodiment of the present invention. In FIG. 1, 1 is a steel plate, 2 is an upper restraining roll (draining roll), 3
Is a lower restraining roll (water draining roll), 4 is a slit nozzle, 5 is a circular pipe nozzle, 6 is a hydraulic cylinder, and 7 is a draining spray nozzle. In this cooling device, the steel plate 1 immediately after rolling is conveyed between the 20 sets of the upper constraining rolls 2 and the lower constraining rolls 3, while the upper side is cooled by the cooling water from the slit nozzle 4 and the lower side is swept by the circular pipe nozzle 5. Each is cooled online by the cooling water. In FIG. 1, three upper restraint rolls and two cooling zones are shown. The pitch of each restraint roll is 1 m.

On the upper side surface between the constraining rolls 2 and 3, from the upper constraining roll 2 on the upstream side in the steel sheet conveying direction to the upper constraining roll 2 on the downstream side, in the traveling direction of the steel sheet 1 from the slit nozzle to the strip width. 2 m ³ / min of cooling water per 1 m is flowed along the steel plate 1. On the other hand, the lower surface is sprayed with water from the circular tube nozzle 5 and cooled by the water flow.

In these 20 sets of restraint rolls 2 and 3,
The lower restraint roll 3 also serves as a transport roll and is a fixed type. The upper restraint roll 2 has a diameter of 250 mm, can be moved up and down, and can be controlled at a pitch of 0.5 mm.

Further, the gap between the upper restraint roll 2 and the lower restraint roll 3 is set to be equal to or less than the thickness of the steel plate 1, and when the steel plate 1 passes, the upper restraint roll 2 resists the pressing force of the hydraulic cylinder 6. Then, the steel plate 1 is constrained by the reaction force of the steel plate 1.

Further, this restraining force is measured by a pressure sensor, and when this value exceeds a value described later, it is possible to adjust the pressure of the hydraulic cylinder 6 of the upper restraining roll. When the pressure of the hydraulic cylinder 6 is adjusted, a restraining force corresponding to the pressure acts on the steel plate 1, and according to the reaction force from the plate,
The upper restraint roll 2 can move up and down following the steel plate 1. Further, a mechanism for quickly retracting the upper restraint roll 2 upward when the position of the upper restraint roll 2 exceeds a certain value is attached. A draining spray nozzle 7 is provided for removing the cooling water leaking from the gap between each upper restraint roll 2 and the steel plate 1 from the plate end portion.

In the present embodiment, when the distance L (mm) between adjacent restraining rolls and the thickness of the steel plate are s (mm), P1 = 6.85 × 10 ⁻⁷ s ³ per upper restraining roll. L ^0.65 … (1) P2 ＝ 1.2 × 10 ⁻⁶ s ³ L ^0.65 … (2) Roll restraining force P1 (t) or more and less than P2 (t) Is done.

The binding force per roll is P2 (t)
When it becomes equal to or more than the roll restraining force obtained from the formula, the pressure sensor detects the reaction force, and first, the pressure applied to the hydraulic cylinder 6 is reduced until the restraining force becomes less than P2. As a result, the upper restraint roll is lifted. Here, if there is no hindrance to the plate and conveyance, the passage of the steel plate is awaited in this state.
However, the cylinder pressure is reduced, the upper restraint roll is released, and the upper restraint roll rises to a certain height (the height is set to 300 mm in the embodiment described later), but the reaction force from the plate (restraint) is still present. Force) is P2 or higher,
The upper restraint roll is quickly opened, and the upper restraint roll is retracted upward.

The above description specifies the restraint force for one upper restraint roll, but if the restraint force for other upper restraint rolls rises to P2 or more, the other restraint rolls will be sequentially examined. Also, the binding force may be adjusted.

With the restraining force exceeding P2, when the upper restraining roll 2 is lifted and the position exceeds a certain height, the upper restraining roll 2 is quickly retracted.
This is because the following threading troubles can be avoided. For example, when the cooling water on the lower surface or the upper surface is not sprayed for some reason or is not sprayed at a predetermined flow rate, and the cooling of the steel sheet becomes vertically asymmetrical, and a large temperature difference occurs between the steel sheet upper surface and the lower surface. Since a large warp of the plate is about to occur due to this temperature difference, the reaction force from the plate for lifting the upper roll greatly exceeds P2 and pushes the upper restraining roll 2 upward.

In this state, it is necessary to immediately stop cooling and take out the steel sheet being conveyed from the cooling device. Therefore,
By adding the function as described above to promptly retract the upper restraint roll, that is, raise it, equipment trouble and equipment damage can be prevented. In this way
The restraining force is reduced, and the roll gap of the cooling device is made to have a gap correspondingly, so that the steel plate in the cooling device is quickly carried out.

[0038]

EXAMPLE Using a cooling system as shown in FIG. 1, the plate thickness s (mm) of the steel sheet, the interval L (mm) between the constraining rolls, and the constraining force P
The strip cooling test was conducted by changing (t). Table 1 shows a comparison of each condition. In the same table, formula (1) and formula (2)
P1 and P2 obtained from the formula are also shown together, but in the embodiment shown here, the relationship of P1 <P <P2 is established. All of these were steel plates having a good plate shape when they passed through the accelerated cooling device without any problem, and were left to cool in the cooling bed and then cooled to almost room temperature.

In the example, in Examples 4 and 6, the actual restraining force exceeded P2 during passing, but at this time, the roll lifted up and the restraining force of P2 or more was not applied. In this case, the cooling device can pass through while the roll is lifted up, and this steel plate initially had a warp in the cooling floor, but after the temperature was lowered by allowing it to cool, the warp disappeared and became flat. It became a plate.

On the other hand, Comparative Examples 1, 3, 5, 7, 9, 11 were cooled while restraining with a restraining force of P1 or less, and Comparative Examples 2, 4, 6, 8, 10, 12 were It is cooled while restrained with a restraining force of P2 or more.

In the case of cooling while restrained at less than P1, the steel plate is lifted due to the C warp generated in the cooling device, and a gap is generated between the steel plate and the restraining roll, and the cooling water leaks from there to locally Temperature unevenness occurred, and after cooling was completed, a large warp occurred in the cooling bed.

Further, in the case of restraining with P2 or more, although no strain was generated in the cooling device, a large L warp was generated at the stage of cooling in the cooling floor. This is because when the stress of the steel sheet generated in the cooling device is cooled to P2 or more, the plate yields in the cooling device, and after that, at the stage of exiting the cooling device, even if it is flat, it is allowed to cool to room temperature. It is considered that the strain was generated at the stage where the temperature became uniform by the amount of yield in the cooling device as the temperature approached. (Table 1)

[0043]

[Table 1]

[0044]

As described above, according to the present invention,
In a cooling device for a high-temperature steel plate, a method for cooling a thick steel plate, which prevents buckling of the steel plate and equipment breakage and can continuously and stably manufacture a steel plate having a flat shape without occurrence of C-warp or L-warp, and It is possible to provide a cooling facility and a method for manufacturing a thick steel plate using this cooling method.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a cooling device for a high-temperature steel plate according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Steel plate 2 ... Top restraint roll (draining roll) 3 ... Lower restraint roll (draining roll) 4 ... Slit nozzle 5 ... Cylindrical nozzle 6 ... Hydraulic cylinder 7. Draining spray nozzle

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Satoshi Ueoka             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F term (reference) 4K034 AA02 AA19 BA05 CA01 DB03                       DB04 EA12 FA05 FB03

Claims (6)

[Claims] 1. A pair of upper and lower restraining rolls, when a high temperature steel plate is conveyed while being constrained by a plurality of sets of upper and lower restraining rolls, and cooling water is poured from above and below the steel plate during cooling to cool the high temperature steel plate. When the distance between rolls is L (mm) and the thickness of the steel plate is s (mm), a pair of upper and lower restraint rolls restrains the roll restraint force P1 (t) or more and less than P2 (t) obtained from the following equation (1). A method for cooling a high-temperature steel sheet, which comprises cooling the steel sheet while restraining the steel sheet with force. P1 = 6.85 × 10 ⁻⁷ s ³ L ^0.65 … (1) P2 ＝ 1.2 × 10 ⁻⁶ s ³ L ^0.65 … (2) 2. A pair of upper and lower restraints which are adjacent to each other when the high temperature steel plate is conveyed while being constrained by a plurality of sets of upper and lower restraint rolls and cooling water is poured from above and below the steel plate during cooling to cool the high temperature steel plate. When the distance between rolls is L (mm) and the thickness of the steel plate is s (mm), a pair of upper and lower restraint rolls restrains the roll restraint force P1 (t) or more and less than P2 (t) obtained from the following equation (1). The steel plate is cooled while restraining the steel plate with a force, and when the restraining force becomes P2 (t) or more, the restraining roll is pressed with a force less than P2 and moved up and down following the warp of the plate. Cooling method for high temperature steel sheet. P1 = 6.85 × 10 ⁻⁷ s ³ L ^0.65 … (1) P2 ＝ 1.2 × 10 ⁻⁶ s ³ L ^0.65 … (2) 3. A pair of upper and lower restraints which are adjacent to each other when the high temperature steel sheet is conveyed while being restrained by a plurality of sets of upper and lower restraint rolls and cooling water is poured from above and below the steel sheet during cooling to cool the high temperature steel sheet. When the distance between rolls is L (mm) and the thickness of the steel plate is s (mm), a pair of upper and lower restraint rolls restrains the roll restraint force P1 (t) or more and less than P2 (t) obtained from the following equation (1). Cooling is performed while restraining the steel plate with force, and when the restraining force becomes P2 (t) or more, the restraining roll is pressed with a force less than P2 and moved vertically following the warp of the plate, and the amount of movement Exceeds the specified limit,
A method for cooling a high-temperature steel sheet, characterized in that the restraining roll is retracted to release the restraining force. P1 = 6.85 × 10 ⁻⁷ s ³ L ^0.65 … (1) P2 ＝ 1.2 × 10 ⁻⁶ s ³ L ^0.65 … (2) 4. A high-temperature steel plate cooling device for cooling a high-temperature steel plate by transporting the high-temperature steel plate while restraining the high-temperature steel plate by a plurality of sets of upper and lower restraining rolls, and injecting cooling water from above and below the steel plate during the transportation. A cooling device for a high-temperature steel plate, which has a function of moving the position of the constraining roll so that the constraining force becomes less than the predetermined value when the constraining force becomes equal to or more than a predetermined value. 5. The cooling device for a high-temperature steel plate according to claim 4, wherein when the movement amount of the constraining roll exceeds a predetermined value, it has a function of expanding the opening degree of the constraining roll to release the restraint. A cooling device for high-temperature steel plates. 6. A method of manufacturing a thick steel sheet, comprising the steps of rolling a slab with a rolling mill, straightening it with a first straightening machine, cooling it with a cooling device, and further straightening it with a second straightening machine. A method for manufacturing a thick steel plate, wherein the cooling by the cooling device is the method for cooling a high-temperature steel plate according to any one of claims 1 to 3.