WO2003097263A1

WO2003097263A1 - Method and device for cooling steel sheet and method of manufacturing steel sheet

Info

Publication number: WO2003097263A1
Application number: PCT/JP2003/005933
Authority: WO
Inventors: Akio Fujibayashi; Akira Tagane; Satoshi Ueoka
Original assignee: Jfe Steel Corporation
Priority date: 2002-05-17
Filing date: 2003-05-13
Publication date: 2003-11-27
Also published as: EP1508388B1; TWI222903B; JP2003334605A; EP1508388A4; KR100598006B1; DE60324272D1; KR20040062691A; JP3925789B2; EP1508388A1; TW200307580A; CN1610584A; CN1290634C

Abstract

A method for cooling a steel sheet, comprising the steps of horizontally conveying the steel sheet while the surface thereof is being arrested by multiple sets of upper and lower rolls and water-cooling the steel sheet during conveyance from the upper and lower directions of the surface of the steel sheet, wherein a steel sheet arresting force (t) by the upper and lower rolls for each set is P1 (= 6.85 x 10-7S3L0.65) to less than P2 (= 1.2 x 10-6S3L0.65) where L (mm) is a distance between the sets of the upper and lower rolls adjacent to each other and S (mm) is the thickness of the steel sheet, whereby the hot-rolled steel sheet can be uniformly cooled without producing warpage due to nonuniform cooling and buckling by the arresting force.

Description

TECHNICAL FIELD The present invention relates to a method for cooling a hot-rolled steel sheet, and more particularly to a method for uniformly cooling a steel sheet without warping or buckling of the steel sheet during cooling. The present invention relates to a cooling method, an apparatus thereof, and a method for manufacturing a steel sheet using the method.

Generally, the steel sheet after hot rolling is conveyed so that the steel sheet surface is horizontal, and is cooled by cooling water injected from above and below the steel sheet surface. At this time, uneven cooling of the steel sheet is likely to occur, causing not only residual stress of the steel sheet and dispersion of the material, but also warping of the steel sheet to cause trouble in operation. In addition, warped steel sheets require a refining process to correct the warpage with a press machine or the like, which leads to an increase in cost. In recent years, in the production of steel sheets by controlled rolling and controlled cooling (TMCP), a combination of rolling and cooling, there is a need to eliminate such cooling unevenness, perform high-precision temperature control, and continuously produce flat steel sheets with low distortion. Is growing. In particular, in the production of thick steel sheets, the width of the steel sheet is as large as 5 m, and the cooling water from the cooling device is prevented from flowing out to the parts of the steel sheet that do not need to be cooled. The issue is how to achieve uniform cooling by so-called "water drainage".

Regarding drainage during cooling of a steel sheet, for example, Japanese Utility Model Application Laid-Open No. 53-39508 discloses a technique in which an air nozzle is disposed on the upper surface of a steel plate so as to be movable up and down, and the drainage is performed by air emitted from the air. ing. Further, Japanese Utility Model Application Laid-Open No. 58-125611 discloses a method of draining water by pressing a steel sheet with a rubber roll. Further, Japanese Patent Application Laid-Open No. 60-206516 discloses that a 7_K cutting roll and a downstream side thereof are provided along the width direction of the steel sheet. There is disclosed a technology in which a water injection nozzle is provided and water is injected from a central portion in the width direction of the steel sheet toward both ends and a drain roll to drain the steel sheet.

However, none of the above methods can completely drain water, and if the steel sheet is to be cooled rapidly, the cooling of the upper and lower surfaces of the steel sheet will not always be the same, and the steel sheet will warp in the width and longitudinal directions. Occurs.

The amount of warpage and the direction of warpage are determined by differences in sheet width, sheet thickness, upper and lower surface temperatures, and temperature histories.However, when this warpage occurs, a gap is created between the steel sheet and the draining roll. A large amount of cooling water flows out, and it becomes difficult to reduce the amount of cooling water to 7 k. The amount of warpage in the longitudinal direction is determined not only by the sheet width, the sheet thickness, the temperature of the upper and lower surfaces, the temperature history, but also by the transfer speed of the steel sheet. As a result, the steel sheet cannot be transported, causing operational problems. In addition, there is a large warp after the steel sheet passes through the cooling device.

Japanese Patent Application Laid-Open No. Hei 10-263670 discloses a technique for cooling while restraining the steel sheet surface during cooling so that warpage in the width direction does not occur. In this method, the steel sheet is cooled while being restrained with a certain force or more, so it is possible to cool the steel sheet while keeping it flat.

However, in the method disclosed in Japanese Patent Application Laid-Open No. 10-263670, if the steel sheet is restrained with a certain force or more, the steel sheet itself buckles, causing a large warp in the cooling device or after passing through the cooling device, so that the steel sheet cannot be transported. Cause ^^. DISCLOSURE OF THE INVENTION An object of the present invention is to provide a method for uniformly cooling a hot-rolled steel sheet without warping due to cooling unevenness and buckling due to a restraining force, an apparatus thereof, and a method for manufacturing a steel sheet using the method. ¾ ^ to do. The purpose is to convey the steel sheet horizontally while constraining the steel sheet surface with a plurality of sets of upper and lower rolls, and to water-cool the conveyed steel sheet from above and below the steel sheet surface. This is achieved by a method of cooling a steel sheet, wherein the binding force of the steel sheet by the upper and lower rolls is not less than PI (t) and less than P2 (t) shown by the following equations (1) and (2).

^{^{P1 = 6.85X10 "7 S 3 L}} 0 - 65 ··· (1)

^{^{P2 = 1.2X10 "6 S 3 L}} 0 - 65 -" (2)

Here, L (mm) represents the distance between a pair of adjacent upper and lower openings, and S (mm) represents the thickness of the steel plate. This method of cooling the steel sheet includes multiple vertical rolls for restraining the steel sheet being transported, means for water cooling the steel sheet being transported from above and below the steel sheet surface, and adjusting the restraining force for restraining the steel sheet. And a means for vertically moving a plurality of sets of upper and lower rolls. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of a steel plate cooling device of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows an example of a steel sheet cooling device of the present invention.

In this cooling device, the steel sheet 1 immediately after rolling is conveyed while being constrained between 20 sets of upper and lower jaws comprising an upper roll 2 and a lower roll 3 arranged at an interval of lm. At this time, the upper surface of the steel plate is cooled by the cooling water from the slit nozzle 4, and the lower surface of the steel plate is cooled by the cooling water from the circular tube nozzle 5, respectively. In FIG. 1, three upper rolls 2 and two cooling zones are shown. The pitch between the upper and lower rolls is lm.

On the upper surface of the steel plate 1 between the upper and lower rolls, from the slit nozzle 4 to the upper roll 2 on the upstream side, and from the upper roll 2 on the downstream side, each upper and lower unit per steel plate unit area along the traveling direction of the steel plate 1. 2m ³ / min of cooling water is injected. On the other hand, cooling water is injected from the circular tube nozzle 5 to the lower surface of the steel plate 1. Of the 20 upper and lower rolls, the lower roll 3 also serves as a transport roll and is fixed. The upper roll 2 has a diameter of 250 and can move up and down at a pitch of 0.5 mm up and down. The gap between the upper roll 2 and the lower roll 3 is set to be equal to or less than the thickness of the steel sheet 1.When the steel sheet 1 passes, a force is applied to the steel sheet 1 by a reaction force against the pressing force of the hydraulic cylinder 6 when the upper roll 2 passes. Steel plate 1 is bound. Further, this restraining force is measured by a pressure sensor, and when the value exceeds a value described later, the pressure of the hydraulic cylinder 6 is adjusted. When the pressure of the hydraulic cylinder 6 is adjusted, the restraining force corresponding to the pressure acts on the steel plate 1, and the upper roll 2 moves up and down along with the steel plate 1 according to the reaction force from the steel plate 1. Can be. Also, a mechanism is provided to quickly move the upper roll 2 upward when the position of the upper roll 2 exceeds a certain value. Further, a drainer spray nozzle 7 is provided for removing cooling water leaking from a gap between the upper roll 2 and the steel plate 1 from the end of the steel plate.

The upper and lower surfaces of the steel sheet are cooled at a water volume of 2 m ³ / min or more per unit area while restraining the steel sheet by setting the binding force of the steel sheet by the upper and lower rolls per set to PI (t) or more and less than P2 (t). If the temperature is diffused, the temperature deviation is eliminated, no warpage occurs, and the drainage can be performed without fail, resulting in no uneven cooling. Therefore, even if the steel sheet is not restrained after cooling, a flat state can be obtained.

With a restraining force less than Pl (t), the upper and lower rolls are lifted by warpage in the width direction, and the cooling water power S leaks out, causing uneven cooling.

Also, with a restraining force of P2 (t) or more, the steel plate buckles, and at that time the steel plate is kept flat, but when water cooling is stopped, the steel plate warps and becomes unable to be conveyed in the cooling device, Damaged equipment or significant distortion left after exiting cooling system.

If the binding force exceeds P2 (t), the steel sheet is transported in the cooling device by moving multiple sets of upper and lower rolls up and down according to the warpage of the steel sheet while pressing with a force less than P2 (t). It will not damage the equipment. Furthermore, after leaving the cooling device, for example, when cooling on the cooling floor, no large distortion remains. On the other hand, when the cooling becomes an imbalance and the steel sheet is about to be warped and pressed against the steel sheet with a large restraining force, reverse warpage occurs in the cooling device, or when the steel sheet leaves the cooling device. Warps more than expected. Actually, when the restraining force becomes P2 (t> or more, the pressure sensor detects the reaction force.First, the pressure applied to the hydraulic cylinder 6 is reduced until the restraining force becomes less than P2 (t>). As a result, the upper roll rises, where the steel sheet is passed in this state so as not to hinder the conveyance of the steel sheet.However, the cylinder pressure is reduced, and the upper roll is raised by a certain height, for example, 300 mm. However, if the reaction force (restraining force) from the steel sheet is still P ² (t) or more, the upper roll is quickly released, the restraining force is reduced to zero, and the force is lifted upward. For example, the cooling water on the lower or upper surface is not sprayed for some reason or is not sprayed at a predetermined flow rate, so that the cooling of the steel plate is vertically asymmetric and a large temperature difference occurs between the upper and lower surfaces of the steel plate. If this temperature difference Therefore, the reaction force from the steel plate that lifts the upper roll greatly exceeds P2 (t) and pushes the upper roll 2 upward. If it is possible to make i トラブル S, equipment troubles and equipment damage can be prevented.

The above description relates to the restraining force of one set of upper and lower rolls. However, if the restraining force of the other upper and lower rolls is equal to or higher than P2 (t), the above measures may be taken.

If the steel slab is rolled into a steel sheet, straightened, cooled by the steel sheet cooling method of the present invention, and the steel sheet after the cooling is straightened, the steel sheet does not warp or buckle during cooling, A flat and uniform steel plate can be manufactured. Example

Using the steel plate cooling device shown in Fig. 1, the steel plate thickness S (mm), the distance L (mm) between the upper and lower roll sets, and the binding force P (t) were changed as shown in Table 1 Was cooled and the occurrence of warpage was investigated. Table 1, the above equation (1)) from the combined P1 and P ² obtained shown but, in the invention examples have established the relationship P1 <P rather P2.

Each of the steel sheets cooled by the method of the present invention passed through the cooling device without any problem, and maintained a good shape even after being cooled to room temperature by the cooling floor.

In Inventive Examples 4 and 6, the actual restraining force exceeded P2 during transport. Was lifted and did not have a binding force higher than P2. The steel sheet was able to pass through the cooling device, and the warp was initially present in the cooling floor, but after cooling down, the warp disappeared and became flat.

On the other hand, in Comparative Examples 1, 2, 5, 7, 9, and 11, where the steel sheet was cooled while being restrained by a restraining force less than P1, the steel sheet was lifted by the warp in the width direction generated in the cooling device, and the steel sheet was rolled. A gap was created between them, and cooling water leaked out from the gap, causing local temperature unevenness, causing a large warpage in the cooling floor.

In Comparative Examples 4, 6, 8, 10, and 12, in which the steel sheet was cooled while being restrained by the restraining force of P2 or more, no strain was generated in the cooling device, but the steel sheet was cooled on the cooling floor. Large warpage occurred in the longitudinal direction. It is considered that the steel plate yielded in the cooling device, and then, when it exited the cooling device, even if it was flat, it was allowed to cool down, and as the temperature approached room temperature, the strain caused by the yielding occurred when the temperature became uniform. Can be

Claims

The scope of the claims

1. transporting the steel sheet horizontally while restraining the steel sheet surface with a plurality of sets of upper and lower rolls;

Water-cooling the steel sheet being conveyed from above and below the steel sheet surface;

Has,

The binding force of the steel sheet by the upper and lower rolls per set is not less than Pl (t) and less than P2 (t) represented by the following formulas (1) and (2):

Cooling method of steel sheet;

^{^{P1 = 6.85X10 "7 S 3 L}} 0 - 65 -" (1)

^{^{P2 = 1.2X10 ~ 6 S 3 L}} 0 - 65 ··· (2)

Here, L (mm) represents the distance between adjacent upper and lower roll sets, and S (mm) represents the thickness of the steel sheet.

2. Furthermore, when the binding force of the steel sheet becomes P2 (t) or more, the vertical movement following the warpage of the steel sheet while pressing the upper and lower rolls of the compound I with a force less than P2 (t) is required. 2. The method for cooling a steel sheet according to claim 1.

3. The method for cooling a steel sheet according to claim 2, further comprising the step of releasing said upper and lower rolls when the amount of vertical movement of a plurality of pairs of upper and lower rolls exceeds a predetermined limit value to reduce the binding force of the steel sheet to zero. .

4. Multiple upper and lower rolls for restraining the steel sheet being conveyed

Means for water cooling the steel sheet being conveyed from above and below the steel sheet surface;

Means for vertically moving the plurality of sets of upper and lower rolls to adjust a binding force for binding the steel sheet;

A cooling device for a steel sheet.

5. When the moving amount of the upper and lower rolls exceeds a predetermined value, the upper and lower rolls are opened. 5. The cooling device for steel sheets according to claim 4, further comprising means for reducing the restraining force of the steel sheets by increasing the degree.

6. Rolling the steel slab into steel plate;

Straightening the steel sheet;

A step of cooling the steel sheet after the straightening, by a method for cooling a steel sheet according to any one of claims 1 to 3,

Straightening the steel sheet after cooling,

The manufacturing method of the steel plate which has.

7. The method for producing a steel sheet according to claim 6, wherein in the cooling step, the upper surface of the steel plate and the lower surface of the steel plate are each cooled with a water amount of 2 m ³ / min or more per unit area.