WO2018159749A1

WO2018159749A1 - Method for cooling steel sheet, cooling device for steel sheet and method for manufacturing steel sheet

Info

Publication number: WO2018159749A1
Application number: PCT/JP2018/007743
Authority: WO
Inventors: 上岡　悟史; 雄太田村; 原田　直樹
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2017-03-02
Filing date: 2018-03-01
Publication date: 2018-09-07
Also published as: EP3560616B1; EP3560616A4; CN110366456A; CN110366456B; KR20190112085A; JP6720894B2; EP3560616A1; JP2018144050A; KR102303872B1

Abstract

The purpose of the present invention is to provide: a method for cooling a steel sheet having less distortion in controlled cooling, in which the hot-rolled steel sheet is cooled while being restrained by rolls; a cooling device for a steel sheet; and a method for manufacturing a steel sheet. Provided is a method for cooling a steel sheet in which a steel sheet is conveyed while being restrained by a plurality of rolls disposed at a prescribed pitch in a steel sheet conveying direction, and cooling water is sprayed on upper and lower surfaces of the steel sheet by cooling nozzles disposed between the plurality of rolls to cool the steel sheet, wherein cooling is performed at a sheet passing speed V that satisfies formula (1): V > 2.21×10-5×Cv ×L3×t-2×(24.2+204.3×(L/W)2)-1 In formula (1): V is the sheet passing speed (m/s); Cv is the cooling rate (oC/s) with respect to the average temperature of the steel sheet in the thickness direction; L is the roll pitch (m); T is the sheet thickness (m); and W is the sheet width (m).

Description

Steel plate cooling method, steel plate cooling device, and steel plate manufacturing method

The present invention relates to controlled cooling in which hot-rolled high-temperature steel sheets are subjected to passing cooling while being constrained by a roll. In particular, a method for cooling a steel plate, which can produce a steel plate with less strain on a thick steel plate (hereinafter sometimes simply referred to as a steel plate) having a plate thickness as thin as 10 mm or less and a plate width of 3000 mm or more, and The present invention relates to a cooling device and a method for manufacturing a steel plate.

When manufacturing steel sheets, it is necessary to ensure the mechanical properties required for steel sheets, especially strength and toughness. In order to achieve this, an operation is performed in which the high-temperature steel sheet after rolling is cooled as it is, or is air-cooled to room temperature and reheated and quenched off-line. In this cooling, it is necessary to increase the cooling rate in order to ensure the material properties required for the steel sheet. At the same time, it is important that the cooling is performed uniformly over the entire surface of the steel sheet in order to ensure the uniformity of the material and suppress the occurrence of distortion during cooling (cooling distortion). When cooling distortion occurs, it is necessary to secure the flatness of the cooled steel sheet using a straightening machine such as a roller straightener or a press, which causes an additional process and is a major obstacle to shortening the delivery time. .

Correspondingly, currently, cooling of steel sheets is constrained by a plurality of rolls, and a cooling nozzle is disposed between the restraining rolls to cool the steel sheets while passing (referred to as passing cooling). As a result, a steel plate with less distortion is manufactured.

The reason for controlled cooling by such a method is that the initial investment cost can be suppressed because it is possible to cool with a short equipment length by using the passing cooling. In addition, the restraining roll suppresses distortion caused by uneven temperature distribution in the steel plate upper and lower surfaces and the steel plate surface during cooling, and disposes cooling water outside the cooling device by arranging a cooling nozzle between the rolls. This prevents the cooling water from staying on the steel plate.

From the above viewpoint, for example, Patent Document 1 predicts the residual stress generated in the steel sheet from the measurement of the temperature distribution of the steel sheet after cooling with respect to the shape defect due to the non-uniformity of the steel sheet temperature distribution after cooling. The method for determining whether or not correction is necessary is described.

In addition, Patent Document 2 focuses on the restraint roll from the viewpoint of suppressing C warpage that occurs during water cooling, and applies a load within the range of restraint force of the restraint roll required as a function of its roll pitch and steel plate thickness. Describes a method for manufacturing a steel sheet with good flatness.

Japanese Patent No. 2843273 Japanese Patent No. 3925789

Although a steel plate with less distortion can be produced by the method described above, even if cooling is performed while ensuring temperature uniformity in the width direction and the upper and lower surfaces, distortion may still occur. Therefore, as a result of investigations on the occurrence of strain by the present inventors, it has been found that cooling strain is generated due to buckling deformation due to contraction in the width direction of the steel sheet during water cooling. In the case of a steel plate having a thin plate thickness and a wide plate width, the cooling strain due to buckling deformation is unlikely to exhibit a reduction effect by the method described above. In particular, the plate thickness is 10 mm or less and the plate width is 3000 mm. It has been found that when the steel sheet is cooled, distortion occurs even if it is cooled with the temperature uniformity in the width direction and the upper and lower surfaces secured.

Buckling deformation due to shrinkage in the width direction of the steel plate during water cooling is a mechanism different from the strain due to temperature deviation of the upper and lower surfaces assumed so far, so it is thought that strain will occur even if cooling is performed by the conventional method . In the method of predicting from the temperature distribution after cooling of the steel sheet as in Patent Document 1, deformation larger than the predicted plate shape occurs. Therefore, the prediction is wrong, and it is difficult to reduce the incidence of correction. Further, in Patent Document 2, although distortion due to temperature deviation of the upper and lower surfaces can be suppressed, buckling deformation due to sheet width contraction caused by water cooling is not taken into consideration, so that the sheet thickness is thin and the sheet width is small. There is no effect on a wide area.

Then, this invention makes it a subject to solve the problem of the said prior art, and in control cooling which cools the steel plate after hot rolling, restraining with a roll, the cooling method of a steel plate with little distortion, the cooling device of a steel plate, and It aims at providing the manufacturing method of a steel plate.

The gist of the present invention is as follows.
[1] A steel plate is conveyed in a state in which the steel plate is restrained by a plurality of rolls arranged at a predetermined pitch in the steel plate conveyance direction, and cooling water is sprayed onto the upper and lower surfaces of the steel plate by a cooling nozzle arranged between the plurality of rolls. In the method for cooling the steel sheet,
A cooling method for a steel sheet that is cooled at a sheet passing speed V that satisfies the following formula (1).
V> 2.21 × 10 ⁻⁵ × Cv × L ³ × t ⁻² × (24.2 + 204.3 × (L / W) ² ) ⁻¹ (1)
However, in Formula (1),
V: Plate speed (m / s)
Cv: Cooling rate with respect to the average temperature of the steel sheet in the thickness direction (° C./s)
L: Roll pitch (m)
t: Plate thickness (m)
W: Plate width (m)
It is.
[2] The method for cooling a steel sheet according to [1], wherein the sheet thickness t is 10 mm or less.
[3] The steel sheet cooling method according to [1] or [2], wherein the plate width W is 3000 mm or more.
[4] A plurality of rolls that are arranged at a predetermined pitch in the steel plate conveyance direction and convey and restrain the steel plate;
A cooling nozzle that is disposed between a plurality of rolls and that cools the steel sheet by injecting cooling water onto the upper and lower surfaces of the steel sheet;
A steel sheet cooling apparatus comprising: a control mechanism that controls a plate passing speed V so as to satisfy the following formula (1).
V> 2.21 × 10 ⁻⁵ × Cv × L ³ × t ⁻² × (24.2 + 204.3 × (L / W) ² ) ⁻¹ (1)
However, in Formula (1),
V: Plate speed (m / s)
Cv: Cooling rate with respect to the average temperature of the steel sheet in the thickness direction (° C./s)
L: Roll pitch (m)
t: Plate thickness (m)
W: Plate width (m)
It is.
[5] The steel sheet cooling apparatus according to [4], wherein the plate thickness t is 10 mm or less.
[6] The steel sheet cooling apparatus according to [4] or [5], wherein the plate width W is 3000 mm or more.
[7] A method for producing a steel sheet, wherein the steel sheet after hot rolling is cooled by using the cooling method according to any one of [1] to [3].

According to the present invention, it is possible to manufacture a steel plate with less distortion. In particular, the effect can be exhibited by applying it to off-line heat treatment of thick steel plates.

FIG. 1 is a schematic diagram showing a partial configuration of a production facility using the steel sheet cooling device of the present invention. FIG. 2 is a diagram for explaining buckling deformation during cooling of a steel plate, (a) is a schematic diagram showing the configuration of the cooling device of the present invention, and (b) is a view of the plate width W of the steel plate during cooling of the steel plate. It is a figure explaining a change. FIG. 3 is a diagram illustrating an example of a defective shape (ear wave) of a steel plate. FIG. 4 is a diagram for explaining the definition of the steepness λ. FIG. 5 is a diagram showing the relationship between the roll pitch L and the steepness λ. FIG. 6 is a diagram showing the relationship between the cooling rate Cv and the steepness λ. FIG. 7 is a diagram showing the relationship between the sheet passing speed V and the steepness λ. FIG. 8 is a diagram for explaining buckling deformation when a part of steel plates (steel plates between roll pitches L) is cut out. FIG. 9 is a diagram showing the relationship between the buckling coefficient k, the roll pitch L, and the square of the plate width W.

First, the buckling deformation due to shrinkage in the steel sheet width direction during water cooling, which is considered to be a cause of cooling strain, will be described. FIG. 1 is a schematic diagram showing a partial configuration of a production facility using the steel sheet cooling device of the present invention. A steel plate 1 having a predetermined thickness produced on a rolling mill line is conveyed to the production line shown in FIG. After the steel plate 1 is heated to a predetermined temperature by the heating furnace 10, the steel plate 1 is conveyed while being restrained by the plurality of rolls 2, and is cooled by the plurality of cooling nozzles 3 installed between the rolls 2. In addition, the arrow in a figure is a conveyance direction of a steel plate. The roll 2 and the cooling nozzle 3 are installed on the upper and lower surfaces of the steel plate 1. The cooling device according to the present invention includes a roll 2, a cooling nozzle 3, and a control mechanism (not shown) that controls the plate passing speed V so as to satisfy formula (1) described later.

FIG. 2 (a) is a schematic diagram showing the configuration of the steel sheet cooling device of the present invention. As shown in FIG. 2A, the upper and lower surfaces of the steel sheet 1 are restrained by a plurality of rolls 2 such as a roll 2-0, a roll 2-1, a roll 2-i, and a roll 2-n along the conveyance direction. Has been. Between each roll 2, the cooling nozzle 3 is installed in the upper and lower surfaces of the steel plate 1, respectively.

FIG. 2B is a diagram for explaining a change in the plate width W of the steel plate during cooling of the steel plate. The plate width W of the steel plate 1 when passing through the steel plate cooling device shown in FIG. It is the figure which looked at change from the top. When the plate width of the steel plate 1 when passing through each roll 2 is W and the roll pitch in the steel plate conveyance direction is L, the steel plate 1 contracts by water cooling. For example, when the steel plate moves from the roll 2-0 to the roll 2-1, as shown in FIG. 2B, the plate width is ΔW (Δ = W ₀ −W ₁ , where W _o : roll 2-0. The sheet width when passing through the roll W ₁ : the sheet width when passing through the roll 2-1). At this time, since the steel plate having a large plate width and the steel plate having a narrow plate width are joined to have the same width, the portion having a large plate width (for example, the plate width W _o ) has a large compressive stress. receive. In the present invention, the deformation of the steel sheet due to the compressive stress is referred to as buckling deformation.

At this time, when the plate passing speed is low or the cooling speed is high, the contraction gradient ΔW / L with respect to the conveying direction becomes steep, so that a large compressive stress is generated and buckling deformation is likely to occur. Further, when the plate thickness is thin and the plate width is wide, the rigidity of the plate is lowered, so that the resistance due to the compressive stress is lowered, and the buckling deformation is also likely to occur.

Therefore, in order to confirm the contraction mechanism of the plate width W, in the actual production line, the shape of each steel plate cooled under various conditions such as the plate passing speed V, the plate thickness t, the plate width W, the cooling rate Cv, and the like. The relationship with cooling conditions was investigated. Specifically, the steel sheet 1 having a thickness of 6 mm to 10 mm manufactured in the rolling mill line is conveyed to the manufacturing line in FIG. 1 and heated to 950 ° C. by the heating furnace (Heath roll heating furnace) 10. The cooling nozzle 3 was used to cool to 100 ° C. It was judged whether or not buckling deformation occurred from the shape of the steel plate after cooling.

FIG. 3 is a diagram showing an example of the shape of a steel plate in which a shape defect has occurred, and a shape defect called a so-called ear wave has occurred in the edge portion of the steel plate 1. This defect of the ear wave shape was quantified using the steepness λ (%) represented by the definition shown in FIG. 4 and the following formula (2). In addition, an ear wave does not generate | occur | produce in one place, but multiple generate | occur | produces in the both ends of a steel plate. Therefore, the value of δ / P in the following formula (2) is the average value of all ear waves generated at both ends of the steel plate.
λ = (δ / P) × 100 (2)
However, in Formula (2),
λ: Steepness (%)
δ: Wave height (m)
P: Wave pitch (m)
It is.

As a result of quantification, the wave pitch P of the steel sheet in which the shape defect occurred was about 0.6 to 1.4 m. With regard to the allowable value of steepness, for example, if there is a large shape defect when welding multiple plates, the work of welding in a flat state by restraining the deformation of the steel plate will occur, as much as possible A smaller steepness is preferable. As a general standard, it is required that the wave height δ is 10 mm or less when the wave pitch P in the steel sheet conveyance direction is 2 m. Therefore, in the present invention, the steepness λ = (10/2000) × 100 = less than 0.5% is considered as no buckling deformation, and it is determined that λ is 0.5% or more as buckling deformation.

FIG. 5 shows the relationship between the roll pitch L and the steepness λ of the acoustic wave shape with a plate thickness t = 10 mm, a plate width W = 3000 mm, a plate passing speed V = 0.58 m / s, and a cooling rate Cv = 220 ° C./s. It is a figure which shows a relationship. It has been confirmed that the steepness λ becomes smaller as the roll pitch L becomes shorter. When the roll pitch L was 600 mm or less, no ear wave was generated.

FIG. 6 shows the relationship between the cooling rate Cv and the steepness λ of the ear wave shape when the plate thickness t = 10 mm, the plate width W = 3000 mm, the plate passing speed V = 0.58 m / s, and the roll pitch L = 750 mm. FIG. It has been confirmed that the steepness λ decreases as the cooling rate Cv decreases. When the cooling rate Cv was 110 ° C./s or less, no ear wave was generated.

FIG. 7 shows a plate speed V and steepness of a steel plate having a plate thickness t = 6 mm, a roll pitch L = 750 mm, a cooling rate Cv = 300 ° C./s, and a plate width W of 1500 mm and a plate width W of 3000 mm. It is a figure which shows the relationship with (lambda). It was confirmed that the steepness λ becomes smaller as the plate passing speed V is higher at any plate width. Further, when the plate width W was 1500 mm, no ear wave was generated when the plate passing speed V was 1.8 m / s or more. On the other hand, when the plate width W was 3000 mm, no ear wave was generated when the plate passing speed V was 3.0 m / s or more. From these results, it was found that the shape deteriorates as the plate width increases for the same plate passing speed.

In thick steel plates, the thicker the plate thickness, the more temperature difference occurs between the steel plate surface and the steel plate center during cooling. Therefore, the cooling rate Cv here is a cooling rate with respect to the average temperature in the plate thickness direction.

From these findings, it can be said that the buckling deformation occurs due to the plate passing speed V, the cooling speed Cv, the roll pitch L, the plate thickness t, and the plate width W. Therefore, as a result of further studies by the present inventors, it has been found that if a plate passing speed V represented by the following formula (1) is satisfied, a steel plate with less strain can be obtained without buckling deformation.
V> 2.21 × 10 ⁻⁵ × Cv × L ³ × t ⁻² × (24.2 + 204.3 × (L / W) ² ) ⁻¹ (1)
However, in Formula (1),
V: Plate speed (m / s)
Cv: Cooling rate with respect to the average temperature of the steel sheet in the thickness direction (° C./s)
L: Roll pitch (m)
t: Plate thickness (m)
W: Plate width (m)
It is.

Hereinafter, the derivation of the above formula (1) will be described.

According to the Elasticity Handbook (Nakahara et al., 2001, Asakura Shoten, P. 264), the compressive stress at the buckling limit is described as follows.

In the above formula,
σ _e : Buckling limit stress (MPa)
k: Buckling coefficient E: Young's modulus (MPa)
π: Circumference ratio ν: Poisson's ratio t: Plate thickness (m)
L: Roll pitch (m)
W: Plate width (m)
m: Wave number (usually 1)
It is.
Note that L is described as the plate length in the elasticity handbook, but this time it is a system constrained by a roll, so it is read from the roll pitch as judged from the direction of stress. Regarding the buckling coefficient k, equation (4) is an example of an elementary analysis. Actually, since the restraint state of the steel plate changes, the buckling coefficient does not become as shown in this equation (4). For this reason, the buckling coefficient k is often used by appropriately modifying it so as to match the actual condition with reference to the equation (4).

As shown in FIG. 8, when considering a steel plate between some rolls (a steel plate between roll pitches L), the compressive stress exerted in the width direction of the steel plate from the inter-roll entry temperature and the inter-roll exit temperature is as follows: It can be described as follows.

In the above formula,
σ _a : compressive stress in the width direction (MPa)
α: Linear expansion coefficient (1 / ° C)
E: Young's modulus (MPa)
T _in : Roll entry temperature (° C)
T _out : roll-side outlet temperature (° C.)
It is.

Assuming cooling between the rolls at a constant cooling rate, the inter-roll entry temperature T _in and the inter-roll exit temperature T _out of the above equation (5) can be described as follows.

In the above formula,
Cv: Cooling rate (° C./s)
V: Plate speed (m / s)
It is.

In other words, the compressive stress sigma _a width direction can be described as follows.

When the compressive stress σ _{a in the} width direction is smaller than the buckling limit stress σ _e , buckling does not occur if the relational expression (8) is satisfied.

Rewriting equation (8) for the plate speed V is as follows.

In the case of steel, since the Poisson's ratio ν and the coefficient of thermal expansion α have eigenvalues, when considered as constants, the plate passing speed V that does not buckle and deform can be described as follows. (Assuming operation in a high temperature range, Poisson's ratio ν and coefficient of thermal expansion α are converted to ν = 0.3 and α = 2.0 × 10 ⁻⁵ respectively)

The buckling coefficient k is represented by the following equation (11) derived from the above equation (10).

Here, since the buckling coefficient k is a value unique to the process, various experiments were performed with actual machines, and the buckling coefficient k was actually obtained. In order to actually determine the buckling coefficient k, the experimental conditions are as follows: the plate thickness t is 5 to 15 mm, the plate width W is 3000 to 5000 mm, the roll pitch L is 500 to 750 mm, and the plate passing speed is 0.3 to 2.0 m. / S.

On the other hand, the buckling constant k at the actual buckling boundary is considered to be related to the square of the roll pitch L and the plate width W from the above equation (4). As described above, the buckling coefficient k may deviate from the theoretical formula of equation (4) due to constraints at each end or deformation conditions. For example, when there is a shear force, the (W / L) term is omitted. There are also examples. Therefore, this time, when the (W / L) term is omitted, the relationship between the buckling coefficient k actually obtained by the actual machine, the roll pitch L, and the square of the plate width W is plotted. The result is shown in FIG. In FIG. 9, ◯ indicates that the steepness λ is less than 0.5%, and x indicates that the steepness λ is 0.5% or more. From FIG. 9, it can be said that there is a correlation between the buckling constant k of the boundary that actually buckles and the steepness λ.

From the result of FIG. 9, the buckling coefficient k can be expressed by the following relationship.
k = 204.3 (L / W) ² +24.2 (12)
By combining Formula (10) and Formula (12), the plate passing speed V that does not buckle can be expressed by the following Formula (1).
V> 2.21 × 10 ⁻⁵ × Cv × L ³ × t ⁻² × (24.2 + 204.3 × (L / W) ² ) ⁻¹ (1)
However, in Formula (1),
V: Plate speed (m / s)
Cv: Cooling rate with respect to the average temperature of the steel sheet in the thickness direction (° C./s)
L: Roll pitch (m)
t: Plate thickness (m)
W: Plate width (m)
It is.

In addition, since the roll pitch L is a parameter that comes from the machine configuration, it cannot be changed after the machine is installed. Further, the plate thickness t, the plate width W, and the cooling rate Cv are parameters related to determining the characteristics of the product and cannot be simply changed. Therefore, the formula (1) is arranged focusing on the plate passing speed V which is a parameter that can be appropriately changed in operation.

From the above formula (1), the buckling deformation is faster in order to prevent buckling deformation when the sheet thickness t is thinner, the roll pitch L is wider, the cooling speed Cv is faster, and the sheet width is wider. It turns out that it is necessary to cool with. Here, the roll pitch L, the cooling speed Cv, and the plate passing speed V are values unique to the cooling equipment, and the plate thickness t and the plate width W are determined by the product. On the other hand, the cooling speed Cv is the flow rate of the cooling water of the cooling device, and the plate passing speed V is the number of rotations of the table roll, which can be changed. Therefore, the roll pitch of the cooling device is designed to be as short as possible (for example, 500 mm pitch) according to the range of production types in the design stage, and the rotation speed of the table roll is set to rotate as fast as possible (for example, 2 m / s or more), the adjustment range of the flow rate of the cooling water should be designed to be wide. If the roll pitch L cannot be shortened, such as using existing equipment, the cooling rate Cv can be slowed by widening the adjustment range of the cooling water flow rate and enabling cooling at a low flow rate. It is effective (for example, 100 ° C./s or less at a plate thickness of 10 mm). Hot strip mills for producing hot-rolled steel strips and on-line controlled cooling of thick steel plates have a plate speed of about 2.5 m / s at a thickness of 10 mm, which is relatively fast. Deformation hardly occurs. On the other hand, in cooling at the time of off-line heat treatment of a thick steel plate, water cooling is performed in conjunction with the extraction rate of the heating furnace, so that the plate passing speed is about 1.0 m / s. Likely to happen.

As described above, in the present invention, it is possible to manufacture a steel sheet with less cooling strain by cooling the steel sheet at a sheet passing speed V that satisfies the above formula (1). In this invention, an effect is expressed regarding the steel plate with a thin plate thickness and a wide plate width. In particular, it is suitable for cooling thick steel plates having a plate thickness of 10 mm or less and / or a plate width of 3000 mm or more, and can be applied to off-line heat treatment of thick steel plates.

The steel sheet was cooled using the manufacturing equipment shown in FIG. Here, the heating temperature in the heating furnace 10 was set to 930 ° C., and the plate thickness was set to 5 mm, 10 mm, and 12 mm where buckling deformation was likely to occur. As the cooling nozzle 3, a plurality of flat sprays arranged in the width direction was used. The amount of cooling water can be changed. The cooling rate of a steel plate having a thickness of 5 mm when the maximum amount of water is injected is 400 ° C./s, and the cooling rate when the minimum flow rate is injected is 100 ° C./s. When cooling is performed by changing only the plate thickness with the cooling water amount being constant, the cooling rate is inversely proportional to the plate thickness. Therefore, when the plate thickness is 10 mm, the maximum cooling rate is 200 ° C./s, and the minimum cooling rate is 50 ° C./s. The roll pitch L was changed for each condition.

The shape of the steel plate was judged by the steepness λ. When the steepness λ was less than 0.5%, the steel plate shape was judged to be flat. On the other hand, when the steepness λ was 0.5% or more, the steel plate shape was judged to be buckled. When obtaining the steepness λ, δ / P was calculated from the average value of all ear waves generated at both ends of the steel sheet.

The results are shown in Table 1.

In the example of the present invention, cooling is performed at a plate passing speed higher than the plate passing speed V obtained by the equation (1). In any of the inventive examples, buckling deformation did not occur and a flat shape was obtained. On the other hand, in all the comparative examples, cooling is performed at a plate passing speed lower than the plate passing speed V obtained by the equation (1). In all the comparative examples, buckling deformation occurred under all conditions. As a result, all the steel plates of the comparative examples were shipped after being subjected to shape correction with a roller straightener after cooling. All the steel sheets of the inventive examples could be shipped as they were without re-correction.

Note that the transfer speed control of a general off-line heat treatment apparatus for thick steel plates is influenced by the driving mechanism of the heating furnace, and the transfer speed can be controlled at a speed of approximately 0.02 to 0.5 m / s. As can be seen from the results of the examples, especially in the experimental condition where the plate thickness is 12 mm, even if the cooling rate is high, the plate passing speed determined by the expression (1) of the present invention, that is, the carrying speed is the carrying speed control of the actual machine. Since it falls within the range, shape adjustment is easy. Furthermore, the shape adjustment of the steel plate having a narrow plate width is also easy because the plate passing speed obtained by the formula (1) of the present invention, that is, the transport speed is within the transport speed control range of the actual machine. On the other hand, in particular, the cooling rate control and roll pitch change of the present invention, for a steel plate having a plate thickness of 10 mm or less and / or a plate width of 3000 mm or more, is the plate passing speed required by the formula (1) of the present invention, that is, The transport speed may be outside the transport speed control range of the actual machine. For this reason, when implementing this invention with respect to the steel plate of 10 mm or less board thickness and / or 3000 mm or more board width, it turns out that cooling rate control, a roll pitch change, etc. are required. In addition, in the condition of a sheet thickness of 5 mm and a sheet width of 5000 mm, in addition to narrowing the roll pitch to 500 mm, the sheet passing speed is controlled to 2.0 m / s slightly faster than general equipment, It can be seen that buckling deformation can be prevented.

1 Steel plate 2 Roll 2-0 Roll 2-1 Roll 2-i Roll 2-n Roll 3 Cooling nozzle 10 Heating furnace (Heath roll heating furnace)
δ Wave height P Wave pitch

Claims

The steel sheet is transported in a state of being restrained by a plurality of rolls arranged at a predetermined pitch in the steel sheet conveyance direction, and cooling water is sprayed onto the upper and lower surfaces of the steel sheet by a cooling nozzle disposed between the plurality of rolls to cool the steel sheet. In the cooling method of the steel sheet,
A cooling method for a steel sheet that is cooled at a sheet passing speed V that satisfies the following formula (1).
V> 2.21 × 10 −5 × Cv × L 3 × t −2 × (24.2 + 204.3 × (L / W) 2 ) −1 (1)
However, in Formula (1),
V: Plate speed (m / s)
Cv: Cooling rate with respect to the average temperature of the steel sheet in the thickness direction (° C./s)
L: Roll pitch (m)
t: Plate thickness (m)
W: Plate width (m)
It is.
The method for cooling a steel sheet according to claim 1, wherein the plate thickness t is 10 mm or less.
The sheet width W is 3000 mm or more. The method for cooling a steel sheet according to claim 1 or 2.
A plurality of rolls that are arranged at a predetermined pitch in the steel plate conveyance direction and restrain and convey the steel plate,
A cooling nozzle that is disposed between a plurality of rolls and that cools the steel sheet by injecting cooling water onto the upper and lower surfaces of the steel sheet;
A steel sheet cooling apparatus comprising: a control mechanism that controls a plate passing speed V so as to satisfy the following formula (1).
V> 2.21 × 10 −5 × Cv × L 3 × t −2 × (24.2 + 204.3 × (L / W) 2 ) −1 (1)
However, in Formula (1),
V: Plate speed (m / s)
Cv: Cooling rate with respect to the average temperature of the steel sheet in the thickness direction (° C./s)
L: Roll pitch (m)
t: Plate thickness (m)
W: Plate width (m)
It is.
The steel sheet cooling device according to claim 4, wherein the plate thickness t is 10 mm or less.
The plate width W is 3000 mm or more. The steel sheet cooling device according to claim 4 or 5.
A method for producing a steel sheet, wherein the steel sheet after hot rolling is cooled by using the cooling method according to any one of claims 1 to 3.