JP2005125351A - Steel plate production line and steel plate production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production line and a production method for producing a steel plate having a good flatness by uniformly cooling even a steel plate having severe rolling conditions such as a very thick steel material and a low temperature finish rolled steel material.
A hot rolling mill, a first shape straightening device, a cooling device, and a second shape straightening device are arranged in this order, and in a steel plate production line having a function of cooling and straightening a steel plate online, A steel sheet production line is provided in which the plate thickness correcting capability of the first shape correcting device is larger than the plate thickness correcting capability of the second shape correcting device.
[Selection] Figure 1

Description

  The present invention relates to a production line for producing a steel plate excellent in flatness and a method for producing a steel plate in the production of a steel plate for online cooling of a hot-rolled high-temperature steel plate.

  Control cooling technology that cools steel sheets online has become routinely used on a global scale due to advances in cooling devices and computer control technology.

  In general, when cooling a steel sheet after undergoing a hot rolling step, uneven cooling is likely to occur due to temperature unevenness of the steel sheet or surface unevenness, and the uneven cooling is caused by the flatness of the steel sheet after cooling. It tends to cause deterioration, camber generation after steel sheet cutting due to residual stress, and variations in mechanical properties. Among steel plates, when cooling thick steel plates online, cooling unevenness is particularly likely to occur in cooling. Thick steel plates with uneven cooling lose the flatness after cooling, so it is necessary to correct the flatness deterioration with a cold leveler or press in the next process. The problem was likely to occur.

  For the purpose of solving this problem, in order to obtain a steel sheet with good flatness after cooling, a leveler is provided in front of the cooling device, and a technique for cooling after flattening is disclosed for a long time. .

  For example, Patent Literature 1 and Patent Literature 2 disclose an apparatus and a method for obtaining a steel plate with good flatness by providing a leveler in front of a cooling device, cooling after performing flatness correction, and further correcting with a hot leveler. Has been. The technique disclosed in Patent Document 1 is a technique for direct quenching, and corrects a steel plate having a temperature equal to or higher than the A3 transformation point with a first shape correction device, subsequently cools, and immediately after cooling, the second This is a technology for obtaining a hardened steel sheet with good flatness by correcting the steel sheet with a shape straightening device. The technique disclosed in Patent Document 2 is a technique related to accelerated cooling, in which a shape correction device is arranged before and after the cooling device, a high-temperature steel plate after rolling is corrected, and the shape is improved by correction, and then the steel plate. This is a technique for obtaining a steel sheet having a good flatness even after cooling by cooling the steel sheet and then reheating the steel sheet and then performing flattening of the steel sheet with a second shape straightening device.

On the other hand, Patent Document 3 and Patent Document 4 are provided with a first shape correction device having a shape correction capability lower than that of the second shape correction device before the cooling device, thereby reducing the equipment cost and improving the flatness. An apparatus and method for obtaining a steel sheet is disclosed. More specifically, the technique disclosed in Patent Document 3 gives the second shape correction device sufficient shape correction capability for all of the cooled steel plates, and provides the correction capability of the first shape correction device. This is a technique for reducing the equipment cost by lowering the straightening ability of the second shape straightening device and obtaining a uniform steel plate. On the other hand, the technique disclosed in Patent Document 4 is similar in basic idea to Patent Document 3, and specifically, two techniques are disclosed. More specifically, in the first technique disclosed in Patent Document 4, the flatness failure of a thick steel plate having a thickness of more than 20 mm is often a warp. Therefore, the warp is corrected without using the repeated bending correction function. This is a technique for improving the manufacturing efficiency of a steel sheet using only the function to perform, and the second technique disclosed in Patent Document 4 is a case where the flatness of a steel sheet having a thickness of 20 mm or less is an ear wave or a medium wave. This is a technology that improves manufacturing efficiency by using only the repeated bending correction function without using the function to correct warpage.
JP 54-124864 A Japanese Patent Laid-Open No. 03-128122 JP 11-226605 A JP-A-11-226642

  However, due to the recent development of controlled cooling technology, the thickness of the steel sheet to be cooled is increasing. For example, an extra-thick steel material having a thickness exceeding 50 mm is used in offshore structures and steel sheets for bridges. It is becoming. Since these steel materials are naturally required to have high weldability, the number of alloy elements is reduced as much as possible, and the number of cases in which the target steel materials are manufactured by controlled cooling is increasing. Among the ultra-thick steel materials, there are steel materials that are rolled under severe conditions such as low-temperature heating and low-temperature finish rolling.

  When the controlled cooling which consists of the above techniques is applied to the very thick steel sheet rolled under such severe conditions, the steel sheet may not be uniformly cooled. For example, in the techniques disclosed in Patent Document 3 and Patent Document 4, in order to reduce the equipment cost, the straightening ability of the first shape straightening device is lowered, and the steel plate having a plate thickness exceeding 20 mm or a low temperature is used. It is difficult to exhibit sufficient correction ability for the finish rolled steel sheet. For this reason, if it is a thin plate or a high-temperature finish rolled steel plate with a plate thickness of 20 mm or less, uniform cooling is possible even with an apparatus composed of the techniques disclosed in Patent Document 3 and Patent Document 4, but the plate thickness is 20 mm. In the case of thick steel plates and low-temperature finish rolled steel plates that exceed the above range, cooling is performed with poor flatness, so that there is a problem that flatness after cooling deteriorates.

  In addition, it is unclear whether the techniques disclosed in Patent Document 1 and Patent Document 2 have the ability to correct the shape of all steel sheets that are cooled online. It is unclear whether or not it has straightening ability up to the rolled steel sheet.

  The present invention has been made to solve the above-described problems, and even a steel plate with severe rolling conditions such as a very thick steel plate or a low temperature finish rolled steel plate having a thickness exceeding 20 mm can be uniformly cooled and flattened. It is an object of the present invention to provide a production line and a production method for producing a steel sheet having a good degree.

In order to obtain a steel sheet with good flatness after cooling by performing uniform cooling, the inventors have intensively studied and obtained the findings 1) to 5) shown below to complete the present invention.
1) The higher the cooling rate of the cooling device, the more the uneven deformation of the steel sheet is promoted. If the steel sheet is deformed before it is cooled by the cooling device, the deformation of the steel sheet is further promoted by the cooling of the steel sheet. Therefore, it is preferable that all steel plates to be cooled are straightened before cooling.
2) Warpage occurs in a thick steel plate having a plate thickness exceeding 20 mm. Although it is possible to correct the thick steel plate to such a degree that it can enter the first shape correcting device, the warp correcting device corrects the thick steel plate to a flatness that can be cooled uniformly. It is difficult. Therefore, in order to cool the steel plate uniformly, it is necessary to carry out both the correction by the warp correction device and the correction by repeated bending correction at the same time.
3) The steel plate temperature after cooling is lower than the steel plate temperature immediately after rolling. Therefore, compared with the steel plate immediately after rolling, the steel plate after cooling has a large deformation resistance, and the reaction force required for correction becomes considerably large. When trying to correct all the cooled steel plates with the second shape correction device, the second shape correction device is required to have a capability to cope with a considerably large reaction force, and the device having such a capability has a high equipment cost. Become. Therefore, it is possible to reduce the equipment cost if the first shape correcting device that corrects the steel sheet having a small deformation resistance immediately after rolling corrects the steel sheet.
4) One of the causes of defective flatness after cooling is temperature unevenness after cooling. As long as this temperature variation is not reduced, flatness will occur no matter how powerful the second straightening device is.
5) The temperature unevenness greatly depends on the flatness of the steel plate before cooling. In this sense, it is important to increase the plate thickness correction capability of the first shape correction device more than the second shape correction device, and to correct the flatness of the steel plate before cooling.

  The present invention will be described below. In order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are appended in parentheses, but the present invention is not limited to the illustrated embodiment.

  In the invention of claim 1, the hot rolling mill (1), the first shape correction device (3), the cooling device (4), and the second shape correction device (6) are arranged in this order, and the steel plate is online. In the production line (100) of the steel plate (10) having the function of cooling and straightening the plate, the plate thickness straightening capability of the first shape straightening device is greater than the plate thickness straightening capability of the second shape straightening device. An object of the present invention is to solve the above-mentioned problems by a production line for steel sheets.

  According to the first aspect of the present invention, even in a steel plate having a large deformation resistance value such as an ultra-high-strength steel plate, the thickness of the plate is reduced at a high temperature with a small deformation resistance value compared to the value at the temperature after cooling. It becomes possible to correct the steel plate shape by the first shape correction device having a large correction capability.

  The invention of claim 2 suppresses the steepness of the steel sheet to 0.2% or less at the end of straightening by the first shape straightening device (3) in the production line (100) of the steel plate (10) according to claim 1. It is characterized by that.

  According to the invention of claim 2, the steel plate can be uniformly cooled by the cooling device, and the temperature unevenness in the steel plate can be suppressed to within ± 30 ° C. Therefore, the steel plate with good flatness after cooling. Can be obtained.

  The invention of claim 3 is characterized in that, in the production line (100) of the steel plate (10) according to claim 1, the warp correction function (2) is provided in the first shape correction device (3).

  According to the third aspect of the invention, since the warp correction function is provided in the first shape correction device, it is possible to correct the warp occurring in the steel sheet that has passed through the hot rolling mill. It is easy to reduce the burden on the correction device.

  Invention of Claim 4 is a manufacturing line (100) of the steel plate (10) of any one of Claims 1-3. Between a cooling device (4) and a 2nd shape correction apparatus (6). The heating device (5) is installed in

  According to the fourth aspect of the present invention, even when a flatness failure occurs in the steel sheet after cooling by the cooling device, the heating device installed between the cooling device and the second shape correcting device is used. By increasing the temperature, the steel sheet can be easily corrected with the second shape correction device, and as a result, steps such as flatness correction and press correction during cold working can be omitted.

  Invention of Claim 5 manufactures a steel plate in the manufacturing line (100) of the steel plate (10) of any one of Claims 1-4 by controlling the cooling condition and shape correction condition of a steel plate online. A method for producing a steel sheet, wherein all steel sheets to be cooled after rolling by a hot rolling mill are cooled by a cooling device (4) after the shape is corrected by a first shape correcting device (3). The manufacturing method is intended to solve the above-mentioned problem.

  According to the fifth aspect of the present invention, it is possible to keep the steepness of the steel sheet low before performing cooling by the cooling device, and it is possible to manufacture a steel sheet with excellent flatness.

  The invention of claim 6 is a method of manufacturing a steel plate (10) according to claim 5, wherein the steel plate is cooled and straightened, and the warp straightening function of the first shape straightening device (3) ( The above-mentioned problem is to be solved by a method for manufacturing a steel sheet, wherein both 2) and the repeated bending correction function are used simultaneously.

  According to the invention of claim 6, the first shape correction device can correct the shape of the steel plate that has corrected the warpage of the steel plate that has passed through the hot rolling mill. It is possible to manufacture a steel plate with excellent flatness while suppressing such a burden.

  According to the present invention, it is possible to uniformly cool a steel plate even if it is a steel plate having severe rolling conditions such as a very thick steel plate having a thickness exceeding 20 mm or a low temperature finish rolled steel plate, and the flatness. It is possible to produce a steel sheet with excellent quality.

  Such an operation and gain of the present invention will be made clear from the best mode for carrying out the invention described below.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings. FIG. 1 shows an example of a production line for steel sheets according to the present invention. As shown in the drawing, the production line 100 for the steel plate 10 of the present invention includes a hot rolling mill 1, a first shape correction device 3, a cooling device 4, and a second shape correction device 6 in this order in the traveling direction of the steel plate 10. It is essential that the plate thickness correcting capability of the first shape correcting device 3 is larger than the plate thickness correcting capability of the second shape correcting device 6.

1. Steel line production line (1) Hot rolling mill The hot rolling mill 1 used in the production line 100 for the steel sheet 10 of the present invention is not particularly limited, and a rolling mill usually used for hot rolling is used. Can be used. For example, a single stand four-high rolling mill, a six-high rolling mill, or a combination of these rolling mills in a plurality of tandems can be used.

(2) First shape correction device The plate thickness correction capability of the first shape correction device 3 used in the production line 100 of the steel plate 10 of the present invention is greater than the plate thickness correction capability of the second shape correction device 6. It shall have a large thickness correction capability. The reason why the first shape correcting device 3 needs to have such capability is as follows.

In recent years, when it is desired to correct an ultra-high strength steel plate (for example, a steel plate of X-100 class or higher, which is an API standard for line pipes) whose yield stress exceeds 600 N / mm ² to an appropriate shape. There is. However, if most of the shape correction of ultra-high-strength steel sheets, etc., depends on the ability of the second shape correction device as in the conventional steel plate production line, the temperature of the steel plate corrected by the correction device is low, and the deformation resistance Therefore, the plate thickness correction capability required for the correction apparatus becomes unrealistically strong. Furthermore, since an apparatus having such a capability is expensive, the equipment cost becomes high. Therefore, in the present invention, the plate thickness correction capability of the second shape correction device 6 is the same as the conventional one, while the plate shape correction capability of the first shape correction device 3 is improved, so It was decided to enable production.

  The problem to be solved by the present invention is to produce a steel plate having a good flatness by uniformly cooling even a steel plate having severe rolling conditions such as an ultra-high strength steel plate. As a method for improving the flatness of the steel plate, a method of increasing the capability of the second shape straightening device 6 can be considered, but the plate thickness straightening capability of the second shape straightening device 6 can be rolled and straightened after cooling. In order to achieve this capability, it is necessary to use a straightening device that can withstand a very large straightening reaction force, which increases both cost and installation area. In addition, when temperature unevenness occurs during cooling, even if the second shape correction device 6 improves the flatness at that time, the flatness collapses due to thermal strain in the subsequent cooling process. It cannot be said that a steel plate with good flatness was produced. On the other hand, by increasing the straightening ability of the first shape straightening device 3, the steepness generated by rolling the steel sheet can be suppressed to 0.2% or less, and the subsequent cooling can be performed uniformly. Since there is no temperature unevenness, the effect of correction by the second shape correction device 6 is directly applied to the shape after cooling. In a steel plate with severe rolling conditions such as an ultra-high strength steel plate, the steepness generated by rolling becomes large, and it is necessary that the first shape correction device 3 has a large plate thickness correction capability. By suppressing the steepness to 0.2% or less by the straightening device 3, the steepness of the steel plate after cooling is much smaller than that after rolling because the steel plate is uniformly cooled, and the plate of the second shape straightening device 6 Even if the thickness correction capability is lower than the plate thickness correction capability of the first shape correction device 3, the shape correction is possible. That is, the plate thickness correction capability of the second shape correction device 6 can be set lower than the plate thickness correction capability of the first shape correction device 3, and the cost can be reduced.

  The steepness referred to here has the definition shown in FIG.

  Further, in a steel plate having a thickness exceeding 20 mm, a warp called “nasal rise” may occur at the longitudinal end of the steel plate. Therefore, the warp is corrected immediately before the first shape correcting device 3. It is preferable to provide a warp correction device 2 having a function of By providing the warp correction device 2, the first shape correction device 3 can be protected and the nose up of the thick steel plate or the like can be corrected to some extent, but in order to completely correct the nose up, the shape correction Need to go through the device. Therefore, even if it is a case where the curvature correction apparatus 2 is provided, the 1st shape correction apparatus 3 is essential.

  The warp correction device 2 may be anything as long as it can correct the warp, such as a knock-down device or an up-and-down lift type described in the cited document 2, and is not particular about the type.

(3) Cooling device In the production line 100 of the steel plate 10 of the present invention, the cooling device 4 to be used may be anything as long as it can cool the steel plate, such as an accelerated cooling device generally used in thick plate manufacturing, I am not particular about the format.

  On the other hand, in order to reduce the flatness of the steel sheet after cooling, it is necessary from experience to suppress temperature unevenness in the cooled steel sheet to 30 ° C. or less. In addition, in order to suppress the temperature nonuniformity in a steel plate to 30 degrees C or less by cooling by the said cooling device 4, as above-mentioned, it is desirable to make the steepness of the steel plate before cooling into 0.2% or less.

  Further, when the heating device 5 is installed between the cooling device 4 and a second shape correcting device 6 described later, even if a flatness failure occurs in the steel sheet after cooling by the cooling device 4, the heating device By increasing the temperature of the steel sheet by 5, the steel sheet is easily corrected by the second shape correcting device 6. In this way, it is possible to omit steps such as flatness correction and press correction during cold working. Therefore, it is preferable to install the heating device 5 between the cooling device 4 and the second shape correcting device 6.

  Note that the heating method of the heating device 5 may be any method such as induction heating, direct current heating, direct or indirect heating with a gas burner, but in order to eliminate temperature unevenness in the steel sheet, induction heating or direct current heating device It is desirable to install.

(4) Second shape straightening device In the production line 100 of the steel sheet 10 of the present invention, the second shape straightening device 6 used is not particularly limited, and is normally incorporated into a rolling facility and used. The shape correction device can be used without limitation.

2. Method for Manufacturing Steel Sheet In the method for manufacturing steel sheet 10 of the present invention, after completion of rolling by the hot rolling mill 1, the shape is corrected by the first shape correction device 3, and then the steel plate is cooled by the cooling device 4. After cooling by, a steel plate with excellent flatness is obtained. This is a characteristic obtained from the manufacturing method of the steel plate 10 according to the present invention in which all the steel plates to be cooled are corrected by the first shape correction device 3 and then cooled. It becomes possible to reduce temperature unevenness after cooling.

  Further, by using the warp correction device 2 provided immediately before the first shape correction device 3 and the repeated bending correction function at the same time, it is possible to more completely correct flatness defects such as warpage generated in the thick plate. Further, temperature unevenness after cooling of the steel sheet is reduced, and further improvement in flatness can be expected.

  In addition, although the cooling device 4 used with the manufacturing method of the steel plate 10 of this invention may be a general on-line accelerated cooling device, the cooling device 4 which this invention makes object the cooling rate of 650 degreeC-550 degreeC. A range of 5 ° C./s or more at the center of a 20 mm plate thickness is preferable.

  Examples of the present invention will be described below. In each example, the mechanical test value was calculated by numerical calculation using various numerical values such as the roll pitch of the shape correction device and the cooling start temperature. The technical scope of the present invention is not limited to these examples.

  FIG. 3 shows a thick plate production line 200 provided with the cooling device 4 and the shape correction devices 3 and 6 together. In FIG. 3, 1 is a hot rolling mill, 3 is a first shape straightening device, 4 is an accelerated cooling device, 5 is a heating device, and 6 is a second shape straightening device. It is arranged in this order toward the side. In FIG. 3, the shape correction devices 3 and 6 are general roller levelers as online shape correction devices, but the shape correction devices 3 and 6 are not limited to roller levelers.

Table 1 shows the specifications of the first shape correction device 3 and the second shape correction device 6.

The specifications of the cooling device 4 are shown in Table 2, and the specifications of the heating device 5 are shown in Table 3, respectively.

ここで、
Ｍ_ｉ：各ロールの曲げモーメント
Ｗ：板幅（ｍｍ）
σ_ｙ：２次元降伏応力（Ｎ／ｍｍ^２）
ｔ：板厚（ｍｍ）
η_ｉ：各ロールでの塑性変形率（無次元）
ｉ：ロールの番号（入り側から１，２・・・ｎ）
である。ただし、Ｍ_ｉにおいて、両端のロールは単なる支持ロールのため、Ｍ_１＝Ｍ_ｎ＝０とする。また、上述の２次元降伏応力の値は、単軸降伏応力の値の１．１５倍とした。
さらに、η_ｉは次式で与えられる。
η_ｉ＝１−２×σ_ｙ×（Ｌ／２）^２／（Ｋ×ｔ×９．８×Ｅ×δ_ｉ） （式２）
ここで、
Ｌ：ロールピッチ（ｍｍ）
Ｋ：補正係数
Ｅ：ヤング率（Ｎ／ｍｍ^２）
δ_ｉ：各ロールの圧下量（ｍｍ）
であり、補正係数Ｋの値は、日本塑性加工学会編「矯正加工」（コロナ社）（２００２年１０月３０日 初版第４刷発行）の第５６頁〜第５７頁に示されているように、ｉ＝３〜ｎ−２の時はＫ＝６、ｉ＝２，ｎ−１の時はＫ＝４．８とした。
ここで、η_ｉ＜０の時は、弾性変形とみなし、

とした。ただし、
ρ_ｉ＝（Ｅ×ｔ）／（２×σ_ｙ）
である。また、ｉ＝２〜ｎ−１において
Ｆ_ｉ＝（Ｍ_ｉ−１＋２Ｍ_ｉ＋Ｍ_ｉ＋１）／Ｌ （式３）
であり、これと
Ｆ_１＝（Ｆ_２×Ｌ／２−Ｍ_３）／Ｌ
Ｆ_ｎ＝（Ｍ_ｎ−２−Ｆ_ｎ−１×Ｌ／２）／Ｌ
とから、ロールのトータル反力Ｆは

より算出される。
ここに、Ｆ_ｉは各ロールの反力である。
なお、上記の式は、材料力学の連続はりの理論式で証明されている。 In addition, the following formula | equation was used in order to obtain | require the maximum plate thickness which can be corrected from the reaction force of a shape correction apparatus.
When the plastic deformation rate at the i-th roll straightening device and eta _i, between the bending moment Mi and eta _i for each role, there is a relation as shown in the following equation (1).

here,
M _i : Bending moment of each roll W: Plate width (mm)
σ _y : two-dimensional yield stress (N / mm ² )
t: Plate thickness (mm)
η _i : Plastic deformation rate in each roll (dimensionless)
i: Roll number (1, 2, ... n from the entry side)
It is. However, in M _i , since the rolls at both ends are simply support rolls, M ₁ = M _n = 0. Further, the value of the above-described two-dimensional yield stress was 1.15 times the value of the uniaxial yield stress.
Furthermore, η _i is given by:
η _i = 1-2 × σ _y × (L / 2) ² /(K×t×9.8×E×δ _i ) (Formula 2)
here,
L: Roll pitch (mm)
K: Correction coefficient E: Young's modulus (N / mm ² )
δ _i : Rolling amount of each roll (mm)
The value of the correction coefficient K is as shown on pages 56 to 57 of “Correction” (Corona Co., Ltd.) edited by the Japan Society for Technology of Plasticity (October 30, 2002, 4th edition issued). In addition, when i = 3 to n−2, K = 6, and when i = 2 and n−1, K = 4.8.
Here, when η _i <0, it is regarded as elastic deformation,

It was. However,
ρ _i = (E × t) / (2 × σ _y )
It is. Further, when i = 2 to n−1, F _i = (M _i−1 + 2M _i + M _{i + 1} ) / L (Expression 3)
And this and F ₁ = (F ₂ × L / 2−M ₃ ) / L
F _n = (M _n−2 −F _n−1 × L / 2) / L
From the above, the total reaction force F of the roll is

It is calculated from.
Here, F _i is the reaction force of each roll.
The above formula is proved by a theoretical formula of continuous beams in material mechanics.

また、鋼板の板幅としては、ラインを通る最大寸法の４６００ｍｍを仮定し、計算を実行した。以下に、具体的な計算方法を記述する。 The steel plate in the calculation of this example is assumed to be JIS SM490A steel, which is a general TMCP high-strength steel, and the maximum straightened plate thickness of the steel plate is calculated using the above formulas (Equation 1) to (Equation 3). Calculated. Furthermore, for the temperature, uniaxial yield stress, and Young's modulus of SM490A steel, the values shown in FIGS. 12 and 13 shown on page 60 of Nippon Steel Technical Report No. 348 (1993) were used. Table 4 shows the steel plate temperature, yield stress, and Young's modulus values used in executing the calculation in this example. Note that the Young's modulus is less dependent on components in the case of low alloy steel, so API X-100 described later also uses this value.

In addition, the plate width of the steel plate was calculated assuming a maximum dimension of 4600 mm passing through the line. The specific calculation method is described below.

First, the plastic deformation rate of the _third roll is η ₃ = 0.8, and the value of δ ₃ is calculated by substituting this value of η ₃ into (Equation 2). In addition to assuming δ ₁ = δ ₂ and assuming that the plate does not warp on the roll exit side, assume that δ _n−1 = δ _n = 0,
δ ₂ = (n−2) / (n−3) × δ ₃ ,
In addition, when i = 4 to n−1,
δ _i = δ ₂ − (i−2) / (n−3) × δ ₂
Assuming that, the rolling reduction amount δ _i of each roll is calculated.
By substituting the value of δ _i calculated in this way into (Equation 2), η _i is calculated, and then by substituting the calculated value of η _i into (Equation 1), the bending moment of each roll is calculated. Calculate M _i . By substituting the value of the obtained bending moment M _i into (Equation 3), the reaction force F _i of each roll is calculated, and by adding all the F _i of i = 1 to n, the total of the rolls is calculated. The reaction force F is calculated.

  Here, in (Equation 1), the plate width, the two-dimensional yield stress, the longitudinal elastic modulus, and the roll pitch are fixed, and only the plate thickness value is changed to obtain the maximum value of the reaction force. The plate thickness is defined as the maximum correctable plate thickness.

  The same method as the above calculation method is introduced in detail in “Development of Shear Line for Thin Steel Plates with a New Combination Leveler” on Iron and Steel, Vol. 74, No. 11, pp. 77-84. .

  Further, as a temperature setting condition at the time of calculation, the first shape correction device 3 assumes a cooling start temperature of 650 ° C. under the strictest condition, and the second shape correction device 6 has a temperature setting after cooling. In consideration of the case of direct quenching, the calculation was performed assuming 100 ° C.

  When the calculation was performed according to such a procedure, in the first shape correction device of the invention example shown in Table 1, the maximum correctable plate thickness was 53.9 mm, and in the first shape correction device of the comparative example shown in Table 1, The maximum correctable plate thickness was 27.4 mm. Further, the maximum correctable plate thickness in the second shape correcting device shown in Table 1 was 34.9 mm. Therefore, in the invention example shown in Table 1, the thickness correction capability of the first shape correction device is larger than the plate thickness correction capability of the second shape correction device, and the maximum correction of the first shape correction device is possible. Since the plate thickness is 54.2 mm, it was found that a steel plate with good flatness can be manufactured even if the plate thickness is more than 40 mm.

  On the other hand, in the comparative example shown in Table 1, since the maximum correctable plate thickness of the shape correcting device is less than 30 mm, a steel plate with good flatness can be manufactured if the plate thickness is less than 30 mm. However, even if the shape of a thick steel plate with a thickness exceeding 30 mm is corrected with the first shape correction device, there is a high possibility that a flat defect will occur, so it may not necessarily be suitable as a production line for thick steel plates. I understood.

ここで、圧延したままの鋼板における急峻度（表５においては、「圧延まま急峻度」と記述する。）の値としては、通常圧延材（ＳＭ４９０Ａクラス）のうちで最大の急峻度の値を用い、形状矯正装置による急峻度変化の計算は、理論式に経験値を入れた独自の簡易式を用いた。なお、ここで用いた独自の簡易式は、
出側急峻度／入側急峻度＝（（１−塑性変形率）／１．５）^１／２
である。 In the production line 200 shown in FIG. 3, when the total number of steel plates to be cooled is straightened using the first straightening device 1 (hereinafter, in the description relating to the second embodiment, this embodiment is referred to as “present invention”). In the description regarding Example 2, this example is referred to as “Comparative Example”. ")" Was calculated by numerical calculation, and the results were compared. Table 5 shows the calculation results.

Here, as the value of the steepness of the steel sheet as rolled (described as “steepness as rolled” in Table 5), the value of the maximum steepness of the normal rolled material (SM490A class) is used. The calculation of the steepness change by the shape correction device used was an original simple formula with an empirical value in the theoretical formula. In addition, the original simple formula used here is
Outgoing steepness / incoming steepness = ((1−plastic deformation rate) /1.5) ^1/2
It is.

  As is apparent from Table 5, in the present invention example, even with a steel plate having a thickness of 40 mm, the steepness of the steel plate can be suppressed to less than 0.2% by the first shape correction device 1. there were. Therefore, according to the example of the present invention, even when the thickness of the steel sheet exceeds 30 mm, the steepness of the steel sheet can be suppressed to less than 0.2%, so that the steel sheet is uniformly cooled by the cooling device 4. Is possible. On the other hand, in the comparative example, regarding the steel plate having a thickness of less than 30 mm, since the first shape correction device 1 is passed in the same manner as in the example of the present invention, there is no difference in the steepness. However, when the plate thickness became 30 mm or more and the first shape correction device 1 could not be passed, the steepness of the steel plate in the comparative example suddenly decreased. Therefore, in this comparative example, it was not possible to correct the flatness so that the steel plate could be uniformly cooled by the cooling device 4.

  According to the present embodiment, the necessity of correcting the shape of all the steel plates to be cooled by the first shape correction device 1 before cooling the steel plate using the cooling device 4 was confirmed.

  In the production line 200 shown in FIG. 3, the effect of the heating device 5 was confirmed by numerical calculation. Specifically, the steel plate cooled by the cooling device 4 and having a steepness of more than 0.2% as a calculation target, the result when the steel plate is heated by the heating device 5, and the case where the steel plate is not heated The results were compared. The calculation conditions in this example are shown below.

As the material of the steel plate , numerical calculation was performed assuming API X-100 class which is a steel material for ultra-high strength line pipe. Steel sheet temperature 490 N / mm ² yield stress at 300 ° C., the steel sheet temperature is assumed to yield stress at 100 ° C. and 686 N / mm ^2, as the value of the Young's modulus of the steel sheet, were used values in Table 4. The plate thickness of the steel plate was assumed to be 22 mm and the plate width was 4000 mm. Further, when the steel sheet was heated by the heating device 5, the temperature was raised from 100 ° C. to 300 ° C. in one pass by induction heating. When the steel plate is heated by the heating device 5, the steel plate corrected by the second shape straightening device 6 after the heating is used as a comparison object. When the steel plate is not heated, the second shape straightening device 6 is not heated. The corrected steel plate was used as a comparison target.

  According to this calculation, when the steel sheet was not heated, the yield stress and Young's modulus of the steel sheet were both high, and the second shape straightening device 6 exceeded the load, so the plastic deformation rate of the third roll The steel sheet could not be corrected using the second shape correction device 6 having a value of 0.8. On the other hand, when the steel plate is heated by the heating device 5 until the steel plate temperature becomes 300 ° C., the yield stress of the steel plate, the Young's modulus value is low compared to the value when the steel plate is not heated, The steel sheet was able to be corrected using the second shape correction device 6 in which the plastic deformation rate of the third roll was 0.8. Therefore, according to the present example, it was confirmed that it is effective to provide the heating device 5 between the cooling device 4 and the second shape correcting device 6 when manufacturing a high-strength steel sheet.

In the production line 200 shown in FIG. 3, numerical calculation was performed using an ultra-high-strength steel plate (corresponding to API X-100) for a line pipe. It was assumed that the yield stress at a steel plate temperature of 650 ° C. was 392 N / mm ² , the yield stress at a steel plate temperature of 100 ° C. was 686 N / mm ^2, and the plate thickness and plate width of the steel plate were 22 mm and 4000 mm, respectively. Here, the temperature setting of 650 ° C. assumes the steel plate temperature when entering the first shape correction device 1, and the temperature setting of 100 ° C. indicates the steel plate temperature when entering the second shape correction device 6. Assumed.

  Calculation in the case where the steel plate temperature is 100 ° C. in the present example is the same as that in the case where the steel plate that is not heated in Example 3 is set in the second shape correction device 6. Therefore, also in the present embodiment, the second shape straightening device 6 is overloaded, so that the steel plate could not be straightened. On the other hand, when the steel plate temperature is 650 ° C., the yield stress and Young's modulus of the steel plate both decrease, and the plate thickness correction capability of the first shape correction device 1 is the plate thickness correction of the second shape correction device 6. Since the plate thickness correction capability was greater than the capability, the steel plate could be corrected with the first shape correction device 1. That is, according to the production line of the steel sheet of the present invention, it was confirmed by this example that even an ultra-high tensile steel sheet equivalent to API X-100 can be produced.

  While the present invention has been described in connection with embodiments that are presently the most practical and preferred, the present invention is not limited to the embodiments disclosed herein. However, the present invention can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and a steel sheet production line and a steel sheet production method that involve such changes are also included in the technical scope of the present invention. It should be understood as encompassed by the scope.

It is a figure which shows an example of the manufacturing line of the steel plate of this invention. It is a figure which shows the calculation method of the steepness of a steel plate. It is a figure which shows the example of the production line of the thick board in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hot rolling mill 2 Warpage correction apparatus 3 1st shape correction apparatus 4 Cooling apparatus 5 Heating apparatus 6 2nd shape correction apparatus 10 Steel plate 100, 200 Production line of steel plate

Claims (6)

The first shape correction is performed in a steel sheet production line in which a hot rolling mill, a first shape correction device, a cooling device, and a second shape correction device are arranged in this order and have a function of cooling and straightening a steel plate online. A steel sheet production line, wherein the thickness correction capability of the apparatus is greater than the thickness correction capability of the second shape correction apparatus. The steel sheet production line according to claim 1, wherein the steepness of the steel sheet is suppressed to 0.2% or less at the end of the shape correction of the steel sheet by the first shape correcting device. The steel sheet production line according to claim 1 or 2, wherein the first shape correction device is provided with a warp correction function. The steel sheet production line according to any one of claims 1 to 3, wherein a heating device is installed between the cooling device and the second shape correction device. The steel sheet production line according to any one of claims 1 to 4, wherein the steel sheet is manufactured by controlling a cooling condition and a shape correction condition of the steel sheet online, and after rolling by the hot rolling mill. A method for producing a steel sheet, comprising: cooling all steel sheets to be cooled with the cooling apparatus after correcting the shape with the first shape correcting apparatus. 6. The method for manufacturing a steel sheet according to claim 5, wherein both the warp correction function and the repeated bending correction function of the first shape correction apparatus are used simultaneously.

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