JP4085541B2 - Sheet warpage control method in hot rolling. - Google Patents

Description

【００４１】
次に、ステップＳ７にて決定した板反り制御条件を適用して板反り制御圧延を実施する（ステップＳ８）。
そして、圧延が完了したか否かを判断し（ステップＳ９）、圧延が完了していない場合には、ステップＳ２〜Ｓ９を繰り返し、圧延が完了している場合には、圧延を終了する。
【００４２】
次に、ステップＳ７におけるパスライン位置制御圧延条件および／または上下ワークロール周速差制御圧延条件の決定方法の一実施態様について詳述する。なお、上下ワークロール周速差制御圧延よりも、パスライン位置制御圧延の方が精度良く板反りを制御することが可能であることから、本実施態様では最も有効な板反り制御方法として、パスライン位置制御圧延と上下ワークロール周速差制御圧延を併用する板反り制御方法であって、パスライン位置制御圧延を優先して適用する板反り制御方法について述べる。
【００４３】
図２は、ステップＳ７における板反り制御圧延条件の決定方法を示すフローチャートである。
【００４４】
同図に示すように、先ず、κinとκaim との差に基づいて、圧延パス出側における板反り量がκaim となるように、板反り制御モデルを用いて圧延パスにおいて付与すべき板反り量κ（以下、κともいう）を算出する（ステップＳ７１）。
【００４５】
次に、前記κとパスライン位置制御圧延で制御可能な板反り量の上限κp とを比較することにより、パスライン位置制御圧延で修正可能な板反り量か否かを判断する（ステップＳ７２）。ここで、κp は、圧下量をΔｈ（以下、Δｈともいう）とすると、次式のようにΔｈとｈとの関数ｇで与えられる
【００４６】
【数２】

【００４７】
ここで、Δｈ＝Ｈ−ｈである。なお、κp は圧延機により異なるので、使用する圧延機毎に予め求めておく。
【００４８】
ステップＳ７２において、パスライン位置制御圧延で修正可能（κ≦κp ）であると判断した場合には、パスライン位置制御圧延のみを行うべくδを決定する（ステップＳ７３）。ここで、κとδは下記（１）式の関係にあることから、ステップＳ７１で求めたκよりδを決定する。
【００４９】
【数３】

【００５０】
ここで、ｂは係数であり、δが正であるか負であるかによって異なる。
【００５１】
ステップＳ７３にてδを決定した場合には、パスライン位置制御圧延のみを行うので、ΔＶをΔＶ＝０とする（ステップＳ７４）。
【００５２】
ステップＳ７２において、パスライン制御で修正不可能（κ＞κp ）であると判断した場合には、形状比χが０．８＜χ＜１．２であるか否かを判断する（ステップＳ７５）。ここで、形状比χ（以下、χともいう）とは、接触弧長Ｌd と平均板厚ｈm との比（Ｌd ／ｈm ）であり、接触弧長Ｌd は、ロール半径をＲとすると次式より与えられ、
【００５３】
【数４】

【００５４】
また、平均板厚ｈm とはＨとｈとの平均値であり、次式で与えられることから、
【００５５】
【数５】

【００５６】
形状比χは、次式により与えられる。
【００５７】
【数６】

【００５８】
ステップＳ７５において、χが０．８＜χ＜１．２であると判断した場合には、パスライン位置制御圧延のみを行うべく、圧延パス出側の板反り量をκaim に可及的に近づけるようにδを決定する（ステップＳ７６）。χが０．８＜χ＜１．２である領域においては、上下ワークロール周速差制御圧延による板反り量の制御が困難であるからである。
【００５９】
ステップＳ７６にてδを決定した場合には、パスライン位置制御圧延のみを行うので、ΔＶをΔＶ＝０とする（ステップＳ７４）。
【００６０】
ステップＳ７５において、χが０．８＜χ＜１．２でないと判断した場合には、パスライン位置制御圧延と上下ワークロール周速差制御圧延とを併用した圧延を行うべく、δとΔＶとを決定する（ステップＳ７７）。
【００６１】
ここで、上下ワークロール周速差制御圧延におけるκとΔＶの関係式は、χの値によって、以下の（２）式又は（３）式によって与えられる。
０＜χ＜０．８の場合：
【００６２】
【数７】

１．２＜χの場合：
【数８】

【００６３】
ここで、ａ₁ 〜ａ₅ は定数であり、また、sign（ΔＶ）は符号の付け替えを行う関数であり、
ΔＶ＜０の場合：sign（ΔＶ）＝−１
ΔＶ≧０の場合：sign（ΔＶ）＝＋１
である。
【００６４】
したがって、κinおよびκaim に基づいて、圧延パス出側の板反り量がκaim となるように、あるいは、κaimに可及的に近づくように、（１）〜（３）式により、δおよびΔＶを決定する。
【００６５】
以上説明した手順に従って板反り制御条件を決定し、板反り制御圧延を実施することにより、腰折れ痕の発生および板反り発生を抑制することができる。
【００６６】
なお、本実施態様においては、パスライン位置制御圧延と上下ワークロール周速差制御圧延を併用する方法について述べたが、本発明はこれに限定されるものでなく、パスライン位置制御圧延または上下ワークロール周速差制御圧延の一方のみを適用してもよい。また、上下ワークロール周速差制御圧延よりもパスライン位置制御圧延を優先して適用する実施態様について説明したが、両者を常時併用しても構わないし、適宜優先順位を変更しても構わない。さらに、δおよびΔＶの決定方法には公知の各種方法を適用しても構わない。
【００６７】
また、第一圧延パス入側における被圧延材の上下面の摩擦係数を予測することは難しく、第一圧延パスにおいて板反り制御を行うことが実際には困難であるので、第一圧延パスにおいては軽度の上反りが発生するように上下面に温度差を付与し、第一圧延パス出側のκout の実績値に基づいて、第二圧延パス以降に本実施態様で示した板反り制御方法を用いてもよい。
【００６８】
【実施例】
本発明の効果を確認するため、ワークロール径１０１０ｍｍ、バックアップロール径２０２０ｍｍの４段熱間圧延機を用いて圧延を行った。試験材は、板厚１２０ｍｍ、板幅３０００ｍｍの低炭素鋼を用い、第一圧延パスにてκ＝１．８×１０^-4ｍｍ^-1とした試験材を圧延温度９８０℃の条件下で板厚２１．５ｍｍまでリバース圧延を行った。また、製品の表面性状について目視検査を行い腰折れ痕の有無を調査した。
【００６９】
本発明例として、第１〜第７圧延パスでκaim ＝０．５×１０^-4ｍｍ^-1、第８圧延パスでκaim ＝０とし、図２に示す手順により板反り制御条件を決定して圧延を行った。
【００７０】
また、比較例として、第１圧延パスにおいては板反り制御を行わずに、第２圧延パス〜第８圧延パスでκaim ＝０として板反り制御圧延を行った場合（比較例１）と、板反り制御を全く行わなかった場合（比較例２）について、板反り制御条件以外の条件を前記本発明例と同一にして圧延を実施した。
【００７１】
表１〜３に、パススケジュール、形状比χ、板反り制御条件（δ、ΔＶ）、各圧延パス出側において測定した板反り量（κ）、腰折れ痕の発生状況を示す。表１は本発明例、表２は比較例１、表３は比較例２についてのものである。なお、表１〜３において、板反り量について、上反りを正、下反りを負として表している。
【００７２】
【表１】

【００７３】
【表２】

【００７４】
【表３】

【００７５】
表１に示すように本発明例では、圧延後の板反り量が０．１×１０^-4ｍｍ^-1であり、板反りの発生を効果的に抑制できており良好であった。また、出側板厚が２０〜６０ｍｍとなる圧延パスにおいて下反りが発生しなかったため、目視検査において腰折れ痕が観察されず、表面性状も良好であった。
【００７６】
表２に示す比較例１では、圧延後の板反り量は０．５×１０^-4ｍｍ^-1と比較的良好であったが、出側板厚が２０〜６０ｍｍとなる第５〜７圧延パスにおいて下反りが発生したため、腰折れ痕が発生しており表面性状が不良であった。
【００７７】
また、表３に示す比較例２では、圧延後の板反り量も２．５×１０^-4ｍｍ^-1と大きく不良であり、また、出側板厚が２０〜６０ｍｍとなる第６および第７圧延パスおいて下反りが発生したため、腰折れ痕が発生し表面性状も不良であった。
【００７８】
【発明の効果】
本発明により、腰折れ痕および板反りの発生を効果的に抑制できるので、表面性状の優れた製品を得ることができる。
【図面の簡単な説明】
【図１】本発明の板反り制御方法を決定する手順を示すフローチャートである。
【図２】本発明の板反り制御条件を決定する手順の一実施態様を示すフローチャートである。
【図３】腰折れ痕の発生機構の概要を示す概要図であり、（a）は下反りが発生した被圧延材がテーブルローラ上を搬送される状態を示す側面図であり、（ｂ）は被圧延材がテーブルローラに衝突することにより座屈が生じた状態を示す側面図であり、（ｃ）は前記被圧延材の製品における腰折れ痕の形態を示す平面図である。
【符号の説明】
１：被圧延材 ２：テーブルローラ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plate warpage control method in hot rolling, and more particularly to a plate warpage control method that suppresses the occurrence of waist break marks.
[0002]
[Prior art]
Up and down warpage (hereinafter referred to as plate warpage) of the steel sheet tip that occurs in thick plate rolling and hot strip rough rolling is equipment troubles such as breakage of the stripper guide, surface defects such as waist fold marks caused by the occurrence of downward warping, controlled rolling This causes various adverse effects such as quality deterioration due to uneven cooling in the material.
[0003]
The warpage that causes various operational problems is complicated by many factors such as the temperature difference between the upper and lower surfaces of the steel sheet, the friction coefficient difference, the peripheral speed difference between the upper and lower work rolls, and the pickup amount of the lower work roll. However, it has been difficult to prevent it, and it has not been completely prevented even though many researches have been conducted.
[0004]
As a method for preventing sheet warpage, the present inventors have disclosed a sheet warpage prevention method for controlling sheet warpage in accordance with the shape ratio during rolling in Japanese Patent Application Laid-Open No. 11-47812. In the sheet warpage prevention method, pass line position control rolling is applied in an area where sheet warpage control becomes unstable in upper and lower work roll circumferential speed difference control rolling, and pass line position control rolling and / or upper and lower work is performed in other areas. This is a sheet warpage prevention method for preventing the occurrence of sheet warpage by applying roll peripheral speed difference controlled rolling. The plate warpage prevention method is very useful because it can effectively prevent and reduce plate warpage.
[0005]
[Problems to be solved by the invention]
However, by applying the plate warpage prevention method, the degree of plate warpage can be effectively reduced, but the measurement error of the plate warpage amount, the vertical work roll circumferential speed difference and the pass line based on the plate warpage amount. Unpredictable uncertain factors such as errors in the control model used to determine the position control conditions and the difference in friction coefficient between the upper and lower work rolls and the material to be rolled remain, so it is possible to completely prevent sheet warpage. It is impossible, and it is the actual situation that slight warpage occurs in each rolling pass.
[0006]
Of the above-mentioned adverse effects caused by the board warp, even a slight board warp is a problem of a linear surface wrinkle called a waist fold mark.
[0007]
FIG. 3 is a schematic view showing an outline of a mechanism for generating a waist fold mark, and FIG. 3 (a) is a side view showing a state in which a material to be rolled with a downward warp is conveyed on a table roller. (B) is a side view showing a state in which buckling has occurred due to the material to be rolled colliding with the table roller, and FIG. 3 (c) is a plane showing the form of waist fold marks in the product of the material to be rolled. FIG. In FIG. 3, the code | symbol 1 shows a to-be-rolled material and the code | symbol 2 shows a table roller.
[0008]
As shown in FIG. 3 (a), when the material 1 to be rolled having been warped is conveyed on the table roller 2, the tip of the material to be rolled collides with the table roller 2, and shown in FIG. 3 (b). As described above, buckling locally occurs in the vicinity of the end point of the downward warped portion, and a linear waist fold mark as shown in FIG.
[0009]
Once buckling as shown in FIG. 3 (b) has occurred, if the amount of reduction after buckling occurs is relatively large, rolling may be repeated after the occurrence of buckling, but the degree of waist fold marks may be reduced. When the amount of rolling reduction in the rolling pass after the occurrence of buckling is relatively small, a significant crease mark remains, resulting in a large yield reduction.
[0010]
Thus, an object of the present invention is to provide a plate warpage control method that suppresses the occurrence of waist fold marks and the occurrence of plate warpage.
[0011]
[Means for Solving the Problems]
The inventors of the present invention have found that hip folding occurs in a specific plate thickness region by conducting a detailed investigation on hip folding marks of hot-rolled products. That is, in the rolling pass in which the plate thickness of the material to be rolled is 20 to 60 mm, when the warp occurs at the tip of the material to be rolled, waist breakage occurs.
[0012]
And it discovered that generation | occurrence | production of a waist fold mark can be suppressed by performing board curvature control so that it may become a slight upward curvature in the intermediate | middle rolling pass from which the plate | board thickness of a material to be rolled will be 20-60 mm. Here, the plate warpage control can be performed by controlling the rolling conditions, and examples of the rolling conditions include known conditions such as a pass line position and an upper and lower work roll circumferential speed difference.
[0013]
In addition, by setting the upward warpage in the intermediate rolling pass to 0.5 × 10 ^{−4 to} 2.0 × 10 ⁻⁴ mm ⁻¹ in terms of the curvature of curvature, equipment damage such as a stripper guide can be prevented, and in the final rolling pass It has been found that it is easy to correct the plate warp by setting the target warp curvature to zero.
[0014]
Here, the intermediate rolling pass means a rolling pass excluding the final rolling pass. The reason for excluding the final rolling pass is that, in the final rolling pass, the target warp amount is normally set to zero.
[0015]
The present invention has been completed based on the above findings, and the gist thereof is in the following (1) .
[0016]
(1) In a rolling pass in which at least the exit side plate thickness of the material to be rolled is 20 mm or more and 60 mm or less, the target value of the curvature of the tip of the material to be rolled is set to 0.5 × 10 ⁻⁴ mm ^{−1 to} 2.0 × 10. A sheet warpage control method in hot rolling, characterized in that the rolling condition is controlled to be set to ^-4 mm ^-1 or less so that the tip of the material to be rolled is warped.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0019]
In the present invention, sheet warpage control is performed so that the warp is at least in the intermediate rolling pass where the sheet thickness is 20 mm or more and 60 mm or less.
[0020]
The reason why the lower limit of the thickness range of the warpage control is 20 mm is that when the thickness is less than 20 mm, the rigidity of the material to be rolled is low and local buckling hardly occurs and deformation occurs in a relatively wide range. This is because it is difficult to generate a noticeable waist break mark. Therefore, there is no particular limitation on the sheet warpage control method in the intermediate rolling pass where the sheet thickness is less than 20 mm.
[0021]
However, in order to more reliably suppress the occurrence of hip fold marks, it is preferable to set the lower limit to 10 mm, and it is more preferable to perform plate warpage control so that the region where the plate thickness is less than 10 mm also warps. .
[0022]
Further, the upper limit of the plate thickness range for plate warpage control is set to 60 mm. When the plate thickness is more than 60 mm, the material to be rolled has high rigidity and is unlikely to buckle. Because. Therefore, there is no particular limitation on the plate warpage control method in the intermediate rolling pass in which the plate thickness exceeds 60 mm.
[0023]
However, the upper limit is preferably set to 70 mm in order to more reliably suppress the occurrence of hip fold marks, and when the warpage occurs in a thick plate region, the equipment breaks by colliding with the table roller or the like. Therefore, it is more preferable to perform the warpage control so that the region where the plate thickness exceeds 70 mm is also warped.
[0024]
In order to impart an upper warp on the first rolling pass entry side, it is desirable to impart a temperature difference to the upper and lower surfaces of the material to be rolled by descaling or the like. This is because it becomes easier to provide a temperature difference between the upper and lower surfaces as the thickness of the plate increases.
[0025]
In addition, in the case of warping in the intermediate rolling pass, in addition to the method of imparting a temperature difference to the upper and lower surfaces of the material to be rolled as described above, pass line position control rolling or upper and lower work roll circumferential speed difference control rolling Should be applied.
[0026]
Further, it is preferable to perform plate warpage control so that the amount of warpage is not less than 0.5 × 10 ⁻⁴ mm ^{−1 and not} more than 2.0 × 10 ⁻⁴ mm ^{−1 in} terms of curvature of curvature.
[0027]
If the amount of warpage exceeds 2.0 × 10 ⁻⁴ mm ⁻¹ , the material to be rolled may collide with equipment such as a stripper guide and the equipment may be damaged, and the amount of warpage in the final rolling pass may be reduced to 0. It is because it may be difficult to do. Further, when the amount of warpage is less than 0.5 × 10 ⁻⁴ mm ^−1, it is difficult to predict such as a measurement error of the amount of warpage of the sheet, an error of the sheet warpage control model, and a difference in friction coefficient between the upper and lower work rolls and the material to be rolled. This is because downward warping may occur due to uncertain factors.
[0028]
Hereinafter, the plate warpage control method of the present invention will be described in detail based on one embodiment.
[0029]
FIG. 1 is a flowchart showing an embodiment of a plate warpage control method of the present invention.
[0030]
As shown in the figure, first, from the rolling schedule determined from the base material plate thickness and the product plate thickness, the plate thickness H (unit: mm, hereinafter also referred to as H) on the entry side of each rolling pass and A plate thickness h (unit: mm, hereinafter also referred to as h) on the delivery side is obtained (step S1).
[0031]
Next, a sheet warpage amount κin (unit: mm ⁻¹ , hereinafter also referred to as κin) on the rolling pass entry side is calculated (step S2). κin is obtained by detecting the amount of warp at the tip of the material to be rolled and quantifying the warp curvature with a plate warp detector arranged in the hot rolling facility. Usually, in order to secure the time required for determining the sheet warpage control condition, the amount of sheet warpage κout (unit: mm ⁻¹ , hereinafter also referred to as κout) of the rolled material on the exit side of the immediately preceding rolling pass is detected. Estimated as the amount of sheet warp κin on the entry side of the rolling pass. Further, when descaling is performed in the rolling pass, it is preferable to correct κin based on the plate thickness, the rolling reduction, etc. in order to estimate κin with high accuracy.
[0032]
Next, it is determined whether or not the rolling pass is a final rolling pass (step S3).
[0033]
Wherein when rolling pass is the last rolling pass is aimed plate warpage Kappaaim in the rolling path outlet side (unit: mm ^-1, hereinafter also referred to as Kappaaim) to a 0 (step S4).
[0034]
If the rolling pass is not the final rolling pass, it is determined whether h is 20 ≦ h ≦ 60 (step S5).
[0035]
When h is 20 ≦ h ≦ 60, κaim is determined within the range of 0.5 × 10 ⁻⁴ ≦ κaim ≦ 2.0 × 10 ⁻⁴ (step S6). The determination of κaim within the range of 0.5 × 10 ⁻⁴ ≦ κaim ≦ 2.0 × 10 ⁻⁴ may be performed in consideration of the actual error between κaim and κout so as to aim at the lower limit within the range. .
[0036]
If h is not 20 ≦ h ≦ 60, κaim is set to κaim = 0 (step S4).
[0037]
Next, from κin and κaim, the passline position δ (hereinafter also referred to as δ) is applied when the passline position controlled rolling is applied, and the different speed ratio ΔV (when the upper and lower work roll peripheral speed difference controlled rolling is applied. Hereinafter, ΔV) is determined (step S7). A method for determining δ and ΔV will be described later.
[0038]
Here, the pass line position δ means that the lower surface of the material to be rolled is the top surface of the table roller on the entrance side of the rolling pass when the sheet thickness center planes on the entrance side and the exit side of the rolling pass are at the same level. The height position of the table roller is based on the height position of the table roller in a state where it is in contact with the table.
[0039]
Further, the different speed ratio ΔV (unit:%, hereinafter also referred to as ΔV) represents the ratio between the upper work roll peripheral speed V _u and the lower work roll peripheral speed V _{L as} shown by the following equation.
[0040]
[Expression 1]

[0041]
Next, sheet warpage control rolling is performed by applying the sheet warpage control conditions determined in step S7 (step S8).
Then, it is determined whether or not the rolling is completed (step S9). If the rolling is not completed, steps S2 to S9 are repeated, and if the rolling is completed, the rolling is finished.
[0042]
Next, an embodiment of a method for determining pass line position controlled rolling conditions and / or upper and lower work roll circumferential speed difference controlled rolling conditions in step S7 will be described in detail. Note that the pass line position control rolling can control the plate warp with higher accuracy than the vertical work roll circumferential speed difference control rolling. A sheet warpage control method using both line position controlled rolling and upper and lower work roll peripheral speed difference controlled rolling, and a sheet warpage controlling method preferentially applied to pass line position controlled rolling will be described.
[0043]
FIG. 2 is a flowchart showing a method for determining sheet warpage controlled rolling conditions in step S7.
[0044]
As shown in the figure, first, based on the difference between κin and κaim, the amount of warpage to be imparted in the rolling pass using the plate warpage control model so that the amount of warpage on the exit side of the rolling pass becomes κaim. κ (hereinafter also referred to as κ) is calculated (step S71).
[0045]
Next, by comparing the κ with the upper limit κp of the plate warp amount that can be controlled by the pass line position controlled rolling, it is determined whether or not the plate warp amount can be corrected by the pass line position controlled rolling (step S72). . Here, κp is given by a function g of Δh and h as shown in the following equation, where the amount of reduction is Δh (hereinafter also referred to as Δh).
[Expression 2]

[0047]
Here, Δh = H−h. Since κp varies depending on the rolling mill, it is determined in advance for each rolling mill to be used.
[0048]
If it is determined in step S72 that correction can be made by pass line position controlled rolling (κ ≦ κp), δ is determined to perform only pass line position controlled rolling (step S73). Here, since κ and δ are in the relationship of the following equation (1), δ is determined from κ obtained in step S71.
[0049]
[Equation 3]

[0050]
Here, b is a coefficient and differs depending on whether δ is positive or negative.
[0051]
When δ is determined in step S73, only pass line position controlled rolling is performed, so ΔV is set to ΔV = 0 (step S74).
[0052]
If it is determined in step S72 that the correction is not possible (κ> κp) by the pass line control, it is determined whether or not the shape ratio χ is 0.8 <χ <1.2 (step S75). . Here, the shape ratio χ (hereinafter also referred to as χ) is a ratio (Ld / hm) between the contact arc length Ld and the average plate thickness hm, and the contact arc length Ld is expressed by the following equation when the roll radius is R: Given more,
[0053]
[Expression 4]

[0054]
The average plate thickness hm is an average value of H and h, and is given by the following equation.
[0055]
[Equation 5]

[0056]
The shape ratio χ is given by the following equation.
[0057]
[Formula 6]

[0058]
If it is determined in step S75 that χ is 0.8 <χ <1.2, the amount of warpage on the rolling pass exit side is made as close as possible to κaim so as to perform only the pass line position control rolling. Is determined as follows (step S76). This is because in the region where χ is 0.8 <χ <1.2, it is difficult to control the amount of warp by the upper and lower work roll peripheral speed difference controlled rolling.
[0059]
When δ is determined in step S76, only pass line position control rolling is performed, so ΔV is set to ΔV = 0 (step S74).
[0060]
If it is determined in step S75 that χ is not 0.8 <χ <1.2, δ and ΔV are set to perform rolling using both pass line position control rolling and upper and lower work roll circumferential speed difference control rolling. Is determined (step S77).
[0061]
Here, the relational expression of κ and ΔV in the upper and lower work roll peripheral speed difference controlled rolling is given by the following expression (2) or (3) depending on the value of χ.
If 0 <χ <0.8:
[0062]
[Expression 7]

If 1.2 <χ:
[Equation 8]

[0063]
Here, a _{1 to} a ₅ are constants, and sign (ΔV) is a function for changing the sign,
When ΔV <0: sign (ΔV) = − 1
When ΔV ≧ 0: sign (ΔV) = + 1
It is.
[0064]
Therefore, on the basis of κin and κaim, δ and ΔV are expressed by the equations (1) to (3) so that the amount of warpage on the rolling pass exit side becomes κaim or as close as possible to κaim. decide.
[0065]
By determining the plate warpage control conditions in accordance with the procedure described above and performing the plate warpage controlled rolling, it is possible to suppress the occurrence of waist fold marks and the occurrence of plate warpage.
[0066]
In the present embodiment, the method of using pass line position control rolling and upper and lower work roll circumferential speed difference control rolling in combination has been described. However, the present invention is not limited to this, and pass line position control rolling or upper and lower work roll circumferential speed control rolling is used. Only one of the work roll peripheral speed difference controlled rolling may be applied. Moreover, although the embodiment which prioritizes and applies the pass line position control rolling over the upper and lower work roll circumferential speed difference control rolling has been described, both may be used together or the priority order may be changed as appropriate. . Furthermore, various known methods may be applied to the method for determining δ and ΔV.
[0067]
In addition, it is difficult to predict the friction coefficient of the upper and lower surfaces of the material to be rolled on the first rolling pass entry side, and it is actually difficult to control sheet warpage in the first rolling pass. Gives a temperature difference between the upper and lower surfaces so that slight warpage occurs, and based on the actual value of κout on the exit side of the first rolling pass, the plate warpage control method shown in this embodiment after the second rolling pass May be used.
[0068]
【Example】
In order to confirm the effect of the present invention, rolling was performed using a four-stage hot rolling mill having a work roll diameter of 1010 mm and a backup roll diameter of 2020 mm. The test material is a low carbon steel with a plate thickness of 120 mm and a plate width of 3000 mm, and the test material with κ = 1.8 × 10 ⁻⁴ mm ⁻¹ in the first rolling pass is subjected to a rolling temperature of 980 ° C. Reverse rolling was performed to a thickness of 21.5 mm. Moreover, the surface property of the product was visually inspected to examine the presence or absence of a waist fold mark.
[0069]
As an example of the present invention, κaim = 0.5 × 10 ⁻⁴ mm ⁻¹ in the first to seventh rolling passes, κaim = 0 in the eighth rolling pass, and plate warpage control conditions are determined by the procedure shown in FIG. Rolled.
[0070]
Further, as a comparative example, in the first rolling pass, the plate warpage control is not performed, and in the second rolling pass to the eighth rolling pass, the plate warpage control rolling is performed with κaim = 0 (Comparative Example 1), In the case where warpage control was not performed at all (Comparative Example 2), rolling was carried out under the same conditions as those of the present invention except for the plate warpage control conditions.
[0071]
Tables 1 to 3 show the pass schedule, shape ratio χ, plate warpage control conditions (δ, ΔV), the amount of plate warp (κ) measured on the rolling pass exit side, and the occurrence of waist break marks. Table 1 shows examples of the present invention, Table 2 shows Comparative Example 1, and Table 3 shows Comparative Example 2. In Tables 1 to 3, with respect to the amount of warp, the upper warp is represented as positive and the lower warp is represented as negative.
[0072]
[Table 1]

[0073]
[Table 2]

[0074]
[Table 3]

[0075]
As shown in Table 1, in the examples of the present invention, the amount of warpage after rolling was 0.1 × 10 ⁻⁴ mm ⁻¹ , and the occurrence of plate warpage could be effectively suppressed, which was good. In addition, since no downward warping occurred in the rolling pass where the exit side plate thickness was 20 to 60 mm, no waist fold marks were observed in the visual inspection, and the surface properties were good.
[0076]
In Comparative Example 1 shown in Table 2, the amount of warpage after rolling was relatively good at 0.5 × 10 ⁻⁴ mm ⁻¹ , but the fifth to seventh rolling passes where the exit side plate thickness was 20 to 60 mm. In this case, the lower surface warp occurred, and a waist break mark was generated and the surface property was poor.
[0077]
Further, in Comparative Example 2 shown in Table 3, the amount of warpage after rolling is as large as 2.5 × 10 ⁻⁴ mm ^−1, and the thickness of the outlet side plate is 20 to 60 mm. Since a downward warp occurred in the rolling pass, a waist break mark was generated and the surface properties were poor.
[0078]
【The invention's effect】
According to the present invention, it is possible to effectively suppress the occurrence of waist break marks and plate warpage, so that a product having excellent surface properties can be obtained.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure for determining a plate warpage control method of the present invention.
FIG. 2 is a flowchart showing an embodiment of a procedure for determining a plate warpage control condition of the present invention.
FIG. 3 is a schematic view showing an outline of a mechanism for generating a waist fold mark, (a) is a side view showing a state in which a material to be rolled with a downward warp is conveyed on a table roller, and (b) is a side view. It is a side view which shows the state which buckled has arisen because a to-be-rolled material collided with a table roller, (c) is a top view which shows the form of the waist crease mark in the product of the to-be-rolled material.
[Explanation of symbols]
1: Rolled material 2: Table roller

Claims (1)

At least in the intermediate rolling pass where the exit side plate thickness of the material to be rolled becomes 20 mm or more and 60 mm or less, the target value of the curvature of the tip of the material to be rolled is set to 0.5 × 10 ⁻⁴ mm ^{−1 to} 2.0 × 10. ^-4 mm ^-1 is set to below the plate warpage control method in hot rolling, characterized in that the material to be rolled tip controls the rolling conditions so that camber.

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