JP2023018813A - Torsion determination method of hot slab width reduction, hot slab width reduction method and manufacturing method of hot rolled steel sheet - Google Patents

Abstract

To provide a determination method of a hot slab width reduction which can determine whether it becomes a width reduction defective slab by torsion before performing width reduction.SOLUTION: A torsion determination method of a hot slab width reduction is given in which: when a width reducing device 12 performs the width reduction of a slab heated with a heating furnace by an edging rate γ(γ=ΔW/W0) that is the width reducing amount ΔW divided by the slab width W0 which is a width before reduction in a hot rolling line 30 where there is the width reducing device between the heating furnace 11 and a roughing mill 13, temperatures at the width end parts of both sides of the slab are acquired by, for example, numerical calculation or a temperature measuring device before the width reduction of the slab is performed by the width reducing device; temperature difference between the acquired temperatures at the width end parts of both sides of the slab is obtained as a width direction temperature deviation ΔT; and when a product by multiplying the width direction temperature deviation ΔT by the edging rate γ exceeds the constant value, torsion of the slab is determined to occur by the width reduction of the slab.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for determining whether or not twist occurs in a slab when the slab is width-reduced in a width reduction device of a hot rolling line that manufactures hot-rolled steel sheets, and uses this twist determination method. The present invention relates to a method for reducing the width of a hot slab and a method for manufacturing a hot-rolled steel sheet.

A hot rolling line for manufacturing hot-rolled steel sheets has a heating furnace, a rough rolling mill, and a finishing rolling mill, and rolls to a target thickness to manufacture hot-rolled steel sheets. In this hot rolling line, a width reduction device is installed between the heating furnace and the roughing mill to reduce the width of the slab. It is possible to adjust the board width. A hot-rolled steel sheet manufactured by hot rolling is wound into a coil shape, so the hot-rolled steel sheet manufactured in a hot-rolling line is also called a hot-rolled coil.

However, since the width of the slab is about 3 to 10 times as large as the thickness, the slab becomes plastically unstable under conditions where the amount of width reduction is large. That is, under conditions where the amount of width reduction is large, troubles such as buckling, bending, and twisting may occur in the slab, and these deformations cause troubles in the processes after the roughing mill and reduce the rolling efficiency.

Conventionally, there have been proposed methods for avoiding rolling troubles caused by such slab width reduction. For example, in Patent Document 1, a load during width reduction is detected, and when the reduction load exceeds a predetermined value, it is determined that there is an abnormality in the shape of the slab. A shape abnormality detection method has been proposed in which the left and right gaps between upper and lower pinch rolls are detected by rolls, and when the difference between the left and right gaps exceeds a predetermined value, it is determined that the slab is twisted.

Further, in Patent Document 2, in a hot rolling line in which a heating furnace, a width reduction device, and a rough rolling mill having a vertical roll mill are arranged, a slab is produced by using the width reduction device and the vertical roll mill together. width reduction to make the width of the slab after rolling in the roughing mill within the target range, the temperature deviation in the width direction of the slab is calculated immediately before extracting the slab from the heating furnace, and the temperature deviation in the width direction exceeds a predetermined threshold, a technique is disclosed for reducing the amount of width reduction by the width reduction device.

JP-A-11-179402 JP 2016-215247 A

However, the above prior art has the following problems.

That is, in the method of Patent Literature 1, twisting of the slab cannot be detected until the leading end of the slab reaches the delivery-side pinch roll of the width reduction device. Therefore, the width reduction is advanced to a certain position and then interrupted, resulting in a slab 1a having a defective width reduction as shown in FIG. Of the slabs 1a with defective width reduction, the slab thickness is increased in the portion where the width reduction is performed, and the thickness of the portion where the width reduction is not performed remains the original thickness. thickness changes.

Therefore, it is difficult to convey the slab 1a with the defective width reduction in the hot rolling line, and it is necessary to temporarily stop the hot rolling line and remove the slab 1a with the defective width reduction from the hot rolling line. As a result, the productivity of the hot rolling line is lowered. Incidentally, FIG. 1 is a schematic plan view of a slab with a defective width reduction. The cross-sectional shape of the slab indicated by reference numeral 9 in FIG. It is the cross-sectional shape of the part.

In the method of Patent Document 2, the amount of bending is predicted based on the temperature deviation, the amount of reduction in the width reduction device is appropriately reduced, and the amount of reduction in width is compensated by the vertical rolling mill. can also contribute to twisting. In addition, we have proposed a technology to suppress slab buckling by installing anti-buckling rolls. It is difficult to deal with torsion through

The present invention has been made in view of the above problems, and its object is to determine whether or not a slab with a defective width reduction due to torsion occurs before width reduction of a hot slab, and to It is an object of the present invention to provide a hot slab twist determination method for hot slab width reduction that can prevent a decrease in productivity of a hot rolling line due to the occurrence of a slab with insufficient reduction, and a hot slab using this twist determination method. It is to provide a width reduction method and a method for manufacturing a hot-rolled steel sheet.

The gist of the present invention for solving the above problems is as follows.

[1] In a hot rolling line having a width reduction device between a heating furnace and a roughing mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperatures of the width edges on both sides of the slab are obtained, and the obtained temperature difference between the width edges on both sides of the slab is determined as the width direction temperature deviation ΔT,
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in a slab due to width reduction of the slab when the product of the width direction temperature deviation ΔT and the width reduction rate γ exceeds a threshold value.

[2] The method for determining twist under hot slab width reduction according to the above [1], wherein the temperature of the width end portions on both sides of the slab is obtained by numerical calculation or a temperature measuring device.

[3] In a hot rolling line having a width reduction device between a heating furnace and a roughing mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperature distribution in the width direction of the slab is obtained, and the temperature difference between the two points at which the temperature deviation is maximum with respect to the center position in the width direction of the slab is calculated as the temperature deviation ΔT in the width direction. defined as
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in a slab due to width reduction of the slab when the product of the width direction temperature deviation ΔT and the width reduction rate γ exceeds a threshold value.

[4] The method for determining twist under hot slab width pressure according to the above [3], wherein the temperature distribution in the width direction of the slab is obtained by numerical calculation or a temperature measuring device.

[5] The method for determining twist under hot slab width reduction according to any one of [1] to [4] above, wherein the temperature deviation ΔT in the width direction is obtained over the entire length of the slab in the longitudinal direction.

[6] In a hot rolling line having a width reduction device between a heating furnace and a roughing mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperatures at the width edges on both sides of the slab are obtained, the deformation resistance at the locations corresponding to the temperatures at the width edges on both sides of the slab is obtained, and the difference in deformation resistance is obtained. is defined as the width direction deformation resistance deviation Δk,
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in the slab due to width reduction of the slab when the product of the width direction deformation resistance deviation Δk and the width reduction ratio γ exceeds a threshold. .

[7] In a hot rolling line having a width reduction device between a heating furnace and a roughing mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperature distribution in the width direction of the slab is determined, and the deformation resistance at the points corresponding to the temperatures at the two points where the temperature deviation is maximum with respect to the center position in the width direction of the slab is determined. , the difference in deformation resistance is defined as the width direction deformation resistance deviation Δk,
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in the slab due to width reduction of the slab when the product of the width direction deformation resistance deviation Δk and the width reduction rate γ exceeds a threshold. .

[8] The method for determining torsion under hot slab width reduction according to the above [6] or [7], wherein the width direction deformation resistance deviation Δk is obtained over the entire length of the slab in the longitudinal direction.

[9] The method for determining torsion in hot slab width reduction according to any one of [1] to [8] above, wherein a planned width reduction amount by the width reduction device is 300 mm or more.

[10] When it is determined that twist occurs in the slab by the method for determining twist under hot slab width reduction according to any one of [1] to [9] above, the slab undergoes width reduction. A hot slab width reduction method in which the hot slab is re-charged into the heating furnace without being carried out.

[11] A method for producing a hot-rolled steel sheet, wherein the width of a hot-rolled steel sheet produced in a hot rolling line is adjusted by the hot slab width reducing method according to the above [10].

According to the present invention, in a hot rolling line that manufactures hot-rolled steel sheets, it is possible to determine the presence or absence of twist in the slab before width reduction of the slab. occurrence can be prevented.

FIG. 4 is a schematic plan view of a slab with poor width reduction; BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows an example of the hot-rolling line which manufactures a hot-rolled steel plate. 1 is a schematic plan view of an example of a width reduction device; FIG. FIG. 4 is a diagram showing an outline of a slab width reduction process by a width reduction device; FIG. 5 is a schematic diagram showing an example of a cross-sectional shape of a slab when deformation of one side of the left and right width edges of the slab is increased. FIG. 4 is a schematic diagram of a slab shape when a slab with no temperature deviation in the width direction is width-reduced. FIG. 4 is a schematic diagram of a slab shape when a slab having a temperature deviation in the width direction of the slab is width-reduced. FIG. 4 is a schematic cross-sectional view of a slab having a dogbone shape asymmetrical in the slab width direction after width reduction. FIG. 10 is a schematic diagram for obtaining a left-right difference _d2 between the upper and lower exit-side pinch rolls in the slab twist determination method proposed in Patent Document 1; FIG. 10 is a diagram showing a comparison of the number of twisted slabs in Comparative Example, Inventive Example 1, and Inventive Example 2; FIG. 10 is a graph showing the result of obtaining the product (ΔT×γ) of the widthwise temperature deviation ΔT and the width reduction rate γ for seven twisted slabs in a comparative example.

Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

<Overview of Hot Rolling Line and Necessity of Slab Width Reduction>
FIG. 2 shows an example of a hot rolling line for manufacturing hot rolled steel sheets. In a hot rolling line 30 for manufacturing hot-rolled steel sheets, a width reducing device 12 for narrowing the width of a slab 1, which is a material to be rolled, is arranged between a heating furnace 11 and a rough rolling mill 13. The heated slab 1 is width-reduced to a predetermined target width by the width reduction device 12, and then rough-rolled by the rough rolling mill 13 and finish-rolled by the finish rolling mill 14 to form a hot-rolled steel sheet (hot-rolled coils).

That is, in the hot rolling line 30 , the slab 1 heated to a predetermined temperature in the heating furnace 11 is width-reduced to a predetermined target width by the width reduction device 12 , and then rough-rolled by the rough rolling mill 13 . Next, finish rolling is performed by a finish rolling mill 14, and the hot-rolled steel sheet after finish rolling is cooled, for example, by a run-out table 15 and coiled by a coiler 16 to obtain a hot-rolled steel sheet as a product having a predetermined thickness and width ( hot-rolled coil). Although not shown in FIG. 2, each facility of the hot rolling line 30 is connected by a roller table, and the slab 1 and the hot rolled steel sheet, which are the materials to be rolled, are conveyed on the roller table.

The width reduction device 12 makes it possible to manufacture products (hot-rolled steel sheets) having different widths even if the slabs manufactured by the continuous casting machine have the same width. Therefore, by making effective use of the width reduction device 12, it is possible to reduce the number of times the slab width is changed in the continuous casting process and reduce restrictions on the rolling order in the hot rolling process (schedule free). As a result, the productivity of the continuous casting process and the hot rolling process is improved, and the effect increases to the extent that the width reduction device 12 can secure a large amount of width reduction.

FIG. 3 shows a schematic plan view of an example of the width reduction device 12. As shown in FIG. The width reduction device 12 shown in FIG. A pair of left and right molds 2a and 2b each having a width pressing surface, a crank 7a and a crank shaft 8a for periodically rocking the mold 2a in the width direction of the slab 1, and the mold 2b attached to the slab 1. A crank 7b and a crankshaft 8b for periodically swinging in the width direction of the plate, and a pair of upper and lower buckling preventions for pressing the slab 1 from its upper and lower surfaces to prevent buckling when the slab width is reduced. A roll 5 and an anti-buckling roll 6 are provided.

The slab 1 is entered into the width reduction device 12, advanced to a predetermined position and stopped, then the slab 1 is sandwiched from above and below by the entry side pinch rolls 3 and the exit side pinch rolls 4, and then by the dies 2a and 2b. The width of the slab 1 is reduced by pressing. FIG. 4 shows an outline of the width reduction process of the slab 1 by the width reduction device 12 . In FIG. 4, FIG. 4(A); "Completion of width reduction" → FIG. 4(B); "Opening mold of width reduction device" → FIG. 4(C); Fig. 4(D); "Constant pitch advance movement of slab" -> Fig. 4(E); "During width reduction" -> Fig. 4(F); Width reduction is intended to reduce the width of the slab 1 . The dashed line in FIG. 4(F) indicates the shape of the slab before width reduction.

When width reduction of the slab 1 is performed using the width reduction device 12 configured in this manner, twisting may occur in the longitudinal direction of the slab 1 after width reduction.

Due to the difference in deformability between the left and right width edges of the slab 1, that is, due to the width reduction, the deformation of one side of the left and right width edges of the slab 1 increases. A case may occur in which the center line Z in the height direction in the cross section is not parallel to the conveying table. FIG. 5 is a schematic diagram showing an example of the cross-sectional shape of the slab when the deformation of one side of the left and right width edges of the slab becomes large. Reference numeral 4L in FIG. It is the exit side pinch roll below the pinch roll.

Twisting of the slab 1 occurs when the width reduction is performed while the height direction center line Z in the slab width direction cross section is not parallel to the conveying table. Twisting, unlike buckling deformation, refers to a situation in which the width edge on one side of the slab is lifted and twisted in the longitudinal direction.

If the slab 1 is twisted, the molds 2a and 2b of the width reduction device 12 cannot roll down the slab 1 at desired positions, and the necessary width reduction amount cannot be obtained. Therefore, in the roughing mill 13 on the downstream side of the width reduction device 12, when centering the width reduction slab with a side guide that is a part of the equipment of the roughing mill 13, the width reduction slab The excessive width portion is caught by the side guides, and the movement (advancement) of the width reduction slab is stopped.

<Cause of twisting>
The inventors of the present invention thoroughly investigated the cause of the twisting of the slab 1 that occurs in the width reduction process of the hot rolling line 30. As a result, twisting occurs when the temperature deviation in the width direction of the slab 1 before width reduction is large. I found out.

When the slab 1 is width-reduced by the width reduction device 12, the left and right width end portions of the slab 1 are plastically deformed by the compressive force of the dies 2a and 2b of the width reduction device 12, and the center of the slab 1 in the width direction. The thickness increases with respect to the part. Here, the shape in which the thickness of the left and right width edges of the slab 1 is larger than the thickness of the central portion of the slab 1 caused by plastic deformation is conventionally called a "dogbone shape".

FIG. 6 shows a schematic diagram of the slab shape when the slab 1 with no temperature deviation in the width direction of the slab 1 is width-reduced. FIG. 6(A) is a schematic plan view, and FIG. 6(B) is a schematic cross-sectional view at the position of the exit-side pinch roll 4. As shown in FIG. When there is no temperature deviation in the width direction of the slab 1, as shown in FIG. The shape is symmetrical in the width direction of the slab 1 . When the longitudinal tip of the slab 1 reaches the exit pinch roll 4 , the thickest part of the width reduction slab comes into contact with the exit pinch roll 4 . At this time, as shown in FIG. 6B, the dogbone shape of the width reduction slab is symmetrical in the width direction of the slab, so that the slab 1 is not twisted.

On the other hand, FIG. 7 shows a schematic diagram of the slab shape when the slab 1 in which the temperature deviation exists in the width direction of the slab 1 is width-reduced. FIG. 7(A) is a schematic plan view, and FIG. 7(B) is a schematic cross-sectional view at the position of the exit-side pinch roll 4. As shown in FIG. When width reduction is performed when there is a temperature deviation in the width direction of the slab 1, as shown in FIG. 1 differ in the width direction deformation amount. Specifically, in the width direction of the slab 1, the amount of reduction (plastic deformation amount) is large on the high temperature side (hereinafter referred to as "high temperature side"), and the low temperature side (hereinafter referred to as "low temperature side"). The reduction amount (plastic deformation amount) is reduced.

As a result, the slab thickness increases more on the high temperature side where the amount of width reduction is greater than on the low temperature side, and as shown in FIG. becomes.

FIG. 8 shows a schematic cross-sectional view of the slab 1 in which the dogbone shape after width reduction is asymmetric in the slab width direction. FIG. 8(A) is a cross-sectional view of the slab, and FIG. 8(B) is a schematic diagram of the slab 1 placed on the delivery side pinch roll 4L. At this time, the plate thickness deviation after deformation between the thickness on the high temperature side (h _{high temperature} ) and the thickness on the low temperature side (h _{low temperature} ) is called a dogbone deviation Δh. Symbol d shown in FIG. 8 is the distance between the vertices of the dogbone in the slab width direction.

In this way, the temperature deviation in the width direction of the slab 1 causes the dogbone deviation Δh, and the torsion of the slab 1 becomes more conspicuous. Since the volume of the slab 1 is constant before and after the width reduction, the dogbone deviation Δh increases as the width reduction amount increases and as the slab width decreases.

When the slab 1 having the dogbone deviation Δh reaches the delivery side pinch roll 4, only the thick side contacts the delivery side pinch roll 4. Therefore, as shown in FIG. It tilts with respect to the transport table in proportion to the bone deviation Δh. On the other hand, since the rear end of the slab 1 is horizontally held by the entry pinch roll 3, the slab 1 is twisted due to the angle difference between the entry pinch roll 3 and the exit pinch roll 4 with respect to the horizontal direction. .

If the dogbone deviation .DELTA.h of the slab 1 can be predicted, the torsion angle of the slab 1 can be geometrically predicted without actually measuring the dogbone deviation .DELTA.h with the exit pinch roll 4 of the width reduction device 12.

First, the inclination angle θ of the delivery side pinch roll 4 due to the dogbone deviation Δh occurring in the slab 1 is obtained by the following equation (1). A schematic diagram is shown in FIG.

tan θ=Δh/2/d=Δh/(2×d) (1)
Here, in equation (1), d is the distance between the vertices of the dogbone in the slab width direction.

Since the entry side pinch roll 3 is horizontal (that is, the inclination angle = 0°) with respect to the inclination angle θ of the delivery side pinch roll 4, the twist angle φ of the slab 1 at the width reduction device 12 located in the middle is Predictable. The twist angle φ of the slab 1 increases in proportion to the longitudinal distance from the entry-side pinch roll 3 and reaches the inclination angle θ at the position of the exit-side pinch roll 4. Therefore, the twist angle φ of the slab 1 is , can be predicted by the following equation (2). The outline of the twist angle φ and the tilt angle θ is shown in FIG.

tanφ∝( _L1 / _L0 )×tanθ=( _L1 / _L0 )×Δh/(2×d) (2)
Here, in the formula (2), the distance from the entrance pinch roll 3 to the width reduction position 12 is L ₁ , and the distance from the entrance pinch roll 3 to the exit pinch roll 4 is L ₀ .

As described above, the dogbone deviation Δh of the slab 1 correlates with the temperature deviation in the width direction of the slab 1, and if the amount of the dogbone deviation Δh can be predicted, the torsion angle φ can also be quantitatively predicted.

<Method for Determining Torsion>
In the hot slab width reduction twist determination method according to the present invention, the twist of the slab 1 that occurs during width reduction is determined by grasping the temperature deviation in the width direction of the slab 1 .

First, the temperature deviation in the width direction of the slab 1 before width reduction is obtained. In obtaining the temperature deviation in the width direction, the temperatures of the width edges on both sides of the slab are used. Here, the width end portion refers to a range from 0 mm to 10 mm toward the center of the width, with the extreme end being 0 mm. The temperatures at these two locations are defined as temperature T ₁ and temperature T ₂ , and the temperature difference between them is defined as width direction temperature deviation ΔT.

Further, preferably, the temperature distribution in the width direction of the entire width of the slab 1 is obtained, and the temperatures at two points at which the temperature deviation is maximum with respect to the center position in the width direction of the slab 1 are defined as temperature T ₁ and temperature T ₂ , and the temperature difference is determined. is the temperature deviation ΔT in the width direction.

When acquiring temperature information for obtaining the temperature T ₁ , the temperature T ₂ and the temperature deviation ΔT in the width direction, it is preferable to acquire the temperature information at the same sheet thickness position. Further, it is more preferable to compare the temperature information of the central portion of the plate thickness of the slab 1 .

In order to determine the slab twist when the slab 1 reaches the delivery side pinch roll 4, it is sufficient to obtain the widthwise temperature deviation ΔT of the slab tip. Here, the tip of the slab is the length of several times of constant pitch movement for each width reduction press from the tip of the slab 1, and refers to a length of about 0.4 to 2.0 m, but it is particularly limited. not something to do. However, when the width direction temperature deviation ΔT changes in the longitudinal direction of the slab 1, the dogbone deviation Δh also changes in the longitudinal direction of the slab 1. Therefore, in order to more accurately determine whether or not the slab 1 is twisted, it is preferable to obtain the widthwise temperature deviation ΔT over the entire longitudinal length of the slab 1 .

Further, since the temperature of the slab 1 extracted from the heating furnace changes due to air cooling until reaching the width reduction device 12, it is preferable to use the temperature of the slab 1 immediately before the width reduction.

The width direction temperature information of the slab 1 may be calculated based on numerical calculation, or may be measured by a temperature measuring device.

When numerical calculation is used, the slab temperature is calculated in consideration of the heating condition of the slab 1 in the heating furnace and the temperature drop from the extraction from the heating furnace 11 to the width reduction device 12 . The slab temperature before charging into the heating furnace 11 is room temperature, the slab temperature is obtained from the furnace temperature setting of the heating furnace 11 and the residence time, and then the temperature from extraction from the heating furnace 11 to the width reduction device 12 Calculate and obtain the amount of decrease.

When using a temperature measuring device, the temperature at the center of the plate thickness of the slab 1 may be directly measured, or based on the actual measurement value of the slab surface with a radiation thermometer or contact type thermometer, the amount of adhered scale The temperature at the central portion of the sheet thickness may be calculated by correcting the influence and the amount of temperature decrease until the width reduction.

The width reduction rate γ of the slab 1 is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction (γ=ΔW/W ₀ ). In obtaining the width reduction ratio γ, a target difference in strip width value, that is, a target value or a set value of the width reduction ratio may be used.

The present invention can be applied to all slabs subjected to width reduction, and the value of the width reduction rate γ is not limited. However, as the amount of width reduction increases, twisting is more likely to occur. In particular, when the amount of width reduction is 300 mm or more, twisting during width reduction tends to occur, and the prediction effect of the determination method of the present invention is high. That is, it is preferable to implement the present invention when the planned width reduction amount is 300 mm or more.

In the hot slab twist determination method under width reduction according to the present invention, when the product (ΔT × γ) of the width reduction rate γ and the width direction temperature deviation ΔT exceeds a certain value, the slab is twisted during width reduction. is determined to occur. Note that the constant value used here, that is, the threshold for the presence or absence of torsion, is empirically determined by collecting performance data.

Further, in order to flexibly cope with changes in the steel type, the widthwise deformation resistance deviation Δk may be used instead of the widthwise temperature deviation ΔT. Specifically, the deformation resistance at the locations corresponding to the temperatures T ₁ and T ₂ of the width direction temperatures described above is obtained, and the difference between them is defined as the width direction deformation resistance deviation Δk. The method of obtaining the width direction deformation resistance deviation Δk is not limited, but the deformation resistance curve of the steel material is obtained in advance, and the value calculated and corrected in consideration of the slab component actual values in addition to the slab temperature. is preferably used. In this case, the threshold for the presence or absence of torsion based on the product (Δk×γ) of the width direction deformation resistance deviation Δk and the width reduction rate γ is the product (ΔT×γ) of the width direction temperature deviation ΔT and the width reduction rate γ. As with the threshold, it is determined empirically.

Furthermore, it is also possible to computationally predict the dogbone deviation Δh and determine the threshold according to the steel composition, temperature, and operating conditions. At that time, an analysis technique such as the finite element method may be used to predict the dogbone shape of the slab 1 .

<Method for width reduction of hot slab when it is determined that twist occurs>
When it is determined that the slab 1 is twisted by the above method, the width reduction of the slab 1 is not performed, and the slab 1 is put into the heating furnace 11 again and heated. The temperature deviation of the slab is eliminated by reheating, and width reduction can be performed without twisting.

In the method for manufacturing a hot-rolled steel sheet according to the present invention, the hot-rolled slab width reduction method is performed as described above, so that the width of the hot-rolled steel sheet manufactured in the hot rolling line 30 is adjusted with high accuracy. , it is possible to prevent the occurrence of a slab with a defective width reduction caused by the twist of the slab 1 .

A width reduction device having a pair of dies for width reduction of the slab, a pair of upper and lower entry side pinch rolls and a pair of upper and lower exit side pinch rolls, and measuring the width direction temperature of the slab on the upstream side of the width reduction device. The present invention was verified using a temperature measuring device. A radiation thermometer was used as a temperature measuring device.

The slab to be hot rolled is an Al-killed low carbon steel slab with a length of 7000 to 8000 mm, a thickness of 260 mm and a width of 1200 to 1800 mm. and The number of slabs to be hot rolled was 10,000. The temperature T ₁ and the temperature T ₂ for determining the width direction temperature deviation ΔT were obtained by measuring the temperature at the center of the thickness of the slab at both width ends with a radiation thermometer. Also, the width reduction amount (ΔW), the slab width before reduction (W ₀ ), and the width reduction rate (γ) were set values obtained from the process computer.

Japanese Patent Application Laid-Open No. 2002-100000 proposes a method of determining a slab twist shape abnormality at the time of width reduction based on the lateral difference _d2 between the upper and lower delivery side pinch rolls 4 and 4L. That is, as shown in FIG. 9, when the lateral difference _d2 between the upper delivery side pinch roll 4 and the lower delivery side pinch roll 4L exceeds the threshold value, the slab is twisted and deformed. This is a judgment method for judging that there is FIG. 9 is a schematic diagram for determining the left-right difference _d2 of the interval between the upper and lower delivery side pinch rolls in the slab twist determination method proposed in Patent Document 1, and the symbol G _op in FIG. and G _dr is the pinch roll spacing on the other side.

Therefore, first, for comparison, the width reduction of the slab was performed according to the determination method described in Patent Document 1 (comparative example). Slabs determined to be twisted required premature termination of the width reduction and removal from the hot rolling line. The slab judged to have no twist was used in the processes after the rough rolling mill on the downstream side. As a result, in the comparative example, as shown in FIG. 10, twist occurred in 7 out of 10,000 slabs, and transport trouble occurred in removing the slabs in the hot rolling line.

Regarding the seven slabs of the comparative example that caused transport trouble due to twisting, the temperature deviation ΔT in the width direction was obtained based on the temperature information measured before the width reduction, and the temperature deviation ΔT in the width direction and the width reduction rate γ were obtained. and the product (ΔT×γ) was calculated. Calculation results are shown in FIG. As shown in FIG. 11, the twisted slab had a value of “ΔT×γ” of 6.3° C. or higher.

Next, "ΔT × γ" of the slab tip (range from the tip of the slab to 1.0 m) is obtained, and based on the obtained "ΔT × γ", it is determined whether or not twisting occurs, and no twisting occurs. Width reduction was performed on the slab determined to be (Invention Example 1). In Example 1 of the present invention, the threshold value of "ΔT×γ" was set to 6° C. based on the results of the comparative example, and when "ΔT×γ" at the tip of the slab exceeded the threshold value, it was determined that twisting occurred. The slab was reloaded into the furnace without width reduction. The number of rolled slabs was 10000, which is the same number as in the comparative example.

As a result, in Example 1 of the present invention, the number of slabs that twisted and caused transport trouble in the hot rolling line was two out of 10,000, as shown in FIG. Diminished. This is because, in Example 1 of the present invention, it was possible to determine whether or not the twist of the slab occurred before performing the width reduction.

Furthermore, temperature data is acquired not only at the tip of the slab, but also over the entire length of the slab in the longitudinal direction, and limited to slabs subjected to width reduction of 300 mm or more, "ΔT × γ" is the threshold value (6 ° C). It was determined that twisting occurred when the slab exceeded , and width reduction was performed on the slab determined not to twist (Invention Example 2). A slab whose "ΔT×γ" exceeded the threshold value (6° C.) was determined to have twisted and was not subjected to width reduction, and the slab was put into the heating furnace again. The number of rolled slabs was 10,000, which is the same number as in Comparative Example and Inventive Example 1.

As a result, in Example 2 of the present invention, as shown in FIG. 10 described above, no transport trouble due to twist occurred. This is because, in Example 2 of the present invention, the torsion occurring behind the slab tip in the longitudinal direction could also be predicted and determined before width reduction.

From the above results, it was confirmed that troubles in the hot rolling line can be prevented by the present invention.

1 slab 1a slab with poor width reduction 2a mold 2b mold 3 entrance pinch roll 4 exit pinch roll 4L exit pinch roll (lower side)
5 Anti-buckling roll 6 Anti-buckling roll 7a Crank 7b Crank 8a Crankshaft 8b Crankshaft 9 Cross-sectional shape of portion where width reduction is not performed 10 Cross-sectional shape of portion where width reduction is performed 11 Heating furnace 12 Width reduction device 13 rough rolling mill 14 finishing rolling mill 15 run-out table 16 coiler 30 hot rolling line

Claims (11)

In a hot rolling line having a width reduction device between a heating furnace and a rough rolling mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperatures of the width edges on both sides of the slab are obtained, and the obtained temperature difference between the width edges on both sides of the slab is determined as the width direction temperature deviation ΔT,
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in a slab due to width reduction of the slab when the product of the width direction temperature deviation ΔT and the width reduction rate γ exceeds a threshold value. 2. The method for determining torsion under hot slab width reduction according to claim 1, wherein the temperature of the width edge portions on both sides of the slab is determined by numerical calculation or temperature measuring equipment. In a hot rolling line having a width reduction device between a heating furnace and a rough rolling mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperature distribution in the width direction of the slab is obtained, and the temperature difference between the two points at which the temperature deviation is maximum with respect to the center position in the width direction of the slab is calculated as the temperature deviation ΔT in the width direction. defined as
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in a slab due to width reduction of the slab when the product of the width direction temperature deviation ΔT and the width reduction rate γ exceeds a threshold value. 4. The method for determining twist under hot slab width pressure according to claim 3, wherein the temperature distribution in the width direction of the slab is determined by numerical calculation or a temperature measuring device. 5. The method for determining twist under hot slab width reduction according to any one of claims 1 to 4, wherein the temperature deviation ΔT in the width direction is obtained over the entire length of the slab in the longitudinal direction. In a hot rolling line having a width reduction device between a heating furnace and a rough rolling mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperatures at the width edges on both sides of the slab are obtained, the deformation resistance at the locations corresponding to the temperatures at the width edges on both sides of the slab is obtained, and the difference in deformation resistance is obtained. is defined as the width direction deformation resistance deviation Δk,
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in the slab due to width reduction of the slab when the product of the width direction deformation resistance deviation Δk and the width reduction rate γ exceeds a threshold. . In a hot rolling line having a width reduction device between a heating furnace and a rough rolling mill,
The slab heated in the heating furnace is width-reduced by the width reduction device at a width reduction rate γ (γ=ΔW/W ₀ ), which is a value obtained by dividing the width reduction amount ΔW by the slab width W ₀ before reduction. Hits the,
Before the slab is width-reduced by the width reduction device, the temperature distribution in the width direction of the slab is obtained, and the deformation resistance at the points corresponding to the temperatures at the two points where the temperature deviation is maximum with respect to the center position in the width direction of the slab is obtained. , the difference in deformation resistance is defined as the width direction deformation resistance deviation Δk,
A method for determining twist in hot slab width reduction, wherein it is determined that twist occurs in the slab due to width reduction of the slab when the product of the width direction deformation resistance deviation Δk and the width reduction ratio γ exceeds a threshold. . 8. The method for determining torsion under hot slab width reduction according to claim 6 or 7, wherein the width direction deformation resistance deviation [Delta]k is obtained for the entire length of the slab in the longitudinal direction. 9. The method for determining twist during hot slab width reduction according to any one of claims 1 to 8, wherein a planned width reduction amount by said width reduction device is 300 mm or more. When it is determined that a twist occurs in the slab by the method for determining twist under hot slab width reduction according to any one of claims 1 to 9, the slab is not subjected to width reduction. (2) a hot slab width reduction method in which the hot slab is recharged into the heating furnace; A method for manufacturing a hot-rolled steel sheet, comprising adjusting the width of a hot-rolled steel sheet manufactured in a hot rolling line by the hot slab width reducing method according to claim 10 .

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