JP5903826B2 - Hot slab sizing rolling method - Google Patents

Description

  The present invention relates to a method for sizing and rolling a hot slab, and more specifically, in forming a slab produced by continuous casting to a desired plate thickness and width, the productivity of continuous casting is improved and the slab leading end is obtained. The present invention relates to a method for sizing and rolling a hot slab, which can reduce the crop loss by controlling the planar shape.

  The hot-rolled steel strip is usually reduced from a slab with a thickness of about 200 mm to 300 mm to a desired plate thickness through a rough rolling process and a finish rolling process, while running at a high speed to ensure the necessary materials. A predetermined cooling process is performed on the table, and the coil is wound up in a coil by a down coiler. In recent years, in the rough rolling process of many hot rolling lines, a sizing press device that performs large width reduction processing with a pair of dies facing each other in the sheet width direction with respect to a slab extracted from a heating furnace is provided. After a width reduction of about 300 mm at the maximum, the sheet bar is formed through multiple passes of rolling. With the introduction of a sizing press, the ability to change the width in the hot rolling line has been greatly expanded, making it possible to consolidate the slab casting width in continuous casting, which occurs with a reduction in the number of mold width changes and width changes during casting. Improvements in productivity and capacity in continuous casting lines, such as reduction of unsteady slabs.

  However, the width of general hot-rolled steel strip products varies from about 700mm to 2200mm. Even if a sizing press is used in the hot rolling line, slabs with multiple levels of width are available at different chances in the continuous casting process. Need to be cast. Even if a sizing press is used, the difference between the cast slab width and the product width cannot be increased to about 300mm or more, so hot rolling including the chance of direct feed rolling that directly connects the continuous casting process and the hot rolling process is included. The actual situation is that the cycle configuration in the line is greatly restricted. Also, since the continuous casting speed hardly depends on the slab width, the narrower the slab width, the worse the productivity in continuous casting. Casting a slab and dividing the sheet width central portion into two slabs in the longitudinal direction by means such as gas fusing in the longitudinal direction is also performed. In this case, although productivity in continuous casting is improved, a slab dividing step is added, and direct feed rolling becomes impossible, and the slab needs to be reheated, resulting in an increase in manufacturing cost.

  For this reason, as a method of expanding the width change amount of the continuous cast slab, a sizing rolling method has been proposed in which vertical rolling mills are arranged before and after the horizontal rolling mill and width rolling and horizontal rolling are repeated ( For example, Patent Document 1 and Patent Document 2). In patent document 1, in order to reduce the defect of the sheet width center part which is easy to generate | occur | produce at the time of sizing rolling, the relationship between the rolling reduction in width reduction and rolling reduction in horizontal rolling is prescribed | regulated. This is because the tensile stress acts in the rolling direction at the recess in the center of the slab, where the plate thickness is relatively thin, compared to the dogbone where the plate thickness increases under horizontal pressure during horizontal rolling. This is to reduce. In Patent Document 2, as a technique for reducing the dent in the thickness direction of the central part of the plate width that occurs during horizontal rolling of the dogbone part, after the slab is horizontally rolled to the target thickness, only the width reduction and the local thickness increase part are performed. There has been proposed a rolling method in which horizontal rolling is repeatedly performed.

  In addition, the concave shape called the fishtail at the leading end that was unavoidable in slab sizing rolling with conventional solid rolling mills is a sheet that has undergone a rough rolling process at the slab stage or hot rolling line. Since it is cut off at the bar stage, the yield is greatly reduced. For this reason, by installing a sizing press device in the sizing rolling line by the solid rolling mill and pre-forming the initial slab leading end with the sizing press, the slab leading end planar shape in sizing rolling is excessive. A technique for suppressing the concave deformation of the film is disclosed (Patent Document 3).

JP 60-106601 A JP-A-62-97701 JP 2008-272807 A

However, the above-described conventional techniques have the following problems.
First, in Patent Document 1 and Patent Document 2, since the width changeable amount for each pass in the vertical rolling mill cannot be increased, a large number of rolling passes is necessary to greatly change the entire width of the slab. Further, the productivity and the slab temperature are remarkably lowered, and there is a problem that it is not suitable particularly when continuous casting and hot rolling are directly rolled. Further, in this process, the fishtail at the leading end increases as the width reduction amount of the slab increases, and it is inevitable that the yield decreases greatly.

  Further, in Patent Document 3, it is assumed that a new sizing press apparatus is introduced in order to reduce the fishtail length of the slab leading end, which was a problem in the methods disclosed in Patent Document 1 and Patent Document 2. There are many problems such as installation space, equipment cost, running cost, etc. In addition, since a slab leading end pre-forming step is added to the sizing rolling, there is a problem that the reduction in productivity and the reduction in the slab temperature are further increased.

  As described above, the conventional hot slab sizing rolling technology increases the number of rolling passes and decreases the efficiency when attempting to increase the width reduction amount, but also increases the fishtail at the leading end and the yield. There is an unsolved problem of lowering, which makes it difficult to promote the consolidation of casting width, which is part of the streamlining process in the continuous casting process, which is the raw material slab supplier.

As a result of intensive studies to solve the above problems, the inventors have minimized the yield reduction due to unsteady deformation at the leading end at the time of slab width reduction, and targeted the slab with high productivity. The present inventors have found a sizing rolling method that can be formed into a thickness and a width.
That is, the present invention is as follows.
(1)
As a facility for forming a hot slab into a target plate thickness and target plate width by rolling, two thickness rolling horizontal rolling mills and one width rolling vertical rolling mill are first rolled. A hot slab sizing rolling method using a hot slab sizing rolling facility arranged in the order of arrangement of a first horizontal rolling mill, a vertical rolling mill, and a second horizontal rolling mill, wherein one hot slab Are simultaneously rolled by the adjacent vertical rolling mill and the first or second horizontal rolling mill, or simultaneously rolled by the adjacent first horizontal rolling mill, vertical rolling mill and second horizontal rolling mill. In addition, when the width of the slab tip is reduced, an upstream horizontal rolling mill is used so that a compressive force acts within a range in which no slip occurs between the rolling roll and the slab between the upstream horizontal rolling mill and the vertical mill. It is characterized by controlling the rolling speed of the vertical mill That, sizing rolling method of hot slabs.

Here, “plate” in “target plate thickness” and “target plate width” refers to a hot slab after forming by the rolling.
(2)
In (1), the forward rolling of the first horizontal rolling mill, vertical rolling mill, and second horizontal rolling mill and the reverse of the second horizontal rolling mill, vertical rolling mill, and first horizontal rolling mill. A method for sizing and rolling a hot slab, characterized by alternately performing rolling in a direction to form the target plate thickness and the target plate width.
(3)
The hot slab before forming is a continuously cast slab having a thickness exceeding the target plate thickness and a width exceeding the target plate width. The hot slab according to (1) or (2), Sizing rolling method.

  According to the present invention, it is possible to significantly change the dimensions of a continuous casting slab used as a sizing rolling material under the conditions of high productivity and high yield. A very large rationalization effect such as direct connection of rolling can be obtained.

It is a profile diagram which shows the example of the planar shape profile of the slab front-end | tip part after rolling by the sizing rolling of this invention compared with a prior art example. It is a profile diagram which shows the example of the slab tail part plane shape profile after rolling by the sizing rolling of this invention compared with a prior art example. It is a profile diagram which illustrates the influence of the indentation force loaded from the vertical rolling upstream side on the slab front-end | tip planar shape profile after rolling by the sizing rolling of this invention. It is a profile diagram which illustrates the influence of the indentation force loaded from the vertical rolling downstream on the slab tail end plane shape profile after rolling by sizing rolling of the present invention. It is a typical side view which illustrates sizing rolling equipment concerning the present invention. It is a rolling pressure pattern diagram which illustrates the influence of the indentation force loaded from the horizontal rolling downstream on the neutral point position in the roll bit of horizontal rolling. It is a rolling pressure pattern diagram which illustrates the influence of the indentation force loaded from the horizontal rolling upstream on the neutral point position in the roll bite of horizontal rolling. It is the schematic which illustrates the slab plane shape after slab width reduction by a vertical rolling mill.

Hereinafter, embodiments of the present invention will be described together with the effects thereof. In the following description and the drawings used for the description, “plate” means a slab.
Under the slab width reduction by a normal vertical rolling mill, the plate width (meaning slab width; the same applies hereinafter) W is wider than the contact arc length Ld between the rolling roll and the slab, that is, W / Ld is significantly greater than 1. Because of the width reduction in a large area, the strain due to width reduction does not penetrate to the center of the plate width, and the material at the width end is more advanced than that at the center of the width, especially at the leading end of the slab that is not constrained in the front and back. In order to move backward, as shown in FIG. 8, the width of the tip portion (decrease in width) and the concave planar shape at the tip end portion, that is, the fish tail are formed (for example, the Japan Iron and Steel Institute Joint Study Group, Rolling Theory Division). "Theory and practice of plate rolling", published in 1983, p83). In slab sizing rolling, the fishtail shape of the slab leading end is greatly expanded by repeating width reduction and horizontal rolling, so means such as a shear should be used so as not to adversely affect the plate-passability in the next rolling process. After being cut, it is rolled. At this time, the cut end portion is called a crop, and the larger the crop, the lower the yield and the lower the manufacturing cost.

  The inventors of the present invention have studied in detail the formation mechanism of the fishtail generated under the width reduction by the vertical rolling mill, and have come up with a reduction method. In rolling, the material (slab) is drawn into the roll bite by the frictional force between the rolling rolling roll (edger roll) rotated by the solid rolling mill. The end is pulled in, and a large shear deformation occurs to form a fishtail shape. This is because the rolling roll speed is faster before the neutral point position in the roll bite, that is, the point where the rolling roll speed and the material speed are the same (upstream side), and the deformation due to width reduction is the free end at the tip. Larger shear deformation can occur because it tends to flow forward. According to this mechanism, if the neutral point position in rolling can be moved in the roll bite inlet direction, it is considered that the shear deformation in the fish tail direction at the material front end portion is reduced. The neutral point in rolling is the position where the longitudinal force in the roll bite is balanced, but the position moves greatly by applying external force of compression or tension to the material on the roll bite entry side or roll bite exit side. (For example, the Japan Iron and Steel Institute Joint Research Group, Rolling Theory Division, “Theory and Practice of Sheet Rolling” published in 1983, p16). For this reason, since the neutral point moves in the direction of the roll bite entrance by applying a compressive force to the material from the roll bite entry side, forward shear deformation due to frictional force with the rolling roll is suppressed. That is, the tip fishtail shape can be reduced.

  FIG. 3 shows a planar shape of a slab tip portion calculated by a finite element method using a vertical rolling mill. A slab having a thickness of 295 mm, a width of 1800 mm, and a temperature of 1000 ° C. is converted into a φ 2500 mm caliber roll (edger roll). The change in the shape of the tip when the pressing force directed to the downstream side of the rolling is applied to the tail end of the slab under the condition of reducing the width by one pass of 300 mm is shown. When the indentation force is not applied, the tip of the slab has a fishtail shape, but the fishtail shape is suppressed as the indentation force to be applied increases. Under this width reduction condition, the tip of the slab is pushed by the indentation force of about 5 MPa. The dent deformation depth of the portion is suppressed to almost zero. However, although the concave shape is suppressed, the width drop (width reduction) in the vicinity of the plate width end is large, and when a large pushing force is applied, the shape shifts to a convex tongue (tongue).

  Also, at the tail end of the slab, the neutral point moves in the direction of the exit of the roll bite by applying a compressive force to the material from the roll bite exit side, as opposed to the tip of the slab. The forward deformation of the part is promoted, that is, the tail end fishtail shape can be reduced. FIG. 4 shows a change in the shape of the tail end when a pushing force toward the rolling upstream is applied to the slab tip under the same conditions as FIG. When the pushing force is not applied, the tail end of the slab has a fishtail shape, but the fishtail shape is suppressed as the pushing force applied increases. However, the change of the fishtail shape with respect to the pushing force is smaller than that of the tip portion, and it is difficult to completely suppress the concave shape.

The inventors have studied in detail the behavior of the planar shape change at the tip and tail ends of the slab due to these pushing force loads, and the planar shape control technology that combines the convex shape of the tip and the concave shape of the tail short part. Inspired.
An embodiment for realizing the present invention will be described with reference to FIG. FIG. 5 is an equipment row in which a first horizontal rolling mill 1, a vertical rolling mill 2 and a second horizontal rolling mill 3 are arranged close to each other, which constitutes a sizing rolling facility according to the present invention (hereinafter referred to as “this”). Rolling in order is called forward rolling or forward pass, and rolling in reverse order is called backward rolling or reverse pass).

Here, the proximity arrangement means that after the continuous casting in which the adjacent arrangement interval between the vertical rolling mill 2 and the first horizontal rolling mill 1 or the solid rolling mill 2 and the second horizontal rolling mill 3 is a sizing rolling material. It means an arrangement that is less than 30% of the minimum slab length.
In the present invention, when forming the slab 4 cast by continuous casting into the target slab size by rolling in the forward pass and the reverse pass in the equipment row of FIG. 5, the material tip in each rolling pass Speed control of the upstream horizontal rolling mill and vertical rolling mill so that the compressive force acts within the range where slip between the rolling roll and slab does not occur between the horizontal rolling mill and vertical rolling mill on the upstream side It is characterized by performing. For example, in the case of the forward pass, a compressive force is applied between the first horizontal rolling mill 1 and the solid rolling mill 2. In the case of the reverse direction pass, a compressive force is applied between the second horizontal rolling mill 3 and the solid rolling mill 2.

  The condition for occurrence of slip in sheet rolling can be determined by whether or not a neutral point exists in the roll bite, and it is assumed that the first horizontal rolling mill 1 applies a pressing force to the vertical rolling mill 2. Rolling analysis was performed. FIG. 6 is an example of the rolling pressure distribution in the roll bite of the first horizontal rolling mill 1 calculated by the primary analysis method. A slab having a thickness of 295 mm and a temperature of 1000 ° C. is rolled up to a thickness of 280 mm with a φ1000 mm roll. This is the condition for horizontal reduction. By generating a compressive stress in the material between the first horizontal rolling mill 1 and the vertical rolling mill 2, that is, by applying an indentation stress from the downstream side of the first horizontal rolling mill 1, the neutral point is the roll bite outlet. Although it moves to the side, it can be seen that slip does not occur if the indentation stress is about 5 MPa or less under the main rolling conditions. This is almost the same as the stress level for generating the change of the tip plane shape shown in FIG. 3, and the planar shape control from the concave shape to the convex shape of the material tip can be performed by this rolling method.

  In addition, when the material tail end width is reduced in each rolling pass, the downstream side is set so that the compressive force acts within the range in which the rolling roll and the slab do not slip between the downstream horizontal rolling mill and the vertical rolling mill. It is characterized by controlling the speed of the horizontal rolling mill and vertical rolling mill. FIG. 7 shows a rolling assuming that compressive stress is generated in the material between the second horizontal rolling mill 3 and the vertical rolling mill 2, that is, indentation stress is applied from the upstream side of the second horizontal rolling mill 3. It is an example of an analysis result, and is a condition in which a slab having a thickness of 290 mm and a temperature of 1000 ° C. is horizontally reduced to a thickness of 265 mm with a roll of φ1000 mm. The neutral point moves to the roll bite inlet side due to the indentation stress from the upstream side, and no slip occurs if the indentation stress is about 13 MPa or less under the rolling conditions. Compared with the stress level for generating the tail end plane shape change shown in FIG. 4, the change in the fish tail shape is small at an indentation stress of 10 MPa which is 13 MPa or less. It can be seen that the planar shape control to the convex shape is difficult.

  However, the present invention is characterized by controlling the planar shape of the slab tip and tail by a combination of forward rolling and reverse rolling, and depending on the rolling conditions for forming from the initial slab size to the target slab size, What is necessary is just to optimize pushing force. Hereinafter, the front end and tail end in forward rolling are referred to as the slab tip and slab tail, respectively, and in both the forward and reverse directions, the front end and tail end in the rolling direction are the rolling front end and rolling tail end, respectively. Call it. In the present invention, the forward path and the reverse path are combined. As a result, by shaping the slab tip into a convex shape in the forward pass, and by optimizing the combination with the concave shape formed in the slab tip that becomes the rolling tail in the subsequent reverse pass, It is possible to minimize the planar shape unevenness of the slab tip. Also, since the slab tail end that becomes concave in the forward pass becomes the rolling tip in the reverse pass, it is possible to minimize the planar shape unevenness of the slab tail end by applying an appropriate pushing force. Is possible.

  In the sizing rolling method of the present invention, when the slab tip is bitten by the vertical rolling mill, the slip generation limit is remarkably improved because the indentation rolling is performed by the torque of the upstream horizontal rolling mill. Another feature is that a large width reduction is possible by one-pass rolling. From this, it is possible to change the plate width exceeding 1000 mm by rolling several passes, and to form a desired plate thickness by horizontal rolling.

  Further, in the sizing rolling method according to the present invention, an indentation force is applied to the width reduction rolling in the vertical rolling mill by horizontal rolling. Therefore, when the thickness reduction amount is too small, slip occurs in horizontal rolling. For this reason, in order to load an appropriate indentation force against width reduction in a vertical rolling mill without causing slip in horizontal rolling, a neutral point may exist in the roll bite in advance in horizontal rolling. What is necessary is just to obtain | require and set an appropriate horizontal rolling condition. According to the study by the present inventors, as long as the horizontal reduction amount required for applying an appropriate pushing force is set, a dent in the thickness direction at the center portion of the plate width, which has been a problem in Patent Document 2, is found. It does not occur.

  As is apparent from the above description, the slab size of the hot slab according to the present invention can greatly change the slab size after continuous casting under the conditions of high productivity and high yield. It is possible to obtain a very large rationalization effect such as improvement of productivity and direct connection between continuous casting and hot rolling. In addition, you may install this sizing rolling installation between the heating furnace of a hot rolling line, and a rough rolling process.

Hereinafter, examples showing the effects of the present invention will be described with reference to FIGS. 1, 2, and 5.
In this example, the deformation behavior during rolling of each of the examples of the sizing rolling method of the present invention and the conventional method (the present invention example and the conventional example) is analyzed by a finite element method (simulation). ). The material to be analyzed was plain carbon steel having an initial slab size of 295 mm in thickness, a width of 1800 mm, and an initial slab temperature equivalent to 1000 ° C. The rolling roll diameters of the first horizontal rolling mill 1 and the second horizontal rolling mill 3 in FIG. 5 are φ1000 mm, and the rolling roll diameter (edger roll diameter) of the vertical rolling mill 2 is φ2500 mm. Is provided with a concave caliber having a bottom height of 235 mm and an inclination angle of 22 degrees. In forward rolling, the roll gap of the first horizontal rolling mill 1 was 280 mm, the roll gap of the vertical rolling mill 2 was 1500 mm, and the roll gap of the second horizontal rolling mill 3 was 265 mm. In reverse rolling, the roll gap of the second horizontal rolling mill 3 was 250 mm, the roll gap of the vertical rolling mill 2 was 1200 mm, and the roll gap of the second horizontal rolling mill 3 was 235 mm. That is, it is a condition for changing the width by a total of 600 mm in all the two width rollings.

  In the example of the present invention, the roll rotation speed of the vertical rolling mill 2 is 40 mpm, the indentation stress to the width reduction rolling entry side by the first horizontal rolling mill 1 in forward rolling is about 5 MPa, and the slab tip is vertical. Immediately after passing through the rolling mill 2, the rotational speed of the first horizontal rolling mill 1 was changed so that the indentation stress was 0 MPa. Then, immediately after the tail end of the slab passes through the first horizontal rolling mill 1, the second horizontal rolling mill 3 so that the indentation stress to the width reduction rolling exit side by the second horizontal rolling mill 3 is about 7 MPa. The roll rotation speed of was changed. In the reverse rolling, the indentation stress to the width reduction rolling entry side by the second horizontal rolling mill 3 is about 7 MPa, and the second in such a manner that the indentation stress becomes 0 MPa immediately after the slab tip passes the vertical rolling mill 2. The rotational speed of the horizontal rolling mill 3 was changed. Further, immediately after the tail end of the slab passes through the second horizontal rolling mill 3, the first horizontal rolling mill 1 is set so that the indentation stress on the width reduction rolling out side by the first horizontal rolling mill 1 is about 5 MPa. The roll rotation speed of was changed.

On the other hand, in the conventional example, the vertical rotation speed of the vertical rolling mill 2 is set to 40 mpm, and the first horizontal rolling mill 1 and the vertical rolling mill 2 are always used in both the forward rolling and the reverse rolling. The roll rotation speed was appropriately changed so that the indentation force between the mold rolling mill 2 and the second horizontal rolling mill 3 was 0 MPa.
FIG. 1 is a profile diagram showing the planar shape of the slab tip after each of two forward and reverse total passes for each of the present invention example and the conventional example. The depth of the fishtail recess in the conventional example is 180 mm. On the other hand, in the example of the present invention, it is less than about 50 mm, which is reduced to about 1/4. FIG. 2 is a profile diagram showing the planar shape of the tail end of the slab after each of two forward and reverse passes for each of the inventive example and the conventional example, and the depth of the fishtail in the conventional example is shown. While the length is about 170 mm, in the example of the present invention, it is about 20 mm, which is greatly reduced to about 1/8.

  From the above examples, it was confirmed that according to the sizing rolling method of the present invention, the slab width can be changed greatly with a small number of rolling passes while controlling the planar shape of the slab leading end.

1 First horizontal rolling mill 2 Vertical rolling mill 3 Second horizontal rolling mill 4 Slab

Claims (3)

As equipment for forming a hot slab into a target plate thickness and a target plate width by rolling, two thickness rolling horizontal rolling mills and one width rolling vertical rolling mill are first rolled. A hot slab sizing rolling method in which a first horizontal rolling mill, a vertical rolling mill, and a second horizontal rolling mill are arranged close to each other in the order of arrangement, and a hot slab sizing rolling facility is used. The slab is rolled simultaneously with an adjacent vertical rolling mill and the first or second horizontal rolling mill, or simultaneously with an adjacent first horizontal rolling mill, vertical rolling mill and second horizontal rolling mill. In addition to rolling, when the width of the slab tip is reduced, the upstream horizontal rolling mill is operated so that the compressive force acts within the range in which the rolling roll and slab do not slip between the upstream horizontal rolling mill and the vertical rolling mill. And controlling the rolling speed of vertical rolling mill To the sizing rolling method of hot slabs.
  In claim 1, the forward rolling of the first horizontal rolling mill, vertical rolling mill, second horizontal rolling mill, and the reverse of the second horizontal rolling mill, vertical rolling mill, first horizontal rolling mill. A method for sizing and rolling a hot slab, characterized by alternately performing rolling in a direction to form the target plate thickness and the target plate width.   The sizing rolling of a hot slab according to claim 1 or 2, wherein the hot slab before forming is a continuous cast slab having a thickness exceeding the target plate thickness and a width exceeding the target plate width. Method.

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