JP6107074B2 - Manufacturing method of sheet bar for hot-rolled steel sheet - Google Patents

Description

  The present invention reduces the yield loss due to the cutting of the rear end portion of the sheet bar when manufacturing a hot-rolled steel sheet, in order to reduce the width of the slab by a width press device (hereinafter also referred to as a width press), by a vertical rolling mill. The present invention relates to a method for manufacturing a sheet bar for hot-rolled steel sheets that optimizes a method of rough rolling involving multiple passes of width rolling and horizontal passes of multiple passes by a horizontal rolling mill.

  In the hot rolling process, there are a variety of sheet widths required for the product. In order to create a sheet width that matches the product width, the uppermost stream in the hot rolling process is a width press device for reducing the width of the slab. There is a vertical width rolling mill (hereinafter also referred to as a vertical rolling mill) attached to the rolling mill. As a method of changing the width of the product, there is a method of changing the casting width in the continuous casting process, in addition to adjusting the width by a width press apparatus and a width rolling mill in the hot rolling process. In the latter case, since the production efficiency is lowered due to the replacement of the mold, it is desirable to adjust the width in the hot rolling process and reduce the number of times of width change in the continuous casting process. In addition, the width adjustment in the hot rolling process can contribute to the improvement and rationalization of the production capacity in steel sheet manufacture, such as the expansion of schedule-free rolling and the increase of the coil unit weight.

The width press device uses a pair of press dies to press the slab in the width direction and advance the slab by a predetermined amount while repeating the opening, and presses the slab from the front end to the rear end in the width direction over the entire length. Device. Each step of the width press and rough rolling is schematically shown in FIG. Figure 2 W ₀ of (a) is a slab width, [Delta] W _P denotes the width pressing amount schematically. This width pressing, the non-stationary part of the slab leading and back ends after horizontal rolling, generally convex shape called a tongue as shown in FIG. 3, the width pressing amount [Delta] W _P smaller when large width pressing amount [Delta] W _P Sometimes a concave shape called a fishtail appears as shown in FIG. Also, the narrower the slab width, the easier it is to form a tongue. Such a shape of the leading and trailing ends resulting from the width press is reduced in a rough rolling process following the width pressing, and finally affects the shape of the leading and trailing end unsteady portion of the sheet bar. In addition, in the width press, the plate thickness at the front and rear ends of the slab increases, and the plate thickness profile in the plate width direction has a shape as shown in FIG. When distortion occurs only in the vicinity of the plate width end, the shape is as shown in FIG. This increased thickness portion is reduced in the rough rolling process that follows the width press, and further affects the shape of the leading and trailing edges of the sheet bar.

As described above, in the rough rolling process, as shown in FIGS. 2B and 2C, a horizontal rolling mill and a width rolling mill (vertical rolling mill) are attached in front of the horizontal rolling mill. is set up. First, the width of the slab is reduced by width rolling with a vertical roll in a width rolling mill. This width rolling amount ΔW _VN is schematically shown in FIG. Next, the sheet thickness is reduced by rolling with a horizontal rolling mill, but the width returns with the horizontal rolling, and the sheet width increases. In addition, a fishtail is formed in the unsteady portion of the slab tip / rear end by width rolling, which affects the final shape of the sheet bar. Further, in the width rolling, a locally thickened portion is generated at the end portion in the slab width direction as shown in FIG. In width rolling, since strain is difficult to enter into the inside of the plate width direction, the plate thickness profile of this thickened portion is different from the plate thickness profile generated by the above-described width press. This locally thickened portion is extended in the longitudinal direction in the subsequent rough rolling step, thereby affecting the final crop shape.

  As described above, the shape of the front and rear ends of the sheet bar that has been subjected to width pressing of the slab and subjected to the rough rolling process becomes a tongue shape or a fish tail shape according to the width pressing conditions, the rough rolling conditions, and the rough rolling pass schedule. Such a shape of the front and rear ends of the sheet bar causes poor sheeting in finish rolling and poor product width after finish rolling. Therefore, generally after cutting the front and rear ends of the sheet bar with a shear. Finish rolling is done. Since the cut crop is a cause of yield loss, it is desirable to make it as small as possible from the viewpoint of productivity. In particular, a material having a large sheet bar thickness and a wide width is a problem because yield loss increases.

From the above, various proposals have been made for the purpose of reducing yield loss due to cutting.
For example, Patent Document 1 proposes a technique for reducing the yield loss by reducing the width of the slab front and rear end portions wider than the target width with a width press device, finishing the target width by width rolling with a vertical rolling mill. .

Moreover, in patent document 2, it does not carry out width press of the slab front-and-rear end part, Then, it finishes to a product width by carrying out the width rolling of the front-and-rear end part with a vertical rolling mill, and also a subsequent slab based on the performance data in operation. We have proposed a technology that adjusts the range where no width pressing is performed and reduces yield loss.
Further, in Patent Document 3, after detecting the leading and trailing end shapes after width pressing and classifying them into tongues, fishtails, and intermediate shapes thereof, width rolling that minimizes yield loss suitable for each shape is performed. We propose a method to give the pattern of operation as an operating condition.

JP-A-63-180301 JP 59-4910 A JP-A-10-258305

However, each of the conventional techniques described above has the following problems.
(1) In the method shown in Patent Document 1, when performing the width press, first, the width press is performed only in the vicinity of the front end of the slab, and then the slab is advanced, and then the width press is performed only on the rear end of the slab. Next, the slab is moved backward, and the width press is performed while moving the slab from the front end to the rear end by a certain amount. Furthermore, width rolling is performed to a predetermined width with a width rolling mill. In this method, the time required to complete the width adjustment becomes very long, and the production efficiency is remarkably lowered.

(2) In the method described in Patent Document 2, the width press condition of the subsequent slab is adjusted during operation. This is only when the width of the slabs that are sequentially fed is constant. This cannot be done when slabs with various plate widths are sent.
(3) In the method described in Patent Document 3, since only the width rolling amount in each pass of rough rolling is used, optimization including the width pressing condition is not performed, and the yield loss cannot be sufficiently reduced. .

  The present invention has been made to solve the above-described problems, and provides a method of manufacturing a hot-rolled sheet bar with reduced yield loss due to cutting of the front and rear end portions of the sheet bar.

In order to solve the above-mentioned problems, the present inventors paid attention to the deformation behavior of the slab leading and trailing end shapes formed by width pressing and width rolling, and by appropriately giving the width pressing amount and the width rolling amount, the sheet bar The present invention has been completed with the following gist configuration in which the shape of the front and rear ends is made close to a rectangle and the yield loss due to cutting of the sheet bar front and rear ends is reduced.
[1] A step of heating a slab, a step of performing width reduction with a width press device, a step of performing rough rolling having a plurality of rolling pass stages using a horizontal rolling mill having a vertical rolling mill on the entry side, In the hot rolling process for producing a sheet bar for hot rolled steel sheet,
In the step of performing the width reduction, the slab tip has a tongue shape,
In the first pass of the rough rolling, only the first horizontal rolling is performed. In the second and subsequent passes, Nth (N is an integer of 2 or more) width rolling and subsequent horizontal rolling are performed.
Wide rising amount [Delta] W _HN of the material to be rolled by the horizontal rolling of the first N (N-1) predicted after pass completion, the predicted value [Delta] W _HN ^* width rolling amount [Delta] W _VN satisfies the following formula in the width rolling of the first N (1) is satisfied, and the width rolling amount ΔW _VN is width-rolled by the vertical rolling mill so as to be 3% or less of the sheet width W _N-1 of the material to be rolled immediately before width rolling. and the width rolling reduction ratio R _VN is the width reduction ratio input side width of the outlet side width of each pass of the second pass and subsequent rough rolling and from 0.17 to 0.38%, the plate width of the material to be rolled The rough rolling to reduce the sheet width after the first pass rough rolling until the sheet bar width,
Width rolling amount and width rolling amount in each pass of rough rolling so that the width of the tongue formed by width pressing and the fishtail formed by width rolling at the width press and width rolling becomes a rectangular shape at the front and rear ends of the sheet bar The total width rolling amount is allocated, and in width rolling, the width rolling amount in each pass of rough rolling is reduced proportionally from the plate width after width pressing to the sheet bar plate width, and width rolling is performed. A method for producing a sheet bar for hot-rolled steel sheets.
ΔW _HN ^* ≦ ΔW _VN (1)
Here, N is an integer of 2 or more.

[ 2 ] The method for producing a sheet bar for hot-rolled steel sheets according to [1 ], wherein the heated slab is subjected to a width reduction of 100 mm or more and 350 mm or less by the width pressing device.

  According to the present invention, it is possible to significantly reduce the yield loss due to the cutting of the rear end portion of the sheet bar in the width press step and the rough rolling step including the vertical rolling mill and the horizontal rolling mill.

It is a figure showing the schedule of a width press and rough rolling. It is a figure which shows typically each step of width press and rough rolling. It is a schematic diagram which shows a tongue shape. It is a schematic diagram which shows a fishtail shape. It is a schematic diagram which shows a plate | board thickness profile when distortion enters into the plate | board width center by width press. It is a schematic diagram which shows the plate | board thickness profile at the time of distortion entering into the board width end part by width press. It is a schematic diagram which shows the plate | board thickness profile by width rolling.

In the present invention, paying attention to the deformation behavior of the slab tip / rear end shape formed by width pressing and width rolling, the sheet bar tip / rear end shape is made close to a rectangle by appropriately giving the width press amount and the width rolling amount. It is possible to reduce the yield loss when cutting the front and rear ends.
Hereinafter, description will be made based on the width press and the width rolling pattern shown in FIG.
In FIG. 1, the horizontal axis represents each step of width pressing and rough rolling, and the vertical axis represents the sheet width after width pressing in each step or after each pass rolling of rough rolling. The plate width increases from the width press to the first pass of the rough rolling because the width rolling is not performed in the first pass of the rough rolling, and the width is returned in the horizontal rolling due to the thickening caused by the width press. It means that.

When the width press is performed for a certain amount or more, the shape of the slab tip rear end is a tongue shape, and the length of the tongue shape is determined by the width press amount and the plate width.
Further, when width rolling is performed by a vertical rolling mill, a fish tail is formed at the end of the plate width, and the length of the fish tail is determined by the amount of width rolling.
Accordingly, the tongue shape by the width press and the fish tail shape by the width rolling are offset by appropriately adjusting the width press amount and the width rolling amount, and the yield loss due to cutting of the front and rear end portions is reduced by making the shape closer to a rectangle. For example, the planar shape of the final rear end of the sheet bar differs between the width press and width rolling pattern shown in pattern 1 in FIG. 1 and the width press and width rolling pattern shown in pattern 2. In pattern 2, a tongue shape is formed larger than pattern 1 by width pressing, and in the width rolling, pattern 1 has a larger fishtail than pattern 2. Accordingly, by appropriately taking the width press amount and the width rolling amount for making the target sheet bar plate width, the shape of the sheet bar front and rear end can be made close to a rectangle.

  In the width pressing step, the front and rear end portions of the slab can be formed into a tongue shape by the width pressing. When a certain amount or more of width pressing is performed, distortion occurs up to the center of the slab width, resulting in an increase in thickness at the center of the plate width, and this increased thickness is horizontally rolled in the first pass of rough rolling, resulting in a tongue shape. Become. Therefore, in the width pressing process, in order to create a tongue shape, the width pressing is performed with the width pressing amount being 100 mm or more. In addition, if the amount of width press increases beyond a certain level, the load limit of the width press mold is exceeded, making it impossible to press, and slippage occurs between the mold and the slab during width press, and the width press can be performed. become unable. Therefore, the width pressing is performed with the width pressing amount being 350 mm or less.

Next, before carrying out the width rolling and horizontal rolling of the Nth pass (N is an integer of 2 or more) schematically shown in FIG. 2 (c) with a horizontal rolling mill having a vertical rolling mill on the entry side. The width spread amount ΔW _{HN in} the N-th horizontal rolling is predicted. This prediction is based on the width of the entrance side of the vertical rolling mill (sheet width after N-1 pass) W _N-1 , vertical roll diameter D _V , horizontal rolling roll diameter D _H , and width rolling amount ΔW _VN of the Nth pass. performs the horizontal reduction ratio _{R N} of the N pass. By performing the prediction, the width rolling amount ΔW _VN in each pass for creating the desired sheet bar width can be determined. In the first rough rolling pass, width rolling is not performed as shown in FIG. The entry shape of the first pass of rough rolling does not make the plate thickness in the width direction of the slab uniform by the width press, and in this case, it is difficult to predict the width return amount ΔWH ₁ by width rolling and horizontal rolling. For this reason, width rolling is not performed, and in the first pass of rough rolling, the width return amount ΔW _H1 is predicted in consideration of width pressing and horizontal rolling. In the prediction of the width return amount ΔW _H1 by the width press and horizontal rolling, the width return amount is calculated from the slab width W ₀ , the slab thickness t, the width press amount ΔW _P , the horizontal reduction amount Δt, the horizontal rolling roll diameter _{DH, and the} like. .

In width rolling, as described above, the cumulative width rolling amount from the first pass to the final pass is appropriately given so that the sheet bar shape approaches a rectangle. Moreover, at the time of width rolling, it is preferable that the amount of width rolling in each pass of rough rolling is 3% or less of the entry side plate width . This is because when the width rolling exceeds 3%, the width rolling may be impossible without being caught in the width rolling mill (vertical rolling mill).

  The above-mentioned width press and width rolling are performed in the process of making a sheet bar from the slab. At this time, the size of the tongue formed by the width press and the fishtail formed by width rolling make the front and rear ends of the sheet bar rectangular. As described above, the total width rolling amount obtained by summing the width pressing amount and the width rolling amount in each pass of rough rolling is allocated. Moreover, in width rolling, it is preferable to perform width rolling by reducing the amount of width rolling in each pass of rough rolling proportionally from the plate width after the width press to the sheet bar plate width. As described above, when the front and rear ends of the seat bar approach a rectangle, unsteady portions are reduced, and yield loss can be reduced.

  Hereinafter, based on an Example, this invention is demonstrated concretely.

A sheet bar for hot-rolled steel sheets having a width of 824 mm and a thickness of 45 mm was manufactured from a slab having a width of 1004 mm and a thickness of 250 mm, using a rough rolling facility consisting of a width press device, one stand for rough rolling and two stands for rough rolling. Here, the rough rolling 1 stand is equipped with a vertical rolling mill before and after the horizontal rolling mill and is capable of reverse rolling, but the rough rolling 2 stand is on the entry side of the horizontal rolling mill (rough rolling). It is a facility equipped with a vertical rolling mill only on the one stand side), and it is a plate in only one direction. Moreover, the roll diameter _{D V} of the vertical rolling mill is 81.3Mm, roll diameter _{D H} of the horizontal rolling mill is 1070 mm.

First, the slab is width-pressed by a width press apparatus, and only the horizontal rolling is performed in the first pass of the rough rolling, and the width rolling is performed in the vertical rolling mill on the horizontal rolling mill input side after the second pass of the rough rolling. Horizontal rolling was performed. The first to seventh passes of rough rolling were reverse-rolled with one stand of rough rolling, and the eighth pass of rough rolling was subjected to width rolling and horizontal rolling with two stands of rough rolling.
The results are shown in Table 1 together with the set values and actual values for each step. Invention Examples A, B, and C are cases where the width press amount is 210, 200, and 190 mm, respectively, and Conventional Example D is 230 mm in width press amount, and the target sheet bar width at the end of the first pass of rough rolling It is the result of implementing the rough rolling schedule which becomes.

Note that “width rolling reduction ratio R _VN ” shown in Table 1 is a width reduction ratio of the exit side width to the entrance side width in each pass of rough rolling, and in the conventional example, the width rolling amount by the vertical rolling mill is horizontal rolling. Is set so as to cancel out the amount of spread of the width, and the width rolling reduction _RVN is 0.00.
From Table 1, it is clear that in the case of A, B and C which are examples of the present invention, the yield loss is remarkably reduced as compared with the conventional example D.

Claims (2)

Heat comprising a step of heating a slab, a step of performing width reduction with a width press device, and a step of performing rough rolling having a plurality of rolling pass stages using a horizontal rolling mill having a vertical rolling mill on the entry side. In the hot rolling process for producing sheet bars for rolled steel,
In the step of performing the width reduction, the slab tip has a tongue shape,
In the first pass of the rough rolling, only the first horizontal rolling is performed. In the second and subsequent passes, Nth (N is an integer of 2 or more) width rolling and subsequent horizontal rolling are performed.
Wide rising amount [Delta] W _HN of the material to be rolled by the horizontal rolling of the first N (N-1) predicted after pass completion, the predicted value [Delta] W _HN ^* width rolling amount [Delta] W _VN satisfies the following formula in the width rolling of the first N (1) is satisfied, and the width rolling amount ΔW _VN is width-rolled by the vertical rolling mill so as to be 3% or less of the sheet width W _N-1 of the material to be rolled immediately before width rolling. and the width rolling reduction ratio R _VN is the width reduction ratio input side width of the outlet side width of each pass of the second pass and subsequent rough rolling and from 0.17 to 0.38%, the plate width of the material to be rolled The rough rolling to reduce the sheet width after the first pass rough rolling until the sheet bar width,
Width rolling amount and width rolling amount in each pass of rough rolling so that the width of the tongue formed by width pressing and the fishtail formed by width rolling at the width press and width rolling becomes a rectangular shape at the front and rear ends of the sheet bar The total width rolling amount is allocated, and in width rolling, the width rolling amount in each pass of rough rolling is reduced proportionally from the plate width after width pressing to the sheet bar plate width, and width rolling is performed. A method for producing a sheet bar for hot-rolled steel sheets.
ΔW _HN ^* ≦ ΔW _VN (1)
Here, N is an integer of 2 or more.   The method for producing a sheet bar for hot-rolled steel sheets according to claim 1, wherein the heated slab is subjected to a width reduction of 100 mm or more and 350 mm or less by the width pressing device.

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