JP2010064123A - Method for shaping slab by sizing press - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a method for shaping a stainless steel slab by a sizing press, which can simultaneously achieve reduction in the wraparound amount of seam flaws at the tip and tail ends and production of a hot rolled stainless steel strip having an even width over the whole length in the longitudinal direction. <P>SOLUTION: In shaping the tip and tail end parts including the tip and tail ends of a stainless steel slab 1, a step press method is adopted in which the width of the tip and tail end parts after width-direction pressing is made larger than the width of the center part in the longitudinal direction. Further, the planar shape of flares 4, 5 produced by thickness rolling with horizontal rolls of a rough rolling machine and those of a finish rolling machine is predicted as a flare length and a flare amount. A sizing press carries out single strike so as to offset the predicted flare, so that the width-direction pressing amount of the tip and tail parts of the slab producing a flare is made larger than the width-direction pressing amount of widened parts 6a, 7a formed by the step press method. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention reduces the amount of seam wrinkles around the leading edge and the tail edge (hereinafter referred to as the leading edge) closer to the leading edge than the leading edge and tail edge, and the width is uniform over the entire length in the longitudinal direction. The present invention relates to a method for forming a slab in a sizing press that is compatible with obtaining a stainless hot-rolled steel strip.

The sizing press arranged in the hot rolling line is a facility for reducing the width of the slab. By reducing the width of the slab with a sizing press, the slab width of the steel cast by the continuous casting machine can be consolidated, and the width of the hot-rolled steel strip can be created separately in the hot rolling line. The cost of the steel strip can be reduced.
FIG. 1 shows a configuration of an example hot rolling line in which a sizing press is arranged. In the hot rolling line, from the upstream side, a heating furnace 11 that heats the slab 1, a descaling device 16 that removes the scale of the slab 1, a sizing press 12 that performs a width press of the slab 1, a rough rolling machine row 13, and a finish A crop shear 17 that cuts and removes the leading end crop before rolling, a finish rolling mill row 14, a cooling device 18, and a coiler 15 that winds up the hot-rolled steel strip 2 are arranged.

The rough rolling mill row 13 includes a plurality of rough rolling mills including a vertical rolling mill having a width reduction roll 13a and a horizontal rolling mill having a horizontal rolling roll 13b. The slab 1 is subjected to multiple passes of width rolling and thickness rolling. It is a treated sheet bar.
By the way, a surface defect called a seam ridge 3 as shown in FIG. 2 occurs in a stainless hot-rolled steel strip which is a kind of hot-rolled steel strip 2 manufactured by a hot rolling line. The seam ridge 3 extends long in the rolling direction along the width edge. When such a surface defect occurs in the stainless hot-rolled steel strip 2, the portion may have to be cut off, resulting in a decrease in yield. There is.

  The formation process of the seam ridge 3 is as shown in FIGS. 3 (a) and 3 (b). That is, at the initial stage of rough rolling, when the thickness of the material to be rolled 10 is rolled by the horizontal rolling roll 13b, wrinkles 8 are formed on the side surface of the material 10 to be rolled which is a free surface (FIG. 3A). . This wrinkle 8 is caused by bulge deformation (barrel deformation) caused by thickness rolling at the horizontal rolling roll 14b of the rough rolling mill and finish rolling mill to be continued and surface defects 9 called seam trough 3 Become. Stainless steel cold-rolled steel strip is manufactured by subjecting stainless steel hot-rolled steel strip 2 to annealing and pickling, followed by cold rolling and finish annealing and pickling. If it occurs, it remains on the front and back surfaces of the stainless cold-rolled steel strip. For this reason, for destinations with strict surface quality, the seam wrinkle generation region where the seam wrinkles 3 are generated is cut into a product. On the other hand, the width of the stainless hot-rolled steel strip 2 needs to be constant over the entire length in the longitudinal direction. Therefore, it is necessary to cut the ears over the entire length in the longitudinal direction at the position where the seam ridges are most circulated in the width direction.

As a result, since it greatly affects the product yield, a technique for reducing the amount of seam wrinkling is desired. The seam wrinkle amount is defined as the distance from the width edge to the seam wrinkle 3 that wraps most inward in the width direction. Note that the amount of seam wrinkles tends to increase in the vicinity of the leading end.
Conventionally, the following techniques are known as width adjustment techniques in hot rolling (Patent Documents 1 to 3).
Japanese Patent Laid-Open No. 10-52701 JP 2005-34875 A Japanese Unexamined Patent Publication No. 2000-15301

The problems of the prior art will be briefly described.
The width adjustment technique using a sizing press described in Patent Document 1 uses a pair of pressing dies 12a provided with convex portions on the pressing surface in order to limit the seam wrinkle generation region to a very wide end. Is a technique for obtaining a stainless hot-rolled steel strip having a uniform width over the entire length in the longitudinal direction, and the amount of seam wrinkling around the foremost end. There is no mention of reducing.

The width adjustment technique by the width reduction roll of the rough rolling mill described in Patent Document 2 prevents the seam wrinkling amount from increasing, so that the width reduction roll 13a can be opened according to the width fluctuation in the longitudinal direction of the material to be rolled. This is a method in which the degree of width reduction of the material to be rolled is made constant by adjusting the degree.
This method has a problem that the width of the stainless hot-rolled steel strip 2 cannot be made constant over the entire length in the longitudinal direction. Further, when the variation in the width is significant, there is a problem that the seam wrinkle generation position changes greatly and the amount of seam wrinkle wraparound cannot be reduced (see FIG. 8).

As shown in FIG. 9, the width adjustment technique by the sizing press described in Patent Document 3 is applied to the tapered slab 1, and a press for making the formed width constant according to the width dimension of the slab 1. This is a slab molding method for changing the opening.
When the slab forming method applied to the tapered slab 1 is applied to a slab whose normal width is substantially constant, the press amount is changed over the entire length in the longitudinal direction. There is a problem in that it cannot be made constant over the entire length in the longitudinal direction, and the amount of seam wrinkling around the foremost end cannot be reduced.

  The present invention eliminates the above-mentioned problems of the prior art, and can reduce both the amount of seam wrinkles at the foremost end and obtain a stainless hot-rolled steel strip having a uniform width over the entire length in the longitudinal direction. An object is to provide a method for forming a stainless steel slab in a sizing press.

The present inventors further studied a step press method using a sizing press and a short stroke method using a width reduction roll of a rough rolling mill.
In the step press method, the difference in the width return amount between the steady part and the unsteady part, which is caused by rolling with the horizontal roll of the rough rolling mill following the sizing press, is predicted, and in the unsteady part (including the vicinity of the leading end) The width press amount is made smaller than that of the steady portion (longitudinal central portion), and the planar shape of the slab 1 after the width press is as shown in FIG. The step amounts a3 and a4 and the step portion lengths b3 and b4 are determined based on the slab width, the width press amount, rolling conditions in rough rolling and finish rolling, and the like.

  On the other hand, in the short stroke method, flare 4 and 5 (see FIG. 6) generated by thickness rolling with a horizontal roll of a rough rolling mill is predicted, and the opening of the width reduction roll 13a of the rough rolling mill is offset so as to cancel it. Adjust. That is, as shown in FIG. 7B, the opening near the leading end is made narrower than the central portion in the longitudinal direction. The opening adjustment amount for offsetting the flares 4 and 5 is determined based on the slab width, the width press amount, the rolling conditions in rough rolling and finish rolling, and the like.

In FIG.7 (c), the planar shape of the stainless hot-rolled steel strip 2 obtained by using both the above-mentioned level | step difference press method and the above-mentioned short stroke method was shown.
From the seam wrinkle line 3L indicated by the broken line, it was found that the amount of seam wrinkle wrapping at the foremost end could not be reduced. This is because the amount of width reduction by the width reduction roll of the rough rolling mill for offsetting the flares 4 and 5 is large at the foremost end.

Therefore, in the present invention, the planar shape of the flare generated at the foremost end of the stainless hot-rolled steel strip is predicted, and one hit with a sizing press is performed to cancel the predicted flare, so that The inventors have found that the amount of seam wrinkles can be reduced, and have made the present invention.
That is, the present invention is as follows.
1. Rolling in the thickness direction with a horizontal roll of a roughing mill and a finish rolling mill in a method of forming a stainless steel slab by a step press that makes the width of the leading end after width pressing wider than the width of the central portion in the longitudinal direction The flat shape of the flare generated in step 1 is predicted as the flare length and the amount of flare, and the width press amount of the slab where the flare is generated so as to offset the predicted flare A method for forming a slab by a sizing press, wherein one hit by a sizing press is performed so as to be larger than a press amount.
2. One hitting by the sizing press is first performed at the slab leading edge, and once the slab is sent out in the slab conveying direction, the slab is conveyed in the direction opposite to the slab conveying direction, and then performed on the slab end. The above 1. A method for forming a slab by the sizing press described in 1.

  According to the present invention, it is possible to obtain a stainless hot-rolled steel strip that can reduce the amount of seam wrinkling at the foremost end and has a uniform width over the entire length in the longitudinal direction. Therefore, the yield of the stainless hot-rolled steel strip can be greatly improved.

First, the width deformation behavior of the slab by the sizing press will be described.
FIG. 4 shows the planar shape of a pair of pressing dies 12a suitable for use in a sizing press. L is the mold parallel part length. The width pressing of the stainless steel slab 1 (also simply referred to as slab 1) is performed by reciprocating a pair of pressing dies 12a. At that time, the feed pitch of the slab 1 is set smaller than the die parallel part length L by a sizing press feeder, and the width adjustment by the sizing press is performed by setting the width press amount given by the formula (1) at the longitudinal position. Change and do.

Width pressing amount = slab width W1 before width pressing 1−slab width W2 after width pressing (1)
The cross-sectional shape of the slab 1 after the width press in the stationary part in the center in the longitudinal direction and the unsteady part (hereinafter referred to as unsteady part) at the slab leading end is shown in FIGS.
When a width press with a constant reduction is performed, the thickness increases locally due to the width press, but the material flow in the longitudinal direction in the unsteady part is more likely to occur than in the steady part. The amount is small. As a result, by the thickness rolling with the horizontal roll of the rough rolling mill, the width return amount in the steady portion increases, whereas the width return amount in the unsteady portion decreases. Therefore, the sheet bar obtained by the rough rolling mill has a width minus in which the width dimension is smaller than that of the steady portion. The same width deformation behavior is also exhibited when width rolling is performed with a constant reduction amount by a width reduction roll by a rough rolling mill.

  When the width hot rolling by the sizing press and the width rolling by the roughing mill are not performed, and the stainless hot rolled steel strip 2 is obtained, the planar shape as shown in FIG. Thus, when neither width press nor width rolling is performed, flares 4 and 5 are generated, and the fluctuation of the width in the steady portion is expanded. On the other hand, when the same amount of width pressing and / or width rolling is performed in the longitudinal direction of the slab, the width variation in the steady portion is suppressed, but the width deformation behavior in which the width minus occurs is superimposed. It becomes the stainless steel hot-rolled steel strip 2 having a planar shape as shown in (b). That is, the width minus portions 6 and 7 are formed following the flares 4 and 5.

  Therefore, in the slab forming method using the sizing press according to the present invention, the width of the leading end after the width pressing is wider than the width of the central portion in the length direction in order to prevent the occurrence of the width minus portions 6 and 7. The step press method is adopted. At the same time, the planar shape of the flares 4 and 5 generated by rolling in the thickness direction with the horizontal rolls of the roughing mill and the finish rolling mill is predicted as the flare length and the flare amount, and the predicted flares 4 and 5 are offset. The slab is struck by one sizing press so that the width press amount of the slab where the flares 4 and 5 are generated is larger than the width press amount of the wide portions 6a and 7a by the step press method.

The planar shape of the slab 1 formed by the present invention is shown in FIG. In FIG. 10, the two-dot chain line shows the planar shape of the above-described typical typical stainless hot-rolled steel strip 2 in terms of the slab position only in the longitudinal direction.
Here, the planar shape of the flares 4 and 5 is predicted as follows.
(Definition of flare length and flare amount)
The flare length was defined as the distance from the leading end to the point where the flares 4 and 5 intersect with the steady part width WM of the stainless hot-rolled steel strip 2 (see FIGS. 6A and 6B). The flare amount was defined by the areas of flares 4 and 5.

The flare length and the flare amount are obtained based on the following formulas (2) and (3) obtained by analyzing the operation data.
Flare length = f (slab thickness, slab width, thickness reduction ratio) (2)
Flare amount = g (slab thickness, slab width, thickness reduction ratio) (3)
However, thickness reduction ratio = finish thickness / slab thickness.

By doing so, the planar shapes of the flares 4 and 5 are predicted based on the flare length and the flare amount obtained by the equations (2) and (3) by approximating the shape of the flare, for example, by a triangle.
In addition, the shape of the reverse level | step-difference part shape | molded by one hit with a sizing press is as having shown in FIG. That is, the reverse step amounts a1 and a2 were measured from the width of the wide portions 6a and 7a formed by applying the step press method to the slab before the width press having a substantially rectangular planar shape. It is the width difference per one side. The reverse step portion lengths b1 and b2 are distances from the leading end to the end of the reverse step portion. The reverse stepped portion for canceling the flare can be determined by experiment.

  According to the method of the present invention described above, the step press method using the sizing press is adopted, and the width press amount of the reverse step portion corresponding to the portion where the flares 4 and 5 are generated can be increased by the step press method. Since it is made larger than the width press amount of the parts 6a and 7a, the amount of seam wrinkles at the foremost end can be reduced, and a stainless hot rolled steel strip having a uniform width over the entire length in the longitudinal direction can be obtained. . The planar shape of the stainless hot-rolled steel strip 2 obtained by the method of the present invention is shown in FIG.

  For example, in the case of a typical stainless steel slab having a thickness of 220 mm and a width of 1500 mm, the longitudinal direction position where the flares 4 and 5 are generated is within 200 mm from the leading end when converted to a slab. In the case of a stainless steel slab having the same dimensions, the longitudinal position where the width minus portions 6 and 7 are generated is within 600 mm from the tip end when converted to a slab. For this reason, b1 and b2 of one hit by the sizing press for offsetting the flares 4 and 5 are set smaller than that when the feed pitch of the slab 1 in the step press method is set to 300 to 400 mm.

  In order to perform one hit with a sizing press, it is preferable to adopt a reverse press method. To do this, first strike one at the tip of the slab, then perform a width press while transporting the stainless steel slab at a feed pitch in the slab transport direction, and leave a single strike from the tail end of the slab. After separating the mold, the stainless steel slab is once sent out in the slab conveying direction, and then the stainless steel slab is conveyed in the direction opposite to the slab conveying direction, and one hit is made against the slab tail end. This method is advantageous because it can reduce crop loss and prevent buckling.

Moreover, there are two ways of moving the pressing die 12a by the sizing press, and either method may be adopted.
(1) Go-stop method: The pressing surfaces of the pair of press dies 12a are arranged so as to face each other, and the slab 1 is conveyed between the pair of press dies 12a. Then, after the pair of pressing dies 12a is moved in a direction perpendicular to the slab conveying direction to perform a one-stroke width press, when the pair of pressing dies 12a are separated from each other, the slab 1 is fixed. A method of repeating the operation of sending at a feed pitch.
(2) Flying method: The place where the slab 1 is conveyed between the pair of press dies 12a is the same. Then, while performing a one-stroke width press with the pair of pressing dies 12a, the operation of feeding the slab 1 at a certain feed pitch is also performed at the same time. When the pair of pressing dies 12a are separated from each other, A system that repeats the operation of returning only the pressing mold 12a in the direction opposite to the slab conveying direction.

  Hereinafter, the results of comparing the amount of seam wrinkling around the leading end with the method of the present invention and the conventional method will be described.

The condition of a single hit with a sizing press that can reduce the amount of flare was investigated.
The present invention was applied to a sizing press arranged in the hot rolling line shown in FIG. 1, and the effect was confirmed as follows. Ferritic stainless steel slabs (thickness 220 mm, width 1500 mm) cast by a continuous casting machine were supplied to the hot rolling line. At that time, the taper-shaped slab is excluded, and the width change amount of the slab in the longitudinal direction of the slab is 5 mm or less. It was. Then, after rolling up by roughing and finish rolling with a coiler, annealing and pickling were performed.
(Sizing press conditions of the present invention example)
The plane shape (FIG. 12) and YY cross-sectional shape (FIG. 13) of the used press die 12a. The feed pitch of the slab 1 by the step press method = 350 mm, the step portion length b3, b4 = 350 to 700 mm of the slab formed by the same method, the step amount a3 of the slab, a4 = 10 to 30 mm (FIG. 7A). Width press amount at the steady portion of the slab 1 by the step press method = 50 to 250 mm.

  The reverse step amounts a1 and a2 and the reverse step lengths b1 and b2 formed by one hit with a sizing press are shown in Table 1 (see FIG. 10).

The difference between the width press amount of the reverse step portion for offsetting flare and the width press amount of the wide portions 6a and 7a by the step press method was set to a value commensurate with the reverse step amounts a1 and a2.
(Conventional sizing press conditions)
The sizing press conditions were the same as in the examples of the present invention, except that one hit with a sizing press was not performed.
(Rough rolling and finish rolling conditions)
In rough rolling, thickness rolling was performed in 7 passes without performing width rolling to obtain a sheet bar having a thickness of 30 mm, and finished to a thickness of 2.5 to 5.0 mm by finish rolling.

  From the results shown in Table 1, with respect to the planar shape of the flare produced by rolling in the thickness direction with the horizontal roll of the roughing mill and the finishing mill, the reverse step amounts a1 and a2 and the reverse step lengths b1 and b2 are increased. It can be seen that the amount of flare can be reduced.

In Example 2, the flare plane shape generated by rolling in the thickness direction on the horizontal roll of the roughing mill and the finishing mill is predicted as the flare length and the flare amount, and the slab in which the flare is generated so as to offset the predicted flare The width press of the most extreme end portion was performed by one stroke with a sizing press.
Specifically, when the flare amounts are predicted to be LL, L, M, and S in Table 1, in order to cancel the flare amount, the tip (a1, b1) and the rear end of the sizing press are formed with a single stroke. (A2, b2) are the same, LL = (100, 20), L = (50, 10), M = (25, 10), S = (0, 0). Same as Example 1.

  In the rough rolling, the width of the width reduction roll 13a was constant, and the width rolling was performed under the condition of a target width reduction amount of 5.0 mm. Then, finish rolling, annealing, and pickling were performed, and the amount of seams sneaking around ds of the stainless hot-rolled steel strip 2 was measured at the position shown in FIG. 14 (the front and back surfaces of both width ends 10 m from the front end). And the average value was calculated | required for every one. The results are shown in FIGS. 15 (a) and 15 (b).

  According to the example of the present invention, as shown in FIG. 15A, it can be seen that the amount of seam wrinkling around the leading end can be reduced as compared with the conventional example. Moreover, the composition ratio average value of the seam wrinkle amount in the conventional example was 21.9 mm, and the value in the present invention example was 18.3 mm.

It is a block diagram of a hot rolling line. It is the top view which showed the generation | occurrence | production state of the seam flaw of a stainless hot-rolled steel strip. It is sectional drawing which showed the formation process of the seam ridge. It is a top view which shows operation | movement of a sizing press. It is sectional drawing which shows the thickness change of the slab which arises under the width pressure by a sizing press. (A), (b) is a top view of a stainless steel hot-rolled steel strip. It is a top view (c) of the stainless hot-rolled steel strip obtained through the level | step difference press method (a) by a sizing press, and the short stroke method (b) by a width reduction roll. It is a top view of the stainless hot-rolled steel strip obtained by the method of patent document 2. It is explanatory drawing of the width reduction method of the taper slab of patent document 3. It is a top view of the slab obtained by the method of the present invention. It is a top view of the stainless hot-rolled steel strip obtained by the method of the present invention. It is a top view of the metal mold | die for press of the sizing press used for the Example of this invention. FIG. 13 is a YY sectional view of the press die shown in FIG. It is a top view which shows the measurement position of the seam wrinkle amount evaluated in the Example of this invention. It is a characteristic view which shows the effect of the example of this invention compared with a prior art example.

Explanation of symbols

W1 Slab width before pressing W2 Slab width after pressing WM Steady section width of stainless steel hot rolled steel strip L Die parallel section length a1, a2 Reverse step amount b1, b2 Reverse step length a3, a4 Step amount b3, b4 Step length dS seam sneak amount 1 slab (stainless steel slab)
2 Hot-rolled steel strip (stainless steel hot-rolled steel strip)
3 Seam seam 3L Seam seam line 4, 5 Flare 6, 7 Width minus part 6a, 7a Wide part 8 Wrinkle 9 Surface defect
10 Rolled material
11 Heating furnace
12 Sizing press
12a Die for press
13 Rough rolling mill
13a width reduction roll
13b Horizontal rolling roll
14 Finishing mill
14b Horizontal rolling roll
15 Coiler
16 Descaling device
17 Cropshire
18 Cooling device

Claims (2)

  When forming the tip end part including the vicinity of the tip and tail end of the stainless steel slab, a step press method is adopted in which the width of the tip end part after the width press is wider than the width of the central part in the length direction. At the same time, the flare plane shape generated by rolling in the thickness direction on the horizontal rolls of the roughing mill and finish rolling mill is predicted as the flare length and the flare amount, and the slab leading to the flare is offset to offset the predicted flare. A method for forming a slab by a sizing press, wherein the sizing press is performed so that a width press amount of a tail end portion is larger than a width press amount of a wide portion by the step press method.   One hitting by the sizing press is first performed at the leading edge of the slab, first sent in the slab conveying direction, then conveyed in the direction opposite to the slab conveying direction, and then performed on the slab end. A method for forming a slab by the sizing press according to claim 1.

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