JPH06339706A - Continuous hot rolling for billet - Google Patents

Abstract

PURPOSE:To effectively prevent drawing near a joining area in the finish rolling, in joining materials having different width, by making the end side in the width direction of the joining end of a wide material into the shape reduced in the part extending to a narrow material. CONSTITUTION:The ends of a preceding wide billet 1b and a trailing narrow billet 2b are brought into contact with each other at the end areas in the width direction of each billet 1b, 2b and worked into a shape having a space between the end areas. Then, the billets are heat-welded and continuously finish-rolled. Here, the planar shape of the joining end of the wide material 1b is made so that the end areas are extended less to the narrow material 2b than the butt-contact area with the narrow material 2b. For example, the planar shape of the joining end of the wide maternal 1b is made into more shallowly recessed type than that of the narrow material 2b, or formed flat or projected. Thus, in joining and finish rolling materials with different width, drawing is not produced and the rolling is stably performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when hot rolling a steel slab, joins a steel slab that is conveyed in advance and a subsequent steel slab that is subsequently conveyed prior to finish rolling, Regarding the method of continuously finish rolling these steel slabs,
Especially, when steel pieces having different widths are connected, it is intended to propose a method which does not cause a defect in the vicinity of the joint.

[0002]

2. Description of the Related Art Conventionally, during hot rolling of steel slabs, the steel slabs extracted from a heating furnace were rolled one by one, so that various troubles as described below occurred particularly in the finish rolling step. . a) The bite on the tip of the steel piece is not properly caught. b) Narrowing down the rear end of the billet c) Trouble running on the runout table at the tip of the billet. d) Dimensional defects at the front and rear ends of the steel piece.

As a solution to the above-mentioned problem, the trailing end portion of the preceding steel piece and the leading end portion of the succeeding steel piece are sequentially joined in the inlet side conveying line of the hot finish rolling mill before being subjected to finish rolling. That is, a continuous rolling method has been proposed, and various joining methods of steel slabs have been developed to enable the continuous rolling method.

[0004] For example, in Japanese Unexamined Patent Publication No. 4-89110, the joint ends of the steel pieces are in contact with each other at least in the widthwise both end areas of the steel pieces in the abutting state, but there is a gap between them. A joining method has been proposed in which the joining area is sequentially increased by cutting into a shape and then locally heating and pressing the portion to be joined.
This joining method is based on the knowledge that joining strength that can withstand finish rolling can be obtained by joining only the both end regions of the billet width direction, and since it is not a full-face joining, the advantage that it can be joined quickly and easily Have.

In this method, as a concrete cutting method for forming the above-mentioned joining end portion shape, there are shearing, gas fusing, laser fusing, and the like.
Cutting with a drum-type crop shear having a single curved blade has been found to be advantageous, and an example of the joining end shape obtained is shown in FIG.

[0006]

In finish rolling after joining using the method disclosed in Japanese Patent Laid-Open No. 4-89110, the steel pieces to be joined are the same as shown in FIG. In the case of the width, the good rolling result without defects was obtained, but the steel pieces with different widths, specifically, the width difference is 20 mm.
When the above steel pieces are joined and rolled, so-called narrowing may occur in which the steel pieces are broken near the joining region.

[0007] Here, in the hot rolling line, it is required to reduce the cost by schedule-free rolling, and therefore, there are many cases of joining different width materials and performing continuous hot rolling. Therefore, as described above. Narrowing down is becoming an important issue.

Therefore, an object of the present invention is to propose a rolling method in which different width materials are joined and continuously subjected to hot finish rolling, which can effectively prevent narrowing in the vicinity of the joining region. Do

[0009]

Means for Solving the Problems The inventors of the present invention have conducted repeated studies to investigate the cause of the narrowing, and found that the narrowing is due to an abnormal extension of the joining end portion of the wide material during finish rolling. It was found that the abnormal elongation depends on the shape of the joint end of the wide material.

From the above knowledge, the present invention in which the joining end portion of a wide material is creatively added to prevent the narrowing down, the present invention is directed to the trailing end portion of the steel piece to be conveyed at the entrance side of the hot finish rolling mill. And the tip of the steel piece to be subsequently conveyed, in the butt contact state of the two, at least in the widthwise both end regions of each steel piece is processed into a shape having a gap between them, then after heat bonding, In the continuous hot rolling method for steel strips to be continuously subjected to finish rolling, when joining steel strips with different widths and finish rolling, the plane shape of the joining end portion of the wide material is changed to a butt contact area with the narrow material. In the continuous hot rolling method for a steel slab, the end portion side in the width direction is formed into a shape having a small number of portions extending to the narrow width material.

At the time of processing the joining end of the steel piece prior to the butt contact, the joining end of the narrow material is made to have a concave planar shape, while the joining end of the wide material is made to have a flat shape. It is preferable that the width direction end portion side of the joining end portion of the wide width material has a shape in which the portion extending to the narrow width material is small by forming the concave shape shallower than the joining end portion.

More preferably, the flat end of the joining end of the narrow material is made flat while the flat end of the joining end of the wide material is made concave when the joining end of the steel piece prior to the butt contact is processed. By using a mold, the end portion in the width direction of the joining end portion of the wide material is formed into a shape having a small portion extending to the narrow material.

[0013]

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows the joining ends of steel pieces having different widths in a state of abutting and contacting each other. The figure (a) is a comparative example, in which the joining end portion of the preceding steel slab (hereinafter simply referred to as the preceding steel slab) 1a and the steel slab to be subsequently conveyed (hereinafter referred to as the following steel slab) 2a It is an example of cutting with a crop shear with the same radius of curvature. When a steel piece having such a joining end shape (for example, the width of the preceding steel piece 1a: 1200 mm, the width of the following steel piece 2a: 1000 mm, the radius of curvature of the joining end portion: 13800 mm) is joined and rolled. The narrowing has occurred.

The reason for this narrowing down is considered to be as follows. Leading billet 1a and trailing billet 2a with the same curvature
The state in which and are joined is shown in FIG. When such a joined steel slab is subjected to finish rolling, at the joining end of the wide preceding steel slab 1a, the narrower trailing steel slab 2a is located at the end in the width direction than the butt contact area with the narrow material. Since there is no restraint of the work roll, the work roll rolls toward the downstream side, that is, the narrow width trailing steel piece 2a, and the metal flows as shown by the arrow in the figure, and as a result, it overlaps on the narrow width trailing steel piece 2a. Occurs. In addition,
This narrowing tends to occur when the preceding billet is a wide material and the following billet is a narrow material, but conversely, it occurs even when the preceding billet is a narrow material and the following billet is a wide material. there's a possibility that.

Therefore, in the narrowing, in the plane shape of the above-mentioned joining end portion of the wide material, the end portion side in the width direction with respect to the contact contact area with the narrow material extends to the narrow material (shown by hatching in FIG. 3). It can be said that the larger the number of), the more likely it is to occur.

Therefore, in the present invention, narrowing is prevented by forming such a region into a shape having a small portion extending to the narrow material. Here, the preceding steel piece and the following steel piece are in contact with each other at least in the widthwise both end regions of the steel piece in a butt contact state, and have a gap between them,
The narrow material inevitably becomes concave, and is characterized by the planar shape of the joining end portion of the wide material.

The plan shape of the joint end of the wide material according to the present invention is shown in FIGS. 1 (b) to 1 (d). Figure (b) is an example of a concave shape that is shallower than the joint end of narrow material, Figure (c) is an example of a flat shape, and Figure (d) is an example of a convex shape. Is. The example of FIG. 1 (c) is more effective than the example of FIG. 1 (b), and the example of FIG. 1 (d) is more effective than the example of FIG. 1 (c). Figure 1
As a lower limit for obtaining the effect in the example of (b), the minimum radius of curvature of the joining end portion of the wide material is about 30,000 mm.

FIG. 4 shows the rate of occurrence of narrowing when the steel pieces having the planar shapes shown in FIGS. 4A to 4D are joined and then subjected to finish rolling. The conditions at this time are: billet thickness: 30m
m, leading billet width: 1200 mm, trailing billet width 1000 mm, constant curvature radius of joining end of trailing billet 13800 mm, (a), (b)
, (C), (d) are the radius of curvature of the joining end of the preceding steel slabs of 13800 mm, 30000 mm, ∞ (straight line) and 25000 mm for the convex type, respectively.
Then, the finished plate thickness is 1.2 mm by finish rolling. The narrowing occurrence rate indicates the number of narrowing occurrences per 3000 rollings in%. As is clear from the figure, (b), (c), and (d) are reduced compared to the narrowing incidence rate of 1.5% in (a) with the same radius of curvature.

FIG. 5 shows another example of the present invention. This figure shows that the joining end of wide material is formed in a straight line,
Fig. 5 (a) shows an example in which the joint shape of the wide material is flat and the concave shape is shallower than that of the narrow material. Fig. 5 (b) shows the flat shape of the joint end of the wide material. FIG. 5C is an example in which the planar shape of the joining end portion of the wide material is convex.

In the above description, as a concrete means for forming the widthwise end portion side of the joining end portion of the wide width material with a small number of portions extending to the narrow width material, mainly cutting the steel pieces prior to the butt joining with a crop shear. However, the present invention is not limited to the above example, for example, after cutting a predetermined shape by a crop shear, before or after the joining of the steel slab, the narrow material at the joining end portion of the wide material. It is also possible to form a shape having a small number of portions extending to the narrow material by cutting only the width direction end side portion from the butt contact area with. Further, there is no particular problem even if the billet thicknesses are different.

[0021]

EXAMPLE FIG. 6 schematically shows an example of a main part of an inlet side conveying line of a hot finish rolling mill suitable for carrying out the present invention. In the figure, reference numeral 3 is a cutting device (crop shear), 4 is a joining device, and 5 is a finishing rolling mill train.

Using such a conveyance line, the width of the preceding billet
A sheet bar with a width of 1200 mm, a width of 1000 mm in the trailing billet, and a thickness of 30 mm is used to make the joining end of the leading billet flat by the cutting device 3 and the joining end of the trailing billet into a concave shape with a radius of curvature of 13800 mm. After cutting, after joining the steel pieces by pressing the steel pieces while applying an alternating magnetic field in the thickness direction of the steel pieces in the joining area by the joining device 4, the steel sheet is joined to the finishing rolling mill train of 7 stands by the entry side rolling. When conveyed at a speed of 32 mpm and rolled to a thickness of 1.2 mm, no narrowing occurred in the vicinity of the joint area.

Next, the joining end portion of the preceding steel slab has a radius of curvature of 25,000.
When continuous hot rolling was performed under the same conditions as described above except that the cutting was performed in a convex shape of mm, narrowing did not occur in the vicinity of the joining region. In the above example, an example was described in which the joint end was pressed while being heated, but in addition to this example, the same result was obtained by pressing the joint end after cutting and heating.

[0024]

The method for continuously hot rolling a steel slab according to the present invention comprises:
When steel strips with different widths are joined and finish-rolled, the planar shape of the joining end portion of the wide material is such that the end portion in the width direction of the butt contact area with the narrow material has a small portion extending to the narrow material. Due to the shape, even if different width materials are joined and subjected to finish rolling, no narrowing occurs and stable rolling is possible.

[Brief description of drawings]

FIG. 1 is a plan view of a joining end portion of steel pieces having different widths.

FIG. 2 is a plan view of a joining end portion of steel pieces having the same width.

FIG. 3 is an explanatory diagram of occurrence of narrowing.

FIG. 4 is a graph showing a narrowing occurrence rate for each joint end shape of a wide material.

FIG. 5 is a plan view of another example of the joint end shape of the wide material according to the present invention.

FIG. 6 is a schematic view of a main part of an inlet side conveyance line of a hot finish rolling mill suitable for carrying out the present invention.

[Explanation of symbols]

 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h Leading steel strip 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h Trailing steel strip 3 Cutting device 4 Joining device 5 Finishing rolling mill train

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takeshi Hirabayashi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Chiba Works, Kawasaki Steel Co., Ltd. (72) Norio Takashima Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Works Co., Ltd. in Chiba Steel Works (72) Inventor Hideyuki Nikaido 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Works Co., Ltd. in Chiba Works (72) Toshiaki Amagasa, 1 Kawasaki-cho, Chuo-ku, Chiba Prefecture Kawasaki Steel Works Co., Ltd. Chiba Works (72) Inventor Kunio Miyamoto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Works (72) Ikuo Wakamoto 4 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture 6-22 No. 6 Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd.

Claims (3)

[Claims] 1. At the entrance side of a hot finish rolling mill, at least each of a trailing end portion of a steel piece to be conveyed first and a tip end portion of a steel piece to be subsequently conveyed is butt-contacted with each other. In the continuous hot rolling method of the steel pieces, which are in contact with each other in the width direction both ends of the width direction and have a gap between them, are heat-bonded, and then continuously subjected to finish rolling. When joining and finishing rolling, the planar shape of the joining end portion of the wide material is made to have a shape in which the end portion in the width direction of the butt contact area with the narrow material has a small portion extending to the narrow material. Hot rolling method for steel billets. 2. The flat shape of the joining end of the narrow material is made concave when the joining end of the steel piece is processed prior to the butt contact, while the flat shape of the joining end of the wide material is changed to the concave shape. 2. The continuous hot rolling method for a steel slab according to claim 1, wherein the width direction end portion side of the joining end portion of the wide material is formed into a shape having a small number of portions extending to the narrow material by forming a concave shape shallower than the joining end portion. 3. When processing the joining end of a steel piece prior to butt contact, the joining end of a narrow material is made to have a concave planar shape, while the joining end of a wide material is made to have a flat or convex shape. The continuous hot rolling method for a steel slab according to claim 1, wherein the widthwise end portion side of the joining end portion of the wide material is formed into a shape having a small number of portions extending to the narrow material.