JPH08141602A - Joining method of billets in hot rolling - Google Patents

Abstract

(57) [Summary] [Structure] At the entry side of the hot finish rolling mill, at least one of the trailing end of the preceding billet and the trailing end of the trailing billet has a convex shape, While contacting the steel piece at its widthwise central portion, applying an alternating magnetic field penetrating in the thickness direction of the steel piece at the widthwise central portion, while heating by an induction current induced by this alternating magnetic field, the steel piece By pressing each other, at least the central region in the plate width direction is sequentially joined from the central portion of the steel piece toward the width end portion. [Effect] A good pre-bonded surface can be obtained, and thus stable continuous hot rolling becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining steel slabs on an inlet side conveying line of a hot finish rolling mill, and particularly to improve the joining state.

[0002]

2. Description of the Related Art Conventionally, when hot rolling a steel slab, the steel slabs extracted from a heating furnace are rolled one by one. With such a method, a) defective biting of the tip of the steel slab, b ) Narrowing of the rear end of the slab, c) Running trouble on the runout table at the front end of the slab, d) Dimensional defects at the front and rear ends of the slab, and so on. A continuous rolling method in which a trailing end portion of a preceding steel piece and a leading end portion of a following steel piece are sequentially joined to each other and then subjected to finish rolling is being adopted in an inlet side conveyance line of a rolling mill.

Here, as a concrete joining method of the steel pieces, a mechanical method in which the end portions of the respective steel pieces are superposed and a wedge is driven into the superposed portion, and the end portions of the respective steel pieces are butted to each other are MIG. , A method of joining by welding such as thermite, or a method of heating the ends of the steel pieces by a burner and pressing the steel pieces to each other when they reach a predetermined temperature, and the like have been proposed. However, all of these methods not only require complicated operations, but also take a long time to join the steel pieces, so that when the steel pieces are joined while being conveyed, they are absorbed. Requires a long loop, and on the other hand, there is a disadvantage such that the equipment length becomes long when the steel slab is conveyed.

As a solution to the above problems,
The inventors previously disclosed in Japanese Patent Laid-Open No. 4-89110 the leading end portion of the preceding steel piece and the leading end portion of the following steel piece at least at both widthwise end portions of each steel piece in a state where they are butted. A method of joining steel pieces has been proposed, which comprises bringing the steel pieces into contact with each other and pressing the steel pieces while applying an alternating magnetic field that preferably penetrates in the thickness direction of the steel pieces to heat them.

However, in the method of sequentially joining from the end in the width direction to the center of the width as described above, when the end of the joint extends to just below the alternating magnetic field generating coil, the rate of temperature rise sharply decreases. , It has been found that joining becomes difficult to proceed. FIG. 1 conceptually shows the eddy current distribution in the steel piece in this joining method. When the end of the joint is outside the alternating magnetic field generating coil, that is, on the width end side, the eddy current flows concentratedly toward the width center of the joint, as shown in FIG. 1 (a). However, when the end of the junction enters the inside of the alternating magnetic field generating coil, the eddy currents do not concentrate near the center of the width, as shown in Fig. 6 (b). As a result, the amount of heat generated in the vicinity of the end of the joint is significantly reduced, making subsequent joining difficult.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to propose a novel joining method which can overcome the above-mentioned problems advantageously and smoothly join the end faces of the steel pieces.

[0007]

Means for Solving the Problems Now, as a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention, as opposed to the conventional method, went from the central portion in the width direction of the steel piece to the width end portion. When they were joined sequentially, the unexpected result was achieved in achieving the intended purpose. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. At the entry side of the hot finish rolling mill, at least one of the trailing end of the preceding steel slab and the leading end of the following steel slab has a convex shape, and both steel slabs are centered in the width direction. By applying an alternating magnetic field penetrating in the thickness direction of the steel slab at the widthwise central portion, and pressing the steel slabs while heating by the induction current induced by the alternating magnetic field, at least the plate About the central area in the width direction,
A method for joining steel pieces in hot rolling, which comprises sequentially joining from the central portion of the steel pieces toward the width end portion (first invention).

2. At the entry side of the hot finish rolling mill, at least one of the trailing end of the preceding steel slab and the leading end of the following steel slab has a convex shape, and both steel slabs are centered in the width direction. By applying an alternating magnetic field that penetrates in the thickness direction of the steel piece at the center in the width direction, and pressing the steel pieces while heating by the induction current induced by the alternating magnetic field, When sequentially joining from the central portion toward the width end portion, even after the joining of the width direction central region is completed, the heat treatment characterized by continuously performing the pressing process until the gap in the width direction end portion is completely closed. A method for joining steel pieces in hot rolling (second invention).

The method of the present invention will be specifically described below. FIG. 2 conceptually shows the eddy current distribution in the billet in the method of the present invention. As shown in FIG. 2 (a), when an alternating magnetic field penetrating the uniform steel piece in the thickness direction is applied, an eddy current is generated around the alternating magnetic field generating coil. However, when the widthwise end of the steel piece is not in contact, the generated eddy current e
Are concentrated at the joint end f. Such concentration of eddy currents similarly occurs even if the end of the junction is directly below the alternating magnetic field generating coil. Therefore, due to the heat generation due to the concentration of such eddy currents, it is possible to perform the smooth heating and joining even directly under the coil.

By the way, the bonding area formed by the above method is
It is not always necessary to cover the whole area in the width direction, and if at least about 30 to 60% of the central area in the plate width direction is pre-bonded, the remaining unbonded area can be effectively blocked in the subsequent finish rolling. . However, on the unbonded surface, 2 after cutting with a crop shear, etc.
Since the next scale is generated, the joining of the unjoined portion may not be completed at the time of finish rolling depending on the thickness, and sufficient joining strength may not be obtained.

That is, as shown in FIG. 3, for example, the rear end of the preceding steel piece 1-a and the leading end of the following steel piece 1-b are cut into arcs and abutted, and then the above method is followed. Pressing at the same time as heating, widthwise central area (joint ratio: 50%)
However, if it is sent to the finishing rolling mill with the widthwise end part unjoined, it takes about 20 to 40 seconds from the time of crop cutting before pre-joining to the arrival of the finishing rolling mill. During this time, the unbonded surface is
A secondary scale of about ~ 60 μm may be generated.

Therefore, in order to stand on the safer side, the joining of the steel pieces is not stopped only in the central region but is performed over the entire width direction, that is, the pressing process is continued until the gap at the width direction end is completely closed. Is desirable.

[0014]

According to the present invention, if the alternating magnetic field generating coil is arranged at the center of the width of the billet and is joined sequentially from the center of the width of the billet toward the width end, the region directly below the coil for generating the alternating magnetic field is obtained. Also, a sufficient amount of heat generation is obtained at the joint,
As a result, a satisfactory joint length can be obtained, and stable finish rolling is possible.

The shape of the ends of the steel slabs is not particularly limited as long as either one of the preceding and following steel slabs has a convex shape so that the two steel slabs come into contact with each other in the central portion in the width direction. However, the preferred shape is shown in FIG. 4 for reference.
In the figure, (a) is a case where the rear and tip parts are cut into a convex shape with the same curvature, (b) is a case where both the rear and tip parts are convex but the curvatures are different, and (c) is one When a straight line is formed and only the other is formed in a convex shape, (d) is a case where one is formed in a concave shape and the other is formed in a convex shape, and the curvature of the convex shape is set to be slightly larger than the curvature of the concave shape.

[0016]

【Example】

Example 1 FIG. 5 schematically shows an inlet side transfer line of a finish rolling mill incorporating a joining device suitable for carrying out the present invention. Numbers 1-a and 1-b in the figure are the leading and trailing billets, respectively.
2 is a coil box, 3-a, 3-b and 3-c are pinch rolls, 4 is a leveler, 5 is a cutting device, and 6 is a joining device. In the figure, the joining device 6 is illustrated as a case where the heating and joining processes are performed in synchronization with the traveling of the steel slab 1. In contrast, when the joining device 6 is heated and joined, the joining process is performed. For this, the looper shown by the broken line 7 is used. 8 is FSB (Descaler),
9 is the first stand of the finish rolling mill.

FIG. 6 shows a heating device of a so-called transverse method in which an alternating magnetic field is applied by penetrating in the thickness direction of the steel slab. An alternating magnetic field generating coil for generating an alternating magnetic field, and the alternating magnetic field generating coil 10 includes a pair of cores 10-a installed with a steel piece vertically sandwiched between them and a coil 10 continuously wound around these cores.
-b and power supply 10-c.

In the present invention, first, the cutting device cuts the trailing end portion of the preceding steel piece and the trailing end portion of the following steel piece. At this time, at least one of the end portions has a convex shape. Then, the alternating magnetic field generating coil 10 is arranged in the center of the width of the steel piece, and the alternating magnetic field is applied while pressing the steel pieces of the preceding material and the following material with the pinch roll 3 under the following conditions. Joined. Joining conditions-Steel thickness: 30 to 50 mm-Steel width: 700 to 1800 mm-Alternating magnetic field generating coil: 600 mm wide × 200 mm long-Power: 1500 kW-Frequency: 1 kHz-1300 ° C (width) for 10 seconds heating 500mm or more joined from the center) ・ Pressing force: 3 to 5 kg / mm ²

After the above-mentioned joining, the sheet thickness was rolled by a 7-stand mill to a thickness of 0.8 to 3 mm. The joining surface was not separated during the rolling, and good continuous rolling could be carried out.

Example 2 Sheet bars were joined in the following manner on the transfer line on the inlet side of the finishing rolling mill (7 tandem mill) shown in FIG. 5 above. The steel pieces used in the experiment were low carbon steel with a thickness of 30 mm and a width of 1000 mm for both the leading and trailing sheet bars, and a drum shear having two curved blades as a cutting device (not shown). Was used.

Now, the trailing end portion of the preceding sheet bar and the leading end portion of the following sheet bar are respectively separated by a drum shear as shown in FIG.
(A) It was cut into an arc shape as shown. Then, after the rear end portion of the preceding sheet bar and the front end portions of the succeeding sheet bars were butted against each other in the width direction, the joining process was performed under the following conditions. Joining conditions a) Alternating magnetic field (C-type electrode) Input power: 2000 kW Frequency: 500 Hz b) Heating temperature: 1400 ° C c) Joining form: Start heating at the same time as pressing d) Amount of gap in width direction after pre-joining : 0 mm, 10
mm

After the pre-bonding was completed under the above conditions, rolling with a reduction ratio of 40% was applied in the first pass of finish rolling. When the gap amount was 0 mm, no secondary scale was generated, The gap was 10mm, although it could be completely joined.
In the case of, the secondary scale remained, and perfect joining could not be performed.

[0023]

As described above, according to the present invention, by sequentially joining the steel slabs from the width center portion to the width end portion, a good pre-joint surface can be obtained, and as a result, stable continuous hot rolling is possible. Becomes In particular, if pressure is continued even after pre-bonding to completely close the gap at the end in the width direction, it is possible to prevent the subsequent scale generation in the gap cross section, which has been a concern in the past. The hot finish rolling can be stably performed under the complete joining.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an eddy current distribution in a steel piece in a conventional joining method.

FIG. 2 is a conceptual diagram of an eddy current distribution in a steel piece in the joining method according to the present invention.

FIG. 3 is an explanatory diagram of a joining region in the joining method according to the present invention.

FIG. 4 is a view showing a preferred end shape of the leading and trailing billets according to the present invention.

FIG. 5 is a schematic view of a rolling line suitable for carrying out the present invention.

FIG. 6 is an explanatory diagram of a transverse heating device.

[Explanation of symbols]

 1-a Leading steel strip 1-b Trailing steel strip 2 Coil box 3-a, 3-b, 3-c Pinch roll 4 Leveler 5 Cutting device 6 Joining device 7 Looper 8 FSB 9 First stand 10 Alternating magnetic field generating coil 10-a core 10-b coil 10-c power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Hirabayashi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Chiba Works (72) Inventor Nozomi Tamura 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Works Co., Ltd. Chiba Works (72) Inventor Hirosuke Yamada 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Works Chiba Works (72) Inventor Hideyuki Nikaido 1 Kawasaki-cho, Chuo-ku, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Shigeru Isoyama 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Ikuo Wakamoto 4-chome, Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture 6-22 No. 22 Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Kiyoshi Izumi 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Work Co., Ltd. Hiroshima within the Institute

Claims (2)

[Claims] 1. On the entrance side of a hot finish rolling mill, at least one of the trailing end of the preceding steel piece and the leading end of the following steel piece has a convex shape, and both steel pieces are While contacting at the widthwise central portion, an alternating magnetic field penetrating in the thickness direction of the steel piece is applied at the widthwise central portion, and the steel pieces are pressed while heating by the induction current induced by this alternating magnetic field. As a result, at least the central region in the strip width direction is sequentially joined from the central portion of the steel piece toward the width end portion, the method for joining steel pieces in hot rolling. 2. At the entry side of the hot finishing rolling mill, at least one of the trailing end of the preceding steel slab and the leading end of the following steel slab has a convex shape, and both steel slabs are While contacting at the widthwise central portion, an alternating magnetic field penetrating in the thickness direction of the steel piece is applied at the widthwise central portion, and the steel pieces are pressed while heating by the induction current induced by this alternating magnetic field. By doing so, when sequentially joining from the central part of the steel piece to the width end part, even after the joining in the width direction central region is completed, the pressing process should be continued until the gap in the width direction end part is completely closed. For joining steel strips in hot rolling.