JPH08294703A - Method for joining slab in hot rolling - Google Patents

Abstract

PURPOSE: To make the flow of a rolling line speedy, and to improve work efficiency by heating a butting part while moving a laser beam along with the butting part. CONSTITUTION: A sheet bar 3 heated by a coil box is cut away at its tip part and rear end part by a cutter 14, and joining surfaces are formed. The rear end face of a preceding sheet bar and the front end face of a succeeding sheet bar 3 are butted. A pressing force is applied between the rear end face of the preceding sheet bar and the front end face of the succeeding sheet bar 3 by pinch rolls 15 and pinch rolls 27. And also, the center part of the butted part is heated by applying an alternating magnetic field in the width direction of the sheet bar 3. And also, the butted part is heated by a laser beam while moving the laser beam by a laser beam irradiation device 22 along the butted part. Consequently, an almost uniform melting area in the thickness direction of a slab is formed, and the occurrence of a large excess weld metal can be eliminated at the butt joined part.

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 pieces in hot rolling. INDUSTRIAL APPLICABILITY The present invention is used for joining a preceding steel piece and a following steel piece in hot rolling of steel pieces such as a sheet bar and a slab.

[0002]

2. Description of the Related Art In the hot rolling of steel slabs such as sheet bars and slabs, the rear end of the preceding steel slab and the front end of the following steel slab are joined together. These steel pieces have a thickness of 20 to
The width is about 50 mm and the width is about 600 to 2000 mm. The temperature of the billet is around 1000 ° C. As one of the methods for joining the steel pieces, there is a method disclosed in JP-A-4-89110 or JP-A-5-237513. In this joining method, as shown in FIG. 3, at least both end portions of the front end portion of the preceding steel piece 1 and the front end portion of the following steel piece 3 in the width direction of the steel piece are butted. Then, an alternating magnetic field penetrating in the thickness direction of the steel slab is applied to the abutting portion, and the pressing is continued until the gap g at the central portion in the width direction of the steel slab is closed, while gradually increasing the joint area by pressing with heating. FIG.
The relationship between the time when an alternating magnetic field is applied and the melting length is shown. As shown in the figure, the gap size and the like differ depending on the butt shape of the steel pieces, so the application time of the alternating magnetic field is controlled to obtain the required melting length.

FIG. 5 shows the relationship between the distance from the joint surface and the temperature gradient of each part of the steel slab during heating by an alternating magnetic field.
Even if the side edges of the steel slab are hot, the temperature at the center is considerably low. When the central portion of the billet is melted, the side end portions are over-melted. On the other hand, as shown in FIG. 6, in order to prevent the joint from breaking, a joint length W of 10% or more of the billet width B is required. If the molten length is increased to obtain the required joint strength, the molten metal will squeeze out at the end of the steel piece side, and the extra bulge will become large. If the extra bulge is not removed by grinding, the next rolling step cannot be started.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a method for joining steel slabs in hot rolling which can reduce the excess of the joint.

[0005]

According to the method for joining steel pieces in hot rolling of the present invention, at least both end portions of the trailing end portion of the preceding steel piece and the front end portion of the following steel piece in the width direction of the steel piece are butted. , In the method of joining both steel pieces by applying a pressing force perpendicular to the butt surface while heating the butt portion, while applying an alternating magnetic field in the thickness direction of the slab, while moving the laser beam along the butt portion, the laser beam is moved. The butt is heated with the beam.

The alternating magnetic field is applied to the widthwise central portion of the steel slab. The laser beam irradiates the regions on both sides of the steel slab, avoiding the alternating magnetic field generator located at the center in the width direction. Two
The pair of laser processing heads are moved along the abutting portions of the both ends of the steel piece to heat the both end portions of the steel piece. Also, 1
The set of laser processing heads may be moved from one side end of the steel slab to the other side end along the abutting portion, and the irradiation of the laser beam may be interrupted when passing the alternating magnetic field generator during the movement. . The laser output with respect to the high frequency power supplied to the alternating magnetic field generator is about 1 to 2%. For example, when the high frequency power is 2000 kW, the laser output is 20 to 4
It is 0 kW.

[0007]

[Function] The alternating magnetic field generates an eddy current, and the current flows mainly near the surface of the steel slab due to the skin effect, heating that portion,
The butt surface surface layer is melted. Further, the laser beam mainly heats the central portion in the thickness direction of the steel slab, and melts the butt surface surface layer portion. For this reason, as shown in FIG. 7, a substantially uniform melting region M is formed in the thickness direction of the billet, so that the extra scale 8 becomes small when the billet is pressed. In the method of the present invention, the surplus 8 is 1/3 to 1/5 of that in the conventional method, and it is not necessary to remove the surplus 8 by grinding or the like. By the way, when the steel piece is heated only by the alternating magnetic field as in the conventional method, as shown in FIG. 8, the melting region M becomes wider near the upper and lower surfaces of the steel piece side end portion. For this reason, the surplus 8 becomes large when pressing the billet, and the surplus 8 must be removed by grinding or the like before rolling.

[0008]

EXAMPLES Examples of the present invention will be described by taking the joining of hot rolled sheet bars as an example. FIG. 1 is a schematic side view of a hot rolling facility equipped with a sheet bar joining apparatus for carrying out the joining method of the present invention. FIG. 2 is a side view of the seat bar joining apparatus.

In the hot rolling equipment, a coil box 11, a pinch roll 12, a leveler 13, a cutting machine 14, a pinch roll 15, a joining device 16, a pinch roll 27, a descaler 28, and a finishing rolling mill row 29 are sequentially arranged. There is. The joining device 16 includes an alternating magnetic field generator 17 and a laser beam irradiation device 22. The alternating magnetic field generator 17 is located at the central portion of the seat bar butt section 5, and is composed of a core 18 arranged above and below the butt section 5, an exciting coil 19, and a power source 20 for supplying a high-frequency current to the exciting coil 19. . The laser beam irradiation device 22 includes a laser oscillator 23, a laser beam transmission optical system 24, and a laser processing head 25. The laser oscillator 23 is a CO ₂ laser oscillator, and the steady output is 25 kW. The focusing lens of the laser processing head 25 has a focal length of 5
00 mm, and the beam spot diameter is 1.0 mm.

In the hot rolling equipment constructed as described above, the sheet bars 1 and 3 heated to 1000 ° C. in the coil box 11 pass through the pinch rolls 12 and the leveler 13 and then in the cutting machine 14 at the leading end and rear end. The end portion is cut off along the bar width direction to form a joint surface. The seat bars 1 and 3 are low carbon steel and have a length of 20 m and a width of 10.
The thickness is 00 mm and the thickness is 30 mm. The feeding speed of the sheet bars 1 and 3 is 90 m / min.

Then, the rear end surface of the preceding sheet bar 1 and the front end surface of the following sheet bar 3 are butted against each other. Then, the pinch roll 15 and the pinch roll 27 apply a pressing force between the rear end surface of the preceding sheet bar 1 and the front end surface of the following sheet bar 3, and at the same time, heat the central portion of the butt portion 5 with an alternating magnetic field. At the same time, the portion near the side edge is heated by the laser beam. By pressing and heating, both ends of the butted portion are joined together over 200 mm. Pressing force is 3kgf /
mm ² . The input power of the alternating magnetic field is 1500 kW, and the laser output is 20 kW. The moving speed of the laser processing head 25 is 10 m / min.

The preceding sheet bar 1 and the succeeding sheet bar 3 that have been pressed against each other are subsequently rolled by the finishing rolling mill train 29. The rolling reduction in the first-stage rolling mill is 50%.

As a result of joining the leading sheet bar 1 and the trailing sheet bar 3 as described above, rolling was possible without bead cutting, and the joining portion was not broken during rolling.

[0014]

According to the present invention, since a substantially uniform melting zone is formed in the thickness direction of the steel slab, a large swell does not occur at the butt joint. Therefore, it is not necessary to remove the surplus, and it is possible to speed up the rolling line and improve the work efficiency.

[Brief description of drawings]

FIG. 1 is a schematic side view of a hot rolling facility equipped with a sheet bar joining apparatus for carrying out the joining method of the present invention.

FIG. 2 is a side view of the seat bar joining device.

FIG. 3 is a diagram illustrating joining by an alternating magnetic field.

FIG. 4 is a diagram showing a relationship between an alternating magnetic field application time and a melting length.

FIG. 5 is a diagram showing the relationship between the distance from the joint surface and the temperature inside the steel slab.

FIG. 6 is a diagram showing the relationship between the joint width and the breakage of a steel slab.

FIG. 7 shows a case where steel pieces are joined by the method of the present invention,
It is drawing which shows typically the melted state of the butt surface surface layer part, and the excess.

FIG. 8 is a drawing schematically showing a melted state of the butt surface surface layer portion and a surplus when steel pieces are joined by this conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Leading steel piece 3 Trailing steel piece 5 Butt part 8 Excessive part 11 Coil box 14 Cutting machine 15 Pinch roll 16 Joining device 17 Alternating magnetic field generator 22 Laser beam irradiation device 23 Laser oscillator 25 Laser processing head 27 Pinch roll 29 Finish rolling Machine train

Claims (1)

[Claims] 1. A rear end portion of a preceding steel piece and at least both end portions of a front end portion of a trailing steel piece in a width direction of the steel piece are butted against each other, and a pressing force perpendicular to the butted surface is applied while heating the butted portion. In the method of joining steel pieces, while applying an alternating magnetic field in the thickness direction of the steel pieces, while heating the butt portion with a laser beam while moving the laser beam along the butt portion, the steel piece in hot rolling How to join.