JPH05237513A - Method for joining billets in hot rolling - Google Patents

Abstract

PURPOSE:To reduce the generation of scale in the section of a gap and to stably carry out hot finish rolling under perfect joining of all the area in the plate width direction. CONSTITUTION:In the inlet side of a hot finish rolling mill, the rear end part of a preceding billet 1 is brought into contact with the tip part of a succeeding billet 2 at least at both end parts in the width direction of respective fillets 1 and 2, then alternating field passing through the thickness direction of billet is applied, when the preceding and succeeding billets are joined by pressurizing the billets while heating by the induction current induced by the alternating field, the pressurization is continuously carried out until the gap in the central part is blocked, after both end-areas are completly joined.

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 in hot rolling, and is particularly intended to improve the joining state.

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line, steel strips to be rolled are heated one by one, rough-rolled, and then finish-rolled to finish a hot-rolled sheet having a desired thickness. With the method, it is easy to cause a line stop due to defective biting of the rolled material in finish rolling, and the yield loss due to the defective shape of the leading and trailing edges of the rolled material is large, so these problems have been avoided recently. In order to achieve this, a rolling method has been adopted in which the rear end portion and the front end portion of these steel pieces are joined prior to finish rolling, and this is continuously supplied to a hot rolling line. Japanese Patent Application Laid-Open No. 61-144203 is referred to as a document relating to such continuous rolling of steel slabs.

The technique disclosed in the above-mentioned Japanese Patent Laid-Open No. 61-144203 is a billet that is conveyed in advance on the entrance side of a rolling mill.
The rear end of (hereinafter referred to as the preceding steel piece) and the tip of the subsequently conveyed steel piece (hereinafter referred to as the succeeding steel piece) are butted against each other over their entire surfaces, and their widthwise both ends are pre-joined, It is intended to roll in this state. However, in the above-mentioned technique, in order to provide the pre-bonded portion with sufficient bonding strength, the bonding time must be lengthened, and therefore, it is necessary to take measures to extend the line.

[0006] In order to solve the above problems, the present inventors first made the rear end portion of the preceding steel piece and the front end portion of the following steel piece contact each other, and in that region, the thickness direction of the steel piece was measured. We developed a joining method consisting of a process of applying an alternating magnetic field penetrating to and heating the joining surface by the induced current induced by this alternating magnetic field, and a process of pressing the steel slab. And No. 2-203992. With the development of the above-mentioned joining method, the joining work has become quicker and easier than ever before.

[0005]

In the above joining method,
Since there is an unbonded gap between the pre-bonded portions, it is desirable to close this gap in the subsequent finish rolling to complete bonding. However, on this unbonded surface, a secondary scale is formed after cutting with a crop shear, etc., so that depending on its thickness, bonding over the entire surface may not be completed during finish rolling, and sufficient bonding strength may not be obtained. , There was some room for improvement in this respect.

That is, for example, as shown in FIG. 1 (a), steel pieces obtained by cutting the trailing end of the preceding steel piece 1 and the leading end of the following steel piece 2 into arcs are butted against each other and pressed simultaneously with heating. By joining the widthwise both end areas and sending it to the finishing mill with a shape with a gap in the widthwise central part, it takes about 20-40s from the time of crop cutting before pre-joining to the arrival of the finishing mill. Since it takes a lot of time for bonding and carrying, a secondary scale of about 30 to 60 μm may be generated on the unbonded surface of the gap during this period, and improvement thereof has been desired.

The present invention advantageously responds to the above-mentioned demands, and an object of the present invention is to propose a method for joining steel slabs in hot rolling, which enables complete joining over the entire area in the sheet width direction in finish rolling.

[0008]

That is, according to the present invention, at the entrance side of a hot finish rolling mill, at least the rear end portion of the preceding steel piece and the leading end portion of the following steel piece are arranged in the width direction of each steel piece. While joining at both ends, when applying an alternating magnetic field penetrating in the thickness direction of the steel slab and pressing while heating with an induction current induced by the alternating magnetic field, when joining while gradually expanding the joining area A method for joining steel slabs in hot rolling, which comprises pressing continuously until the gap in the central portion is closed even after the joining in both end regions is completed.

FIG. 2 schematically shows a rolling line suitable for carrying out the present invention. In the figure, number 1 is a preceding steel slab (hereinafter referred to as the preceding sheet bar), 2 is a trailing steel slab following the preceding sheet bar 1 (hereinafter referred to as the following sheet bar), 3
Is a group of hot finish rolling mills, 4 is a pinch roll which controls the conveyance of the sheet bars 2 and 3 and pressurization at the time of joining them, and 5 is an alternating magnetic field generator, which is a core 5a and a coil 5b which form magnetic poles. And a power source 5c.

In the present invention, first, pre-bonding is started with a gap between at least a part of the abutting regions including both ends in the width direction of each sheet bar. The pre-joining method is not particularly limited, but as shown in FIG. 3, for example, the rear end portion of the preceding sheet bar and the leading end portion of the following sheet bar are each cut into an arc shape and then heated. The method of pressing and joining is particularly advantageous in terms of shortening the joining time. In FIG.
(A) is the case where after the tip is cut into a concave shape with the same curvature,
When (b) is a concave shape at both ends, but their curvatures are different, (c) one is straight and the other is concave, (d) is one convex and the other concave, This is the case where the concave curvature is made slightly larger than the convex curvature.
In all of the above examples, only the widthwise both end regions of the seat bar are contacted, and a gap is provided in the central region, but the cutting shape in the present invention is not limited to this.
As shown in (e) and (f) of FIG.
It is also possible to make contact at points and provide a gap between them, or, although not shown, the contact portion may have four or more contact portions and a gap may be provided between them.

Further, as the cutting method of the leading end portion after each of the preceding and following sheet bars, any of the conventionally known methods such as shearing, gas fusing and laser fusing are suitable, but a drum shear having two curved blades. Cutting with is particularly suitable.

Next, the heating and pressing processes will be described.
As the heating and pressing treatment, a) a method of stopping the heating at the time when the temperature of the joining scheduled portion reaches the target temperature and then pressing, b) if the temperature of the joining scheduled portion reaches the joining possible temperature,
Method of starting pressing while heating is continued (however, the melting temperature of the sheet bar does not exceed), c) Method of pressing the sheet bars together from the beginning and simultaneously heating the contact part, d) Predetermined joining margin Any method may be used, such as a method in which the material is pressed to the surface and then heated, but the method c) is particularly effective. This is because the sheet bar is still at a high temperature of about 1000 to 1100 ° C before the hot finish rolling.
Although the joining of the sheet bars will proceed to some extent even by simple pressing, if the heating is performed while performing the pressing process, the joining is effectively promoted, and the joining time is shortened and the amount of input electric power required for heating is reduced. This is because reduction can be expected.

[0013] The temperature at which good bonding proceeds is 1250 ° C.
However, if the heating temperature is too high, the end portion of the sheet bar may be melted.
It is preferably 1450 ° C or lower.

[0014]

In the past, at the time of completion of pre-joining, the sheet is transferred to the finish rolling mill 3 with a gap in the center, and at this finish rolling stage, the preceding sheet bar 1 and the following sheet bar 2
The gap is reduced by promoting the metal flow in the widthwise central region of the rear end and the front end, and the end faces at the joints of the respective sheet bars are planned to be joined across the entire width as shown in FIG. Was. However, as described above, at this time, if a secondary scale is formed in the gap cross section at the center of the width, sufficient bonding cannot be expected depending on the thickness of the secondary scale.

In this respect, according to the present invention, as shown in FIG. 1 (b), even after the joining of the both end regions is completed, the pressing is continuously continued to close the gap in the central portion, and the subsequent finishing is performed. It is possible to effectively prevent the generation of secondary scale that occurs during the transfer time until the rolling mill is bitten, and therefore it is possible to sufficiently increase the bonding strength of the central gap in finish rolling.

[0016]

EXAMPLE A sheet bar was joined in the following manner on the transfer line on the inlet side of the finishing rolling mill (7 tandem mill) shown in FIG. 2 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 cutting device (not shown) was 2
A drum shear with a curved blade was used.

Now, the rear end portion of the preceding sheet bar and the front end portion of the following sheet bar are respectively separated by a drum shear as shown in FIG.
It was cut into an arc shape as shown in (a). Then, both ends of the trailing end portion of the preceding sheet bar and the leading end portion of the following sheet bar were butted against each other in a contact state, and then joined under the following conditions. a. Alternating magnetic field (C-type magnetic pole) Input power: 2000 kW Frequency: 500 Hz b. Heating temperature: 1400 ° C (initial temperature: 1000 ° C) c. Joining form: Start heating at the same time as pressing d. Center gap after pre-bonding completion: 0 mm (invention method),
10mm (conventional method) After pre-bonding is completed under the above conditions, first finish rolling
When a rolling reduction of 40% was applied in a pass, when the method of the present invention with a gap amount of 0 mm was used, no secondary scale was generated at all, and complete bonding was possible.
In the case of 10 mm, the secondary scale remained, and perfect joining could not be performed.

[0018]

As described above, according to the present invention, the pressing is continued even after the pre-joining of the widthwise both end regions to close the gap in the central portion, so that the subsequent scale generation in the gap cross section, which has been a concern in the past, can be prevented. As a result, hot finish rolling can be stably carried out under complete joining over the entire width direction of the sheet.

[Brief description of drawings]

FIG. 1A is an explanatory diagram of a joining procedure using heating by an alternating magnetic field. (B) is a diagram showing a state in which the pressing is continued and the central gap is eliminated even after pre-joining of both end regions.

FIG. 2 is a schematic view of a rolling line suitable for carrying out the present invention.

FIG. 3 is a diagram showing preferred end shapes of a leading seat bar and a trailing seat bar according to the present invention.

FIG. 4 is a diagram showing a joining state of a preceding sheet bar and a following sheet bar in finish rolling.

[Explanation of symbols]

 1 Leading sheet bar 2 Trailing sheet bar 3 Hot finishing rolling mill group 4 Pinch roll 5 Alternating magnetic field generator 5a Core 5b Coil 5c Power supply

Claims (1)

[Claims] 1. On the entry side of a hot finish rolling mill, the trailing end portion of the preceding steel piece and the leading end portion of the following steel piece are brought into contact with each other at least at both widthwise end portions of each of the steel pieces, and Applying an alternating magnetic field penetrating in the thickness direction of the steel slab and pressing while heating with the induced current induced by the alternating magnetic field while gradually increasing the joint area and joining, even after the completion of joining of both end regions A method for joining steel slabs in hot rolling, characterized in that pressing is continuously performed until the central gap is closed.