JPH06122003A - Continuous hot rolling method for billet - Google Patents

Abstract

(57) [Summary] [Structure] Each of the trailing end of the preceding billet and the leading end of the succeeding billet is cut, and then the billets are brought into contact with each other at the cut surface and heated.・ After joining at least both ends in the plate width direction by pressing, it is fed to the finishing rolling mill group and continuously hot-rolled. An antioxidant is applied, and the antioxidant is removed immediately before finish rolling. [Effect] The effect of secondary scale on the unbonded surface of the gap remaining during pre-bonding of steel slabs is extremely small, and hot finish rolling can be performed stably under the bonding across the entire width of the plate. Highly continuous hot rolling can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of joining steel pieces suitable for continuously rolling several to several tens of steel pieces such as sheet bars, slabs, billets and blooms. .

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line for billets, the billets to be rolled are individually heated, rough-rolled and finish-rolled to finish a hot-rolled sheet having a desired thickness. In such a rolling method, stoppage of the line due to defective biting of the rolled material in finish rolling is unavoidable, and the yield reduction due to defective shape of the leading end and the trailing end of the rolled material has a significant disadvantage. .

For this reason, recently, a rolling system has been adopted in which the rear end portion and the front end portion of the steel pieces to be rolled are joined prior to the finish rolling, and this is continuously supplied to the hot rolling line for rolling. It's starting to happen. Reference is made to JP-A-61-144203 as prior art regarding this point.

In the technique disclosed in the above publication, the trailing end portion of the preceding steel piece and the trailing end portion of the trailing steel piece are butted against each other over their entire surfaces, and the widthwise end portions of the butted portions are pre-joined before rolling. According to this joining method, the biting failure of the material, which was inevitable in the conventional rolling method of heating, rough rolling, and finish rolling the steel pieces one by one, is reduced, and the front and rear ends of the rolled material are reduced. It was also possible to avoid a decrease in yield due to a defective end shape.

However, this joining method has a disadvantage that the joining time must be lengthened in order to secure a sufficient joining strength in the pre-joint portion, and the line must be extended for that reason.

In order to solve such a problem, the inventors of the present invention contact the trailing end portion of the preceding steel piece and the leading end portion of the trailing steel piece at least at both end portions in the width direction to make the steel in that area. We have developed a joining method consisting of a combination of heating and pressing treatments, in which an alternating magnetic field penetrating in the thickness direction of the piece is applied and the joint surface is heated and pressed by the induced current induced by this, and JP-A-4-89109 and It was disclosed in each of the gazettes of the same 4-89110. With the development of this joining method,
The joining work can be done quickly and easily.

[0007]

By the way, in the above joining method, since there is an unjoined gap between the pre-joined portions, it is desired to close this gap in the subsequent finish rolling to complete the joining. However, a secondary scale after cutting with a crop shear, etc., is generated on such unbonded surface. (It takes about 20 to 40 seconds for bonding and transportation time from crop cutting before pre-bonding to arrival at the finishing rolling mill, The thickness is about 30 to 50 μm), and depending on the thickness, the entire surface of the joint cannot be completed during finish rolling, and sufficient joint strength cannot be obtained.Therefore, there is some room for improvement in this respect. Was left.

It is an object of the present invention to propose a method capable of performing stable continuous hot rolling by enabling joining in the entire sheet width direction in finish rolling.

[0009]

SUMMARY OF THE INVENTION According to the present invention, a cutting process is performed on each of a trailing end portion of a preceding steel piece and a leading end portion of a succeeding steel piece that follows, and then the steel pieces are mutually cut at a cutting surface. After joining at least both ends of the steel strip in the plate width direction by bringing them into contact with each other and heating / pressing them, they are fed to a finishing rolling mill group and continuously hot-rolled,
This is a continuous hot rolling method for a steel slab, characterized in that an antioxidant is applied to each cut surface of the steel slab immediately after cutting, and the antioxidant is removed immediately before finish rolling.

In the present invention, it is particularly preferable to use an antioxidant containing a substance having a reducing action on iron oxide, and the cutting of the steel slab and the application of the antioxidant are carried out in an inert atmosphere or a reducing atmosphere. Is preferred.

[0011]

[Operation] At the time of completion of pre-joining, there is a gap of approximately 5 to 50 mm (dimension in the longitudinal direction of the steel pieces) in the widthwise central portions of the steel pieces, but there is such a gap. Even if the finish rolling can promote the metal flow in the widthwise central region of the steel strip at the rear end and the tip, it is possible to weld over the entire width direction of the strip, and thus the welding of steel strips with a gap left. It can be said that the joining method of finishing is extremely effective in terms of shortening the joining time and reducing the pressing force at the time of pressing the steel piece.

However, at this time, 2
As described above, if the next scale is generated, sufficient joining cannot be expected in the rolling process depending on the thickness of the next scale.

According to the present invention, the antioxidant is applied to each cut surface of the steel slab immediately after the cutting work of the steel slab, so that even if the oxidative atmosphere is applied thereafter, all the coated metal becomes an oxide. Unless otherwise changed, oxidation at the cut surface is almost completely prevented. It is considered that even if this antioxidant is rolled as it is, it is naturally discharged to the outside due to the mutual pressing of steel pieces by the metal flow during rolling, but it seems that this remains at the joint. If this happens, it cannot be said that the bonding strength is not adversely affected, so in the present invention, such an antioxidant is removed immediately before rolling.

As described above, according to the present invention, the production of impurities such as secondary kale on the unbonded surface of the gap can be prevented almost completely from the cutting process to the rolling process. If the metal flow in the central area of the plate width is promoted so as to block the area, the area is firmly bonded over its entire surface under the action of high compressive stress in the roll gap (strength equivalent to the base metal). Therefore, there is no possibility that the part will break and separate during rolling.

It is particularly preferable that the antioxidant contains a substance having a reducing effect on iron oxide. This is because it is advantageous for decomposing the oxide film generated between the cutting process of the steel slab and the application of the antioxidant to obtain a more preferable joined state. By adjusting the inert atmosphere or reducing atmosphere between the cutting process of the steel slab and the application of the antioxidant, the antioxidant can be applied without the oxide film on the cut surface of the steel slab. In this way as well, a more suitable joining state can be obtained.

FIG. 1 shows the configuration of equipment suitable for carrying out the present invention.

In the figure, 1 is a tip steel piece that has passed through a rough rolling mill a, 2 is a trailing steel piece that is conveyed following the preceding steel piece 1, and 3 is a rolling mill F.
1, F2, ... Tandem arrangement hot finish rolling mill group, 4 is a cutting processing device for cutting the front and rear end portions of the steel pieces 1, 5 is an apparatus for applying an antioxidant to the cut surface of the steel pieces. The device 5 has a function of freely changing the application area, such as applying an antioxidant while leaving a pre-bonding margin.

An atmosphere adjusting device 6 surrounds the cutting device 4 and the antioxidant coating device 5, and adjusts the atmosphere in this region to an inert or reducing atmosphere. Reference numeral 7 denotes a thickness reducing processing apparatus such as a partial rolling method, a pressing method or a cutting method. The thickness reducing processing apparatus 7 is provided for at least one of the trailing end portion of the preceding steel piece 1 and the leading end portion of the following steel piece 2. Reduce the thickness. Further, 8 is a heating and joining device for gradually expanding the joining area of the steel pieces by bringing the steel pieces 1 and 2 into contact with each other at the cut surface and pressing while heating, and connecting at least both ends in the plate width direction. Although this device 8 is not shown in detail, for example, an alternating magnetic field generator capable of heating in a predetermined temperature range in a short time (an alternating magnetic field penetrating in the thickness direction of the steel slab is applied to this alternating magnetic field). And a plurality of sets of pinch rolls (for pressing the steel pieces) that sandwich the steel pieces 1 and 2 in the vertical direction. Reference numeral 9 is a scale breaker for removing the scale formed on the surface of the steel slab prior to finish rolling, and 10 is a removing device for removing the antioxidant applied on the exit side of the cutting processing device 4. High-pressure water system etc. are applied.

After the preceding steel piece 1 and the following steel piece 2 are joined together, hot rolling is performed as follows.

As shown in FIGS. 2a and 2b (in FIG. 2, only the cutting state of the preceding steel slab 1 is shown), the rear end portion of the preceding steel slab 1 and the leading end portion of the following steel slab 2 are cut and machined. After cutting off at 4, the antioxidant is immediately applied by the antioxidant application device 5 in the manner shown in FIG. Here, the application area of the antioxidant may be the entire cut surface or may be applied with the pre-bonding margin left. Next, as shown in FIG. 4, at least one of the leading end of the preceding steel slab 1 and the leading end of the trailing steel slab 2 is subjected to a thickness reduction processing device 7 in the plate width direction in a butted state at the cut surface of the steel slab. After reducing the thickness so that at least both ends come into contact, both steel pieces 1 and 2 are joined by the combination of heating and pressing by the heating and joining device 8 (joining at the time when the target pre-joining margin is obtained). Then, when the pre-bonded portion of the steel slab reaches the device 10, the antioxidant applied to the unbonded surface of the gap g is removed by spraying high pressure water, and then the finishing slab of the rolling mill group 3 is used. Perform hot rolling. FIG. 5 shows the situation at the time of completion of pre-bonding.

As the antioxidant used in the present invention, for example, oxides such as SiO ₂ , B ₂ O ₃ and CaO are further mixed with a fluoride typified by CaF ₂ and melted, then solidified and pulverized to a certain particle size. Is preferred. Further, a substance obtained by pulverizing metal aluminum, metal silicon, or the like as a substance having a reducing action on iron oxide as an antioxidant is also suitable.

[0022]

EXAMPLE A sheet bar having a width of 1000 mm and a thickness of 32 mm was hot-rolled by a first pass to reduce the rolling reduction to 40 by using the equipment shown in FIG. 1 equipped with a 7-stand tandem rolling mill.
% Reduction, and in the second pass that follows, a reduction rate of 30% was performed to join the seat bars on the exit side (gap part).
Was investigated. Both the leading and trailing sheet bars are cut off at their ends by a cutting machine (there is no gap between them when the sheet bars abut each other), and an antioxidant is immediately applied, followed by a reduction. The thickness of the trailing edge of the preceding sheet bar and the leading edge of the trailing sheet bar is reduced by the thickness processing equipment (thickness reduction of 6 mm at both ends in the width direction), and then the combination of heating and pressing by the heating and joining equipment is performed. Joining both seat bars (pre-joining margin 200mm,
Gap 20 mm, heating / pressing condition: 10 seconds, 1 kgf / mm ² ),
Immediately before the entrance side of the rolling mill, the antioxidant was removed and then fed to the rolling mill. The results are shown in Table 1 together with the results when various processing conditions were changed.

[Table 1]

When the antioxidant is applied immediately after cutting the sheet bar and removed immediately before rolling (No. 1, 3, 5,
7,9,11), especially N that is a refractory antioxidant mixed with Al powder.
The bonding condition was extremely good for o.9 and No. 11 in which the region from cutting to application of the antioxidant was adjusted to an inert atmosphere. On the other hand, if the antioxidant was not removed prior to rolling (No. 2, 4, 6,
(8,10,12) it was confirmed that they were not joined even on the exit side of the second pass.

[0024]

According to the present invention, the effect of the secondary scale on the unbonded surface of the gap remaining during the pre-bonding of steel slabs is extremely small. Therefore, hot finish rolling is performed under the bonding over the entire width direction of the plate. Continuous hot rolling can be carried out stably and with high productivity.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of equipment suitable for implementing the present invention.

FIG. 2A and FIG. 2B are explanatory views of a procedure for cutting a steel slab.

FIG. 3 is a diagram showing a coating state of an antioxidant.

FIG. 4 is a diagram showing a condition of reducing thickness of a steel slab.

FIG. 5 is a diagram showing a state of pre-bonding.

[Explanation of symbols]

 1 Leading steel slab 2 Trailing steel slab 3 Finishing and rolling mill group 4 Cutting machine 5 Antioxidant coating machine 6 Atmosphere adjusting machine 7 Thickness reducing machine 8 Heat bonding machine 9 Scale breaker 10 Antioxidant remover

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunio Isobe, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Pref., Technical Research Division, Kawasaki Steel Co., Ltd. (72) Inoue Masuda, Kawasaki, Chiba (72) Inventor Tadamasa Yamaguchi, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Technical Research Division, Kawasaki Steel (72) Inventor Norio Takashima Kawasaki-cho, Chuo-ku, Chiba-shi No. 1 Kawasaki Steel Co., Ltd. Chiba Steel Works

Claims (3)

[Claims] 1. A cutting process is applied to each of a trailing end portion of a preceding steel piece and a leading end portion of a succeeding steel piece subsequent thereto,
Then, the steel pieces are brought into contact with each other at the cut surface and heated and pressed to join at least both ends in the plate width direction, and then fed to the finishing rolling mill group for continuous hot rolling. A continuous hot rolling method for a steel slab, which comprises applying an antioxidant to each cut surface of the steel slab immediately after cutting and removing the antioxidant immediately before finish rolling. 2. The continuous hot rolling method for a steel slab according to claim 1, wherein the antioxidant contains a substance having a reducing action on iron oxide. 3. The continuous hot rolling method for a steel slab according to claim 1, wherein cutting of the steel slab and application of an antioxidant are performed in an inert atmosphere or a reducing atmosphere.