JPH0623406A - Continuous hot rolling method for slabs - Google Patents

Abstract

PURPOSE:To provide the continuous hot rolling method capable of joining parts of slabs with high strength. CONSTITUTION:After a rear end part of a preceding slab 1 via a rough rolling stage 6 and a tip part of a succeeding slab 2 carried following this slab 1 are cut, respectively by cutting devices 4, parts of the tip part and the rear end part thereof are joined in advance by heating and joining devices 5, then, fed to a finishing mill 3 and unjoined parts are finish-rolled while being rolled and joined at a first stand F1 provided with work rolls of high-speed steel material, by which very stable continuous hot rolling is made possible without causing rupture and separation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling method suitable for continuously hot rolling several to several tens of steel pieces represented by a sheet bar and a slab.

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line, steel pieces to be rolled are heated one by one, rough-rolled and finish-rolled to finish them to a desired thickness. There is a problem that the yield of the hot rolled product is reduced due to the defective shape of the front end portion and the rear end portion of the material. Further, a time interval from rolling one steel piece to rolling the next steel piece is required, which is not preferable from the viewpoints of time saving, energy saving, and cost saving.

Therefore, recently, in order to avoid such a problem, a rolling method in which the leading end and the trailing end of these steel pieces are connected to each other prior to finish rolling and continuously supplied to a hot rolling line. Has come to be adopted. As a technique relating to such continuous rolling of billets, for example, JP-A-61-144209 discloses that a trailing end portion of a billet previously conveyed at the entrance side of a finishing rolling mill and a subsequent conveyer. There is disclosed a technique in which the front end of a steel slab to be formed is butted against the entire surface thereof, and then both widthwise end portions thereof are pre-bonded and rolled in this state.

Further, the present inventors have already disclosed in Japanese Patent Laid-Open No. 4-891.
In the publications of No. 09 and No. 4-89110, the rear end portion of the preceding steel piece and the leading end portion of the following steel piece are contacted at least at both widthwise end portions of each steel piece, and a gap is provided between them. A joining method has been proposed which comprises locally heating and pressing the contact portion. Furthermore, in Japanese Patent Application No. 3-229755,
We have proposed a technology to reduce the thickness of the pre-bonded part at the end by an appropriate amount so that both steel pieces are firmly bonded by finish rolling.

[0005]

However, in the case where the preceding steel piece and a part of the following steel piece are pre-joined and the width center portions of both steel pieces are joined by the subsequent finish rolling as described above, the finish In order to prevent the steel pieces from breaking at the steel piece joining portion due to the tension between the mill stands between the mill stands, it is necessary to firmly join the two steel pieces at least in the pre-finish rolling stand. For this purpose, the above-mentioned JP-A-61-144209 and JP-A-4-144209 are used.
The 89109 and 89110 technologies are not enough. In addition, when reducing the thickness of the end pre-bonded portion as in Japanese Patent Application No. 3-229755, processing equipment and a pre-forming process for the end portion are newly required, which means that the equipment cost increases. There's a problem.

It is an object of the present invention to provide a continuous hot rolling method for a steel slab that solves the problems of the prior art as described above.

[0007]

The present invention is directed to hot rolling by continuously feeding a preceding billet having undergone a rough rolling step and a subsequent billet subsequently conveyed to this billet to a finish rolling mill. In the method described above, after joining the trailing end of the preceding billet and a part of the leading end of the following billet in advance, rolling is performed using a finishing mill using at least the work roll of the first stand as a high-speed steel sheet. It is a feature of the continuous hot rolling method for billets.

[0008]

[Operation] The configuration of the present invention will be specifically described below. FIG. 1 schematically shows a hot rolling facility suitable for carrying out the present invention. 1 is a preceding steel slab that has passed through a roughing mill 6 and 2 is a subsequent steel that is conveyed subsequently to the preceding steel slab 1. Billet,
3 is a finishing rolling mill having a tandem arrangement of rolling mill stands F1, F2, ..., At least the work roll WR1 mounted on the first stand F1 is made of high speed steel. Also, 4
Is a cutting device for cutting and processing the front end and the rear end of the steel slab, and 5 is a heating and welding device for heating and joining the widthwise end of the steel slab.

When hot rolling a steel slab according to the present invention using the hot rolling equipment constructed as described above, first the cutting device 4 is used to cut the rear end of the preceding steel slab 1 and the subsequent steel slab 2. Each tip is cut into a shape as shown in Fig. 2 (a). In this example, the steel pieces 1 and 2 are in contact with each other at both ends in the width direction while the steel pieces 1 and 2 are butted against each other, and there is a gap between them.

Then, as shown in FIG. 2 (b), both ends of the preceding steel piece 1 and the following steel piece 2 are combined by a combination of heating by the heating and joining device 5 and pressing operation by adjusting the conveying speed of the steel pieces 1, 2. A compressive stress is generated in the vicinity area to bring them into close contact with each other. At this time, only the widthwise end portions of the preceding steel piece 1 and the following steel piece 2 are closely joined, and a gap of g is formed in the central portion. When these steel slabs are fed to the hot finish rolling mill 3 to perform hot finish rolling, as shown in FIG.
As shown in (c), the work roll WR1 attached to the first stand F1 is roll-bonded at the center in the width direction.

Here, the work roll WR1 of the finishing first stand F1 usually made of adamite or high chromium cast iron.
The reason for using high-speed steel as the material is that by using a high-speed steel roll for the finishing first stand F1, it is possible to join the steel strip in the widthwise center with high strength during finish rolling. Can be found from. In addition, as a component of this high speed steel, Fe is mainly used, and other elements in weight% are C: 1.0 to 3.0%, Cr: 4.0 to 7.0%, Mo: 1.5%.
~ 6.0%, V: 3.0 to 10.0% is preferred, 6
% Or less W and 2% or less Nb may be included.

[0012]

Example Continuous hot rolling was carried out in the following manner using the hot rolling equipment of finishing 7-stand tandem shown in FIG. First, as a billet, the width of both the preceding and following billets:
A sheet bar with a thickness of 1000 mm and a thickness of 30 mm was used.

Next, the materials of the work rolls used for each stand are the combinations shown in Table 1.

[0014]

[Table 1]

Here, the case is made of high speed steel only for the work rolls of the finishing first stand, the case is for the work rolls of the first and second stands, and C:
2.2%, Cr: 6.0%, V: 5.0%, W4.0% made of HSS material as the main component. The case is used for the conventional work roll in both the first and second stands for comparison. The high chrome cast iron roll is used, and the case uses the high chrome cast iron roll for the first stand and the high speed steel for the second stand. In all cases, high-chrome cast iron rolls are used as the work rolls for the finishing third and fourth stands, and nickel-grain cast iron rolls are used as the work rolls for the fifth to seventh stands.

Now, after cutting the rear end portion of the preceding sheet bar and the front end portion of the succeeding sheet bar into predetermined shapes (see FIG. 2 (a)), as shown in FIG. When 100 mm at both ends in the direction were pre-bonded by heat pressing, the size of the gap g formed at the center of the width was 5 mm. Then, this was fed to a finishing rolling mill to finish a hot rolled sheet having a thickness of 3 mm. At this time, in each case, the reduction ratio of the finishing first stand was 38%, the reduction ratio of the second stand was 35%, and 10 sheet bars were rolled for each case.

As a result, it was confirmed that, in the case where the finishing first stand and the second stand were made of HSS material, the joint portion of the sheet bar did not break and separate during rolling, and rolling could be performed extremely stably. It was also confirmed that rolling can be performed stably even in the case where high-speed steel is used only for the finishing first stand. On the other hand, in the case of using the high chrome cast iron roll for both the finishing first stand and the second stand, the sheet bar between the second stand and the third stand is rolled while rolling the seventh sheet bar. A very serious accident occurred in which the joint was broken and separated. Further, in the case of the case, the state of the sheet bar joint portion during rolling was the same as that of the case, so the rolling was stopped after rolling five sheet bars.

Next, one sheet bar is prepared for each case, rolled to the finishing second stand under the same rolling conditions as above, and then rolled after the third stand without rolling. It was taken down from the line and the joint strength of the joint was investigated. The results are shown in Table 2.

[0019]

[Table 2]

From this table, it can be seen that the strength of the base metal is almost the same in the case.
It was found that an extremely strong joint strength equivalent to 40 kgf / mm ² was obtained, and in the case it was slightly inferior to the base metal strength.
It can be seen that the strength is relatively high. On the other hand, in the case and the case, the strength is about 50% of the strength of the base material, and sufficient bonding strength is not obtained. From these results, it can be said that it is necessary to use the high-speed steel roll for at least the work roll of the finishing first stand, and it is more desirable to use the high-speed steel roll for the work roll of the second finishing stand.

[0021]

As described above, according to the present invention, the preceding steel piece and the following steel piece are first partially joined at the entrance side of the finishing rolling mill, and at least the finishing first stand is made of a work roll made of high-speed steel. Since it is rolled, the joints of the steel slabs can be joined with high strength, and therefore the joints do not break and separate during rolling, and continuous hot rolling with high productivity can be realized. Becomes

[Brief description of drawings]

FIG. 1 is a schematic diagram of hot rolling equipment suitable for use in carrying out the present invention.

FIG. 2 is a perspective view showing a procedure for joining steel pieces.

FIG. 3 is a perspective view showing a state of pre-bonding by a heating and pressing process.

[Explanation of symbols]

 1 Preceding steel slab 2 Subsequent steel slab 3 Finishing rolling mill 4 Cutting device 5 Heat joining device 6 Rough rolling mill

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Takebayashi 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefectural Technology Research Division, Kawasaki Steel Co., Ltd. (72) Inventor Norio Takashima, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works

Claims (1)

[Claims] 1. A method of hot-rolling by continuously feeding a preceding billet that has undergone a rough rolling step and a subsequent billet that is subsequently conveyed to this billet to a finish rolling mill. A continuous heat treatment for a steel slab, characterized in that the rear end and a part of the front end of a subsequent steel slab are joined together and then rolled using a finishing mill using at least the work roll of the first stand as a high-speed steel sheet. Hot rolling method.