JP2701628B2 - Slab connection method in continuous casting of dissimilar steels - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting a front slab and a rear slab when continuously casting different types of molten steel.

[0002]

2. Description of the Related Art In a continuous casting method, when molten steels of different types are continuously cast, the molten steels are mixed with each other at a joint portion, resulting in a steel slab that cannot be used as either steel type. The length of such a seam portion varies depending on the thickness, width and the like, but is about 4 to 5 m, which is a factor that significantly reduces the yield.

In order to increase the yield by shortening the length of the joint, various continuous casting methods of different types of steel have been considered. For example, in the method for continuously casting different types of steel described in Japanese Patent Application Laid-Open No. 61-140354, after the first molten steel has been cast from the tundish into the mold, the upper surface of the rear end of the front slab in the mold is cooled by a cooling block. Then, different kinds of molten steel are cast into the mold. According to this method, the component mixing zone between different types of molten steel can be substantially eliminated. This has the disadvantage that the joint between the front slab and the rear slab is weakened, while the length of the seam can be shortened. In addition, the front end of the rear slab is insufficiently solidified, and there is a possibility that molten steel leaks from the joint.

[0004] As another method of continuously casting different kinds of steel, after the molten steel has been poured from the tundish into the mold, a slab connecting member is inserted into the rear end of the front slab in the mold, and then a different kind of molten steel is cast. Is injected little by little into the mold, and after about 90 seconds, the gate of the immersion nozzle of the tundish is opened widely to start casting of the dissimilar molten steel. In the case of this method, the front end of the rear slab tends to be insufficiently solidified, and there is a possibility that molten steel leaks from the joint and the operation must be stopped. In such a case, it takes a long time to recover, and the damage is serious.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for connecting slabs in a continuous casting of different steels, which can reliably connect the front slab and the rear slab in a short time without leaking molten steel. Is to provide.

[0006]

In order to solve the above-mentioned problems, a method for connecting a slab according to the present invention comprises connecting a slab to a rear end of a front slab in a mold after casting molten steel from a tundish into a mold. and inserting the use member, before the step of solidifying the slab rear end, then the molten steel heterologous injected from a tundish into a mold, the height of said heterologous of molten steel before the slab of the rear end portion or al 1 50 to 2
The step of stopping the injection at the time of reaching 00 mm, and maintaining the state as it is for 60 to 120 seconds, completely dispersing the injected molten steel at the rear end of the front slab and around the slab connecting member. Solidifying and then initiating the casting of the dissimilar molten steel from the tundish into the mold.

[0007]

[Action] is inserted a slab connecting member to the rear end portion in a mold over the prior slab has solidified, to 1 50 Height 20
Injecting molten steel heterogeneous such that 0 mm, to 6 0 1
If the state is maintained for 20 seconds, only a small amount of the injected molten steel is completely solidified at the rear end of the front slab and around the slab connecting member. Also, the injected small amount of different kinds of molten steel melts a part of the rear end of the front slab and mixes with the molten steel to form a component mixing zone having a relatively short length. A region around the slab connection member centered on the component mixture region forms a connection portion between the front slab and the rear slab. In this way, if the casting of the different molten steel from the tundish to the mold is started after the injected small amount of the different molten steel is completely solidified, the seam between the front slab and the rear slab is reliable. The connected state can be maintained.

[0008]

FIG. 1 (a) shows a state in which molten steel has been cast from a tundish 1 into a mold 2 and a slab connecting member 4 has been inserted into the rear end of the front slab 3 in the mold 2. . Molten steel is poured from the ladle 5 into the tundish 1 and cast from the tundish 1 into the mold 2 through the immersion nozzle 6 with a sliding gate.

As the slab connecting member 4, for example, a pipe-shaped member can be used, but other forms may be used.

[0010] FIG. 1 (b), then at the time the molten steel 7 heterologous injected from the tundish 1 into the mold 2, to Do et al 1 50 rear end of the front slab 3 its height became 200mm The sliding gate is closed and the injection is stopped. This state is maintained for 60 to 120 seconds.

The small amount of the different types of molten steel 7 injected can be completely solidified at the rear end of the front slab 3 and around the slab connecting member 4 in this short time. . Further, the injected molten steel 7 of a different kind melts a part of the rear end of the front slab 3 and mixes with the molten steel to form a component mixture zone (not shown) having a relatively short length. At this stage, the area around the slab connecting member 4 centered on the component mixture area is the front slab 3 and the rear slab 8 (FIG. 1).
(See (c)), it is formed in a completely solidified state.

FIG. 1C shows that after a small amount of the molten steel 7 is completely solidified, the sliding gate is opened again and the molten steel 7 is transferred from the tundish 1 into the mold 2.
5 shows a state in which casting of molten steel of the same type as above has started. Since the connecting portion between the front slab 3 and the rear slab 8 has already been once solidified and formed, even at this stage, a reliable connection state can be maintained at the joint between the slabs.

The injection amount of the different types of molten steel 7 at the stage of FIG. 1 (b) has the appropriate range as described above. If the injection amount is too small, when the casting of molten steel 7 of a different kind is started at the stage of FIG. 1 (c), all of the connecting portions formed by solidification are melted, and the molten steel leaks later. The possibilities increase. On the other hand, if the injection amount at the stage of FIG. 1B is too large, it takes too much time for solidification, and the seam tends to be insufficiently solidified. Will increase. These facts have been confirmed by experiments. As can be seen from FIG. 2 which graphically shows the relationship between the molten steel injection amount (height) and the molten steel leakage occurrence rate at the stage of FIG. It either et 1 50 parts height of 200mm preparative ing.

There is an appropriate range for the time during which the molten steel 7 of a different kind is injected at the stage of FIG. If the length is too short, the solidification becomes insufficient. If the length is too long, the molten steel 7 of the different kind is solidified and contracted, so that the sealing of the molten steel becomes incomplete and there is a possibility that the molten steel leaks later. Further, if the time during which the molten steel injection is stopped is too long, there is also a disadvantage that the success rate of the nozzle opening decreases when the casting of the molten steel is started again in the next stage. FIG. 3 is a graph showing the relationship between the time for maintaining the state of FIG. 1B and the rate of occurrence of molten steel leakage and the success rate of nozzle opening. .

[0015]

According to the method for connecting slabs in the continuous casting of dissimilar steels of the present invention, the front slab and the rear slab can be reliably connected in a short time without leaking molten steel.

[Brief description of the drawings]

FIG. 1 is a series of diagrams illustrating a slab connection method according to the present invention. (A) shows a state in which the slab connecting member is inserted into the rear end of the front slab in the mold after the molten steel has been cast into the mold. (B) shows a state in which a different amount of molten steel is then injected into the mold in a small amount, and then the injection is stopped. (C) shows a state where, after a small amount of different kinds of molten steel has completely solidified, casting of molten steel of the same kind as the different kinds of molten steel into the mold is started again.

FIG. 2 Injection amount (height) of dissimilar molten steel at the stage of FIG. 1 (b)
6 is a graph showing a relationship between the rate of occurrence of molten steel and the rate of occurrence of molten steel.

FIG. 3 is a graph showing the relationship between the time for maintaining the state of FIG. 1 (b), the molten steel leakage occurrence rate, and the nozzle opening success rate.

[Explanation of symbols]

1 Tundish, 2 molds, 3 front slabs, 4
Slab connecting member, 5 ladle, 6 immersion nozzle, 7
Different types of molten steel, 8 after slab.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yuichi Tsukaguchi 1850 Minato, Wakayama-shi, Wakayama Sumitomo Metal Industries, Ltd.Wakayama Works (72) Inventor Masaya Asano 1850 Minato, Wakayama-shi, Wakayama Sumitomo Metal Industries, Ltd. Inside the Wakayama Works (56) References JP-B-61-32105 (JP, B2)

Claims (1)

(57) [Claims] 1. After casting molten steel from a tundish into a mold, inserting a slab connecting member into the rear end of the front slab in the mold ;
A step of solidifying, then the molten steel heterologous injected from a tundish into a mold, to Do et al 1 50 rear end of the front slab height of said heterologous of molten steel to stop the injection at the time point when 200mm stage Holding the state as it is for 60 to 120 seconds to completely solidify the injected molten steel at the rear end of the front slab and around the slab connecting member, and then mold from the tundish. Starting the casting of the dissimilar molten steel into the slab in the continuous casting of different types of steel.