JPH05146847A - Method for connecting slabs in continuous casting for different kinds of steels - Google Patents

Abstract

PURPOSE:To surely connect the previous slab and the following slab in short time without leaking molten steel in a continuous casting for different kinds of the steels. CONSTITUTION:After the molten metal is completed to cast into a mold 2 from a tundish 1, a member 4 for connecting the slabs is inserted into the rear end part of the previous slab 3 in the mold 2. Successively, the molten steel 7 having the different kind of steel with the previous molten steel is poured into the mold 2, and when the height of the molten steel 7 having this different kind of steel becomes about 150-200mm from the rear end part of the previous slab 3, the pouring is stopped. This condition is kept in about 60-120sec and the poured molten steel 7 having the different kind of steel is perfectly solidified in the circumference of the member 4 for connecting the slab with the rear end part of the previous slab 5. Thereafter, the pouring of the molten steel 7 having the different kind of steel into the mold 2 is started.

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 kinds of molten steel.

[0002]

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

Therefore, in order to shorten the length of the joint portion and increase the yield, various continuous casting methods for different steel types have been considered. For example, in the continuous casting method for different steel types described in JP-A-61-140354, after the first molten steel is 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. It is to cover and then cast different kinds of molten steel into the mold. According to this method, it is possible to substantially eliminate the component mixing region between different kinds of molten steel. This makes it possible to reduce the length of the seam portion, but on the other hand, it brings about a drawback that the front slab and the rear slab are weakly coupled. Further, the front end portion of the rear slab may be insufficiently solidified, and molten steel may leak from the joint.

As another method for continuously casting different steel types, after the molten steel has been cast from the tundish into the mold, a slab connecting member is inserted at the rear end of the front slab in the mold, and then a different molten steel is cast. There is also a method in which the molten steel is poured little by little into the mold, and after about 90 seconds, the gate of the immersion nozzle of the tundish is wide open to start casting the different molten steel. In the case of this method, the front end portion of the rear slab is likely to be insufficiently solidified, which may lead to a situation in which molten steel leaks from the joint portion and the operation must be stopped. In such a case, it takes a long time to recover, which is a great loss.

[0005]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to provide a method for connecting slabs in continuous casting of dissimilar steel types, which can reliably join the front slab and the rear slab in a short time without leaking molten steel. To provide.

[0006]

In order to solve the above-mentioned problems, the slab connection method according to the present invention is to connect the slab to the rear end of the front slab in the mold after the molten steel has been cast from the tundish into the mold. And then injecting different kinds of molten steel into the mold from the tundish, and when the height of the different kinds of molten steel is about 150 to 200 mm from the rear end of the front slab, the injection is stopped. And maintaining the state as it is for about 60 to 120 seconds to completely solidify the injected molten steel at the rear end portion of the front slab and the periphery of the slab connecting member, and then to the tundish. Starting the casting of the different molten steel into the mold.

[0007]

Function: The height is about 150 to 200 m on the front slab in which the slab connecting member is inserted at the rear end in the mold.
About 60 to 12 by injecting different kinds of molten steel to
If the state is kept as it is for 0 seconds, only a small amount of the injected molten steel of a different type is brought into a completely solidified state at the rear end portion of the front slab and the periphery of the slab connecting member.
Further, the injected small amount of molten steel of a different type melts a part of the rear end portion of the front slab and mixes with it to form a relatively short-length component mixing region. The area around the slab connection member centering on this component mixing area constitutes the connection portion between the front slab and the rear slab. In this way, if the pouring of the different molten steel from the tundish into the mold is started after the injected small amount of different molten steel is completely solidified, the joint between the front slab and the rear slab can be ensured. The connected state can be maintained.

[0008]

EXAMPLE FIG. 1A shows a state in which a molten steel is cast from a tundish 1 into a mold 2 and then a slab connecting member 4 is inserted into a rear end portion of a front slab 3 in the mold 2. .. Molten steel is poured from the ladle 5 into the tundish 1 and cast into the mold 2 from the tundish 1 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 members may be used.

In FIG. 1 (b), molten steel 7 of a different type is then poured from the tundish 1 into the mold 2, and when the height of the molten steel 7 reaches about 150 to 200 mm from the rear end of the front slab 3, the sliding is performed.・ Indicates that the gate is closed and injection is stopped. This state is maintained for about 60 to 120 seconds.

The injected molten steel 7 of different kinds can be completely solidified in the rear end portion of the front slab 3 and the periphery of the slab connecting member 4 in this short time because of a small amount. .. The injected molten steel 7 of a different type melts a part of the rear end portion of the front slab 3 and mixes with it to form a relatively short-length component mixing region (not shown). At this stage, the area around the slab connecting member 4 centering on this component mixing area is the front slab 3 and the rear slab 8 (see FIG. 1).
It will be formed in a completely solidified state as a connecting portion with (see (c)).

In FIG. 1 (c), after a small amount of the different molten steel 7 is completely solidified, the sliding gate is opened again to start casting the molten steel of the same kind as the different molten steel 7 from the tundish 1 into the mold 2. Shows the state of being done. Since the connecting portion between the front slab 3 and the rear slab 8 has already been solidified and formed, a reliable connection state can be maintained at the joint between the slabs even at this stage.

The injection amount of the different molten steel 7 at the stage of FIG. 1 (b) has an appropriate range as described above. If this injection amount is too small, when the casting of the different molten steel 7 is started at the stage of FIG. 1 (c), all the connected portions formed by solidification will be melted, and molten steel may leak later. The nature is enhanced. On the other hand, if the injection amount in the stage of FIG. 1 (b) is too large, it takes too much time for solidification, and the joint portion is likely to be insufficiently solidified, so that molten steel leakage may occur later. Will increase. These facts have been confirmed by experiments. As can be seen from FIG. 2 which is a graph showing the relationship between the molten steel injection amount (height) and the molten steel leakage occurrence rate at the stage of FIG. 1 (b), the proper injection amount is the rear end of the front slab 3. The height is about 150 to 200 mm from the part.

There is an appropriate range for the time for injecting the different molten steel 7 and maintaining this state at the stage of FIG. 1 (b). If it is too short, the solidification will be insufficient, and if it is too long, the different molten steel 7 will solidify and shrink, so that the sealing of the molten steel will be incomplete and the molten steel may leak later. Further, if the time during which the molten steel injection is stopped is too long, there is also the inconvenience that the success rate of nozzle opening decreases when the casting of the molten steel is started again in the next stage. According to FIG. 3 which is a graph showing the relationship between the time for maintaining the state of FIG. 1B, the molten steel leak occurrence rate, and the nozzle hole success rate, an appropriate range of the holding time is 60 to 12.
It turns out that it is 0 second.

[0015]

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

[Brief description of drawings]

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

FIG. 2 is the injection amount (height) of different molten steel at the stage of FIG. 1 (b).
It is a graph which shows the relationship between molten steel leak occurrence rate.

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

[Explanation of symbols]

1 tundish, 2 molds, 3 front slabs, 4
Slab connection member, 5 ladle, 6 immersion nozzle, 7 different molten steel, 8 rear slab.

Front page continuation (72) Inventor Yuichi Tsukaguchi, 1850 Minato, Wakayama, Wakayama Sumitomo Metal Industries, Ltd. Wakayama Works (72) Inventor, Masaya 1850, Minato, Wakayama, Wakayama Sumitomo Metal Industries, Ltd. Inside the steel mill

Claims (1)

[Claims] 1. A step of inserting a member for connecting a slab into a rear end portion of a front slab in a mold after the molten steel is cast from the tundish into the mold, and then a different kind of molten steel is introduced from the tundish into the mold. And the height of the different molten steel is about 150 to 20 from the rear end of the front slab.
At the time of reaching 0 mm, the step of stopping the injection and maintaining the state as it is for about 60 to 120 seconds, completely injecting the injected different molten steel between the rear end of the front slab and the periphery of the slab connecting member. A method for connecting slabs in continuous casting of different steel types, comprising the steps of solidifying and then initiating casting of the different molten steel from the tundish into the mold.