JP2609676B2 - Continuous casting method and apparatus for multilayer slab - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for continuously producing a slab having a multilayer structure in which an outer layer and an inner layer are clearly separated from a molten state.

[Prior Art] As a method of producing a composite steel material by continuous casting, two immersion nozzles having different lengths are inserted into a pool of molten metal in a mold, and the discharge hole positions of the respective nozzles are different in the casting direction. Japanese Patent Publication No. 27361/44 proposes a method of pouring a different type of molten metal at a position. In addition, Japanese Patent Publication No. 49-44859 proposes providing a partition wall made of a refractory material in the mold in order to prevent mixing of different metals injected into the mold at this time.

The present inventors have also developed a method using a static magnetic field as a means for damping the flow of a different molten metal injected into a mold in order to suppress mixing between different molten metals, and Japanese Patent Application No. 61-
Filed as No. 252898. In this method, a static magnetic field is formed such that the lines of magnetic force extend over the entire width of the slab in a direction perpendicular to the casting direction, and different kinds of molten metal are supplied above and below the static magnetic field as a boundary. An electronic brake works by this static magnetic field, and the flow of the molten metal in the static magnetic field band is braked. As a result, mixing of the upper and lower layers at the position where the upper and lower layers are in contact can be minimized.

[Problems to be Solved by the Invention]

However, in the continuous casting methods described above, a plurality of immersion nozzles are inserted into the casting space in the mold. Therefore, it is unavoidable that an irregular flow and temperature distribution occur in the outer layer molten metal bath injected into the casting space. As a result, the solidified shell formed from the molten metal for the outer layer on the inner wall of the mold becomes non-uniform, and a multi-layer cast product having a constant quality cannot be obtained.

Also, depending on the size of the slab to be manufactured, 2
In some cases, the space in which the book immersion nozzles are arranged cannot be taken in the mold. For example, in a mold for bloom casting or the like, the internal space of the mold is narrow, and it is extremely difficult to arrange two immersion nozzles in this narrow space.

Therefore, the present invention relates to a method of directly connecting a container containing a molten metal for an outer layer and a mold, taking a molten metal surface of the molten metal for an outer layer in the container, and statically supplying the molten metal for an outer layer to the mold to form an outer layer. It is an object of the present invention to grow a solidified shell to be a stable condition and to produce a multilayer slab of constant quality even when the internal space of the mold is narrow.

[Means for Solving the Problems]

The continuous casting method of a multilayer cast product of the present invention is, in order to achieve the object, a molten metal for forming an outer layer of a multilayer cast product in which a container insulated from the mold is connected to the mold. While containing and continuously casting, a static magnetic field in a direction perpendicular to the casting direction is applied to the molten metal in the solidified shell generated from the molten metal, and the complex magnetic field in the solidified shell below the static magnetic field is applied. The method is characterized in that a molten metal for forming an inner layer of a layer slab is supplied.

Further, the continuous casting apparatus for a multilayer cast product of the present invention is provided on a container having an opening at the bottom, a mold connected to the opening of the container, and an inner wall of a boundary between the container and the mold. A heat insulating ring, a magnet provided so as to sandwich the opposing outer surface of the mold, and a magnet that applies a static magnetic field in a direction perpendicular to the casting direction, and the discharge hole is inserted through the container and inserted into the mold. A pouring nozzle located below the magnet is arranged. In addition, a solenoid coil that is wound around a mold and generates a magnetic field in a direction parallel to the casting direction is arranged instead of the magnet.

[Action]

Hereinafter, the continuous casting method and apparatus of the present invention will be described specifically with reference to FIG.

The container 2 has an opening 3 at the bottom, and a mold 4 is connected to the opening 3, and a heat insulating ring 9 is provided on the inner wall at the boundary between the container 2 and the mold 4.

The molten metal 1 to be the outer layer of the multilayer slab is contained in a container 2 such as a tundish, and is supplied from the container 2 into the mold 4. At this time, the outer layer molten metal 1 is continuous between the inside of the container 2 and the inside of the mold 4 via the opening 3. Therefore, the supply of the outer layer molten metal 1 from the container 2 to the mold 4 is performed by static pressure based on the head pressure, and flows to the molten metal in the mold 4 as in the case of using a conventional immersion nozzle. It does not give kinetic energy that causes things such as.

Thus, when the molten metal 1 for the outer layer is supplied, the mold 4
The outer layer molten metal bath 1a formed therein is maintained in a quiet state, and its temperature distribution becomes uniform. Therefore, the molten metal bath for outer layer 1a is cooled and solidified, and the solidified shell 1b is uniformly formed on the inner wall of the mold 4 in the circumferential direction. In particular, the formation of a solidified shell having a non-uniform thickness, which occurred when pouring the molten metal into the mold 4 using the immersion nozzle, is not observed.

In order to keep the formation start position of the solidified shell 1b formed on the inner wall of the mold 4 constant, an insulating ring 9 is provided on the inner wall at the boundary between the container 2 and the mold 4.

On the other hand, the pouring nozzle 6 penetrates the container 2 and is inserted into the mold 4, and the discharge hole 10 is located below the magnet 8 described later. The molten metal 5 forming the inner layer is injected into the mold 4 from the pouring nozzle 6 which penetrates the container 2 and the molten metal bath 1a for the outer layer and enters the mold 4, and the molten metal bath for the outer layer is formed.
An inner layer molten metal bath 5a is formed below 1a. The molten metal 5 for the inner layer is removed from the mold 4 by the heat of the solidified shell.
It cools and solidifies inside 1b to form a solidified shell 5b.

Here, in order to apply a static magnetic field to the interface 7 between the outer layer molten metal bath 1a and the inner layer molten metal bath 5a and its vicinity, only a predetermined distance from the position where the surface layer of the outer layer molten metal starts to solidify. The magnet 8 is arranged so as to sandwich a certain opposing surface of the slab in the lower part, which is a prior application of Japanese Patent Application No. 61-2528.
Similar to No. 98. The static magnetic field suppresses the flow of the molten metals 1 and 5 in the mold 4, and the molten metal bath for outer layer 1a and the molten metal bath for inner layer 5a are maintained in a vertically separated state without being mixed with each other. A similar braking force can be obtained by winding a solenoid coil in place of the magnet 8 around the mold 4 and applying a direct current thereto to generate a magnetic field having magnetic lines of force parallel to the casting direction.

Due to this electromagnetic braking force, the solidified shell 1b and the solidified shell 1a and the solidified shell 1a from the outer layer molten metal bath 1a and the inner layer molten metal bath 5a
Each 5b grows and they no longer mix with each other. Further, since the molten metal 1 for the outer layer is statically supplied, the solidified shell 1b for the outer layer has a uniform thickness, and the layered structure of the obtained multilayer slab is constant. In addition,
The thickness of the outer layer and the inner layer should be controlled by adjusting the level of the molten metal 1 for the outer layer in the container 2, the supply amount of the molten metal 5 for the inner layer from the pouring nozzle 6, and the position of the static magnetic field zone. You can

In addition, the nozzle to be inserted into the mold 4 is only the pouring nozzle 6 for injecting the molten metal 5 for the inner layer.
Even if the internal space of the is small, it does not hinder the pouring work. Since the pouring nozzle 6 can be held in the center of the mold 4, the inner layer molten metal 5 flowing out of the pouring nozzle 6 can reach a large distance to reach the solidified shells 1b and 5b, and the high temperature state As it is, the remelting due to the inner layer molten metal 5 coming into contact with the solidified shells 1b, 5b is prevented.

〔Example〕

Example 1. As the molten metal 1 for the outer layer, a SUS304 composition having a temperature of 1500
C. Molten steel was used, and the distance from the molten metal level in the container 2 to the interface 7 was maintained at 1000 mm. On the other hand, molten metal for inner layer 5
The molten steel having a normal steel composition and a temperature of 1550 ° C. was used, and was poured into the mold 4 from the pouring nozzle 6 at a flow rate of 1152 kg / min. In addition, a static magnetic field of 5000 gauss was applied to suppress the flow of the molten metal bath for outer layer 1a and the molten metal bath for inner layer 5a at the interface 7 which is 600 mm below the upper end of the mold 4. Under these conditions, a slab having a cross section of 200 mm × 1000 mm and a thickness of the outer layer of 20 mm was produced at a casting speed of 1 m / min.

FIG. 2 is a graph showing the thickness variation of the outer layer in the obtained cast slab. In addition, FIG. 2 shows a slab obtained by a conventional method in which two dipping nozzles are inserted into the mold 4 to perform casting, as a comparative example. As is clear from this comparison, it can be seen that the outer layer of the cast piece obtained in this example has a constant thickness. This is because the outer layer molten metal 1 is statically supplied, and the outer layer molten metal 1 in the outer layer molten metal bath 1a is reduced in contact with the solidified shell 1b and remelting in a high temperature state. It is thought to be due to. The change in the Cr content from the outer layer to the inner layer was steep, and the outer layer and the inner layer had a very clear boundary.

Example 2. The shape of the mold 4 was a circular size having an inner diameter of 170 mm.
On the other hand, in order to shorten the pouring nozzle 6 from the viewpoint of strength and cost, the shape of the container 2 has a low height of 400 mm. Further, in order to suppress heat radiation through the vessel wall, the longitudinal length and the lateral length of the container 2 are set to 400 mm and 300 mm, respectively. A heat insulating ring is provided on the inner wall at the boundary between the container 2 and the mold 4, and a static magnetic field zone having a magnetic flux density of 3000 gauss by the magnet 8 within a range of ± 100mm with respect to the casting direction around a position 1000mm below the heat insulating ring. Was formed.

Under this condition, the molten metal 1 having the SUS304 composition is placed in the container 2
Was poured into the mold 4. On the other hand, a molten metal 5 having a general medium carbon steel composition was injected from a pouring nozzle 6 below the static magnetic field zone. Then, a multilayer slab was continuously cast at a casting speed of 1.0 m / min.

The obtained multilayer slab was a round bloom having a diameter of 170 mm and an outer layer having a thickness of 30 mm and having a SUS304 composition. Further, only a mixed layer having a thickness of about 1 mm was formed at the boundary between the SUS304 forming the outer layer and the medium carbon steel forming the inner layer.

Example 3 As the mold 4, a mold having a square internal space with one side of 150 mm was used. Further, the container 2 is the same as that of the second embodiment.
The same one was used. Then, a static magnetic field zone having a magnetic flux density of 3000 gauss was formed by the magnet 8 in a range of ± 100 mm with respect to the casting direction around a position 1200 mm below the heat insulating ring provided on the inner wall at the boundary between the container 2 and the mold 4. .

Under this condition, molten metal 1 having a general medium carbon steel composition was poured into vessel 2 and molten metal 5 having an 18-8 stainless steel composition containing 2.0% by weight of B was poured below the static magnetic field zone. The hot water was injected from the nozzle 6. Then, a multilayer slab was continuously cast at a casting speed of 1.2 m / min.

The obtained multilayer slab was a square bloom with a side of 150 mm, the outer layer had a multilayer structure of 30 mm thick carbon steel, and the inner layer had a B-containing 18-8 stainless steel. Only a mixed layer having a thickness of about 1 mm was formed at the boundary between the outer layer and the inner layer.

Since B-containing 18-8 stainless steel is susceptible to solidification cracking, it has been considered unsuitable for the conventional continuous casting method. On the other hand, in this example, since the B-containing 18-8 stainless steel was poured and slowly cooled after the outer layer made of carbon steel was formed, solidification cracking did not occur in the inner layer. Also, B-containing 18-8 stainless steel is a material that is difficult to hot work, but the slab obtained in the present example is covered with an outer layer of carbon steel, and thus causes defects such as rolling cracks. It was hot worked without, and a material with a smaller cross section was obtained. Moreover, when the carbon steel of the outer layer is removed after processing, the carbon steel can be easily removed by pickling or the like because the thickness of the outer layer is uniform and the mixed layer at the boundary is thin. A B-containing 18-8 stainless steel having the following characteristics:

〔The invention's effect〕

As described above, in the present invention, the molten metal serving as the outer layer is continuous from the container to the mold, so that the molten metal can be poured in a static state. Therefore, the temperature of the molten metal in the mold becomes uniform, the solidified shell generated on the inner wall of the mold grows uniformly in the circumferential direction of the slab, and a multilayer slab having an outer layer with a constant thickness can be manufactured. Also, since the nozzle to be inserted into the mold only needs to inject the molten metal that forms the inner layer, even if the internal space of the mold is narrow, the casting operation should be performed without any hindrance. You can Furthermore, according to the present invention, as a metal for the inner layer, a material that could not be continuously cast in the past or a material that could be continuously cast but could not be hot worked can be used, so that the combination of the inner layer and the outer layer can be widely used. It is possible to obtain a multi-layer slab according to demand.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a continuous casting apparatus of the present invention, and FIG. 2 is a graph specifically showing the effect of the present invention.

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Claims (3)

(57) [Claims] 1. A solidification produced from the molten metal, wherein a mold and a container insulated from the heat are connected to the mold, and the molten metal forming the outer layer of the multi-layer slab is accommodated in the container to continuously cast the molten metal. A static magnetic field is applied to the molten metal in the shell in a direction perpendicular to the casting direction, and a molten metal that forms an inner layer of the multilayer cast product is supplied into the solidified shell below the static magnetic field. Continuous casting method for multi-layer cast slab. 2. A container having an opening at a bottom, a mold connected to the opening of the container, a heat insulating ring provided on an inner wall at a boundary between the container and the mold, and a mold facing the mold. A magnet provided so as to sandwich the outer surface and applying a static magnetic field in a direction perpendicular to the casting direction, and a pouring nozzle inserted through the container and inserted into the mold and having a discharge hole located below the magnet A continuous casting apparatus for multi-layer cast slabs, characterized in that and are arranged. 3. A container having an opening at the bottom, a mold connected to the opening of the container, a heat-insulating ring provided on the inner wall of the boundary between the container and the mold, and around the mold. A solenoid coil that is wound and generates a magnetic field in a direction parallel to the casting direction, and a pouring nozzle that penetrates the container and is inserted into the mold and has a discharge hole located below the solenoid coil. A continuous casting apparatus for multilayer cast slabs.