JPH0464770B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a dummy bar used when continuously manufacturing from a molten state a multi-layer slab having surface layers of different compositions formed thereon.

[Conventional technology]

As a method for manufacturing composite steel materials by continuous casting, two immersion nozzles of different lengths are inserted into a pool of molten metal in a mold, and the discharge holes of each nozzle are set at different positions in the casting direction. , a method of injecting different types of molten metal was published in
This is proposed in Publication No. 27361.

Furthermore, Japanese Patent Publication No. 49-44859 discloses a method of continuous casting while preventing the different types of molten metals from mixing with each other by providing partition walls made of refractory between different types of molten metals poured into the mold. Proposed.

The present inventors have also developed a method of manufacturing this type of multi-layered slab using a static magnetic field that partitions different types of molten metal poured into a mold, and published this method in Japanese Patent Application No. 61-252898. The application was filed as In this method, a static magnetic field is created in which lines of magnetic force extend across the entire width of the slab in a direction perpendicular to the casting direction, and molten metals of different types are supplied above and below this static magnetic field as a boundary. There is. This static magnetic field acts as an electromagnetic brake, and the flow of molten metal in the static magnetic field is braked. As a result, mixing of the upper and lower layers at the position where the upper and lower layers contact can be suppressed to a minimum.

[Problem to be solved by the invention]

Even with these methods, mixing of dissimilar metals cannot be avoided at the start of casting. For example, in order to withdraw the slab from the casting space, it is necessary to grow a solidified shell with a predetermined thickness on the inner wall of the mold.

FIG. 3 is a diagram for explaining a method of forming this solidified shell at the start of casting.

That is, as shown in FIG. 3a, a dummy bar 2 and a dummy bar head 3 are placed inside a continuous casting mold 1. In this state, different types of molten metals 6 and 7 are supplied into the continuous casting mold 1 from the immersion nozzles 4 and 5, respectively. These molten metals 6 and 7 are cooled and solidified by contacting the inner wall of the continuous casting mold 1, and a solidified shell 8 is formed on the inner wall. This solidified shell 8
As the dummy bar 2 grows, the dummy bar 2 is lowered as shown by the arrow.

Then, when the dummy bar 2 reaches a predetermined position, the immersion nozzle 5 is lowered as shown in FIG. 3b to form vertically separated molten metal baths 6a and 7a in the continuous casting mold 1. . When the dummy bar 2 is lowered in this state, a solidified shell 8a formed from the molten metal bath 6a becomes the outer layer, and a solidified shell 8 formed from the molten metal bath 7a is inside the outer layer.
A multilayer slab with b is obtained. At this time, a static magnetic field is applied by the magnet 9 near the interface between the molten metal baths 6a and 7a, and the flow of the molten metals 6 and 7 is braked.

However, a considerable amount of time is required until the solidified shell 8 formed from the mixed molten metals 6 and 7 is separated into solidified shells 8a and 8b. The slabs cast during this period do not have the desired multilayer structure and are therefore discarded. As a result, the yield of products decreases.

In order to avoid this, the molten metal 7 forming the lower molten metal bath 7a is prevented from being injected into the continuous casting mold 1 at the start of casting, and the molten metal 7 is not injected when the state shown in Fig. 3b is reached. The immersion nozzle 5 is lowered in this state, and when it reaches a predetermined position, injection of the molten metal 7 is started. But in this case,
The air accumulated in the immersion nozzle 5 causes a problem in that injection cannot be started stably.

In addition, the tip of the immersion nozzle 5 is pressed against a part of the dummy bar head 3, and the immersion nozzle 5 is lowered at the same time as the dummy bar 2 is lowered, and when it reaches a predetermined position, it is separated from the dummy bar head 3 and the injection of the molten metal 7 is started. Another possible method is to do so. However, even in this case, when the molten metal is inserted between the tip of the immersion nozzle 5 and the dummy bar head 3 or around the contact area and solidifies, the immersion nozzle 5 is There is also a risk of breakage.

Therefore, the present invention uses a dummy bar with a cavity formed at its tip to accommodate the molten metal that will become the inner layer at the early stage of casting. The purpose is to produce layer slabs.

[Means to solve the problem]

In order to achieve the purpose, the dummy bar for continuous casting of multi-layer cast slabs of the present invention cools and solidifies dissimilar molten metals that are vertically injected separately into the casting space in a mold to form multi-layer cast slabs. The apparatus for manufacturing the above is characterized in that a space for accommodating the molten metal in the lower layer is formed at the tip.

[Effect]

FIG. 1 shows a dummy bar according to the invention being inserted into a continuous casting mold.

This dummy bar 2 has a space 10 at its tip. The upper outer surface of the space 10 is arranged near the interface between the upper and lower molten metal baths formed inside the continuous casting mold 1. The immersion nozzle 5 is inserted into the space 10 and the molten metal 7 is poured into the space 10.
inject. Molten metal 7 enters opening 1 of space 10
When the mold is filled to 1, the injection of molten metal 7 is stopped, and molten metal 6 is injected into the continuous casting mold 1 from the immersion nozzle 4. Alternatively, the molten metals 6 and 7 may be simultaneously injected from the immersion nozzles 4 and 5 with the amount of molten metal 7 poured within the internal volume of the internal space of the space 10, filling the space 10 with the molten metal 7, and performing continuous casting. It is also possible to fill the mold 1 with molten metal 6. Although a small amount of molten metal 6 may flow into the space 10, it is necessary to minimize the molten metal 7 from entering into the continuous casting mold 1.

Therefore, since the continuous casting mold 1 is filled with molten metal 6 at the start of casting, the solidified shell 8a formed by cooling and solidifying the molten metal 6 is filled in the continuous casting mold 1.
formed on the inner wall of Thereafter, while pulling down the dummy bar 2, the molten metals 6 and 7 are injected from the respective immersion nozzles 4 and 5 at a constant injection rate. Then, a static magnetic field by a magnet 9 is applied near the boundary between the molten metals 6 and 7 to exert a braking force, thereby maintaining a molten metal bath vertically separated in the continuous casting mold 1.

In this way, according to the present invention, since the molten metal baths 6a and 7a are maintained vertically separated from each other from the beginning of casting, the molten metal baths 6a and 7a are mixed as described in FIG. The generation of coagulated shell 8 generated from 7 is suppressed. Therefore, the manufactured multilayer slab also has a predetermined multilayer structure substantially from the bottom side, and the yield is significantly improved.

Note that it is preferable that the opening 11 of the space 10 is designed to have a size with some distance between it and the immersion nozzle 5. If the distance between the opening 11 and the immersion nozzle 5 is too small, not only will it be difficult to insert the immersion nozzle 5 into the space 10, but the immersion nozzle 5 will become stuck to the dummy bar 2 due to solidified metal. Otherwise, the opening 11 or the tip of the immersion nozzle 5 may be damaged. On the other hand, the molten metal 6 flowing into the space 10 through the space between the opening 11 and the immersion nozzle 5 does not adversely affect the growth of the solidified shell 8a on the inner wall of the continuous casting mold 1.
It is acceptable.

〔Example〕

A dummy bar 2 having a space 10 with an internal volume of 20000 cm ³ at its tip was inserted into a continuous casting mold 1 having an internal space with a horizontal cross section of 200 mm x 1000 mm. The immersion nozzle 5 enters this space 10 at a temperature that has a composition of ordinary steel.
Molten metal 7 at a temperature of 1550°C was injected, and at the same time, the interior of the continuous casting mold 1 was filled with molten metal 6 having a composition of SUS304 and a temperature of 1500°C from the immersion nozzle 4. The amount of molten metal 5 injected was adjusted so as not to exceed the internal volume of the space 10. Thereafter, the dummy bar 2 was lowered to form vertically separated molten metal baths 6a and 7a within the continuous casting mold 1. Next, the multilayer slab was pulled out from the continuous casting mold 1 at a casting speed of 1 m/min.

FIG. 2 is a graph showing changes in the Cr content contained in the outer layer of the obtained multilayer slab along the casting direction. As is clear from FIG. 2, in the multilayer slab obtained in this example, an outer layer with a predetermined Cr content (18%) was formed in a short period of time from the start of casting. Therefore, the part that is cut off because the target Cr content is not reached is
It was no more than 0.5m from the bottom of the slab.

On the other hand, when the normal dummy bar 2 shown in Fig. 3 is used, 4 to 5
An outer layer having the target Cr content is finally formed at the point m. Therefore, from this bottom 4
The yield was poor because up to 5 m was cut off and the rest was used as a product.

〔Effect of the invention〕

As explained above, in the dummy bar of the present invention, a space is formed at the tip to accommodate the molten metal that becomes the inner layer of the multilayer slab. The internal space of the continuous casting mold above the dummy bar is filled only with molten metal to form multiple layers. Therefore, the two molten metals do not mix, and only the latter molten metal cools and solidifies on the inner wall surface of the continuous casting mold to form a solidified shell. As a result, the outer layer has the target components and composition from the beginning of casting, and it becomes possible to manufacture a multilayer slab with a high yield.

[Brief explanation of drawings]

FIG. 1 shows a state in which the dummy bar of the present invention is inserted into a continuous casting mold, and FIG. 2 is a graph specifically showing the effects of the present invention. On the other hand, FIG. 3 is a diagram for explaining the start of casting using a conventional dummy bar. 1: Continuous casting mold, 2: Dummy bar, 3: Dummy bar head, 4, 5: Immersion nozzle, 6, 7: Molten metal, 6a, 7a: Molten metal bath, 8, 8a, 8b:
Solidification shell, 9: magnet, 10: space, 11: opening.

Claims (1)

[Claims] 1 In an apparatus for producing a multi-layer slab by cooling and solidifying different types of molten metals that are injected into the casting space in a mold in vertical directions, a space portion for accommodating the lower layer molten metal is formed at the tip. A dummy bar for continuous casting of multiple slabs.