JPH0464780B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for continuously producing a multilayer slab in which layers of different compositions are formed on a portion or multiple locations of the surface from a molten state.

[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.

The present inventors have also developed a method for manufacturing a multilayer slab with a clear boundary between the outer layer and the inner layer by partitioning different types of molten metal poured into a mold using the braking force of a static magnetic field, and have filed a patent application for this method. The application was filed as No. 1983-252898.

FIG. 4 is a schematic diagram illustrating this method.
Immersed nozzles 1 and 2 of different lengths are inserted into a casting space in a mold M, and molten metals 3 and 4 are supplied from these immersed nozzles 1 and 2, respectively. The molten metal 3 serving as the outer layer is heat removed from the wall surface of the mold M and becomes a solidified shell 5. On the other hand, the molten metal 4 serving as the inner layer
is cooled and solidified by heat removal through this solidified shell 5, and becomes a solidified shell 6.

At this time, in order to prevent the molten metals 3 and 4 from mixing with each other in the mold M, a static magnetic field having lines of magnetic force extending in a direction perpendicular to the casting direction is applied to the molten metal by an electromagnet 7 or a permanent magnet. It is applied to 3 and 4. This static magnetic field acts as an electromagnetic brake, suppressing the flow of the molten metals 3 and 4 in the static magnetic field zone, and suppressing mixing.

[Problem to be solved by the invention]

However, with the growth of solidified shells 5 and 6,
The space in which the fluid flows within the mold M becomes narrower. Moreover, the distance between the elongated immersion nozzle 2 and the coagulation shells 5, 6 is also reduced. Therefore, when the molten metal 4 is discharged from the immersion nozzle 2 as shown in FIG. 4, the solidified shells 5 and 6 are washed with the molten metal 4. Since the molten metal 4 immediately after exiting the immersion nozzle 2 is at a high temperature, the solidified shells 5 and 6 near the discharge part of the immersion nozzle 2 are remelted, resulting in uneven thickness of the shell in the circumferential direction, and as a result, the thickness of the surface layer. This results in a slab in which the thickness is not uniform in the circumferential direction.

Therefore, the present invention prevents the solidified shell from becoming non-uniform in the circumferential direction by imparting a horizontal and transverse flow component to the molten metal discharged from a long immersion nozzle, and under stable conditions. The purpose is to manufacture multilayer slabs.

[Means to solve the problem]

In order to achieve its purpose, the continuous casting method of the present invention applies a static magnetic field in which lines of magnetic force extend across the entire width of the slab at a position below the level of the molten metal supplied to the mold. When continuously casting multilayer slabs by supplying different metals above and below this static magnetic field zone, a horizontal flow component is given to the molten metal supplied below the static magnetic field zone. It is characterized by

As a specific means for imparting a horizontal flow component, it is possible to use a submerged nozzle with a discharge port on the side, or an electromagnetic stirring device placed around the slab or mold.

[Effect]

FIG. 1 shows a state in which molten metal 4 is flowing out in a horizontal direction from a discharge port 8 opened on the side surface of a long immersion nozzle 2. Moreover, FIG. 2 is a diagram showing this discharge flow 9 in a horizontal cross-sectional view.

In this way, by discharging and swirling the molten metal 4 from the immersion nozzle 2 in the horizontal direction, the temperature distribution in the plane perpendicular to the casting direction is made uniform. As a result, the solidified shells 5 and 6 grow under uniform temperature conditions, and an outer layer having a uniform thickness in the circumferential direction of the slab is obtained. Note that the discharge port 8 from the immersion nozzle 2 does not necessarily have to be in the horizontal direction;
The discharge port 8 may be formed so that the discharge flow 9 is slightly inclined downward as shown by the dotted line in the figure.

FIG. 3 shows a case in which a flow component in the horizontal direction F is applied to the molten metal 4 flowing out from the immersion nozzle 2 by the electromagnetic stirring device 10. This electromagnetic stirring device 10 has long sides M ₁ and M ₂ of a mold M (see Fig. 2).
The molten metal 4 is made to flow in the horizontal direction. In this manner, as in the case of FIGS. 1 and 2, uniform growth of the solidified shell in the circumferential direction of the slab is promoted, and a multilayer slab having a uniform outer layer in the circumferential direction is obtained.

In addition, in FIG. 3, it is also possible to use the immersion nozzle 2 in which the discharge port 8 is opened on the side surface as shown in FIG. 1. In this case, it is preferable that the direction of the electromagnetic stirring force be reversed on both sides of the long pieces M ₁ and M ₂ of the mold M so as not to go against the discharge flow from the nozzles 1 and 2. By this,
A horizontal swirling flow can be formed, resulting in a greater effect.

Also, the molten metal 4 discharged from the immersion nozzle 2
Since it does not flow vertically downward, the reverse flow is also reduced. Therefore, the motion component that disturbs the interface between the molten metals 3 and 4 is reduced, and mixing of the molten metals 3 and 4 with each other is also suppressed. As a result, the boundary between the outer layer and the inner layer in the obtained multilayer slab becomes clear, and no transition phase is formed at this interface.

〔Example〕

Molten metal 4 having a composition of ordinary steel (melting point 1496°C) is injected from a submerged nozzle 2 having a discharge port 8 on the side,
Molten metal with SUS304 composition from immersion nozzle 1 3
(melting point: 1450°C) was injected to produce a multilayer slab with a wall thickness of 200 mm at a casting speed of 1 m/min. The obtained multilayer slab had an outer layer with an average thickness of 20 mm. The maximum thickness of this outer layer was 21 mm, the minimum thickness was 19 mm, and the wall thickness deviation was only 0.05%.

On the other hand, when casting was carried out using the immersion nozzle 2 with a discharge port at the lower end as shown in Fig. 4 under the same conditions, the thickness of the outer layer in the obtained multilayer slab was 15 mm. The wall thickness varied between ~25 mm, and the wall thickness deviation was as large as ±25%.

As is clear from this comparison, by giving a horizontal flow component to the molten metal 4 serving as the inner layer, it was possible to manufacture a multilayer slab of constant quality.

〔Effect of the invention〕

As explained above, in the present invention, by giving a horizontal flow component to the molten metal flow discharged from the long side immersion nozzle, the molten metal remains in a high temperature state and becomes a solidified shell. Preventing contact. Therefore, remelting of the solidified shell is suppressed, and a plurality of slabs having an outer layer of constant thickness can be manufactured. In addition, since the discharge flow with a horizontal flow component is less likely to disturb the interface between different types of molten metals, the mixing of different types of metals with each other is reduced, and the interfacial phase formed between the outer layer and the inner layer is also extremely thin. becomes. As described above, according to the present invention, a plurality of slabs having excellent quality can be manufactured under stable conditions.

[Brief explanation of the drawing]

Figure 1 shows the state in which a multilayer slab is manufactured using a submerged nozzle with a discharge port opened on the side.
FIG. 2 is a diagram for explaining the flow of molten metal at that time, and FIG. 3 shows a state where an electromagnetic stirring device is used to form a discharge flow having a horizontal flow component. On the other hand, FIG. 4 is a diagram for explaining a method for manufacturing a multilayer slab previously proposed by the present inventors. 1, 2: Immersion nozzle, 3, 4: Molten metal, 5,
6: Solidification shell, 7: Electromagnet, 8: Discharge port, 9:
Discharge flow, 10: electromagnetic stirring device, M: mold.

Claims (1)

[Claims] 1 A static magnetic field with lines of magnetic force extending across the entire width of the slab is applied at a position below the level of the molten metal supplied to the mold, and different metals are supplied above and below with this static magnetic field as a boundary. A continuous casting method for a multi-layer slab, characterized in that when continuously casting a multi-layer slab, a horizontal flow component is imparted to the molten metal supplied below the static magnetic field zone.