JPH01271031A - Continuous casting method for multilayer slabs - Google Patents

Abstract

PURPOSE:To improve boundary quality of a double-layer cast slab by arranging a DC solenoid coil around a mold, impressing static magnetic field over the whole width of the cast slab and supplying the different kinds of metals at upper and lower parts in this static magnetic field, respectively. CONSTITUTION:The solenoid coil 9 is wound around the mold 6 and the DC current is supplied. The submerged nozzles 7, 8 having different lengths are inserted in the mold 6 and the molten metals 1, 2 forming an inner layer solidified shell 3 and an outer layer shell 4 are poured from the nozzles 7, 8, respectively. Then, formed line of magnetic force 10 is effectively acted to flowing component to vertical direction and interfacial flow between the molten metals 1, 2 is restrained. By this method, the mixture between the molten metals 1, 2 is prevented and the interface between the solidified shells 3, 4 is made to clear. Therefore, the quality at the boundary of the complex cast slab is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for continuously producing multilayer slabs from the molten state, in which a clear boundary is provided between the inner layer and the outer layer.

[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 metals is proposed in Japanese Patent Publication No. 44-27361. However, simply injecting dissimilar metals at different positions in the mold in the casting direction using two immersion nozzles will not work.
No matter how the discharge position or discharge flow pattern of the dissimilar metals within the mold is adjusted, mixing between the dissimilar molten metals occurs as the pouring progresses, ie, as the casting progresses. Therefore, a boundary layer is formed in which the concentration changes in the thickness direction from the surface layer to the inside of the slab. Alternatively, the boundary between the surface layer and the interior becomes extremely unclear.

Therefore, in Japanese Patent Publication No. 49-44859, a partition wall made of refractory is provided between different types of molten metal poured into a mold,
A continuous casting method has been proposed. However, in order to suppress mixing of dissimilar molten metals, it is necessary to insert a sufficiently large refractory partition into the casting space. Therefore,
New casting problems arise. For example, the larger the refractory barrier, the greater the risk of it contacting the solidifying shell. This contact can cause the shell to become trapped and damage the refractory, or even cause the shell to rupture and cause a breakout. In addition, refractory bulkheads immersed in high-temperature molten metal have problems in terms of physical strength, and not only can they melt or break during casting, making it impossible to achieve their original purpose, but the refractory walls that have been immersed in the strands may materials have a negative impact on casting operations and product quality.

In order to eliminate the drawbacks of this refractory@wall, the present inventors developed a method that utilizes a static magnetic field as a means to partition dissimilar molten metals poured into a mold, and applied for this method in a patent application filed in 1983.
The application was filed as No.-252898.

In this method, a static magnetic field is formed in which lines of magnetic force extend across the entire width of the slab in a direction perpendicular to the casting direction, and different types of molten metal are supplied above and below this static magnetic field as a boundary. This static magnetic field acts as an electromagnetic brake, and the flow of molten gold 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]

According to the method proposed in Japanese Patent Application No. 61-252898, there is no need to place refractories @walls in the pool within the mold, so problems such as shell destruction and defects caused by damaged refractories are eliminated. However, subsequent research has revealed that the static magnetic field may not be sufficient to damp the molten metal.

Therefore, the present invention aims to improve the damping effect on molten metal by improving the application form of the static magnetic field, eliminate mixing between different types of metals, and produce a multilayer slab with clearer boundaries. purpose.

[Means to solve the problem]

In order to achieve the purpose of the continuous casting method of the present invention,
By supplying a direct current to a solenoid coil wound around the mold at a position below the level of the molten metal supplied to the mold, lines of magnetic force parallel to the casting direction are created across the entire width of the slab. It is characterized by applying an extending static magnetic field and supplying different metals above and below this static magnetic field band.

[Effect]

Different types of molten metals are supplied to each position in the strand pool at a predetermined ratio, and the application of a static magnetic field suppresses the flow of the molten metals in the mold, thereby suppressing mixing of the four different types of metals. At this time, it is presumed that the interface between different kinds of molten metals above and below the static magnetic field is in a wave state as shown in FIG. 4. That is, molten metals 1 and 2 injected into a casting space separated by a mold are cooled and solidified by heat removal through the mold wall, and become solidified shells 3 and 4, respectively.

At this time, since a static magnetic field is applied by the magnet 5, a braking force is generated to suppress the flow of the molten metal and metals 1 and 2.

However, in the earlier Japanese Patent Application No. 61-252898, a static magnetic field having lines of magnetic force perpendicular to the casting direction is applied. Therefore, it is not effective against the waves generated between the molten metal 1 and the molten gold 11g2 as shown in FIG. In this regard, the magnetic field applied in the present invention has lines of magnetic force parallel to the casting direction. As a result, the continuous wave movement as shown by the arrow in FIG. 4 is suppressed, and the mixing between the molten metals 1 and 2 is suppressed.

FIG. 1 is a schematic diagram showing a mechanism for generating a static magnetic field having lines of magnetic force parallel to the casting direction, and FIG. 2 is a diagram showing how the static magnetic field is generated.

Immersed nozzles 7 and 8, each having a different length, are inserted into the pool within the mold 6. Then, the solidified shell 3 which becomes the inner layer
The molten metal 1 forming the outer layer and the molten metal 2 forming the outer solidified shell 4 are each injected through a submerged nozzle 7.8. The injected molten metal 1.2 flows in the strand pool as indicated by the arrows in FIG. the result,
As shown in FIG. 4, waves are generated between the molten metals 1 and 2.

Therefore, a coil 9 is wound around the mold 6 in the shape of a solenoid, and a direct current is supplied to the solenoid coil 9. As a result, a static magnetic field having lines of magnetic force 10 parallel to the casting direction is formed as shown in FIG. These lines of magnetic force 10 effectively act on the vertical flow components shown by the arrows in FIG. 4, suppressing the wave motion at the interface between the molten metals 1 and 2. As a result, mixing between the molten metals 1 and 2 is suppressed,
A multilayer slab with well-defined interfaces between the solidified shells 3.4 is produced.

In addition, in FIG. 2, a static magnetic field with upward magnetic lines of force 10 is applied. However, it goes without saying that the same effect can be obtained even if a static magnetic field having downward magnetic lines of force 10 is applied.

〔Example〕

Molten metal 1 (melting point 1496°C) having a common steel composition (Cr 0%) is injected from the immersion nozzle 7, and molten metal 2 (melting point 1450°C) having an S U 3304 composition (Cr 18%) is injected from the immersion nozzle 8. Injected. Then, a solenoid coil 9 was installed at the bottom of the mold 6 so as to surround the mold 6, and a magnetic field zone was provided. The center of this magnetic field band in the casting direction was set at a position 600 mm below the meniscus. Further, a direct current was supplied to the solenoid coil 9 so that the magnetic flux density in the magnetic field band was 3000 Gauss.

In this way, a multilayer slab with a target outer layer thickness of 15 mm and a target board thickness of 200 mm was continuously cast. FIG. 3 shows the change in Cr content from the outer layer to the inner layer around the obtained multilayer. Further, FIG. 3 shows, as a comparative example, the change in Cr content when applying the static magnetic field proposed in Japanese Patent Application No. 61-252898, which is an earlier application. As is clear from Figure 3, by applying a static magnetic field with lines of magnetic force parallel to the casting direction, mixing between ordinary steel and stainless steel is suppressed, and an outer layer and an inner layer are formed with clear boundaries. It can be seen that

Therefore, no concentration transition phase was generated at the boundary between the outer layer and the inner layer, and a clad material in which the outer layer and the inner layer were clearly separated was obtained.

〔Effect of the invention〕

As explained above, in the present invention, mixing between different types of molten metals is suppressed by a static magnetic field having lines of magnetic force parallel to the casting direction. This static magnetic field has the effect of suppressing waves generated at the interface of dissimilar molten metals, and a multilayer slab with clearly differentiated outer and inner layers can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an installation according to the invention, and FIG.
The figure shows the generation situation of a static magnetic field, and FIG. 3 is a graph specifically expressing the effects of the present invention. Moreover, FIG. 4 is a diagram for explaining that a braking force is applied to the molten metal in the mold by a static magnetic field. 1.2 = Molten metal 3, 4: Solidified shell 5: Magnet 6: Mold 7.8: Immersion nozzle 9: Solenoid coil Patent applicant Nippon Steel Corporation (and 1 other person) Agent Masu Kobori (and others) 2 people) Figure 1 Figure 3 Distance from the surface (m) Figure 2 Figure 4

Claims (1)

[Claims] 1. By supplying a direct current to a solenoid coil wound around the mold at a position below the level of the molten metal supplied to the mold, the casting direction is parallel to the casting direction over the entire width of the slab. A continuous casting method for multilayer slabs, characterized by applying a static magnetic field in which lines of magnetic force extend, and supplying different metals above and below the static magnetic field zone.