JPH05285614A - Continuous casting method - Google Patents

Abstract

PURPOSE:To reduce inclusion defect by arranging a discharging opening part in the casting direction and specifying interval between a long side mold and a nozzle. CONSTITUTION:By generating static magnetic field to the whole zone in the width direction in the continuous casting mold, brake is applied to molten steel spouting flow. In this case, the molten steel is poured by using the nozzle 1 which arranges the discharging opening part in the casting direction and can secure the interval between the long side mold 2 and the nozzle 1 at least at >=50mm. By this method, the internal inclusion defect developed, by which the descending flow caused by the discharged spouting flow of the nozzle becomes large, can be restrained, and as the stagnating part can efficiently be eliminated, the surface inclusion defect can drastically be reduced, as well, because of solidified shell washing promoting effect, and the high quality slab can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method capable of suppressing internal and surface inclusion defects in continuous slab casting of steel.

[0002]

2. Description of the Related Art In order to suppress internal inclusion defects in continuous slab casting of steel, it is effective to reduce the jet flow of molten steel discharged from an immersion nozzle, especially the downward flow velocity, and to suppress the deep penetration of inclusions such as alumina. . Conventionally, molten steel flow control using electromagnetic force has been performed as the method.

For example, Japanese Patent Application Laid-Open No. 57-17356 discloses a technique in which a static magnetic field generator is installed in a continuous casting mold to apply a braking force to a molten steel jet from an immersion nozzle. Then, when damping is applied to the molten steel jet, most of the jet is attenuated, but part of the jet leaks to the part without magnetic field (the center of the two magnetic poles corresponding to both ejection holes of the immersion nozzle), which causes The descending flow velocity could not be sufficiently reduced and the defects of internal inclusions could not be sufficiently suppressed.

Therefore, recently, Japanese Patent Laid-Open No. 2-284750
The publication discloses a technique of generating a static magnetic field in the entire width direction, eliminating locally a portion having no magnetic field in the width direction, and reducing the downward flow of molten steel.

However, in this technique, as shown in FIG.
Although the downward flow can be suppressed, as shown in FIG. 7, the molten steel flow is small between the immersion nozzle 7 and the mold 2, a stagnation occurs, and the inclusions 5 adhere to the solidified shell 6 to cause surface defects. Had the drawback that.

Further, Japanese Patent Laid-Open No. 142049/1993 discloses a method in which a static magnetic field is disposed vertically above and below the position of an ejection nozzle discharge hole and the magnetic field strength of the upper and lower static magnetic fields is controlled to suppress defects. However, the molten steel flow was suppressed by the magnetic field at the upper part, and the surface defects could not be suppressed due to the formation of the stagnation part described above.

[0007]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to release the suppression of molten steel flow, prevent the formation of stagnation, and significantly improve internal defects and surface defects.

[0008]

DISCLOSURE OF THE INVENTION The present invention is a steel slab for applying a damping force to a molten steel jet by generating a static magnetic field in the entire width direction with magnetic poles disposed on the back surface of the opposite side wall of a continuous casting mold. In continuous casting, there is a discharge opening in the casting direction, and the distance between the long piece mold and the nozzle is at least 50.
This is a continuous casting method characterized by injecting molten steel with a nozzle capable of ensuring a thickness of at least mm.

[0009]

The present inventor has studied for many years to eliminate the stagnation between the immersion nozzle and the mold. As a result, the stagnation between the immersion nozzle and the mold can be eliminated by increasing the distance between the immersion nozzle and the mold. I found what I could do.

However, in order to secure this distance with the conventional immersion nozzle, it is necessary to reduce the nozzle diameter, and there is a problem that the required casting speed cannot be obtained.

Therefore, in order to have a discharge opening area which can secure a required casting speed and to secure a space between the dipping nozzle and the mold, a flat discharge opening portion is provided in the casting direction as shown in FIG. The nozzle is optimal.

FIG. 1 is a schematic view of a casting apparatus according to the present invention, showing a casting condition viewed from the long piece side.

In the mold 2 in which the static magnetic field 4 has been generated over the entire width, the jet flow discharged from the immersion nozzle 1 as shown in the figure is suppressed by the static magnetic field 4 to suppress the downward flow 8 and further react. The flowing reverse flow 9 spreads the flow in the width direction.

At this time, in the casting condition viewed from the short piece, as shown in FIG. 2, since the gap between the immersion nozzle 1 and the mold 2 is large, the reverse flow 9 can easily penetrate between the immersion nozzle 1 and the mold 2. The molten steel flow accelerates the molten steel solidified shell washing, and it is possible to prevent inclusions from adhering to the solidified shell 6 and suppress surface defects.

The inventors cast molten steel by changing the distance between the dipping nozzle 1 and the long piece mold 2, and make 10 m from the L surface in the cast piece.
The slime extraction amount of alumina inclusions present within m was measured.

10 from the L surface in the slab generated by the conventional cylindrical nozzle (distance between the dipping nozzle and the long piece mold is 30 mm).
When the slime extraction amount of the alumina-based inclusions present within mm is expressed as a standardized inclusion index, the result as shown in FIG. 4 is obtained, and the distance between the immersion nozzle 1 and the long piece mold 2 is set to 50 mm or more. Therefore, it was found that the index of alumina inclusions can be made almost zero.

Therefore, it is necessary to secure the space 2 between the main immersion nozzle 1 and the mold of at least 50 mm or more.

[0018]

EXAMPLE As an example of the present invention, a low carbon aluminum killed steel for tin plate was continuously cast by using a dipping nozzle having a shape shown in FIG. 3 and a casting apparatus shown in FIGS. The detailed casting conditions at this time are shown in Table 1.

As a comparative example, the same steel grade was cast using a conventional dipping nozzle having a circular cross section in the casting apparatus shown in FIGS. The casting conditions are also shown in Table 1.

[0020]

[Table 1]

The cast slab was examined for internal defects and surface defects.

When the number of surface defects generated per 100 m of the product coil was measured and standardized to be 1 in the case of casting by the casting method of the comparative example, as shown in FIG. 5, surface defects are caused by the casting method of the present invention. It was significantly reduced, and it was found that a high quality slab can be manufactured.

[0023]

As described above, according to the present invention, it is possible not only to suppress the internal inclusion defect caused by the large downflow due to the jet flow discharged from the immersion nozzle, but also to effectively eliminate the stagnation portion, so that the surface can be effectively eliminated. Inclusion defects can be significantly reduced by the effect of promoting solidified shell washing, and high quality slabs can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic view of the method of the present invention (a view seen from a long piece side).

FIG. 2 is a schematic view of the method of the present invention (view seen from the short piece side).

FIG. 3 is a diagram showing the shape of an immersion nozzle used in an example of the present invention.

FIG. 4 is a diagram showing the relationship between the distance between the immersion nozzle and the mold and the inclusion index investigation result.

FIG. 5 is a diagram showing internal defect and surface defect suppression record data of the present invention.

FIG. 6 is a schematic view of a conventional casting method in which a static magnetic field is generated in the entire width direction (viewed from the long piece side).

FIG. 7 is a schematic view of a conventional casting method in which a static magnetic field is generated in the entire width direction (viewed from the short piece side).

[Explanation of symbols]

 1 Immersion Nozzle 2 Mold 3 Molten Steel 4 Electromagnetic Coil 5 Inclusion 6 Solidification Shell 7 Immersion Nozzle 8 Downflow 9 Reverse Flow

Claims (1)

[Claims] 1. A slab continuous casting of steel in which a static magnetic field is generated in the entire width direction to dampen a molten steel jet at magnetic poles arranged on the back surface of the opposite side wall of a continuous casting mold, and discharge is performed in the casting direction. A continuous casting method characterized by injecting molten steel with a nozzle having an opening and capable of ensuring a distance between the long piece mold and the nozzle of at least 50 mm or more.