JP2990555B2 - Continuous casting method - Google Patents

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 from an immersion nozzle, particularly the descending flow velocity, and to suppress the penetration of inclusions such as alumina into the deep part. . Conventionally, flow control of molten steel using electromagnetic force has been performed.

For example, Japanese Patent Laying-Open No. 57-17356 discloses a technique in which a static magnetic field generator is installed in a continuous casting mold to apply braking to a molten steel jet from an immersion nozzle. When braking is applied to the molten steel jet, most of the jet is attenuated, but some of the jet leaks to a part without a magnetic field (the center of the two magnetic poles corresponding to both the discharge ports of the immersion nozzle), thereby causing the molten steel to flow. The descending flow velocity could not be sufficiently reduced, and internal inclusion defects could not be sufficiently suppressed.

Therefore, recently, Japanese Patent Laid-Open No. 2-284750 has been proposed.
Japanese Patent Application Publication No. JP-A-2005-115125 discloses a technique for generating a static magnetic field in the entire area in the width direction, eliminating a portion having no magnetic field locally 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 flow of molten steel is small between the immersion nozzle 7 and the mold 2, stagnation occurs, the inclusions 5 adhere to the solidified shell 6, and surface defects are generated. Had the disadvantage of occurring.

Japanese Patent Application Laid-Open No. 3-14049 discloses a method in which a static magnetic field is disposed vertically above and below the position of an immersion nozzle discharge hole, and a defect is suppressed by controlling the magnetic field strength of the upper and lower static magnetic fields. However, the flow of molten steel was suppressed by the upper magnetic field, and surface defects could not be suppressed due to the occurrence of the stagnation described above.

[0007]

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

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a steel slab in which a static magnetic field is generated in the entire width direction by a magnetic pole disposed on the back surface of the opposing side wall of a continuous casting mold to brake a molten steel jet. In continuous casting, it has a discharge opening in the casting direction, and the distance between the long mold and the nozzle is at least 50 mm.
This is a continuous casting method characterized by injecting molten steel through a nozzle capable of ensuring a length of at least 1 mm.

[0009]

The inventor has long studied the elimination of the stagnation portion between the immersion nozzle and the mold, and as a result, the stagnation portion between the immersion nozzle and the mold is eliminated by increasing the distance between the immersion nozzle and the mold. I found what I could do.

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

Therefore, in order to have a discharge opening area capable of securing a required casting speed and to secure an interval between the immersion 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 state viewed from one long side.

The jet jet from the rinsing nozzle 1 as shown in FIG. 1 is braked by the static magnetic field 4 into the mold 2 in which the static magnetic field 4 has been generated in the entire width thereof, whereby the downward flow 8 is suppressed, and furthermore, it is reactive. Due to the flowing reverse flow 9, the flow spreads in the width direction.

At this time, the casting condition viewed from the short piece is such that, as shown in FIG. 2, since the distance between the immersion nozzle 1 and the mold 2 is large, the reverse flow 9 can easily enter between the immersion nozzle 1 and the mold 2. The molten steel flow promotes the washing of the solidified shell of the molten steel, thereby preventing inclusions from adhering to the solidified shell 6 and suppressing surface defects.

The inventors cast molten steel by changing the distance between the immersion nozzle 1 and the long piece mold 2 and set a distance of 10 m from the L plane in the slab.
The amount of slime extracted from alumina-based inclusions existing within m was measured.

A conventional cylinder nozzle (the distance between the immersion nozzle and the long piece mold is 30 mm), which is 10 mm from the L plane in the slab.
When the slime extraction amount of the alumina-based inclusions present within mm is expressed as a standardized inclusion index with 1 being taken, the result as shown in FIG. 4 is obtained. As a result, it has been found that the alumina-based inclusion index can be made substantially zero.

Thus, the distance 2 between the main immersion nozzle 1 and the mold must be at least 50 mm or more.

[0018]

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

As a comparative example, the same steel type was cast using a conventional immersion nozzle having a round cross section in a casting apparatus shown in FIGS. Table 1 also shows the casting conditions.

[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 as 1 when casting by the casting method of the comparative example, as shown in FIG. It was greatly reduced, indicating that high quality cast slabs could be produced.

[0023]

As described above, according to the present invention, it is possible to suppress internal inclusion defects caused by an increase in the downflow caused by the jet flow discharged from the immersion nozzle. Inclusion defects can also be significantly reduced by the effect of promoting solidification shell washing, and high-quality slabs can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view of the method of the present invention (a view as viewed from one long side).

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

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

FIG. 4 is a graph showing the relationship between the distance between an immersion nozzle and a mold and the result of an inclusion index survey.

FIG. 5 is a diagram showing actual data of suppression of internal defects and surface defects according to 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 region in the width direction (a view as viewed from one long side).

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 immersion nozzle 2 mold 3 molten steel 4 electromagnetic coil 5 inclusion 6 solidified shell 7 immersion nozzle 8 downward flow 9 reverse flow

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-158860 (JP, A) JP-A-58-55157 (JP, A) JP-A-3-142049 (JP, A) JP-A-2- 284750 (JP, A) JP-A-3-243260 (JP, A) JP-A-5-77008 (JP, A) JP-A-53-22813 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/10 350 B22D 11/10 330 B22D 41/50 520

Claims (1)

(57) [Claims] 1. A slab continuous casting of steel in which a static magnetic field is generated in the entire width direction by a magnetic pole disposed on a back surface of an opposite side wall of a continuous casting mold to brake a molten steel jet, and is discharged in a casting direction. A continuous casting method characterized by injecting molten steel through a nozzle having an opening and capable of ensuring a distance between a long piece mold and a nozzle of at least 50 mm or more.