JPH0523803A - Method for casting cast slab having little defect of surface and inner part - Google Patents

Abstract

PURPOSE:To produce a high clean cast slab by preventing accumulation of inclusions at meniscus part and below a mold in a continuous caster. CONSTITUTION:At the time of continuously casting a steel by using the continuous caster having vertical part, an electromagnetic stirrer is used so as to obtain flowing speed of molten steel at 0.1-0.4m/sec in the mold, and further, the uniform static magnetic field is acted in width direction of the cast slab at position in interval from 1.5m below the meniscus to start of changing the shape from the vertical part to the bending part in the continuous caster. By this method, as the accumulation of inclusions to the cast slab surface and the inner part is restrained, the cast slab having excellent cleanness 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 method for producing a highly clean slab by preventing accumulation of inclusions penetrating into a mold in the slab in a continuous casting method of steel.

[0002]

As is well known, in continuous casting of steel, a method of supplying molten steel from a dipping nozzle into a mold is used.

Further, in order to improve the floating separation effect of inclusions in the mold, the steel is cleaned by cleaning the molten steel during refining and changing the nozzle shape during casting.

However, since the discharge flow rate from the nozzle is high, these measures alone cannot drastically improve the internal defects because inclusions penetrate deep into the mold and are trapped in the solidified shell.

Further, since the inclusions floating in the slab are captured by the shell immediately below the meniscus, surface defects of the slab cannot be prevented.

[0006] Various proposals have been made to suppress the trapping of inclusions in the solidified shell in a slab and produce a slab with high cleanliness.

For example, as disclosed in Japanese Patent Laid-Open No. 49-52725, a method of suppressing inclusion of inclusions in a solidified shell in a meniscus portion by stirring molten steel by electromagnetic stirring in a mold. And JP-A-61-
As disclosed in Japanese Patent No. 1459, there is a method of preventing the intrusion of inclusions by reducing the discharge flow from the nozzle.

Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 56-160862, there is a method in which a moving magnetic field is applied in parallel with the discharge flow from the immersion nozzle to reduce the discharge flow velocity.

[0009]

However, these techniques for reducing inclusions aim to control the trapping of inclusions in the mold, and therefore, they penetrate into the mold deeply along with the discharge flow from the immersion nozzle. It has no effect on the inclusions that end up.

That is, although the method of applying electromagnetic stirring in the mold can suppress the accumulation of inclusions on the surface of the slab, it cannot prevent the inclusions from entering the lower part of the mold.
The inclusions that have floated to the mold will be pushed deeper and deeper below the meniscus, and the quality of the slab will be deteriorated.

Further, the electromagnetic force installation method used in these methods assumes that the direction of the discharge flow from the nozzle is always in a constant direction during casting, and the electromagnetic force is applied directly to this. Since the purpose is to calm the flow by using force, there are problems such as lack of stability in the casting operation of steel where the discharge direction from the nozzle fluctuates, especially at the end of casting. When the supply of molten steel from the nozzle becomes unstable, these methods cause deterioration of the operation.

The present invention seeks to radically solve the above-mentioned problems of the conventional method, and provides a method for producing steel capable of producing a cast slab having excellent cleanliness without accumulation of inclusions on the surface and inside of the cast slab. To do.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a continuous casting of steel using a continuous casting machine having a vertical portion, in which 0.1 to 0.4 m is cast in a mold.
Electromagnetic stirring was used to obtain a molten steel flow velocity of 1 / sec. Furthermore, in the width direction of the slab between the position 1.5m below the meniscus part and the position where the shape started to change from the vertical part to the curved part in the continuous casting machine. It is a method for casting a highly clean slab, which is characterized by applying a uniform static magnetic field.

Here, in a uniform static magnetic field installed in the lower part of the continuous casting machine in the width direction, the magnetic flux density at which the effect of the present invention works effectively is 1500 gauss or more.

[0015]

The operation of the present invention will be described in detail below.

FIG. 2 is a diagram showing the movement behavior of inclusions during conventional continuous casting. An immersion nozzle (1) is inserted in the center of the mold (2).

During casting, the inclusions (4) penetrate deep into the lower part of the mold by the downward flow (7) generated by the immersion nozzle.

Here, since the intruding inclusions float in the direction opposite to the gravity, when the continuous casting machine is a curved type continuous casting machine, the inclusions are captured by the upper solidified shell of the melting portion. On the other hand, in the case of a continuous casting machine having a vertical portion, it floats in the meniscus (9) direction.

Among these inclusions, the inclusion (4) having a diameter whose floating speed is equal to or higher than the casting speed, which is the moving speed of the slab (3) during casting, opposes the drawing speed and causes a meniscus inside the molten portion. Since it floats in the direction, it is almost completely separated.

On the other hand, the inclusions having a diameter smaller than that cannot reach the meniscus (9) only by ascending because the ascending speed in the molten steel is smaller than the casting speed.
It rides on the downward flow generated by the discharge flow and penetrates deep into the mold.

Some of the inclusions that have penetrated deep into the mold are carried further deeply by the movement of the slab, and then float up to the upper surface inside the slab at the curved portion and are captured.

On the other hand, some of the remaining inclusions are reverse flow (8).
It is carried to the vicinity of the meniscus (9) again, but at that time, it is captured by the stagnation part of the flow of the meniscus part.

FIG. 1 is a diagram showing the position of a magnetic field in a continuous casting machine having a vertical portion according to the present invention.

In the figure, an electromagnetic stirrer (5) is installed in the mold (2) and the molten steel flow velocity in the mold is 0.1 to 0.4 m.
The inclusion is prevented from being accumulated on the meniscus portion by stirring so that it is within / sec.

Here, if the molten steel flow velocity is less than 0.1 m / sec, deckling may occur in the mold. Further, it is because continuous casting powder is involved during casting at 0.4 m / sec or more.

On the other hand, if the molten steel in the mold is simply stirred,
Inclusions in the meniscus part are generated by the downward flow generated in the mold,
It is carried deep down the mold.

Therefore, inclusions that have penetrated into the lower part of the mold do not penetrate into the curved part, but circulate only in the vertical part of the continuous casting machine, and further, in the region under the magnetic field, the molten steel flow is uniform, A static magnetic field (6) that is uniform in the width direction is placed in the lower part of the mold.

Here, it is desirable to set the uniform magnetic field below the mold within a range where the shape of the continuous casting machine begins to curve from the vertical direction 1.5 m below the discharge nozzle of the immersion nozzle.

FIG. 3 shows the levitation ratio of inclusions penetrating in the slab with respect to the distance of the uniform magnetic field from the immersion nozzle. The position of the uniform magnetic field in the continuous casting machine should be 1.5 m or more away from the nozzle. The reason is that, as described above, the inclusion having a small floating speed cannot float at its own floating speed, and floats up to the meniscus portion by riding on the upward flow in the continuous casting machine.

However, when the static magnetic field is installed near the nozzle, the molten steel becomes a uniform flow after the magnetic field and the generation of the upward flow is suppressed, so that the inclusions whose levitation speed is lower than the descending speed of the slab are levitation. This is because it cannot be done at all.

On the other hand, when the position of the uniform magnetic field is set in the curved portion after the vertical portion, the molten steel flow velocity sharply decreases in the curved portion, so that the inclusions are trapped in the upper shell of the molten portion in the curved portion, This is because the effect of setting a uniform magnetic field is lost.

By the above method, two kinds of magnetic fields are applied in the continuous casting machine to suppress the accumulation of inclusions inside the slab and stably produce a slab with few surface and internal defects. Will be possible.

[0033]

EXAMPLE Referring to FIG. 1 described above, in this experimental example, a continuous casting machine having a vertical portion of 3 m above a curved portion was used, and an electromagnetic stirring (5) was used in a mold (2) of the continuous casting machine. ) Was installed, and a uniform static magnetic field (6) was used 2.5 m below the immersion nozzle (1) in the width direction of the slab.

The operating condition of this experiment is that the slab size is 98 width.
A low carbon aluminum killed steel is continuously cast at 0 mm, a thickness of 250 mm and a casting speed of 1.0 m / min.

The electromagnetic stirrer used in the mold was operated so that the flow velocity of the meniscus was 0.2 to 0.3 m / sec.

The uniform static magnetic field below the mold has a generating capacity of 3000 gauss. In this experimental example, a maximum magnetic flux density of about 7,000 gauss is generated, and the magnetic flux is evenly distributed in the molten portion in the width direction of the slab. Granted to work.

FIG. 4 (a) shows the cleanliness in the thickness direction of the slab produced by this experimental example in comparison with the conventional method.

In the figure, casting is performed without using electromagnetic force (b), only electromagnetic stirring in the mold is applied (c), and only a uniform magnetic field is applied 1 m below the meniscus. The results of (d) are also shown. However, as shown in the figure, when only electromagnetic stirring in the mold is applied, the accumulation of inclusions on the surface of the slab can be suppressed, but the inclusions floating on the meniscus descend. Inclusions are accumulated inside the slab to be pushed into the slab by the flow.

When casting is performed using only a uniform static magnetic field 1 m below the meniscus, inclusions floating in the continuous casting machine are trapped near the meniscus, so that the inclusions accumulate on the surface layer of the slab. In addition, since the installation position of the uniform magnetic field is close to the meniscus portion, the floating separation of the minute inclusions cannot be performed completely, and the effect of removing the inclusions in the cast piece deteriorates.

On the other hand, when casting is performed according to the present invention, it is possible to manufacture a slab with high cleanliness accuracy without accumulating inclusions on the surface and inside of the slab.

[0041]

As described above, since the inclusion of inclusions in the surface layer and inner layer of the slab can be suppressed by carrying out the present invention, a slab with excellent cleanliness can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an internal state of a continuous casting machine according to the present invention.

FIG. 2 is a diagram illustrating a floating state of inclusions in a continuous casting machine in conventional continuous casting.

FIG. 3 is a diagram showing the relationship between the distance between the immersion nozzle and the uniform static magnetic field below the mold and the levitation rate of inclusions that have penetrated into the slab.

FIG. 4 is a diagram illustrating that it is possible to prevent the accumulation of inclusions on the surface and inside of the slab by performing casting according to the present invention.

[Explanation of symbols] 1 immersion nozzle 2 mold 3 solidification shell 4 inclusions 5 electromagnetic stirring 6 uniform static magnetic field 7 downflow 8 reverse flow 9 meniscus

Claims (1)

Claim: What is claimed is: 1. When continuously casting steel using a continuous casting machine having a vertical portion, 0.1 to 0.4 in a mold.
Electromagnetic stirring was used to obtain a molten steel flow velocity of m / sec, and the slab was squeezed at a location 1.5 m below the meniscus until the shape started to change from a vertical portion to a curved portion in the continuous casting machine. A method for casting a highly clean cast slab, which comprises applying a uniform static magnetic field in the width direction.