JPH10263771A - Method for removing non-metallic inclusion in cast slab in continuous casting and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out casting of a cast slab having high cleanliness on the surface layer by casting while again solidifying after melting the surface layer of the cast slab drawn out from a mold with high frequency magnetic field generated from a high frequency coil arranged at just below a ferromagnetism body. SOLUTION: The ferromagnetism body 4 is arranged just below the mold 1 and the high frequency coil 5 is arranged just below the body 4 to generate AC magnetic field. A temp. detecting device 21 for detecting the surface temp. of the melting part 6 on the surface layer of the cast slab to control the temp. to the constant, and a current control device 7 for fixing the thickness of the melting part, are arranged. The control of the melting part is executed by adjusting the current of the high frequency coil 5. By this method, the surface layer of the cast slab is melted by impressing the high frequency magnetic field just below the mold 1, and non-metallic inclusion caught on the surface layer of the cast slab is shifted onto the uppermost surface of the cast slab with the reaction of electromagnetic force worked to the molten metal, and the non-metallic inclusion together with oxidized scale on the cast slab surface are separated and then, the cast slab having high cleanliness on the surface layer, is obtd.

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 for removing nonmetallic inclusions in the surface layer of a slab during continuous casting of metal during casting in a continuous casting machine to produce a slab having few surface defects. It is.

[0002]

2. Description of the Related Art A number of proposals have been made for controlling the flow of molten steel in a mold by means of an electromagnetic brake to reduce the trapping of nonmetallic inclusions by a solidified shell. This proposal is to slow down flow of molten metal in the slab by electromagnetic brake, reduce the penetration depth of non-metallic inclusions, and remove non-metallic inclusions by positively applying levitation force Not a technology.

[0003] Japanese Patent Application Laid-Open No. 8-19841 discloses a shape of a magnetic field generating coil for promoting the floating of deoxidized products. However, as shown in FIG. 5, the non-metallic inclusions 11 that have floated to the claw-shaped solidified shell 10 are likely to be trapped near the meniscus during continuous casting. It is not enough as an object reduction technology.

JP-A-5-154620, JP-A-8-1126
No. 52 discloses a technique of causing an appropriate molten steel flow in a meniscus by an electromagnetic force or the like to flush a solidification interface to prevent nonmetallic inclusions from adhering to a solidification shell. Japanese Patent Application Laid-Open No. HEI 8-90183 discloses that a container for melting and holding a molten metal is installed above a mold where the molten metal starts to solidify, and that impurities floating near a free surface of the molten metal are captured by a solidified shell. Techniques to prevent this are shown.
However, while these techniques can prevent non-metallic inclusions from being trapped in the solidified shell, they cannot remove non-metallic inclusions once trapped in the solidified shell.

In controlling the flow of molten steel in a mold, the trapping of non-metallic inclusions in the solidified shell of the slab surface layer can be reduced, but it is difficult to completely prevent the trapping of non-metallic inclusions.
In addition, in order to remove the nonmetallic inclusions trapped in the solidified shell, there is a problem that a step of caring the slab surface with a scarfer or the like must be added after casting. Furthermore, even if the slab surface is cut with a scarfer,
There was also a problem that nonmetallic inclusions trapped under the machined portion were exposed on the surface of the slab and caused defects.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention allows the surface layer of a slab that has been drawn in a continuous casting machine to be maintained online, and the cleanness of the surface layer of the slab is further improved. It is an object of the present invention to provide a method and an apparatus for removing non-metallic inclusions in a slab which are improved.

[0007]

As shown in FIG. 6, by applying an AC magnetic field from a high-frequency coil 5 around a molten metal, an electromagnetic force directed from the surface of the molten metal to the inside thereof is applied to a metal portion having high electric conductivity. 15 acts, and as a result, there is a phenomenon that the nonmetallic inclusions 11 having lower electric conductivity than the metal are extruded to the surface of the molten metal.

The present inventors have found a method for efficiently removing nonmetallic inclusions in a slab during continuous casting by utilizing this principle, and have accomplished the present invention. The present invention
While generating magnetic force from the ferromagnetic material installed directly under the continuous casting mold, the high-frequency magnetic field generated from the high-frequency coil installed directly under the ferromagnetic material melts the solidified shell surface layer of the slab drawn from the mold. And then casting while solidifying again.

According to the present invention, nonmetallic inclusions trapped in the induction-melted solidified shell are moved and separated to the outermost layer of the slab, while the outermost layer of the slab becomes oxidized scale during transportation of the slab and is separated. The non-metallic inclusions detached together with the oxide scale, and a slab with high cleanliness of the surface layer could be produced. Also, the present invention provides a high-frequency coil for melting a slab surface layer immediately below a continuous casting mold, a ferromagnetic material surrounding the high-frequency coil and concentrating a magnetic field on the slab, and a slab melting portion temperature in the high-frequency coil. And a current control device for the high-frequency coil for adjusting the temperature of the slab melting portion to be constant from a signal of the temperature detector. The moving means is provided on the magnetic body. A high-frequency coil that melts the slab surface layer immediately below the continuous casting mold, a ferromagnetic material that surrounds the high-frequency coil and concentrates a magnetic field on the slab, and a temperature detector that measures the temperature of the slab fusion zone in the high-frequency coil, A non-metallic inclusion removal device in the slab, comprising: a position control device for adjusting the slab melting portion temperature to a constant value, and controlling the shape of the slab melting portion by adjusting the interval between the slab and the yoke. Can also.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
Shown in If the slab surface is to be melted away from the mold 1, the slab temperature will rapidly decrease due to secondary cooling as the distant from the mold, so more energy is needed to raise the slab temperature to the melting point. Becomes Therefore, in order to reduce the energy required to raise the temperature of the solidified shell 2 to the melting point, the high-frequency coil 5 for melting the surface layer of the slab is installed immediately below the mold.

By using a high-frequency magnetic field, only the surface layer of the slab is melted. When the frequency is low, the penetration depth of the magnetic field is deep, the melt thickness is too thick, the risk of breakout increases, and the separation effect of nonmetallic inclusions decreases,
In continuous casting of steel, the high frequency is preferably 500 kHz.
Since the continuous casting mold 1 is made of a copper alloy having higher electric conductivity than the slab 30, when an AC magnetic field is generated in the immediate vicinity of the mold, the applied magnetic field is reduced by the magnetic field generated by the induced current generated in the mold. The magnetic field permeating the slab to be heated is reduced. Therefore, the ferromagnetic material 4 just below the mold
Is installed, and the high-frequency coil 5 is installed immediately below the coil to generate an AC magnetic field, so that the magnetic field toward the mold is reduced,
The magnetic field penetrating the slab is prevented from being reduced by the magnetic field due to the induced current generated in the mold.

If the molten thickness of the surface layer of the slab varies and becomes large, breakout occurs. Therefore, in order to detect the surface temperature of the slab surface layer fusion zone 6 and control this temperature to be constant, a fusion zone surface layer temperature detector 21 and a current control device 7 for making the fusion thickness constant are installed. The temperature of the melting part is controlled by adjusting the high-frequency coil current. When the slab surface layer is melted, the molten portion hangs down due to the static iron pressure acting on the molten portion, and the slab surface shape becomes wavy. Due to the interaction between the magnetic field applied by the high-frequency coil and the induced current generated in the slab fusion zone, a magnetic pressure is generated in the fusion zone inward from the surface. In order to generate a magnetic field distribution that balances the magnetic force pressure and the static iron pressure, the distance between the ferromagnetic material and the slab is set. As shown in FIG. 2, since the static iron pressure increases from top to bottom, the distance between the ferromagnetic material 4 and the slab 1 is
The magnetic pressure distribution is made closer to the static iron pressure distribution by making it wider at the upper part and narrower at the lower part.

As shown in FIG. 3, during operation, the shape of the slab surface melted portion 6 is observed by the temperature detector 21 of the slab surface melted portion, and the distance between the yoke (ferromagnetic material) and the slab is determined on-line by the yoke. By controlling the upper part 16 and lower part 17 of the slab independently by operating the drive unit 18 and controlling the surface shape of the slab surface layer fusion zone 6 to approach vertical, a more stable surface layer slab can be cast. become.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to an embodiment shown in FIG. The high-frequency coil 5 is surrounded by a U-shaped ferromagnetic yoke 4 and concentrates a magnetic field on the surface layer of the slab 30 to reduce leakage of the magnetic field to surrounding electric conductors. In order to prevent the slab surface molten portion 6 from drooping downward due to the static iron pressure, a drive device 18 is provided so that the gap between the slab at the upper part 16 and the lower part 17 of the yoke can be changed independently. Control is performed so that the iron pressure distribution and the magnetic pressure distribution substantially match.
The temperature of the slab surface layer in the high-frequency coil 5 is measured by a non-contact type temperature detector 21, and the temperature of the slab melting portion is controlled by the coil current.

The current of the high frequency coil was changed to change the molten thickness of the slab to 0.4 mm, 0.8 mm and 1.2 mm. However, according to the present invention, as shown in FIG. It is clear that Here, the melt thickness is measured by melting the surface of the dummy sample and observing the cross section after melting, and determining the relationship between the coil frequency, the coil current, the surface temperature of the melted portion during melting, and the melt thickness. ,
This is a value estimated from the coil frequency during casting, current, and surface temperature of the melted part. Steel plate surface defects are scabs and scales caused by non-metallic inclusions.

[0016]

According to the present invention, the following effects can be obtained. That is, the surface layer of the slab is melted by applying a high-frequency magnetic field immediately below the mold, and the nonmetallic inclusions trapped in the surface layer of the slab are moved to the outermost surface of the slab by the reaction of the electromagnetic force acting on the molten metal. The non-metallic inclusions are removed together with the oxide scale, and a cast slab with high cleanliness on the surface layer can be cast.

Blowholes and cracks on the slab surface are also repaired by remelting the slab surface layer to reduce surface defects. No need for surface care in the next step.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an apparatus according to the present invention.

FIG. 2 is a distribution diagram of static iron pressure in a molten metal.

FIG. 3 is an explanatory diagram of ferromagnetic material position control.

FIG. 4 is a characteristic diagram showing a relationship between a molten thickness and a steel sheet surface defect according to the present invention.

FIG. 5 is an illustration of trapping of non-metallic inclusions in an initially solidified shell in a continuous casting mold.

FIG. 6 is an explanatory diagram of separation of nonmetallic inclusions in a molten metal by an alternating magnetic field.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 solidified shell 3 melting part temperature detector 4 yoke (ferromagnetic material) 5 high-frequency coil 6 slab surface melting part 7 current control device 8 secondary cooling spray 9 roll 10 claw-shaped solidified shell 11 nonmetallic inclusion 12 non Direction of floating magnetic inclusions 13 Direction of applying magnetic field 14 Force acting on non-metallic inclusions 15 Electromagnetic force acting on molten metal 16 Upper part of yoke 17 Lower part of yoke 18 Drive unit 19 Ferromagnetic material position controller 20 Ferromagnetic substance moving direction 21 Slab surface melting point temperature detector 22 Molten metal 23 Slab surface 30 Slab

Claims (3)

[Claims] 1. A slab extracted from a mold by a high-frequency magnetic field generated from a high-frequency coil installed immediately below the ferromagnetic material while generating magnetic force from a ferromagnetic material installed immediately below the continuous casting mold. A method for removing nonmetallic inclusions in a slab in continuous casting, wherein the solidified shell is melted and then cast while solidifying again. 2. A high-frequency coil for melting a slab surface layer immediately below a continuous casting mold, a ferromagnetic material surrounding the high-frequency coil for concentrating a magnetic field on the slab, and a slab melting portion temperature in the high-frequency coil. An apparatus for removing non-metallic inclusions in a slab, comprising: a temperature detector to be measured; and a current control device for the high-frequency coil for adjusting the temperature of the slab melting portion to be constant based on a signal from the temperature detector. 3. The apparatus for removing nonmetallic inclusions in a slab according to claim 2, wherein a moving means is provided on said ferromagnetic material.