JPH08197195A - Method for continuous casting of molten steel and device therefor - Google Patents

Abstract

PURPOSE: To obtain a slab free from surface defects occurring in casting mold oscillation by forming the initially solidified shell of molten steel in the spacing formed between a tundish nozzle and a continuous casting mold and further progressing solidification in the casting mold. CONSTITUTION: The initially solidified shell is formed by solidifying the molten steel in the region of the spacing formed between the tundish nozzle 2 and the continuous casting mold 3. The holding of the side faces of the molten steel in the spacing is executed by control of magnetic materials 5 for applying an adequate magnetic field distribution to the molten steel. The initially solidified shell is preferably formed to the sectional shape nearly equal to the inlet side sectional shape of the continuous casting mold 3 to prevent the deformation, crack, etc., at the time of infiltration into the continuous casting mold 3. The formation of the initially solidified shell is executed simply by generating a rapid temp. gradient in the molten steel in such a manner that the temp. below the solidification temp. is attained, for which the heating by a high-frequency induction coil 4 and the force cooling in the continuous casting mold 3 in the region of the spacing are combined. The slab free from the surface defects is obtd. in such a manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to stably produce a cast slab excellent in surface cleaning in which surface defects caused by mold oscillation are reduced in continuous casting of steel.

[0002]

2. Description of the Related Art Conventionally, in continuous casting of molten steel, in order to obtain a good cast slab with no surface defects by preventing cracks and slag biting that occur with mold oscillation, the molten metal surface and initial solidification starting point are A casting method using a high-frequency magnetic field in a separate type continuous casting machine has been tried, and literatures on this point are disclosed in Japanese Examined Patent Publication No. 3-69615, Japanese Unexamined Patent Publication No. 1-284469, and Japanese Examined Patent Publication No. 64-5985. Reference is made to publications and the like.

Japanese Patent Publication No. 3-69615 discloses a continuous casting mold in which a hardly conductive heating zone (using an electromagnetic induction coil) is used from the molten metal entering side, and subsequently a conductive cooling zone. Each zone is arranged, and further, a molten metal introduction pipe is placed over the entire length of the inside of the heating zone and the cooling zone, and the generation of the initial solidified shell in the mold is controlled by the heating action to separate the molten metal surface and the solidification starting point as much as possible It is a technology that improves the surface quality without being affected by fluctuations in the molten metal level.
Further, in JP-A 1-284469 direction, in a molten steel casting method using an apparatus in which a tundish or a hot water supply nozzle and a continuous casting mold are directly connected, a current-carrying pipe is made to circulate along the mold immediately before the mold inlet. A high-frequency current is supplied, and the electromagnetic force generated thereby casts molten steel as non-contact at the boundary of the direct connection part, avoids burrs at the boundary part of the direct connection part, and reduces surface defects such as cold shut. In addition, in Japanese Patent Publication No. Sho 64-5985, in order to prevent the molten steel from sticking at the boundary between the tundish nozzle and the mold, a space is provided between the nozzle and the mold, and the molten steel is subjected to electromagnetic force near the boundary. With the technology to deviate in the circumferential direction and reduce the diameter, the thickness of the solidified shell that is cooled on the inner surface of the mold and generated on the surface layer of the molten metal becomes uniform around it. is there.

[0004]

By the way, in the technique disclosed in Japanese Patent Publication No. 3-69615, the heat transfer along the introduction pipe is large, so that the solidification start position is not stable and the initial solidification is discontinuous. There was a problem that surface defects were generated with the formation of the shell. Further, in JP-A 1-284469, the solidification start position is not stable in the same manner as described above in order to bring the mold and the conductive tube into contact with each other, and in particular, so that molten steel does not contact at the boundary between the tundish nozzle and the continuous casting mold. When the molten steel is reduced in diameter, surface defects such as cracks remain when the initial solidified shell is generated in the reduced diameter portion when the diameter is expanded, and the initial solidified shell is generated in the downstream side beyond the reduced diameter portion. When this happens, the initial solidification shell is generated in the part that is in contact with the mold, so the initial solidification rate is fast and the surface defects such as cracks are generated under the influence of the nonuniformity of the mold cooling, and eventually the surface defects are eliminated. There was a fear that it could not be exhausted.

An object of the present invention is to perform stable and continuous generation of the initial solidified shell, and to reduce the surface defects such as cracks and burrs that occur along with the oscillation mark, and to achieve good quality casting. There is a proposal for a method and an apparatus capable of producing a slab.

[0006]

The present invention, when performing continuous casting of molten steel using a vertical continuous casting machine, forms a gap between a tundish nozzle and a continuous casting mold, and melts the molten steel in this gap. Is a continuous casting method for molten steel (first invention), characterized in that an initial solidified shell is formed by solidifying the molten steel, and the solidification is further advanced in the mold.
In the invention, the initial solidified shell is held so that the cross-sectional shape of the initial solidified shell is substantially the same as the cross-sectional shape of the inlet side opening of the continuous casting mold (second invention).

Further, according to the present invention, in the first invention or the second invention, the initial solidified shell is retained while providing an appropriate magnetic field distribution in the gap formed between the tundish nozzle and the continuous casting mold (third invention). Invention) or first
In the invention, the second invention or the third invention, an airtight space is formed between the tundish nozzle and the continuous casting mold, and the pressure of the airtight space is increased to hold the initial solidified shell (fourth
Invention).

As a vertical continuous casting apparatus for molten steel according to the present invention, a tundish nozzle and a continuous casting mold arranged with a gap between the tundish nozzle and the tundish nozzle are provided. It is preferable that the high-frequency induction coils are arranged between each other to hold the initial solidified shell of molten steel formed in the gap and heat the initial solidified shell (fifth invention), The tundish nozzle and the continuous casting mold are connected to each other, and an airtight container capable of pressurizing inside is provided (sixth invention).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a gap is formed between the tundish nozzle and the mold, and molten steel is solidified in the region of this gap to form an initial solidified shell. The surface defects such as .. are extremely reduced.

The side surface of the molten steel is held in the gap by the surface tension, the surface tension of the molten steel and the electromagnetic force of the high frequency magnetic field, or the surface tension of the molten steel and the gas pressurization in the airtight container by the pressure pump, or the surface of the molten steel. It is held by electromagnetic force by tension and high frequency magnetic field and gas pressurization in an airtight container by a pressure pump.

In the present invention, since the tundish nozzle and the continuous casting mold are separated, there is an advantage that continuous casting can be easily interrupted and restarted.

As a more preferable condition in the present invention, it is desirable that the cross-sectional shape of the initially solidified shell of the molten steel in the gap be substantially equal to the cross-sectional shape of the inlet side opening of the continuous casting mold. This is because it is possible to prevent the initial solidified shell of the molten steel formed in the gap region from being greatly deformed when entering the continuous casting mold to generate cracks or cold shut.

In order to form the initial solidification of the molten steel, it is sufficient to measure the temperature in the gap region with a radiation thermometer or the like and to generate a sharp temperature gradient in the molten steel so that the temperature is below the solidification temperature of the applicable steel type. Can be achieved by performing strong cooling on the molten steel in the mold, or by combining strong cooling in the mold and heating with a high-frequency induction coil placed in the gap region, whereby the initial solidified shell of the molten steel is formed. Stable formation.

As described above, since the initial solidified shell forming the surface layer of the cast strand is not restricted by the mold, there is no possibility of generating surface defects under the influence of non-uniformity of cooling of the mold, and the initial stage. It is possible to obtain a slab having a good surface property without the generation of cracks generated by the shrinkage of the solidified shell or the deformation at the time of expanding the diameter or the generation of surface defects due to cold shut or the like.

According to the present invention, an airtight space is formed between the tundish nozzle and the continuous casting mold, and pressurization is performed inside the airtight space, or by controlling the electromagnetic force by the high frequency induction coil, the molten steel is initially heated. It is possible to maintain and correct the shape of the solidified shell. In carrying out the present invention, when pressurization is performed inside the airtight space, the internal pressure is as large as the molten metal static pressure in the gap minus the pressure due to the electromagnetic force, and the molten metal in the gap is balanced. Need to be adjusted. The size of the gap is preferably 100 mm or less in view of the electromagnetic force that can be applied and the stability of the molten metal surface in the gap. The frequency of the continuous casting mold was 84.6 when the casting speed was 1.2 m / min.
It is about cpm.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a continuous casting apparatus according to the present invention, in which 1 is a tundish,
2 is a tide dish nozzle, 3 is a continuous casting mold (vibration mold), 4 is a high frequency induction coil, 5 is a magnetic body for controlling the distribution of the magnetic field, and the high frequency induction coil 4 and the magnetic body 5 are tundish. It is arranged in a gap formed between the nozzle 2 and the continuous casting mold 3. Further, 6 is a mold powder supply mechanism, and 7 is a solidification shell.

2 to 4 show another example of the configuration of the device according to the present invention. In these examples, an airtight container 8 that can be pressurized by a pump P is arranged between the tundish nozzle 2 and the continuous casting mold 3, and the initial solidified shell 7a can be held by this.

Using the apparatus having the structure shown in FIG. 2, casting speed: 1.2 m / min Mold frequency: 85 cpm Mold size: 1200 mm × 260 mm Power supply of high frequency induction coil: 800 kW, Frequency: Pressure in a 20kHz airtight container: Continuous casting was performed under the condition of 1.6 atm, and the oscillation mark depth,
The surface defect generation index of the slab (indicating the rate at which defects such as cracks and bite bite are generated on the surface of the slab) was investigated. The results are shown in FIGS. 5 and 6 together with the results when a conventional apparatus (a normal casting apparatus in which molten steel in a tundish is supplied to a continuous casting mold through an immersion nozzle to perform casting).

As is clear from FIGS. 5 and 6, it was confirmed that a cast slab having an extremely good surface quality can be produced by performing continuous casting according to the present invention.

[0020]

EFFECTS OF THE INVENTION According to the present invention, no extraneous force is applied during the initial solidification shell formation of molten steel, and the initial solidification proceeds continuously, so that surface defects caused by mold oscillation are reduced and the surface quality is improved. A good cast slab can be stably manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a casting apparatus according to the present invention.

FIG. 2 is a diagram showing a configuration of a casting apparatus according to the present invention.

FIG. 3 is a diagram showing a configuration of a casting apparatus according to the present invention.

FIG. 4 is a diagram showing a configuration of a casting apparatus according to the present invention.

FIG. 5 is a diagram showing results of investigating the quality of cast slabs.

FIG. 6 is a diagram showing a comparison of surface defect occurrence indexes of slabs.

[Explanation of symbols]

 1 Tundish 2 Tundish nozzle 3 Continuous casting mold 4 High frequency induction coil 5 Magnetic material 6 Mold powder supply mechanism 7 Solidification shell 8 Airtight container

Claims (6)

[Claims] 1. When performing continuous casting of molten steel using a vertical continuous casting device, a gap is formed between a tundish nozzle and a continuous casting mold, and the molten steel is solidified in this gap to form an initial solidified shell. A continuous casting method for molten steel, characterized in that the molten steel is formed and further solidified in the mold. 2. The method according to claim 1, wherein the initial solidified shell is held so that the cross sectional shape of the initial solidified shell is substantially equal to the cross sectional shape of the inlet side opening of the continuous casting mold. 3. The initial solidified shell is held while giving an appropriate magnetic field distribution in the gap formed between the tundish nozzle and the continuous casting mold. Method. 4. The method according to claim 1, wherein an airtight space is formed between the tundish nozzle and the continuous casting mold, and the pressure in the airtight space is increased to hold the initial solidified shell. . 5. A vertical continuous casting apparatus for molten steel, comprising a tundish nozzle and a continuous casting mold arranged in the tundish nozzle with a gap between the tundish nozzle and the continuous casting mold. A continuous casting apparatus for molten steel, in which a high-frequency induction coil that holds the initial solidified shell of molten steel formed in the gap and heats the initial solidified shell is arranged. 6. The apparatus according to claim 5, further comprising an airtight container that connects the tundish nozzle and the continuous casting mold to each other and that can pressurize inside thereof.