JPH08300113A - Method for reducing non-metallic inclusion in continuous casting - Google Patents

Abstract

PURPOSE: To prevent the deep invasion of molten steel downward in molten steel pool and to remove non-metallic inclusion at the upper part in a mold by arranging a molten steel parting plate at the lower end of an immersion nozzle and stirring the molten steel at the upper part in the mold. CONSTITUTION: The molten steel 4 flowed into the mold 1 through spouting holes 9 of the immersion nozzle 2 during casting is flowed into the upper range with a molten steel parting plate 3. The molten steel 4 is solidified by a heat alleviation from the molten steel 4 to the mold 1 to form solidified shell 6. The molten steel 4 at the upper part of the partition plate 3, too, is passed through a gap between the parting plate 3 and the solidified shell 6 at the straightening slow flowing speed and shifted downward accompanied with the shift of the solidified shell 1. By this method, the invading depth of the desending flow can be reduced. Further, the molten steel 4 at the upper part of the parting plate 3 is stirred by using an electromagnetic stirring device 5 and the inclusion is efficiently floated up and removed in a narrow range at the upper part in the mold 1. By this method, the clean steel 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 for molten steel.

[0002]

2. Description of the Related Art In continuous casting of steel, molten steel in a ladle is poured into an internal water-cooled copper mold through a tundish, and then cooled and solidified by removing heat in a mold part and a secondary cooling zone to form a solid. Make a slab.

In the molten steel flowing into the mold through the immersion nozzle, there are non-metallic inclusions generated in the deoxidizing process and non-metallic inclusions mixed from the outside. Reduction of inclusions has been desired because of deterioration of properties and surface defects of steel sheets.

Regarding the method of reducing inclusions in the mold, a method of controlling the discharge flow of molten steel by adjusting the angle of the discharge hole of the nozzle, materials and processes, Volume 3, 1990,
The method of electromagnetically stirring molten steel in a mold disclosed on pages 1102 to 1105 to reduce inclusions has been tried.

[0005]

The non-metallic inclusions present in steel cause deterioration of material properties of steel and surface defects of steel sheet.

Regarding the method of reducing the inclusions in the molten steel flowing into the mold in the mold, conventionally, the discharge angle of the nozzle is adjusted to be upward or horizontal so that the discharge flow penetrates deep into the molten steel pool. However, there is a problem that a large amount of inclusions remain in the slab because the molten steel flow in the mold cannot be properly controlled only by changing the nozzle discharge angle.

Further, in the method of promoting the removal of inclusions in the molten steel by electromagnetically stirring the molten steel in the mold, the discharge flow of the molten steel from the nozzle penetrates deep into the molten steel pool, and However, the quality of the slab is not improved because inclusions remain in the slab after solidification due to the invasion of the slab into the solidification shell.

[0008]

Means for Solving the Problems In the continuous casting of steel, the present invention provides a molten steel partition plate at the lower end of a dipping nozzle when pouring molten steel in a ladle into a mold through a tundish to produce a slab. The installation prevents molten steel flowing from the nozzle from penetrating deep inside the molten steel pool, and
This is a continuous casting method in which an electromagnetic stirrer is installed on the upper part of the mold to stir the molten steel to promote the floating and removal of non-metallic inclusions in the molten steel at the upper part of the mold.

[0009]

FIG. 1 is a schematic diagram showing a case where molten steel 4 is poured into a mold 1 through a dipping nozzle 2 when a molten steel partition plate 3 and an electromagnetic stirrer 4 are installed at the lower end of the dipping nozzle in continuous casting. .

FIG. 2 is a sectional view taken along the line AA in FIG. 1, showing a method for continuously casting small lot cast pieces by adding a molten steel partition plate and wires.

During casting, the molten steel 4 flowing into the mold 1 through the discharge holes 9 of the immersion nozzle 2 flows into the castle above the molten steel partition plate 3. The molten steel 4 in the mold is solidified by heat removal from the molten steel to the mold, forming a solidified shell 6.

The solidified shell is drawn downward at a certain casting speed, but with the movement of the solidified shell,
The molten steel above the partition plate 3 also passes between the partition plate 3 and the solidification shell 6 at a rectified slow flow velocity and moves downward.

In FIG. 2, when the partition plate 3 is not provided, the flow of molten steel discharged from the dipping nozzle normally collides with the solidified shell on the short side of the mold, and then the molten steel surface 1 of the molten steel in the mold.
It is divided into an upward flow toward 0 and a downward flow toward the bottom of the molten steel pool.

Generally, the downward penetration depth of this downward flow is
Although it depends on the casting speed, it is about 3 to 15 m, and the nonmetallic inclusions in the molten steel ride on the descending flow and penetrate deeply, making it difficult to remove in the mold.

When the partition plate 3 is used, the downflow in the mold is slowed down and rectified by passing between the solidification shell and the partition plate, and the penetration depth of the downflow can be greatly reduced.

When a partition plate is used and molten steel above the partition plate is stirred by an electromagnetic stirrer, aggregation of inclusions and floating / removal on the molten metal surface are promoted.

This partition plate is fixedly installed at the lower end of the dipping nozzle, and there is no drop or damage due to the discharge flow, and the formation of solidification on the surface of the partition plate causes the passage of molten steel between the partition plate and the solidification shell. It is essential that there is no blockage,
Any plate that meets these requirements can be used, and industrially, it is convenient to use a refractory plate.

According to the present invention, the flow of molten steel discharged from the nozzle is controlled by the molten steel partition plate to prevent inclusions from penetrating deep into the molten steel pool, and to perform electromagnetic stirring in a narrow region above the mold. With this, inclusions can be efficiently floated and removed, and inclusions in the slab can be significantly reduced.

[0019]

Example A molten steel of Al killed steel whose main component is 0.015% C (molten steel weight in ladle: about 240 t) is used, and a thickness of 30
A continuous casting test was performed on a bloom slab of 0 mm and a width of 500 mm.

In continuous casting of an ordinary vibration type copper mold, molten metal was poured from a ladle to a tundish using a mold flux and then poured into the mold using an immersion nozzle.

As the casting conditions, the casting speed in the steady part is 0.9 m / min, the superheat degree of molten steel in the tundish is in the range of about 20 to 30 ° C., and the secondary cooling of the slab after the casting part is performed. Adopted water spray.

The molten steel partition plate has a length of 200 mm and a width of 400
mm, 50 mm thick, made of alumina graphite.
It was fixed to the lower end of the immersion nozzle as shown in, and installed so as to be immersed at a position about 300 mm below the molten steel meniscus.

In order to stir the molten steel on the upper part of the mold,
As shown in FIG. 2, a moving magnetic field type electromagnetic stirrer (electromagnet center position: 200 mm below the molten metal surface, coil current: 200 amperes) was used above the mold.

Regarding the investigation of the inclusions in the slab obtained in the experiment, from the steady part of the slab where the casting speed is constant, the total thickness in the thickness direction and the width of 10 cm at the center in the width direction, A test piece having a dimension of 1 cm in the longitudinal direction of the cast piece was cut out and the amount of alumina inclusions was investigated by the slime extraction method.

As a result of investigation of inclusions, 10 per 1 kg of steel
The number of inclusions of 0 μm or more is 1000 to 20 unless (1) electromagnetic stirring is used and a molten steel partition plate is not used.
00 pieces / kg, 700-1300 pieces / when using a partition plate
(2) When electromagnetic stirring is applied to stir molten steel on the upper part of the mold, 500 to 100 unless a partition plate is used.
It was found that 0 pieces / kg, 50-100 pieces / kg when using a partition plate.

As described above, it was found that when the molten steel in the upper part of the mold is agitated by using the molten steel partition plate, inclusions are removed at the upper part of the mold, and the cleanliness of the inclusions with respect to the inclusions is greatly improved.

[0027]

EFFECTS OF THE INVENTION According to the present invention, the downward flow of molten steel in the molten steel pool can be prevented, the molten steel can be efficiently stirred in a narrow region in the upper part of the mold, and inclusions in the slab can be greatly reduced. Then, clean steel can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic diagram when a partition plate and an electromagnetic stirring device are installed in a continuous casting mold.

FIG. 2 is a sectional view taken along the line AA in FIG. 1, showing a schematic diagram of continuous casting.

[Explanation of symbols]

 1 Mold 2 Immersion Nozzle 3 Partition Plate 4 Molten Steel 5 Electromagnetic Stirrer 6 Solidification Shell 7 Moving Direction of Cast Piece 8 Flow Direction of Molten Steel 9 Discharge Hole 10 Metal Surface

Claims (1)

[Claims] 1. In continuous casting of steel, when molten steel in a ladle is poured into a mold through a tundish to produce a slab, a molten steel partition plate is installed at the lower end of the dipping nozzle to flow from the nozzle. It prevents the molten steel from entering deep inside the molten steel pool and stirs the molten steel by installing an electromagnetic stirrer on the upper part of the mold to float and remove non-metallic inclusions in the molten steel at the upper part of the mold. Continuous casting method to promote the.