JP2921352B2 - Discharge flow control method for continuous casting machine - 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 machine for effectively reducing slab defects caused by air bubbles and inclusions by controlling molten steel discharge flow from an immersion nozzle in continuous casting of steel. The present invention relates to a discharge flow control method.

[0002]

2. Description of the Related Art Bubbles trapped under the surface of a slab during continuous casting are caused when an inert gas blown to prevent nozzle clogging of an immersion nozzle or a steel type having a relatively high oxygen content in steel is cast. It is generated due to oxygen that is discharged as the molten steel solidifies. In addition, inclusions trapped under the surface of the slab during continuous casting are alumina contained in molten steel. A slab containing such bubbles and inclusions, or agglomeration of bubbles and inclusions, becomes a defect such as blistering when rolled into a coil in a later step. FIG. 4 (a)
As shown in FIG. 5B, regardless of the width of the mold 11, the molten steel 13 is discharged from one dipping nozzle 12, and the powder 15 is supplied onto the meniscus 14 to perform continuous casting. As shown in FIG. As a result, as shown in FIG. 6, blister flaws are more likely to occur as the width of the mold increases.

Conventionally, as a method of solving the above-mentioned defects, in order to adjust the flow velocity and the direction of the molten steel discharge flow from the immersion nozzle, the shape of the discharge hole of the nozzle is improved, or the immersion is performed by applying an electromagnetic brake. A method for controlling the flow of molten steel from a nozzle (Japanese Patent Laid-Open No. 57-17356) has been proposed. However, in the above method, it is impossible to reduce the increase in the enlargement and agglomeration of bubbles or inclusions in the mold due to the increase in the width of the casting mold, and this can be an effective measure against the defects in the slab. Did not.

As another method, a discharge flow from a continuous casting immersion nozzle is reduced below a long side wall of a continuous casting mold having a pair of short side walls and a pair of long side walls. Flow control device of a continuous casting immersion nozzle provided with an electromagnetic stirrer for generating a horizontal flow in molten steel supplied to a continuous casting mold is disposed above the long side wall. JP-A-63-119959) has been proposed.

[0005]

SUMMARY OF THE INVENTION The above-mentioned JP-A-63-11
The device disclosed in Japanese Patent No. 9959 is capable of completely reducing the flow velocity of molten steel from an immersion nozzle by an electromagnetic brake and causing horizontal flow of molten steel above a mold by an electromagnetic stirrer, thereby causing bubbles or inclusions. It is intended to prevent blistering flaws, and it is difficult to sufficiently reduce the increase in the enlargement and aggregation of bubbles or inclusions in the casting mold as the casting mold width increases.

An object of the present invention is to provide a method for controlling a discharge flow of a continuous casting machine, which can sufficiently reduce the increase in the enlargement and agglomeration of bubbles or inclusions in the casting mold due to the increase in the casting mold width.

[0007]

Means for Solving the Problems The present inventors have intensively studied and studied to achieve the above object. As a result, if the electromagnetic brake is arranged vertically at the center of the mold in the width direction and the molten steel flow deceleration wall is formed by the electromagnetic brake, the mold width becomes an apparent half, and for each half mold, It has been clarified that continuous casting using one immersion nozzle at a time can prevent an increase in the enlargement and agglomeration of bubbles or inclusions in the casting mold due to an increase in the casting mold width, and reached the present invention.

That is, the present invention relates to a method for controlling a discharge flow of a continuous casting machine in which an electromagnetic brake is disposed in a mold of a continuous casting machine and the discharge flow of molten steel from an immersion nozzle is reduced. Using two immersion nozzles for one, an electromagnetic brake is vertically arranged at the center of the mold in the width direction, and the electromagnetic brake causes a molten steel flow deceleration wall to be formed vertically at the center of the mold in the width direction. A method for controlling a discharge flow of a continuous casting machine, characterized in that continuous casting is performed using one immersion nozzle for each half mold divided by a reduction wall.

[0009]

In the present invention, when the mold width is 1300 mm or more, two immersion nozzles are used for one mold,
An electromagnetic brake is vertically disposed at the center of the mold in the width direction, and the molten steel flow deceleration wall is vertically formed at the center of the mold in the width direction by the electromagnetic brake, and is immersed in each half mold divided by the molten steel flow deceleration wall. Since continuous casting is performed using one nozzle at a time, the width of the mold formed by the electromagnetic brake at the center in the width direction of the molten steel flow reduction wall reduces the mold width to an apparent half,
The degree of freedom of the molten steel discharge flow from the immersion nozzle decreases with the increase in the mold width, the increase in the enlargement and agglomeration of bubbles or inclusions in the mold for continuous casting is suppressed, and the blister defect, which is an internal defect of the slab, Can be prevented from occurring.

In the present invention, the mold width of the continuous casting machine is set to 1
The reason for being 300 mm or more is that if the mold width is less than 1300 mm, no increase in the agglomeration and aggregation of bubbles or inclusions in the continuous casting mold is observed, and the quality after cold rolling in the subsequent process does not deteriorate, If the width of the mold exceeds 1300 mm, flaws occur after cold rolling and the quality is deteriorated.

[0011]

【Example】

Embodiment 1 The details of the method of the present invention will be described below with reference to FIG. 1 showing an embodiment. FIG. 1 is a longitudinal sectional view showing a width direction of a continuous casting mold showing an example of an apparatus for carrying out the method of the present invention. In FIG. 1, 1 is a mold of a continuous casting machine, 2 and 3 are immersion nozzles of a tundish (not shown) provided in the width direction of the mold 1, 4 is molten steel in the mold 1, 5 is a meniscus of molten steel 4, and 6 is a mold. 100m below the meniscus 5 at the center in the width direction of 1
m, a powder covering the meniscus 5 of the molten steel 4, a solidified shell 8, and a flow of the molten steel discharged from the immersion nozzles 2, 3. An electromagnetic brake 6 arranged in the mold 1 forms a molten steel flow deceleration wall perpendicular to the center of the mold 1 in the width direction, so that the degree of freedom of the molten steel 4 discharge flow from the immersion nozzles 2 and 3 as the width of the mold 1 increases is reduced. It is configured.

With the above construction, the molten steel flow discharged from the immersion nozzles 2 and 3 into the mold 1 is perpendicular to the center of the mold 1 in the width direction by the electromagnetic brake 6 disposed vertically in the center of the mold 1 in the width direction. Is formed, the width of the mold 1 is reduced to an apparent half, and the degree of freedom of the molten steel 4 discharge flow from the immersion nozzles 2 and 3 with the increase of the mold width is reduced. As a result, the increase of bubbles and inclusions is promoted, and the increase of bubbles and inclusions in the casting mold for continuous casting is prevented from increasing, and the occurrence of blistering defects, which are defects in the slab, can be prevented. Further, under the condition that the discharge flow rate from the immersion nozzles 2 and 3 is constant, the casting speed can be approximately doubled as compared with the conventional method, and the productivity in the actual operation can be improved.

Example 2 The apparatus of Example 1 was installed in a curved continuous casting machine having a mold width of 1800 mm × 210 mm, and the immersion nozzle for supplying molten steel into the mold was a box type.
The penetration depth is set to 230 mm, and the electromagnetic brake is vertically arranged at the center of the mold width at 100 to 400 mm below the meniscus,
Continuous casting of a Ti-containing ultra-low carbon steel, which is a steel plate for an automobile, was performed at a molten steel discharge flow rate of 2.5 Ton / min. Then, the obtained slab was rolled, and the occurrence of blister defects, which are typical defects, was investigated. FIG. 2 shows the result in comparison with the conventional example. In addition, the relationship between the discharge flow rate from the immersion nozzle and the inclusions and the bubble index was investigated. The result is shown in FIG.

As shown in FIG. 2, by applying the method of the present invention, blistering defects, which are defects caused by bubbles and inclusions during continuous casting, can be significantly reduced as compared with the conventional method. Further, as shown in FIG. 3, by applying the method of the present invention, the incorporation of bubbles and inclusions during continuous casting can be greatly suppressed as compared with the conventional method.

[0015]

As described above, according to the method of the present invention, blistering flaws due to bubbles and inclusions due to an increase in the mold width in continuous casting can be significantly reduced, and under the condition of a constant discharge flow rate, The casting speed can be approximately doubled, and the production amount can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a width direction of a continuous casting mold showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a graph showing blistering flaw indices of the conventional method and the method of the present invention in Example 2.

FIG. 3 is a graph showing the relationship between the discharge flow rate and the inclusion and bubble index in the conventional method and the method of the present invention in Example 2.

4A and 4B are explanatory views of a conventional casting method, wherein FIG. 4A is a cross-sectional view in the width direction when the mold width is large, and FIG.

FIG. 5 is a graph showing a relationship among a casting speed, a discharge flow rate, and a slab width in a conventional casting method.

FIG. 6 is a graph showing a relationship between a slab width and a blistering flaw occurrence index in a conventional casting method.

[Explanation of symbols]

 1,11 Mold 2,3,12 Immersion nozzle 4,13 Molten steel 5,14 Meniscus 6 Electromagnetic brake 7,15 Powder 8 Solidified shell

Claims (1)

(57) [Claims] 1. A discharge flow control method for a continuous casting machine in which an electromagnetic brake is disposed on a mold of a continuous casting machine to reduce the flow of molten steel from an immersion nozzle. On the other hand, using two immersion nozzles,
An electromagnetic brake is vertically disposed at the center of the mold in the width direction, and the molten steel flow deceleration wall is vertically formed at the center of the mold in the width direction by the electromagnetic brake, and is immersed in each half mold divided by the molten steel flow deceleration wall. A discharge flow control method for a continuous casting machine, wherein continuous casting is performed using one nozzle at a time.