JP2000061599A - Continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method of molten metal, with which a cast slab excellent in the surface quality and the inner quality can be obtd. SOLUTION: In the continuous casting method of molten metal, the molten metal is circularly fluidized in the horizontal direction by giving the molten metal near the meniscus in a mold the electro-magnetic force with an electro- magnetic stirring device 7, and the electro-magnetic force is given to spouting flow 6a from an immersion nozzle 1 dipped into the molten metal in the mold with the electro-magnetic stirring devices 8a, 8b to fluidize the spouted flow 6a of the molten metal upward. The direction of the electro-magnetic force acting on the molten metal near the meniscus in the mold can be the same direction at the faced positions in two long sides of the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal continuous casting method for obtaining a slab having excellent surface quality and internal quality.

[0002]

2. Description of the Related Art In continuous casting of steel, an immersion nozzle having two discharge holes whose discharge directions are downward is generally used from the viewpoint of ensuring the surface quality and internal quality of the slab.

FIG. 4 is a diagram schematically showing a flow state of molten steel in a mold when an immersion nozzle having two discharge holes whose discharge directions are downward is used. Discharge hole 2 of immersion nozzle 1
The discharge flow 6a of the molten steel 6 cast into the mold 3 collides with the short side 3a of the mold and is branched into an upflow 6b and a downflow 6c. The upward flow 6b becomes a horizontal flow 6d in the vicinity of the meniscus from the short side of the mold toward the center of the long side.

When the flow velocity of the horizontal flow 6d is low, the oxides and bubbles present in the molten steel are easily trapped by the solidified shell 5 near the meniscus. When the flow velocity is high, unmelted mold powder 4a and molten mold powder 4b added on the surface of the molten steel are likely to be caught in the molten steel. The oxides and bubbles trapped in the solidified shell as described above, and the powders caught in the molten steel are likely to cause defects in the cast slab.

In order to prevent the defects of these cast pieces, a method of applying an electromagnetic stirring force to the molten steel near the meniscus in the mold in a direction perpendicular to the casting direction to adjust the flow rate of the molten steel has been generally adopted. It was For example, for molten steel near the meniscus,
Horizontal swirling flow, flow from the center of the long side of the mold to the direction of the short side, or flow in the opposite direction, or by changing the direction with time to give flow Is proposed.

However, these methods only adjust the flow rate of the molten steel by stirring the molten steel in the vicinity of the meniscus, and in particular, the internal quality of the cast piece cannot be said to be sufficient.

In JP-A-6-226409 and JP-A-7-112247, an electromagnetic force is applied to molten steel near a meniscus in a mold to cause horizontal stirring, and a dipping nozzle is used. A method has been proposed in which a static magnetic field type electromagnetic force is applied to the molten steel discharge flow to attenuate the flow velocity of the discharge flow.

According to the methods of these publications, it is possible to prevent the discharge flow from the dipping nozzle from deeply penetrating below the mold, so that oxides, bubbles, unmelted mold powder, etc. in the molten steel form a slab. It can be prevented from mixing inside.

However, in order to attenuate the flow velocity of the discharge flow,
The high-temperature molten steel discharge flow does not branch to reach the vicinity of the meniscus after colliding with the short side of the mold. Therefore, the mold powder added to the surface of the molten steel in the mold is less likely to be melted, and the oxide floating on the surface of the molten steel is less likely to be adsorbed by the molten mold powder. As a result, the solidified shell,
That is, oxides and the like in the molten steel are likely to be captured near the surface of the slab, which may deteriorate the surface quality of the slab.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a molten metal continuous casting method capable of obtaining a slab having excellent surface quality and internal quality.

[0011]

The gist of the present invention resides in the continuous casting method for molten metal described in (1) and (2) below.

(1) An electromagnetic force is applied to the molten metal near the meniscus in the mold to swirl the molten metal in the horizontal direction, and the discharge flow from the dipping nozzle immersed in the molten metal in the mold. A continuous casting method for molten metal in which an electromagnetic force is applied to the molten metal to exert an upward force on the discharge flow of the molten metal.

(2) By applying an electromagnetic force to the molten metal in the vicinity of the meniscus in the mold, the molten metal is caused to flow in the horizontal direction in the same direction at the positions where the two long sides face each other.
A continuous casting method for molten metal, in which an electromagnetic force is applied to a discharge flow from a dipping nozzle immersed in the molten metal in a mold so that an upward force is applied to the discharge flow of the molten metal.

In the present invention, in continuous casting of molten metal, particularly steel, defects on the surface and inside of the slab due to oxides and bubbles in molten steel, unmelted mold powder (hereinafter simply referred to as powder), etc. are generated. Was prevented by the following means.

An electromagnetic force is applied to the molten steel to cause the molten steel near the meniscus in the mold to swirl in the horizontal direction. This prevents oxides, bubbles, or unmelted powder in the molten steel from adhering to the solidified shell near the meniscus.

At the same time, an electromagnetic force is applied to the discharge flow from the discharge hole of the immersion nozzle. At this time, instead of attenuating the flow velocity of the discharge flow by the electromagnetic force, an upward force is applied to the discharge flow to prevent the discharge flow from flowing downward. This causes an upward flow in the discharge flow that collides with the short side of the mold.

By controlling the flow of the molten steel as described above, it becomes difficult for oxides and bubbles in the molten steel or unmelted powder on the surface of the molten steel to penetrate into the slab. Therefore, the internal quality of the slab can be improved. Also,
Since the temperature of the molten steel near the meniscus in the mold can be maintained at a high temperature, melting of the powder added in the mold is promoted and the surface quality of the slab is improved.

The flowing directions of the molten steel in the vicinity of the meniscus in the mold may be the same at the positions where the two long sides face each other. That is, the flow from the vicinity of the central part of the long side of the mold to the direction of the short sides on both sides, or the flow from the short sides on both sides of the mold to the vicinity of the central part of the long side, from the short side on one side of the mold to the other short side. It may be a flowing flow.

The method of the present invention is effective not only for continuous casting of steel but also for quality improvement of the surface and the inside of a slab by continuous casting of molten metal such as Al.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining the method of the present invention, and is an example in which steel is continuously cast using an immersion nozzle having two discharge holes.

An electromagnetic force is applied to the molten steel 6 in the vicinity of the meniscus in the mold by a pair of opposing electromagnetic stirring devices 7 arranged in the direction perpendicular to the paper surface, and a molten steel discharge flow 6a from the discharge hole 2 is provided. 2 shows a case where an electromagnetic force is applied by two opposing sets of electromagnetic stirring devices 8a and 8b arranged in the direction perpendicular to the paper surface.

As shown in FIG. 1, an electromagnetic force is applied to the discharge flow 6a toward the center of the mold by electromagnetic stirring devices 8a and 8b. As a result, the downward flow of the discharge flow downwardly of the mold is reduced, and after the discharge flow collides with the short sides on both sides of the mold, the discharge flow is directed toward the vicinity of the meniscus.

FIG. 2 is a view showing an example in which an electromagnetic force is applied to the molten steel in the vicinity of the meniscus in the mold, as seen from above the mold. The electromagnetic stirrer 7 and the molten steel flow 6e near the meniscus are schematically shown. (A) in the figure is a view showing an example in the case of using one set of the electromagnetic stirring device 7 which covers almost the entire width of the mold. This is an example in which the molten steel flow 6e is one horizontal swirling flow in the mold. (B) in the figure
Is an electromagnetic stirrer 7a, 7b having a width of about half the width of the mold.
This is an example in which the molten steel flow 6e is two left and right swirling flows on the paper surface. (C) in the figure
Is an example in which the molten steel flow 6e is made to have the same direction at the positions where the two long sides face each other by using the two sets of electromagnetic stirring devices 7a and 7b as described above. The flow of molten steel 6e
This is an example of the flow from near the center of the long side of the mold to the short sides on both sides. (D) in the figure is an example shown in (c), in which the molten steel flow 6e flows from the short sides on both sides of the mold to the vicinity of the central portion of the long side. Any of the methods shown in FIGS. 2A to 2D may be used.

FIG. 3 is an explanatory view in the case of using an immersion nozzle having only one downward discharge hole at the bottom. The electromagnetic stirrer 7 near the meniscus and the electromagnetic stirrer 8 below the discharge hole exert an upward force on each discharge flow, so that the same effect as in the case of the immersion nozzle having two discharge holes can be obtained. it can.

[0025]

EXAMPLE A vertical bending type continuous casting machine having a vertical portion length of 3 m was used to arrange an electromagnetic stirrer having the configuration shown in FIG. 1 or 3, and the cross-sectional shape was 250 mm thick and 1600 m wide.
m low carbon steel slab was cast. Casting speed is 1.8
m / min.

For the immersion nozzle, use is made of an immersion nozzle which is open on both sides of the mold in the direction of the short side and has only two discharge holes downwardly angled with respect to the horizontal direction or one discharge hole downward at the bottom. I was there.

In each of the tests, a set of electromagnetic stirrer having the structure shown in FIG. 2 (a) was installed near the meniscus in the mold so that the upper end of the coil and the meniscus of molten steel were aligned with each other. An electromagnetic force was applied so that the molten steel inside could swirl horizontally. At this time, the strength of the electromagnetic force was adjusted so that the maximum horizontal flow velocity of the molten steel was about 30 cm / sec.

A sample of a slab having a length of 1 m in the casting direction was sampled from a slab cast at a constant casting speed, and foamed defects on the surface of the slab and from the surface to the inside of the slab. Was investigated.

The method for investigating the bubble defects on the surface of the slab is as follows. 5 pieces per side from the obtained slab sample
A sample including a 0 mm square slab surface was cut out and ground to a depth of 1 mm from the slab surface. The polished surface was examined under an optical microscope at a magnification of 100 times for the number of perforated bubble-like defects of 100 μm or more.

The cleanliness of the slab from the surface to the inside was investigated as follows. A sample of the entire thickness of the slab including a rectangular slab surface having a length of 10 mm and a width of 50 mm was sampled at a position ¼ of the width of the slab. From this sample, dice-shaped samples were cut out at intervals of 10 mm in the thickness direction of the slab. Regarding the cross section of this sample facing the slab surface, J
The cleanliness was examined by an optical microscope at a magnification of 400 times according to the test method specified in IS G 0555. The cleanliness of the section where the cleanliness was the worst was taken as the cleanliness of the slab.

Table 1 shows the shape of the immersion nozzle, the test conditions for the electromagnetic stirrer, and the test results.

[0032]

[Table 1]

Test No. of the present invention example In No. 1, a dipping nozzle having a discharge angle of 20 ° downward from the horizontal direction and having two discharge holes opening in the short side direction on both sides of the mold was used. Two sets of electromagnetic stirring devices 8a and 8b having the configuration shown in FIG. 1 were installed below the two discharge holes. At this time, the center of the height of the coil of the electromagnetic stirrer in the casting direction was aligned with the lower end of the immersion nozzle. The obtained slab had few bubble defects and the slab had good cleanliness. This test No.
The other test results were evaluated by setting the number of bubble defects and the cleanliness value of the slab in the test result of No. 1 to 1.0, respectively.

Test No. of the present invention example In No. 2, an immersion nozzle having only one discharge hole at the bottom was used. One set of electromagnetic stirrer having the structure shown in FIG. 3 was installed at a position corresponding to the discharge flow. At this time, the upper end of the coil of the electromagnetic stirrer was aligned with the position of 100 mm from the lower end of the immersion nozzle. The index of bubble defects on the surface of the obtained slab was 1.1, and the index of cleanliness of the slab was 0.9, which were both good results.

Test No. of the present invention example 1 and No. In both cases, the discharge flow was prevented from flowing downward in the mold, and after the discharge flow collided with the short side of the mold, it was directed toward the vicinity of the meniscus, that is, upward flow was secured. As a result, it was possible to prevent oxides, bubbles, etc. in the molten steel from entering the inside of the slab, and the slab had good cleanliness.
Further, since the temperature of the molten steel near the meniscus in the mold could be maintained at a high temperature, the melting of the powder was promoted, the oxide in the molten steel, the unmelted powder, etc. were not captured on the surface of the slab, A sound slab was obtained.

Test No. of the comparative example. In No. 3, a dipping nozzle having two discharge holes whose discharge angle was 50 ° downward from the horizontal direction was used. No electromagnetic stirrer below the discharge holes was used. The index of bubble defects on the surface of the slab was 2.5, and the index of cleanliness of the slab was 3.2, both of which were poor.

Test No. of the comparative example. In No. 4, an immersion nozzle having only one discharge hole at the bottom was used. No electromagnetic stirrer below the discharge holes was used. The index of bubble defects on the surface of the slab was 3.5, and the index of cleanliness of the slab was 5.2, which markedly caused bubble defects and was poor in cleanliness.

Test No. of the comparative example. 3 and No. In No. 4, since the downward flow of the molten steel discharge flow was not prevented, the cleanliness of the slab was poor. In particular, test No. 1 having a discharge hole at the bottom of the immersion nozzle. The cleanliness of 4 was bad.
This is because oxides, bubbles, etc. in the molten steel penetrated deep inside the slab. In addition, the test No. 3 and No. In both cases, the temperature of the molten steel in the vicinity of the meniscus could not be maintained at a high temperature, and the oxide in the molten steel and unmelted powder were trapped in the solidified shell, so the surface quality of the slab was also poor.

[0039]

By applying the method of the present invention, it is possible to obtain a slab having excellent surface quality and internal quality.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method of the present invention when an immersion nozzle having two discharge holes is used.

FIG. 2 is a diagram showing an example of the flow of molten steel caused by applying an electromagnetic force to the molten steel near the meniscus in the mold.

FIG. 3 is a diagram illustrating a method of the present invention when using a submerged nozzle having only one downward discharge hole on the bottom.

FIG. 4 is a diagram schematically showing a flow state of molten steel in a mold when an immersion nozzle having two discharge holes is used.

[Explanation of symbols]

1 Immersion Nozzle 2 Discharge Hole 3 Mold 3a Short Side 4a of Mold 4a Unmelted Mold Powder 4b Melted Mold Powder 5 Solidified Shell 6 Molten Steel 6a Discharge Flow 6b Upflow 6c Downflow 6d Horizontal Flow 6e Molten Steel Flow 7 Electromagnetic Near Meniscus Stirrer 8 Electromagnetic stirrer for discharge flow

Claims (2)

[Claims] 1. An electromagnetic force is applied to molten metal in the vicinity of a meniscus in a mold to swirl the molten metal in a horizontal direction, and a discharge flow from a dipping nozzle immersed in the molten metal in the mold. A continuous casting method for molten metal, which comprises applying an electromagnetic force to exert an upward force on a molten metal discharge flow. 2. The molten metal is horizontally moved in the mold by applying an electromagnetic force to the molten metal near the meniscus in the mold.
Flow in the same direction at the positions where the two long sides face each other, and apply an electromagnetic force to the discharge flow from the immersion nozzle immersed in the molten metal in the mold to apply an upward force to the discharge flow of the molten metal. A method for continuously casting molten metal, comprising: