JPH06114511A - Method for heating molten steel in tundish - Google Patents

Abstract

PURPOSE:To prevent the short-circuit flow along the bottom part of a tundish, improve the heat efficiency in the heating and advantageously achieve the float-up of inclusion in molten steel by utilizing electromagnetic force caused by mutual action between DC current and static magnetic field. CONSTITUTION:A static magnetic field generating device 12 is fitted to the bottom part of the tundish under a heating box 6 and the magnetic field B having the direction orthogonally crossing flowing direction of molten steel in parallel with the bottom surface of the tundish. In the molten steel, by a cathode 7 and an anode 8 generating plasma arc for heating, the DC current having the direction orthogonally crossing the magnetic field B is generated. By this mutual action between the DC current and the static magnetic field, the electromagnetic force F having the reverse direction to the short-circuit flow of the molten steel is generated in the molten steel. By this method, the short-circuit flow along the bottom part of the tundish is prevented, and as the flowing speed on the surface of the molten steel is increased, the heating efficiency by the plasma arc is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating molten steel in a tundish to be used for continuous casting, and more particularly, it applies plasma arc heating to the molten steel contained in the tundish and applies a direct current to the tundish. By applying a static magnetic field, efficient heating of molten steel and levitation separation of non-metallic inclusions (hereinafter simply referred to as "inclusions") are promoted to produce clean steel.

[0002]

2. Description of the Related Art When continuously casting molten steel, the heating degree of the molten steel in the tundish is controlled to prevent nozzle clogging due to low temperature of the molten steel, to prevent skinning of the mold surface and to trap inclusions and bubbles in the solidified shell. To prevent each
The molten steel in the tundish is heated by a DC plasma arc.

For example, as shown in FIG. 1, molten steel in a ladle 1 is supplied to a tundish 3 via a long nozzle 2, where it is heated by a direct current plasma arc and then a dipping nozzle 4 to mold it. 5 is poured. The direct current plasma arc heating in this device is performed by plasma arc between the cathode 7 and the anode 8 in the heating box 6 arranged at a position corresponding to the molten steel flow path from the long nozzle 2 to the pouring port (immersion nozzle 4). Is generated, and the molten steel 9 flowing in the heating box 6 is heated. The cathode 7 is made of W alloy or Cu alloy, and the anode 8 is made of carbon-containing brick or steel.

However, the above heating method has the following problems. Since the area to be heated is limited to only the surface of the molten steel in the heating box 6 and is heated from above (hereinafter, this is referred to as “upper heat”), the thermal efficiency is poor. The falling flow of the molten steel from the long nozzle 2 forms a short-circuit flow A that flows along the bottom of the tundish toward the immersion nozzle in a short-circuited manner, making it difficult to float inclusions in the molten steel in the tundish.

Therefore, in order to solve these problems,
A method in which a gas is blown from a blowing plug 10 into a heating zone in a tundish to accelerate the stirring of molten steel (Japanese Patent Laid-Open No. 59-
No. 107755 and FIG. 2), and a method of providing a weir 11 in the tundish to prevent the formation of a short circuit flow and stirring the molten steel in the heating zone (see FIG. 3) has been proposed.

In the former method, for example, when Ar gas is blown from the bottom of the tundish, all of the fine gas in the steel bath does not float up, and a part of it penetrates into the mold and adheres to the solidified shell. This will cause defects inside or on the surface of the piece.

On the other hand, the latter method is effective as long as the shape of the weir is maintained, but since the life of the weir constructed of refractory is short, the weir will continue to rise as the number of heats in the tundish increases. The cost of refractory is naturally high because of the disadvantage that the effect of the weir disappears due to melting or damage and the life of the weir is short. Furthermore, if there is a weir when discharging the residual steel in the tundish, it becomes difficult to discharge the residual steel and the amount of residual steel increases.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to propose a technique for improving the thermal efficiency of heating and for advantageously achieving the floating of inclusions in molten steel without causing such disadvantages. To do.

[0009]

SUMMARY OF THE INVENTION The present invention is a method for heating molten steel in a tundish for continuous casting by a plasma arc. A method for heating molten steel in a tundish characterized by controlling the direction of molten steel flow by applying an electrostatic magnetic field to the passage. Further, in the present invention, it is preferable that the molten steel is heated and an electrostatic magnetic field is applied in the direct current passage formed with the generation of the plasma arc.

[0010]

Next, the structure and operation of the present invention will be described with reference to FIG.
A detailed description will be given in accordance with 5 and 5. 4 (a) and (b) are
1 shows an example of an apparatus used in a method for heating molten steel according to the present invention. In this example, a static magnetic field generator 12 is attached to the bottom of the tundish 3 below the heating box 6 to generate a magnetic field B parallel to the bottom of the tundish and orthogonal to the molten steel flow direction. A permanent magnet may be used as the means for generating the static magnetic field, but it is more preferable to use an electromagnet.

Further, in the molten steel, a direct current in the direction I orthogonal to the magnetic field B flows through the cathode 7 and the anode 8 which generate a plasma arc for heating the molten steel. Due to the interaction, according to Fleming's left-hand rule, an electromagnetic force F opposite to the short-circuit flow of the molten steel is generated in the molten steel to prevent the short-circuit flow A along the bottom of the tundish, and the molten steel surface flow velocity increases. The heating efficiency of the plasma arc can be increased, and the inclusion can be levitated. In the above example, the DC plasma arc generating circuit is used as it is as a DC current passage, but a DC current passage may be provided separately from the plasma generating circuit.

Further, in the examples shown in FIGS. 5 (a) and 5 (b), the static magnetic field is generated in parallel with the molten steel flow direction parallel to the bottom of the tundish, and the mutual position of the cathode 7 and the anode 8 is Is shifted in the width direction of the tundish so that the direct current I flows. Then, when the static magnetic field is applied, the flow of the molten steel in the tundish flows so as to make a circular motion within the cross section in the height direction of the tundish, as shown in FIG. This flow prevents the formation of short-circuit flow A in the tundish, and the movement of the steel bath improves the heating efficiency.

[0013]

[Examples] Oxygen concentration in steel was adjusted to 45 to 55 ppm by ladle refining, and continuous casting was performed under the casting conditions shown in Table 1 using the following four types of tundish. The magnetic flux density of the static magnetic field in the methods 1 and 2 of the present invention was 2000 gauss.

(1) Conventional method 1 (see FIG. 1) (2) Conventional method 2 (with Ar gas injection) (see FIG. 2) (3) Conventional method 3 (with single weir) (see FIG. 3) (4) ) Inventive method 1 (see FIG. 4) (5) Inventive method 2 (see FIG. 5)

[0015]

[Table 1]

Table 2 shows the results of the investigation of the thermal efficiency in each of the above casting methods, and Table 3 shows the results of the investigation of the deoxidizing efficiency and the product defect ratio in the tundish of each casting method. The thermal efficiency was evaluated by measuring the molten steel temperature near the long nozzle and immediately above the immersion nozzle. Deoxidation efficiency was evaluated by sampling and analyzing molten steel using a silica tube from the steel bath in the mold near the discharge nozzle of the dipping nozzle.Product defects were 1.0 mm thick when hot and cold rolled. And evaluated. All the results show the average value of 20 heats (one heat of 300 t) in succession in the tundish.

[0017]

[Table 2]

[0018]

[Table 3]

As shown in Tables 2 and 3, the conventional method 1 is
Heat efficiency is 60% because there is no stirring means in the heating zone and heat is generated
And the deoxidation efficiency and product quality were also low. In Conventional method 2, the number of bubbles that penetrate into the mold increases due to Ar blowing, and product defects increase, so the gas blowing rate was set to 40 Nl / min at the maximum, but the result was similar to Conventional method 1. . In Conventional Method 3, the life of the weir was less than 6 heats, and the heat efficiency, deoxidation efficiency and product quality were good up to this point, but the effect of the weir diminished after 7 heats, and the average value up to 20 heats. Fell below the results for the 6th heat. It can be seen that, compared with these conventional methods, both the methods 1 and 2 of the present invention significantly improve thermal efficiency, deoxidizing efficiency, and product quality.

[0020]

As described above, according to the present invention,
By utilizing the electromagnetic force due to the interaction between the direct current and the static magnetic field, the short-circuit flow along the bottom of the tundish can be prevented and the molten steel in the heating zone can be agitated. You can realize surfacing.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a method for heating molten steel in a tundish with direct current plasma.

FIG. 2 is a schematic diagram showing a method of blowing Ar gas in heating molten steel in a tundish with direct current plasma.

FIG. 3 is a schematic diagram showing a method of using a weir in the heating of molten steel in a tundish by direct current plasma.

FIG. 4 is a schematic diagram showing a method for heating molten steel in a tundish according to the present invention.

FIG. 5 is a schematic diagram showing another method for heating molten steel in a tundish according to the present invention.

FIG. 6 is a schematic diagram showing the flow of molten steel.

[Explanation of symbols]

 1 Ladle 2 Long Nozzle 3 Tundish 4 Immersion Nozzle 5 Mold 6 Heating Box 7 Cathode 8 Anode 9 Molten Steel in Tundish 10 Injection Plug 11 Weir 12 Static Magnetic Field Generator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Miki 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Satoshi Idogawa 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Corporation Technical Research Division

Claims (2)

[Claims] 1. A method for heating molten steel in a tundish for continuous casting by a plasma arc, wherein a direct current passage is formed in the flow passage of the molten steel in the tundish and an electrostatic magnetic field is applied to the current passage. A method for heating molten steel in a tundish, characterized in that the direction of the molten steel flow is controlled by. 2. When the molten steel in the continuous casting tundish is heated by the plasma arc, an electrostatic magnetic field is applied to the direct current passage formed by the plasma arc to control the direction of the molten steel flow. The heating method according to claim 1, which is characterized in that.