JPH0647506A - Method for cleaning molten metal in tundish and device therefor - Google Patents

Abstract

PURPOSE:To improve the efficiency for floating up and removing inclusion in molten steel by arranging a static magnetic field generating device and an energizing device in molten steel flowing course in a tundish and generating ascending flow. CONSTITUTION:The static magnetic field generating device 7 is fitted in the width direction of the bottom part of the tundish 3 and the magnetic field B having parallel direction to the molten steel flowing direction is generated. On the other hand, the energizing device electrodes 8, 8 are arranged to the side walls at both ends of the magnetic field generating device 7 in the tundish and DC current having the crossing direction at the right angle to the static magnetic field B direction is energized to the molten steel 4. By this method, upward electromagnetic force F is generated with the electromagnetic action following of Fleming's left hand rule in the molten steel 4 and the ascending flow is developed in the molten steel. By this method, the float-up of the inclusion in the molten steel can be promoted, and as a weir at the bottom of the tundish can be abolished, the discharge of the remained steel is facilitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning molten steel contained in a tundish attached to a continuous casting machine and an apparatus therefor, and particularly to a method for cleaning molten steel flowing in the tundish. By applying a magnetic field and an electric current, the flow direction of this molten steel is changed to promote the levitation of non-metallic inclusions in the steel, thereby proposing a novel technique for cleaning the molten steel.

[0002]

2. Description of the Related Art In continuous casting of molten steel, in order to obtain a clean steel slab, it is necessary to reduce the amount of nonmetallic inclusions in steel (hereinafter simply referred to as "inclusions") as much as possible. That is, when the concentration of non-metallic inclusions in the steel is high, for example, in the case of aluminum killed steel, when the amount of alumina is large, the alumina itself is trapped in the solidification shell in the continuous casting mold, and as a result, Surface defects or internal defects occur. Alumina not only adheres and accumulates in the immersion nozzle to cause nozzle clogging, but also causes entrainment of mold powder due to drift of molten steel in the mold, and deterioration of slab quality due to increase in penetration depth of inclusions. Nozzle clogging due to the accumulation of alumina becomes severe, and it becomes difficult to secure a predetermined molten steel injection rate, resulting in a decrease in productivity. Therefore, reducing inclusions in steel is extremely effective in ensuring the improvement of slab quality and productivity.

Conventionally, the method of deoxidizing molten steel has been the most general technique for reducing inclusions in steel. In addition, a method of promoting the floating of inclusions contained in the molten steel in the tundish is also used.

As a conventional technique for cleaning molten steel by promoting floating of inclusions, for example, (a) a method using a weir
(See, for example, Japanese Patent Laid-Open No. 51-138537), (b) a method of increasing the capacity of the tundish to increase the residence time of the molten steel, (c) a method of blowing gas into the molten steel in the tundish, etc. Has been done.

FIG. 1 is a schematic view of a method (conventional method 1) for continuous casting using a tundish having no weir. As shown in the figure, the molten steel in the ladle 1 is supplied to one end of the tundish 3 via the long nozzle 2. The molten steel is poured into the mold 6 from the immersion nozzle 5 provided at the other end of the bottom of the tundish 3. Observing the flow of the injected molten steel in the tundish 3 in the case of this conventional technique, the molten steel drop flow from the long nozzle 2 becomes an ascending flow A toward the surface of the steel bath while circumventing a part of it. Is a short-circuit flow B that goes straight along the bottom portion directly above the immersion nozzle 5. Further, the molten steel flow in the tundish 3 is the short circuit flow B
When the main component is, the inclusions contained in the molten steel 4 are injected into the mold 6 without losing the floating chance.

In order to solve these problems, conventionally,
As shown in FIG. 2, a tundish 3 ′ having a weir 9 provided in the flow path of the molten steel in the tundish was developed.
According to this technique, by providing the weir 9 in the tundish 3, the short-circuit flow B shown in FIG. 1 can be diverted to an upward flow that goes over the weir 9 toward the steel bath surface. The generation of the upward flow C enables the inclusions in the steel to be effectively floated on the bath surface.

The effect of providing the weir 9 has been confirmed in actual operation and has already been put to practical use, but the problems described below still remain. In other words, (a) The life of the weir constructed of refractory is short, and therefore the effect cannot be maintained for a long time. In particular, as the number of tundish (the number of heats of tundish) increases, the wetting damage of the weir becomes more severe, and the effect of removing inclusions gradually diminishes. (B) If there is a weir in the tundish, when trying to discharge the residual steel, this weir interferes with the discharge of the residual steel, and at the same time the residual steel amount increases. (C) Since the life of refractory is limited by the life of the weir with severe melting loss, refractory cost increases.

[0008]

As described above, in the conventional technique using the tundish without the weir, the floating removal of the inclusions is insufficient, while in the conventional technique using the tundish with the weir, the fire resistance is increased. In addition to the drawback that the life of the object is short, there are problems that the effect of floating inclusion removal cannot be maintained for a long time. An object of the present invention is to propose a technique that reliably overcomes the problems of such conventional techniques. That is, a molten steel cleaning technique is proposed which is configured so that the floating removal action of inclusions can be stably exerted for a long period even with a tundish without a weir.

[0009]

[Means for Solving the Problems] While earnestly studying for achieving the above-mentioned object, the present inventors have found that in order to effectively perform the inclusion floating removal action in a tundish without a weir, With the knowledge that the application of electromagnetic force by the magnetic field energization method is effective, the present invention as described below was conceived.

That is, according to the present invention, in controlling the flow direction of the molten steel in the tundish for continuous casting to promote the floating of the non-metallic inclusions for cleaning, in the middle of the flow path of the molten steel in the tundish, A method for cleaning molten steel in a tundish, which comprises applying an electromagnetic force that urges a flowing molten steel flow in an upward direction and / or an opposite direction by applying a static magnetic field and a direct current. And in order to carry out this method for cleaning molten steel,
In a continuous casting tundish, a cleaning device, in which a static magnetic field generator and a current-carrying device are installed at a position where molten steel discharged from a long nozzle hits the middle of a flow path toward an immersion nozzle, is advantageously suitable. I knew it was.

[0011]

The structure and operation of the present invention will be described in detail below. 3 (a) and 3 (b) show an embodiment of the present invention. In this example, the static magnetic field generator 7 is mounted in the width direction of the bottom of the tundish 3 to generate a magnetic field B in a direction parallel to the molten steel flow direction. A permanent magnet may be used as a means for generating the static magnetic field B, but a DC electromagnet is more preferable. On the other hand, energizing device electrodes 8 and 8 ′ are arranged on the side walls of the tundish that correspond to both ends of the magnetic field generating device 7, and a direct current in a direction orthogonal to the direction of the static magnetic field B is applied to the molten steel 4. In this way, when the static magnetic field generator 7 and the current-carrying device 8 are arranged in the tundish 3 and the static magnetic field and the direct current are applied to the molten steel 4 at the position where the dam is originally provided, the molten steel 4 in the tundish An upward electromagnetic force F is generated by the electromagnetic action according to Fleming's left-hand rule, and the molten steel flow is generated by this electromagnetic force F
Since the upflow is generated by the action of, the formation of the short-circuit flow B along the bottom of the tundish, which has been conventionally seen, can be prevented, and the flow can be converted into the upflow.

FIGS. 4A and 4B show another embodiment of the present invention. This example shows a static magnetic field generator 7 on the side wall of the tundish and a magnetic field B perpendicular to the side wall of the tundish in the middle of the molten steel flow path (the position where the weir should originally be formed). It is arranged as follows. On the other hand, electrodes 8 and 8'are provided on the top and bottom of the tundish 3, respectively, and a direct current is applied to the molten steel in a direction perpendicular to the static magnetic field B direction. With such a configuration, due to the action of the static magnetic field B and the direct current I, an electromagnetic force F opposite to the original molten steel flow is generated in the molten steel in the tundish 3, so that the bottom portion of the tundish 3 is The molten steel flow flows backward due to the electromagnetic force F opposite to the direction of the short-circuit flow B along the direction, and turns into the upward flow C, generating a flow advantageous for floating removal of inclusions. In addition, as the electrode material,
Refractory such as ZrB ₂ , alumina graphite, zirconia graphite, or water-cooled metal is used.

[0013]

[Example] The oxygen concentration in steel was adjusted to 30 to 40 ppm by ladle refining, and continuous casting was performed under the casting conditions shown in Table 1 using the following four types of tundish. Conventional method (without weir) (see FIG. 1) Conventional method (with single weir) (see FIG. 2) Inventive method I (see FIG. 3) Inventive method II (see FIG. 4)

[0014]

[Table 1]

Table 2 shows the magnetic field and current application conditions of the methods I and II of the present invention. Further, Table 3 shows a comparison of the analysis results of the oxygen concentration for each of the above-mentioned methods. The oxygen concentration shown in Table 3 is an average value of the oxygen concentration in the steel in the ladle and the oxygen concentration in the steel bath in the mold after the ladle refining for 25 heats in succession in the tundish. The oxygen in the steel in the mold in Table 3 was evaluated by analyzing molten steel sampled using a silica tube from the steel bath in the mold near the discharge nozzle of the immersion nozzle.

[0016]

[Table 2]

[0017]

[Table 3]

As is clear from the results shown in Table 3,
The method I and method II of the present invention are
It can be seen that the deoxidizing ability in the ash is very high. sand
That is, the conventional method (with a weir) is O until 8 heats_M= 20
The effect of the weir was confirmed to be ppm, but after that, the weir was damaged.
The deoxidizing capacity is further reduced, and the final average of 25 heats is O. _M
Is 25 ppm, which is inferior to the method of the present invention.

[0019]

As described above, according to the present invention, even when the molten steel is cleaned by using a tundish without a weir, an electromagnetic force by a static magnetic field energization method is used instead of the weir. As a result, the floatation promoting action of inclusions can be maintained for a long period of time, so that steel with a higher degree of cleanliness can be stably produced as compared with the method using a tundish with a weir. Further, according to the present invention, it is effective in extending the tundish life.

[Brief description of drawings]

FIG. 1 is an explanatory view of a conventional continuous casting method using a weirless tundish.

FIG. 2 is an explanatory view of a conventional continuous casting method using a tundish with a weir.

FIG. 3 is an explanatory view showing an example of the continuous casting method of the present invention by a static magnetic field energization method.

FIG. 4 is an explanatory view showing another example of the continuous casting method of the present invention by the static magnetic field energization method.

[Explanation of symbols]

 1 Ladle 2 Long Nozzle 3 Tundish 4 Molten Steel in Tundish 5 Immersion Nozzle 6 Mold 7 Static Magnetic Field Generator 8 Energizer (Electrode) 9 Weir

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[Procedure amendment]

[Submission date] August 5, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

[Table 2]

Claims (2)

[Claims] 1. A static magnetic field and a direct current are provided in the middle of the flow path of the molten steel in the tundish during cleaning to promote the floating of non-metallic inclusions by controlling the flow direction of the molten steel in the tundish for continuous casting. By applying an electric current,
A method for cleaning molten steel in a tundish, which comprises applying an electromagnetic force that urges a flowing molten steel flow in an upward direction and / or an opposite direction. 2. A tundish comprising a static magnetic field generating device and a current-carrying device at a position where a molten steel discharged from a long nozzle hits the middle of a flow path toward an immersion nozzle of a continuous casting tundish. Equipment for cleaning molten steel.