JPH07256413A - Apparatus and method for continuously casting molten steel - Google Patents

Abstract

PURPOSE:To obtain a cast slab having good quality without defect by arranging an induction coil connected to an AC power source at a position along the inner periphery of a mold and giving AC magnetic field to a meniscus part. CONSTITUTION:Molten steel 3 is poured into a mold 2 for continuous casting from an immersion nozzle 1 and cooled to form solidified shell 4. The induction coil 8 is arranged at the position above the molten steel surface level and along the inner periphery of the mold in the mold and connected to the single phase AC power source 7 to generate the AC magnetic field near the meniscus part of the molten steel. In the meniscus part of the molten steel, downward flow is developed and also, Joule heat is generated to heat the neighborhood of the meniscus part. By this method, gas bubble and inclusion, etc., are not stored in the meniscus part and the defect is not developed and claw-like projection caused by oscillation mark is not developed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for continuously casting molten metal such as molten steel, and more particularly, to an apparatus and a method using the same which can cast a good quality slab without defects.

[0002]

2. Description of the Related Art In a conventional method for continuously casting molten metal, a molten metal injected from a casting nozzle into a mold is cooled by the mold and solidified to form a shell, which is then drawn downward. In this casting, it is usual to introduce a lubricant between the mold and the molten metal and to pull out the slab while vibrating the mold.

In the case of the above casting, a slab (solidified shell)
Intermittent oscillation marks are generated on the surface due to the vibration of the mold, and claw-shaped protrusions T are formed inside the oscillation marks (on the inner surface side of the solidified shell) as shown in FIG. May be When the protrusion T is generated, the bubble B or the inclusion K is easily caught on the protrusion T, which causes a slab subcutaneous defect. In addition, problems such as segregation H and structural abnormalities easily occur in the valleys of such marks.

Therefore, conventionally, an electromagnetic field is applied from above the mold to the upper part of the molten steel in the mold to squeeze the molten steel in the radial direction by a pinch force to prevent the formation of oscillation marks and the above-mentioned claw-shaped projections. A proposal has been made (see, for example, Japanese Patent Publication No. 57-21408).

[0005]

However, in the method in which an electromagnetic field is applied from the surroundings to the molten metal in the mold to exert a pinch force on the upper portion of the molten metal, the above-mentioned generation of marks and claws can be suppressed, but it is induced by the electromagnetic field. However, there is a problem in that the melted lubricant is caught in the molten metal because the flow passes through the front surface of the solidified shell from top to bottom. Further, since an electromagnetic field is usually applied with a mold wall interposed, mold loss is inevitably generated, which is also disadvantageous in terms of efficiency.

The present invention solves the above-mentioned problems of the prior art, makes the surface of the molten metal as close as possible to effectively heat the peripheral portion thereof without mold loss, and from the bottom to the top in the vicinity of the solidification shell. It is an object of the present invention to provide a continuous casting apparatus and method capable of obtaining a slab of good quality without imparting a flow toward the end and inducing the entrainment of molten flux.

[0007]

The gist of the present invention is as follows. (1) An induction coil connected to an AC power source for applying an AC magnetic field to the meniscus portion of the molten metal at a position above the molten metal level of the continuous casting mold of the molten metal and along the inner circumference of the mold in the mold. A continuous casting apparatus for molten metal, characterized in that (2) The continuous casting apparatus for molten metal according to the above (1), wherein the induction coil is suspended by a holding arm, and the arm is connected to an elevating / rotating device provided outside the mold. (3) An induction current is induced in the molten metal of the meniscus portion by the induction coil described in (1) or (2) above to heat the vicinity of the upper end of the solidification shell and generate an upward melt flow at the front surface of the solidification shell. A continuous casting method for molten metal, characterized by squeezing.

[0008]

The present invention will be described below with reference to the drawings. Figure 1
Shows a basic configuration of the present invention. Molten steel 3 injected into a continuous casting mold 2 by a dipping nozzle 1 provided at the bottom of a tundish (not shown) is cooled by the mold and solidified. It is pulled downward while forming the shell 4. The surface of the molten steel is covered with continuous casting powder 5 to lubricate the boundary surface. A vibration 6 having a constant amplitude is applied to the mold 2.

In the continuous casting equipment of the present invention, the induction coil 8 connected to the single-phase AC power source 7 is arranged at a position above the molten steel level and along the inner circumference of the mold, and the molten metal meniscus portion is arranged. An alternating magnetic field is generated in the vicinity. The induction coil 8 is intended to heat the meniscus portion where solidification begins and to regulate the flow of molten steel. The conductor wire is wound in a ring shape for one or more turns, surrounded by a refractory material such as alumina graphite, and further water cooled if necessary. It is structured. The width and thickness of the cross section of the induction coil 8 including the refractory are set to be about 20 to 50 mm.

The installation position of the coil 8 is in non-contact with the inner wall of the mold, and the lower part thereof is embedded in the powder 5. If the coil 8 is too far from the wall surface of the mold, the above-described object cannot be suitably achieved, and if it is too close to the wall surface of the mold, the coil and the mold may come into contact with each other or the powder may be clogged. For example, it is desirable to separate them by about 5 to 15 mm. Furthermore, the distance between the bottom surface of the coil and the molten steel meniscus should be as close as possible because it is not possible to expect an effect if it is too far away, but if it is too close, durability will be a problem.
It is preferable to make an interval of at least about 40 mm.

By installing the induction coil 8 as described above, a downward flow is generated in the molten steel meniscus portion. That is, as shown in FIG. 3, when an alternating current is applied to the coil, an induced current 9 is also induced in the molten steel 3 in the same direction, which causes a downward electromagnetic force 10 to rise along the shell. Flow 11 and flow 12 rising from the center
Then, this downward electromagnetic force acts and causes a downward molten steel flow. In addition, the induced current 9 generates Joule heat and heats the vicinity of the meniscus portion. Due to the flow and the heating action, bubbles and inclusions do not stay in the meniscus portion where they are easily floated, and defects are not generated. In addition, the generation of the claw-shaped projections, which is caused by the oscillation mark, is also suppressed.

Next, FIGS. 2 (a) and 2 (b) show specific examples of the continuous casting apparatus of the present invention. In the drawings, the same symbols as those in FIG. The induction coil 18 in FIG. 2 sandwiches the injection nozzle 1,
It is configured by arranging two rectangular objects 18a and 18b,
Each of the coils 18 is connected via a holding arm 13 to a coil raising / lowering device 14 arranged outside the mold. In this way, the coil is held independently of the vibration of the mold, and it moves up and down between the retracted position and the use position.
The swivel device 14 can freely move up and down and rotate. For example, when the coil 18 is set, the coil is stopped to rotate above the use position from the retracted position, and then the coil is lowered to a predetermined position and fixed. If the coil is damaged, it can be easily replaced in the retracted position. The coils are connected to AC power supplies 7a and 7b, respectively.

[0013]

EXAMPLE Ultra-low carbon steel was cast at a casting speed of 1.6 m / min in a casting space having a rectangular cross section of 1200 mm × 250 mm. At this time, the lower end is located 50 mm above the molten steel meniscus in the mold, and the end is separated from the mold wall by 10 mm, and the cross section is 30 mm.
Two × 30 mm rectangular one-turn coils were arranged so as to sandwich the injection nozzle as shown in FIG. 2, and a current of 10,000 A was applied to each coil.

As a result, the trapping index of the bubbles containing the alumina particles (inert gas Ar bubbles) with and without the application of current to the surface of the slab 10 mm is shown in the figure.
The number of trapped particles is remarkably reduced by applying the current. Further, in consideration of this effect, when the depth of the claw formed in the valley portion of the oscillation mark generated by the mold vibration on the surface of the slab was investigated, the former was 3 mm or less, whereas the latter was 10 mm or less. It was found that the length was up to 20 mm, and the length of this claw was shortened to suppress trapping of air bubbles that had risen.

[0015]

According to the continuous casting apparatus of the present invention described above, the electromagnetic force of the induction coil can be most efficiently applied to the molten metal meniscus portion, and compared with the conventional apparatus using electromagnetic force, It is possible to have a compact structure. Further, according to the casting method of the present invention using the above apparatus, it is possible to obtain a good quality slab having no defects on the surface of the molten metal or the subepithelium.

[Brief description of drawings]

FIG. 1 is a front sectional view for explaining the principle of the present invention.

FIG. 2 is a schematic explanatory view showing an embodiment of a continuous casting device according to the present invention.

FIG. 3 is a schematic diagram showing the trend of molten metal in the meniscus portion in the present invention.

FIG. 4 is an explanatory diagram of defects that occur in a solidified shell in normal continuous casting.

[Explanation of symbols]

 1 Injection Nozzle 2 Mold 3 Molten Steel 4 Solidification Shell 5 Continuous Casting Powder 6 Mold Vibration 7 AC Power Supply 8,18 Induction Coil 9 Induction Current 10 Downward Magnetic Force 11, 12 Molten Metal Flow 13 Holding Arm 14 Coil Lifting / Swiveling Device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keisuke Fujisaki 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

Claims (3)

[Claims] 1. A continuous casting mold for molten metal, which is connected to an AC power source for applying an AC magnetic field to the meniscus portion of the molten metal at a position above the molten metal level of the molten metal and along the inner circumference of the mold. An apparatus for continuously casting molten metal, characterized in that an induction coil is arranged. 2. An induction coil is suspended by a holding arm,
2. The continuous casting apparatus for molten metal according to claim 1, wherein the arm is connected to an elevating / revolving device provided outside the mold. 3. An induction current is induced in the molten metal of the meniscus portion by the induction coil according to claim 1 or 2,
A continuous casting method for molten metal, comprising heating the vicinity of the upper end of the solidified shell and causing an upward molten metal flow at the front surface of the solidified shell.