JPH06142854A - Continuous casting method of steel using electromagnetic force and mold for continuous casting - Google Patents

Abstract

PURPOSE:To provide a continuous casting method capable of obtaining a good quality cast slab and utilizing control of an initial solidified shell with using electromagenetic force effective for high speed casting. CONSTITUTION:In the continuous casting method of steel by means of supplying a molten steel into a mold 1 through an immersed nozzle, when a steel slab is casted with controlling a shape of an initial solidified shell 5a (this invention) by means of directly causing an high frequency electric current 7 to flow to the upper part of the mold 1, a high frequency applied region 12 is arranged in an upper of the mold 1, further, the mold 1, which is made of a material having such a conductivity that the conductivity at the high frequency applied region 12 is higher in comparison with other high frequency applied regions, is used. Thus, it improves the quality and productivity of ingot, further, making a high continuous casting possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting steel using electromagnetic force and a mold for continuous casting, and more particularly, by controlling the shape of an initially solidified shell formed in the mold, a slab (steel slab) ) It is a continuous casting technology that enables smooth high speed casting with further improvement of quality.

[0002]

2. Description of the Related Art In general continuous casting of steel, as shown in FIG. 1, solidification of molten steel starts on the wall surface of a continuous casting mold to form an initial solidified shell. At this time, the mold is longitudinally oscillated at a predetermined amplitude (frequency 100 to 300 cpm) (mold oscillation) to promote the inflow of the mold powder between the oscillating solidification shell and the inner wall surface of the mold. Lubrication between the shell and the inner wall surface of the mold was ensured.

On the other hand, the state of the molten steel at the meniscus interface is usually curved due to the balance of the interfacial tension between the mold powder molten layer and the molten steel. Therefore, the initial solidified shell is also curved toward the center of the mold (the molten steel side). Was present.

Moreover, since the pressure of the molten powder layer interposed between the mold and the solidified shell fluctuates due to the above-described mold oscillation, the initial solidified shell falls toward the center of the mold, as shown in FIG. 1 (c). The phenomenon of forming the nail of the oscillation mark as shown was often seen. In addition, the oscillation mark claw portion tends to easily capture air bubbles or inclusions contained in the molten steel, which has been a major cause of deterioration of the surface quality of the continuous cast slab.

Therefore, in order to continuously cast a steel slab having a good surface quality, it is effective to reduce the depth of the oscillation mark claw portion. To reduce the depth of the claw portion, it is effective. ． Shortening the curved length of the initial solidified shell at the meniscus interface ,. It was considered effective to reduce the pressure fluctuation in the molten powder layer existing between the mold and the solidified shell.

Further, in the conventional continuous casting method, if it is attempted to realize high-speed casting at a drawing speed of 3 m / min or more, the powder consumption amount per unit volume of cast slab tends to be insufficient, which results in a solidified shell. There was a tendency that smooth lubrication with the mold was not performed and so-called restraint breakouts frequently occurred.

On the other hand, conventionally, various techniques have been proposed for overcoming the above-mentioned problems and preventing the surface defects of the steel slab. First, in JP-A-2-137653, a nozzle, a mold, and a casting metal are in a non-contact state with each other by using an electromagnetic pinch force generated by providing an energizing coil around the outer periphery of the upper part of the mold and flowing a high frequency current. While proposing a method of casting. This conventional method
A characteristic is that a closed mold is used to hold the molten steel, an induction coil is arranged above the mold, and a lubricant is injected between the molten steel and the coil and the mold. However, in this conventional method, since the coil is arranged in the upper part of the mold, the efficiency for keeping the molten steel and the mold in a non-contact state by electromagnetic induction is poor, and in the end, the molten steel can be stably and continuously supplied at high speed. Casting was very difficult.

Further, Japanese Patent Application Laid-Open No. 2-70361 proposes a method of casting by disposing an electromagnetic coil outside the mold near the outer circumference of the meniscus. The feature of this conventional method is that the interaction between the magnetic field generated by the coil and the induced current in the molten steel controls the meniscus shape and the flow of the molten metal in the mold, so that more mold is formed in the gap between the solidified shell and the mold. By supplying the powder, it is possible to improve the shape of the cast piece and the internal quality of the cast piece. However, in this conventional technique, a coil is arranged outside the mold and a high frequency is applied to the molten steel in the mold, so that the efficiency is high in that the distance from the molten steel is long and part of the high frequency is absorbed by the mold. There was a problem of being bad.

[0009]

As described above,
In order to solve the above-mentioned problems of the conventional continuous casting technique, one is to surely heat the vicinity of the meniscus including the initial solidified shell to shorten or eliminate the curved shape part of the initial solidified shell. It seems that the method is effective, but the proper method for doing this has not yet been developed.

Therefore, an object of the present invention is to solve the above problems in continuous casting, obtain a steel slab of good quality, and use an electromagnetic force effective for enabling high speed casting. It is to propose a continuous casting technique with control of an initially solidified shell.

[0011]

[Means for Solving the Problems] In order to achieve such an object, the inventors of the present invention have a carbon concentration of 500 ppm or less,
As a result of various investigations and studies on the surface quality during continuous casting using aluminum-killed aluminum deoxidized with Al, the following findings were obtained.

That is, it became clear that the surface quality of the steel slab shows a certain tendency due to the flow of molten steel in the mold, the temperature of the molten steel, the cooling capacity of the cooling water in the wall surface of the mold, and the like. Moreover, it has been found that even if the molten steel flow in the mold is suppressed, the surface quality of the steel slab does not deteriorate unless the initial solidified shell develops abnormally. That is,
The inventors have found that if the development of the initially solidified shell in the mold can be controlled, the surface quality of the steel slab can be reliably improved. Furthermore, from the conventional knowledge that the molten mold powder plays a role of lubrication,
It was also found that if the molten mold powder is sufficiently supplied between the mold wall surface and the solidified shell, the frictional resistance between the mold wall surface and the solidified shell is reduced, and high-speed continuous casting is possible.

Based on these various findings, the inventors of the present invention have found that as a method for achieving the above object, a high frequency wave is formed on the upper part of a continuous casting mold composed of a pair of short side walls and long side walls. We have found a method of controlling the shape of this solidified shell by directly applying an electric current and inducing an induced current in the upper part of the initial solidified shell along the width direction of the slab. In particular, the present invention is a technique developed in order to realize the above method more effectively.

That is, the present invention provides a steel slab by supplying molten steel in a tundish into a continuous casting mold composed of a pair of short side walls and long side walls, respectively, through a dipping nozzle. In the method of continuous casting,
When casting a steel slab while controlling the shape of the initial solidification shell by directly passing a high-frequency current to the upper part of the mold, the conductivity of the high-frequency energized region of this mold upper part, compared to other high-frequency non-energized region Is a continuous casting method for steel using electromagnetic force, which is characterized by using a mold formed of a material exhibiting high electrical conductivity. The present invention, as a structure of a continuous casting mold suitable for carrying out this method, has a high-frequency energization region on the upper part of the mold, and the conductivity of this high-frequency energization region is higher than other high-frequency non-conduction regions. We propose a mold made of a material that exhibits electrical conductivity. Further, in this mold, it is preferable that the conductivity in the high frequency non-conduction region is 1/2 or less of the conductivity in the high frequency conduction region, and
It is preferable that the high frequency conduction region and the high frequency non-conduction region are insulated from each other. Further, it is a more preferable embodiment that the high frequency conduction region is internally cooled.

[0015]

FIG. 1 is a schematic view showing a conventional continuous casting method. Reference numeral 1 in the drawing indicates a pair of short side walls 1a, 1'a.
And the long side walls 1b and 1'b for continuous casting, 2
Is an immersion nozzle for supplying molten steel in the tundish into the mold 1. 3 is a powdery mold powder, and 4 is a molten mold powder of 3. Reference numeral 5 is molten steel, and 5a is an initial solidified shell produced by cooling the molten steel. In addition, vertical vibration is applied to the above-mentioned mold as mold oscillation.

FIG. 1- (c) exemplifies the shape of the initially solidified shell produced by the conventional continuous casting method which is cast under such a structure. Oscillation marks which adversely affect the quality of the slab are shown. The claw portion 5b is generated.

FIG. 2 shows the outline of the continuous casting method of the present invention. As shown in this figure, a characteristic of the method of the present invention is that the generation of the initial solidified shell is controlled by directly supplying a high frequency current to the mold 1 using the high frequency generator 6, for example.

2 (b) and 2 (c), when comparing the conventional solidification morphology with the solidification morphology of the method of the present invention, the initial solidification shell produced by the conventional casting method is 5a '. The shell is 5a, and the gaps between the long side walls and the initial solidified shells 5a and 5a 'are δ and δ', respectively. In the present invention, the gap δ due to the magnetic pressure of the high frequency current.
Is larger than the conventional one, and therefore, it becomes possible to easily supply the powder, and at the same time, it is possible to reduce the depth of the nail, that is, the length of the curved portion. This will be described in detail below.

That is, as shown in FIG. 3, when a high frequency current 7 is passed through the mold 1, a magnetic field 9 is formed around it. On the other hand, in the vicinity of the initial solidification shell 5a, an induction current 8 opposite to the high frequency current 7 is generated in the direction of canceling the magnetic field 9,
A magnetic field 10 opposite to the magnetic field 9 is also generated around the induced current 8. Here, the induction current 8 flows only in the vicinity of the initial solidification shell 5a because the electromagnetic waves generated by the high frequency current 7 do not penetrate too deeply due to the skin effect.

The induced current 8 generated in the vicinity of the initial solidification shell 5a heats the initial solidification shell 5a itself so that the initial solidification is performed as in the conventional example shown by the chain line in FIG. 2 (b). The shell has a function of preventing the generation of the oscillation mark claw portion 5b that extends long while curving along the meniscus.

The magnetic field 10 generated in the vicinity of the initial solidification shell 5a induces a repulsive force F due to the interaction with the induced current 8, whereby the gap δ between the mold wall surface and the solidification shell is set.
To expand.

Therefore, according to the present invention, as shown in FIG. 2 (c), the generation of the curved portion of the initial solidified shell 5a at the meniscus interface can be effectively suppressed. In addition to it,
Since the pressure in the powder passage between the inner wall surface of the mold and the initial solidification shell 5a decreases as the gap δ increases, this also reduces the collapse of the initial solidification shell 5a into the mold center (molten steel side). As a result, the claws of the oscillation mark can be made small, and the cast slab surface defects can be significantly reduced.

Moreover, the gap δ between the mold wall surface and the solidified shell δ
Can be made significantly larger than the gap δ'when a high-frequency current is not applied, so that the molten powder can easily enter and the lubricity by the molten powder is improved, which enables high-speed casting.

In order to more effectively control such an initial solidified shell, it is necessary to efficiently apply a high frequency current to the vicinity of the meniscus inside the wall surface of the mold. Therefore, in the present invention, as shown in FIG. 4, in the continuous casting mold, in particular, the material in the high frequency conduction region provided on the upper part of the mold and the material in the other high frequency non-conduction region have different electric conductivity.
That is, the material in the high frequency conduction region has a higher conductivity. Above all, the conductivity in the high frequency non-conducting region of the mold is 1 with respect to the conductivity in the high frequency conducting region above the mold.
By setting it to be equal to or less than / 2, it becomes possible to pass a larger high frequency current near the initial solidified shell. As a result, the effect of controlling the initial solidification shell by the high-frequency current becomes more remarkable. In addition, the high-frequency current flows efficiently in the high-frequency energized region by insulating the high-frequency energized region made of a material having a high electrical conductivity from the high-frequency non-energized region made of a material having a low electrical conductivity. Can be controlled. Furthermore, by internally cooling the high-frequency energization area, it is possible to prevent heat generation due to the high-frequency energization, so that it is possible to efficiently energize a large current, so that the initial solidification shell can be controlled more effectively. You can

[0025]

【Example】

(Example 1) Two strand continuous casting machine Using a continuous casting machine,
Under the casting conditions shown below, an experiment was conducted in which low-carbon aluminum killed steel with an oxygen concentration of 35 ppm or less was continuously cast for 3 charges at 280 tons per heat. Casting mold size: 260mm in thickness direction,
Width direction 1600mm Height direction 900mm Mold material: Copper alloy (conductivity 60
IACS%) Super heat in tundish: 26-30 ° C Casting speed: 2.2m / min Mold oscillation: Frequency 130cpm, Amplitude 4mm In this casting experiment, one strand is energized with high frequency current at the top of the mold. Continuous casting according to the method of the present invention, also on the other strand, continuous casting by a conventional method not energizing a high frequency current, each 25 heat, the slab obtained is 1.2 mm hot and cold rolled respectively.
A cold-rolled steel sheet having a thickness was manufactured. The shape of the current-carrying part of the mold, the intensity of the current, the frequency and the magnetic field generated are as follows. Current-carrying part shape: 85 mm (height) x 7
mm (thickness) Conductivity of current-carrying part: 92IACS% ^{* 1} Current in mold wall: 2500 A Frequency: 10kHz Maximum magnetic flux density: 0.05T * 1: IACS% is based on 100% conductivity of pure steel Shows the relative conductivity of

The surface defect occurrence rate of the cold-rolled steel sheet thus obtained is shown in FIG. As is clear from this figure, it was found that the surface quality of the cold-rolled steel sheet produced by the method of the present invention produced from the slab cast by passing a high-frequency current through the mold was significantly better than that of the comparative example.

(Embodiment 2) The conductivity in the high frequency non-conduction region of the mold is 1/2 of the conductivity in the high frequency conduction region.
A cold-rolled steel sheet was manufactured in the same manner as in Example 1 except for the following. As a result, the surface defect occurrence rate of the obtained cold rolled steel sheet is shown in FIG. As is clear from the results shown in this figure, by providing a high-frequency energization area with higher conductivity near the meniscus, the initial solidified shell is more susceptible to heating and magnetic pressure, and the surface quality is improved. It was

Example 3 Two Strand Continuous Casting Machine A continuous casting machine was used to carry out an experiment of continuously casting a low carbon aluminum killed steel having an oxygen concentration of 35 ppm or less under the following casting conditions. Casting mold size: 260mm in thickness direction,
Width 1600mm Height 900mm Mold material: Copper alloy (conductivity 35
IACS%) Super heat in tundish: 25 ~ 30 ℃ Casting speed: 2.0m / min Mold oscillation: Frequency 130cpm, Amplitude 4.0mm Heat size: 280 ton Conducting part shape: 100mm (height) ×
5mm (thickness) Mold adhesion type Conductivity of current-carrying part: 92IACS% Current in mold wall: 2500 A Frequency: 10kHz Maximum magnetic flux density: 0.05T In this casting experiment, one strand was selected from materials with high conductivity. Continuous casting according to the method of the present invention in which a high-frequency current is applied using a mold formed by insulating a current-carrying region and a non-current-conducting region made of a material having low conductivity, and a conventional method in which the high-frequency current is not applied in the other strand. The continuous casting was performed for 15 heats each, and the obtained slabs were hot-rolled and cold-rolled to produce cold-rolled steel sheets with a thickness of 1.2 mm. The conditions such as the size of the mold, the casting speed, and the pouring amount were set to be the same for both strands.

FIG. 7 shows the surface defect occurrence rate of the cold rolled steel sheet thus obtained. As is clear from this figure, assuming that the surface defect occurrence rate of the steel sheet cast by the conventional method is 1, the surface defect occurrence rate of the steel sheet cast by the method of the present invention is 0.37 or less, which clearly demonstrates the effectiveness of the present invention. did.

(Example 4) Two-strand continuous casting machine A continuous casting machine was used to carry out an experiment of continuously casting low carbon aluminum killed steel having an oxygen concentration of 35 ppm or less under the following casting conditions. Casting mold size: 260mm in thickness direction,
Width 1200mm Height 900mm Mold material: Copper alloy (conductivity 35
IACS%) Super heat in tundish: 25-31 ℃ Casting speed: 1.8m / min Mold oscillation: Frequency 130cpm, Amplitude 4.0mm Heat size: 250 ton Conducting part shape: 100mm (height) × 2
0 mm (thickness), mold side of current-carrying part, internal water cooling type Conductivity of current-carrying part: 92IACS% Current in mold wall: 3800 A Frequency: 10 kHz Maximum magnetic flux density: 0.08T In this casting experiment, one strand was used. The continuous casting according to the method of the present invention in which high-frequency current is applied using a mold as shown in FIG. 5 (a) in which the high-frequency current region is internally cooled, and the continuous casting by the conventional method in which the high-frequency current is not applied to the other strand Each of them was subjected to 15 heats, and the resulting slabs were hot-rolled and cold-rolled to produce cold-rolled steel sheets having a thickness of 1.2 mm. The conditions such as the size of the mold, the casting speed, and the pouring amount were set to be the same for both strands.

FIG. 8 shows the surface defect occurrence rate of the cold-rolled steel sheet thus obtained. As is clear from this figure, assuming that the surface defect occurrence rate of the steel sheet cast by the conventional method is 1, the surface defect occurrence rate of the steel sheet cast by the method of the present invention is 0.30 or less, which clearly demonstrates the effectiveness of the present invention. did.
That is, a large current can be passed by internally cooling the high-frequency conduction area, and therefore the shape of the initial solidified shell can be easily controlled, and the surface defects of the cold-rolled steel sheet obtained by rolling can be significantly reduced. It was

[0032]

As described above, according to the continuous casting method and continuous casting mold of the present invention, the shape of the initially solidified shell formed in the mold can be effectively controlled, resulting in surface quality. It is possible to obtain an excellent steel slab and to improve productivity at the same time. Moreover,
Stable high speed continuous casting becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic view showing a conventional continuous casting method, (a),
(b) is a figure which shows the structure, (c) is a figure which shows the state of an initial solidification shell.

FIG. 2 is a schematic view showing a continuous casting method of the present invention,
(a) is a schematic diagram showing a method of passing a high frequency current, and (b) and (c) are diagrams comparing the states of the initial solidification shell in the method of the present invention and the conventional method.

FIG. 3 is a conceptual diagram showing the effect of high frequency current in the present invention.

FIG. 4 is a diagram showing a specific example of the configuration of the continuous casting mold of the present invention, in which (a) is a diagram showing a mold in which the materials of the high-frequency conducting region and the high-frequency non-conducting region have different electrical conductivity; b) is a diagram showing a mold in which a high-frequency energized region is internally cooled.

FIG. 5: Regarding the surface defect occurrence rate, the method of the present invention (high-frequency current application)
It is the figure which compared with the conventional method.

FIG. 6 is a diagram comparing a method of the present invention (when a mold whose conductivity in a high frequency non-conduction region is 1/2 or less with respect to a conductivity in a high frequency conduction region) is used with a conventional method regarding a surface defect occurrence rate. Is.

FIG. 7 relates to the surface defect occurrence rate between the method of the present invention (when a mold in which a high frequency conducting region made of a material having a high conductivity and a high frequency non-conducting region made of a material having a low conductivity are used as an insulator) and a conventional method. It is the figure which compared.

FIG. 8 relates to the surface defect generation rate, a mold in which the method of the present invention (a high frequency conducting area made of a material having a high conductivity and a high frequency non-conducting area made of a material having a low conductivity are insulated, and the high frequency conducting area is internally cooled. FIG. 6 is a diagram comparing a conventional method with a case of using).

[Explanation of symbols]

 1 Continuous casting mold 1a, 1'a Short side wall 1b, 1'b Long side wall 2 Immersion nozzle 3 Mold powder (powder) 4 Mold powder (molten) 5 Molten steel 5a, 5a ', 5b Solidified shell 6 High frequency generator 7 High frequency current 8 Induction current 9 Magnetic field generated by high frequency current 10 Magnetic field generated by induction current 11 Internal cooling section 12 High frequency conduction area

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Keiji Taguchi, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Headquarters (72) Koichi Tozawa 1-kawasaki, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Hisao Yamazaki 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Bessho Nagayasu No. 1 Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Tetsuya Fujii No. 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Division

Claims (5)

[Claims] 1. A method for continuously casting a steel slab by supplying molten steel in a tundish into a continuous casting mold comprising a pair of a short side wall and a long side wall, respectively, through a dipping nozzle. In the case of casting a steel slab while controlling the shape of the initial solidification shell by directly passing a high-frequency current to the upper part of the mold, the conductivity of the high-frequency energization area provided on the upper part of the mold is A continuous casting method for steel using electromagnetic force, characterized in that a mold formed of a material having a higher conductivity than that of a current-carrying region is used. 2. A continuous casting mold comprising a pair of a short side wall and a long side wall, each of which has a high frequency conduction region on the upper part of the mold, and the conductivity of the high frequency conduction region is
A casting mold for continuous casting, which is made of a material having a higher conductivity than other high frequency non-energized regions. 3. The mold according to claim 2, wherein the conductivity in the high frequency non-conducting region is 1 / the electric conductivity in the high frequency conducting region.
A mold for continuous casting, which is 2 or less. 4. The continuous casting mold according to claim 2 or 3, wherein the high frequency energization region and the high frequency non-conduction region are insulated from each other. 5. The continuous casting mold according to any one of claims 2, 3 and 4, wherein the high-frequency energization region is internally cooled.