JP3127762B2 - Continuous casting method of molten metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to continuous casting of molten metal, and more particularly to a continuous casting method of molten metal in which the productivity and the surface properties of the slab are improved after the slab width is changed during continuous casting. Things.

[0002]

2. Description of the Related Art On a surface of a slab produced by a continuous casting method of molten steel, a surface defect called an oscillation mark is generated due to vibration of a mold. The oscillation mark may cause lateral cracks in the cast slab, or a segregation layer may be formed at a valley of the oscillation mark, and the segregation layer may remain on the surface of the steel sheet product and become a surface defect. For this reason, it is required that the depth of the oscillation mark be reduced as much as possible.

Conventionally, as a method of reducing the depth of the oscillation mark, there are methods such as increasing the frequency of the mold and changing the vibration waveform (using a non-sine waveform).

However, each of these methods is a method of shortening the time during which the downward speed of the mold vibration becomes higher than the moving speed of the slab (casting speed), that is, the time during the negative strip period. Also in this method, there is a limit in reducing the depth of the oscillation mark.

[0005] In continuous casting, mold powder is used to reduce the oscillation mark so as to improve the lubricity of the mold and the slab. However, due to the characteristics of molten steel behavior in the mold of continuous casting, The corner between the short side of the mold and the long side of the mold is cooled by the mold from two directions, so that the thickness of the molten layer of the mold powder is reduced, and the molten metal discharge flow from the tundish immersion nozzle collides with the short side of the mold As a result, the mold becomes short and the short side of the mold tends to have a bare metal surface, and the thickness of the mold powder is reduced. For this reason, the surface properties of the slab are inferior at the short side of the slab, particularly at the corner, as compared with the long side of the slab.

As a method for solving these problems, Japanese Patent Application Laid-Open No. H5-115952 discloses a method in which a high-frequency coil 3 is installed inside a mold 1 and an electromagnetic force is applied to a molten metal as shown in FIG. Proposed. In this method, a high-frequency magnetic field is applied to a meniscus portion in a mold, and Joule heat is generated in a solidified shell portion by a magnetic pressure and an induced current. The heat causes a solidification delay of the solidified shell, reduces the depth of the oscillation mark to improve the surface properties of the slab, and furthermore, bends the solidified shell tip by magnetic pressure to cause a gap between the mold and the solidified shell. This method increases the consumption of the mold powder by increasing the space between the mold powders flowing in, increases the lubrication by the mold powder, and reduces the tensile stress applied to the solidified shell in the casting direction.

In this method, one high-frequency coil 3 applies an electromagnetic force to the entire slab width. Therefore, the slab width and the length of the high-frequency coil are substantially the same, and the high-frequency coil is installed near the surface of the molten metal in order to apply a strong electromagnetic force to the surface of the molten metal. This is a method for producing a cast piece with few surface defects in this way.

[0008]

Recently, in order to improve the productivity of a continuous casting machine, the short side of the mold is translated along the long side of the mold during the casting of molten metal. A method of continuously casting slabs having different slab widths has been used.

[0009] However, when the technique disclosed in Japanese Patent Application Laid-Open No. H5-115952 is applied to width change during casting,
When narrowing the slab width, the short side of the mold and the high-frequency coil physically interfere with each other.

[0010] As a countermeasure, when changing the width of the short side of the mold: Stop the continuous casting of the molten metal and install another high-frequency coil on the molten metal: Remove the high-frequency coil and continuously cast the molten metal However, in this case, the productivity of the continuous casting machine is reduced because the continuous casting operation of the molten metal is interrupted. In the case of (1), there was a problem that the surface properties of the cast slab after use of no high-frequency coil deteriorated.

When the slab width is increased, the short side of the mold and the high-frequency coil do not physically interfere with each other. There is a problem that the high-frequency magnetic field is not applied to the short side where the high-frequency magnetic field is to be applied, and the surface property of the short side of the slab cannot be improved.

The present invention has been made in view of such circumstances, and in particular, a cast slab having a small number of surface defects without lowering the productivity after changing the slab width during continuous casting. An object of the present invention is to provide a continuous casting method of a molten metal to be manufactured.

[0013]

The continuous casting method for molten metal according to the present invention is a continuous casting method for molten metal in which a high-frequency coil is disposed inside a mold and a high-frequency magnetic field is applied to a meniscus portion to perform casting. At least one high-frequency coil is separately arranged on the meniscus on the short side, and the high-frequency coil is moved so as to follow the movement of the short side of the mold, and casting is performed while applying a high-frequency magnetic field from the high-frequency coil to the meniscus portion. It is characterized by the following.

[0014]

[Function] At least one high-frequency coil is separately arranged on the molten metal meniscus on both short sides of the mold, and when the short side of the mold is moved by changing the slab width during continuous casting, the short side of the mold is moved. Since the high-frequency coil follows the high-frequency coil, the short side of the slab is always cast with a high-frequency magnetic field applied. or,
Since the high-frequency coil is separated and arranged on both short-side meniscuses with the immersion nozzle as a boundary, the immersion nozzle and the high-frequency coil do not physically interfere with each other even during width change during casting. Therefore, the width can be freely changed.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a schematic view of a continuous casting mold used in an embodiment of the present invention, in which (a) is a plan view and (b) is a sectional view taken along line XX of (a). In the figure, 1 is a mold, 2 is an immersion nozzle, 3 is a high frequency coil, 4 is a high frequency coil support jig, 5 is molten steel, 6 is mold powder, 7 is a tundish, 8 is cooling water, 9 is a solidified shell, 10 Is the long side of the mold,
11 is a short side of the mold, and 12 is a meniscus.

The molten steel is poured from the ladle into the tundish 7 and then into the mold 1 (short side width 250 mm, long side width 1500 mm) cooled by the cooling water 8 via the immersion nozzle 2. . On the meniscus 12 in the mold 1, high-frequency coils 3 are arranged on both sides of the immersion nozzle 2. The mold 1 is composed of a mold long side 10 and a mold short side 11, and when changing the width of the slab during continuous casting, the mold short side 1
By moving 1 in parallel with the direction of the arrow along the long side 10 of the mold, the target slab width can be obtained.

Since the high-frequency coil 3 is supported by the high-frequency coil support jig 4 disposed on the short side 11 of the mold, the high-frequency coil 3 moves following the movement of the short side 11 of the mold. Therefore, in the case of a normal width change, since the immersion nozzle and the high-frequency coil do not physically interfere with each other, not only can the width be changed freely, but also if the mold short side 11 moves, the mold short side is moved. 11 can be heated by high frequency.
When making the slab width extremely narrower than the slab that has been cast so far, and when making the slab extremely wide than the slab that has been cast so far, it is best to remove the high-frequency coil 3 from the high-frequency coil support jig 4. A high-frequency coil 3 of an appropriate size is installed.

In the present invention, each of the high-frequency coils 3 has one turn and is connected to a separate power source (not shown), and the application timing of both coils can be changed in accordance with the vibration cycle of the mold. The high-frequency oscillators of the two power supplies have frequencies of 10 KHz and 300 KW, respectively, and the maximum high-frequency coil current value is 8000 A.

The number of turns of the high-frequency coil is theoretically higher when the number of turns is larger, and the magnetic flux density is higher at the same high-frequency coil current. However, as the number of turns increases, the impedance of the high-frequency coil increases. High frequency coil current)
However, there is a disadvantage that it is necessary to increase In an actual machine, the number of turns may be determined by comprehensively judging the effect obtained by increasing the number of turns and the disadvantage of increasing the voltage.

In the present embodiment, the mold short side 11
Although the high-frequency coil 3 is supported by the high-frequency coil support jig 4 disposed thereon, the high-frequency coil 3 follows the movement of the short side 11 of the mold, but may be followed by a servo mechanism or the like.

FIG. 2 is a graph showing a vibration velocity waveform of a mold used in one embodiment of the present invention and a pattern of application of a high-frequency magnetic field. FIG. 2A shows a mold vibration velocity of a sine waveform, and FIG. ) Is the non-sine waveform mold vibration velocity. A period in which the mold descending speed is higher than the casting speed in one cycle is referred to as a negative strip (hereinafter, referred to as NS) period, and a period in which the mold descending speed is lower than the casting speed is referred to as a positive strip (hereinafter, referred to as PS) period.

The following two types of high-frequency coil current application patterns are available. The contents are: a high-frequency coil current is weakly applied in the PS period and a strong application is performed in the NS period.: A high-frequency coil current is applied only in the NS period without being applied in the PS period. Shows the above current application pattern. This is because the two current application patterns have strong and weak currents, but are more effective than continuous application.

The steel type used was low-carbon steel having a carbon concentration of 0.04%, and the degree of superheat of molten steel in the tundish was adjusted to 20 ° C. to 30 ° C. in each of the examples. As the used mold powder, a low-viscosity, low-melting-point mold powder advantageous for lubrication as shown in Table 1 was used.

The amount of mold powder consumed is determined by dividing the amount of mold powder consumed during casting by the surface area of the slab, and the depth of the oscillation mark is determined by cutting the slab in the casting direction after casting. The surface was polished and measured.

[0026]

[Table 1]

(Embodiment 1) Embodiment 1 is an example in which the slab width during continuous casting is reduced. The slab width of the first charge is 1000.
mm, the slab width of the next charge was changed to 750 mm.

For comparison with the continuous casting mold of the present invention shown in FIG. 1, the continuous casting mold used in the prior art shown in FIG.
The same casting conditions (steel type, degree of superheat of molten steel, mold powder, etc.) and the same current application pattern shown in FIG. The high-frequency coil current is a constant condition of 6000 A.

Table 2 shows the casting conditions at the time of casting, the consumption of mold powder and the depth of the oscillation mark as a result of the investigation. The casting conditions were two types of casting vibration waveforms, a sine waveform and a non-sine waveform, and the frequencies and amplitudes were changed, and the casting speed was 2.0 m to 4.0 m / min. The distortion rate of all non-sine waveforms was 40%.

[0030]

[Table 2]

Table 2 shows the slab size in two columns in the column of slab size. The first column shows the slab size of the first charge, and the second column shows the next slab size after the width change during casting. Represents the slab size of the charge. In Table 2, the values enclosed by the double line of the consumption amount of the mold powder and the depth of the oscillation mark in the investigation result are those of the conventional example.

In the present invention, the dimensions of the high-frequency coil 3 are such that the length in the slab width direction is 300 mm and the length in the slab thickness direction is 240 mm.
The casting of the first charge was started using mm. At this time, the gap between the high-frequency coil 3 and the mold short side 11 is 5
mm, the high frequency coil was placed as close as possible to the short side of the slab. The gap with the long side of the mold is also 5 mm. In this case, the range of 400 mm around the immersion nozzle 2 is outside the cover range of the high-frequency coil 3, but there is no problem because the central portion in the width direction of the slab does not need to apply a high-frequency magnetic field because the surface properties are good. . The width change during casting of the next charge was performed by moving both mold short sides 11 in the direction of the immersion nozzle 2 by 125 mm. At this time, both mold short sides 11
Since the high-frequency coil 3 supported by the coil also moves following the direction of the immersion nozzle 2, even if the width of the slab is changed during casting, the positional relationship between the high-frequency coil 3 and the short side of the slab does not change. Since a high-frequency magnetic field can be applied and there is no interference between the high-frequency coil 3 and the immersion nozzle 2, the continuous casting operation is not interrupted.

In the conventional example, the length of the high-frequency coil 3 in the slab width direction was set to 990 mm to secure a length for applying high-frequency magnetic force to the short side of the slab. The length in the slab thickness direction was 240 mm as in the present invention. That is, in the conventional example, the dimensions of the high-frequency coil are set to 990 mm in length and 240 m in width according to the size of the slab having a width of 1000 mm of the first charge.
m was placed at a position 5 mm away from the short side 11 of the mold. In the next charge, when each mold short side 11 is moved in the direction of the immersion nozzle 2 so that the slab size is adjusted to 750 mm, the high-frequency coil 3 and the mold short side 11 physically interfere with each other, and the high-frequency coil Since the high-frequency coil 3 was retracted from the molten metal because 3 could not be set in the mold 1, the high-frequency magnetic field could not be applied to the slab after the charge in which the slab width was changed.

Regarding the depth of the oscillation mark related to the surface texture, as is apparent from Table 2, the embodiment of the present invention improves the charge after the width change as well as the charge before the width change. Have been.

As to the surface properties of the charge before the width change and the charge after the width change in the conventional example, the charge after the width change has a worse surface property than the charge before the width change. The reason is that the high-frequency coil cannot be used for the charge after the width change.

According to the present invention, the mold powder consumption is also
It has been improved after width change during casting. The result similar to the application pattern of FIG. 2C was obtained also in the application pattern shown in FIG.

(Embodiment 2) Embodiment 2 is an example in which the slab width during continuous casting is increased in the middle.

The same casting conditions (steel type, molten steel superheat degree, mold powder, etc.) and the same current application pattern are used for the continuous casting mold of the present invention shown in FIG. 1 and the continuous casting mold used in the conventional technique of FIG. I went in. This current application pattern is the pattern shown in FIG.
00A is a constant condition.

The slab width of the first charge in continuous casting is 10
At 00 mm, the slab width of the next charge is changed to 1250 mm. At this time, both short sides 11 of the mold were moved by 125 mm in the direction opposite to the immersion nozzle 2.

In the embodiment of the present invention, the dimensions of the high-frequency coil 3 are 420 mm in the slab width direction and 2 mm in the slab thickness direction.
The thing of 40 mm was used. The high-frequency coil 3 was arranged at a position 5 mm away from the short side 11 and the long side 10 of each mold.

In the case of the conventional example, the high-frequency coil 3 is
The size of the high-frequency coil 3 is 990 mm in length and 2 mm in width according to the slab size of 1000 mm.
40 mm, 5 m from short side 11 and long side 10
m away from each other.

Also in this case, according to the embodiment of the present invention, even if the casting width during continuous casting is changed, the short side 11 of the mold and the high-frequency coil 3 follow and move. Does not change, the surface properties of the short side of the slab are improved, there is no interference between the high-frequency coil and the immersion nozzle, and the continuous casting operation is not interrupted. On the other hand, in the case of the conventional example, the high-frequency coil 3 and the mold short side 11 do not physically interfere with each other even if the casting side width is widened during casting, but the high-frequency magnetic field is applied only to the molten metal near the mold short side 11 on one side. Although the high frequency magnetic field was not applied to the molten metal near the short side of the mold on the opposite side, the surface properties of the short side of the slab to which the high frequency magnetic field was not applied deteriorated.

Note that both the first and second embodiments show examples in which two high-frequency coils are arranged, one each on the meniscus on the short side of both molds. , The same result as in Example 1 and Example 2 was obtained.

[0044]

According to the continuous casting method of molten metal according to the present invention, at least one high-frequency coil is separately disposed on the meniscus of the molten metal on both short sides of the mold, and the cast slab is continuously cast. Also in the case of the short side movement of the mold due to the width change, the high frequency coil moves following the movement of the short side of the mold, so that the short side portion of the slab is cast with the high frequency magnetic field always applied.
Further, since the high-frequency coil is separated and arranged on both short side meniscuses with the immersion nozzle as a boundary, the immersion nozzle and the high-frequency coil do not physically interfere with each other even during width change during casting. Therefore, the width can be freely changed.

Therefore, even if the width change is performed during casting, the application of the high frequency magnetic field is not stopped, and the operation is not interrupted due to the width change. Reduction is prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view of a continuous casting mold used in an embodiment of the present invention, in which (a) is a plan view and (b) is a view taken along line XX of (a).
It is sectional drawing.

FIG. 2 is a graph showing a vibration velocity waveform of a mold used in an example of the present invention and a pattern of application of a high-frequency magnetic field.

FIG. 3 is a schematic view of a conventional continuous casting mold, in which (a) is a plan view and (b) is a cross-sectional view taken along line XX of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Immersion nozzle 3 High frequency coil 4 High frequency coil support jig 5 Molten steel 6 Mold powder 7 Tundish 8 Cooling water 9 Solidification shell 10 Mold long side 11 Mold short side 12 Meniscus

Continuation of front page (56) References JP-A-5-115595 (JP, A) JP-A-7-256413 (JP, A) JP-A-6-79410 (JP, A) JP-A-7-1085 (JP) JP-A-6-190520 (JP, A) JP-A-7-96360 (JP, A) JP-A-6-297709 (JP, A) JP-A-6-170497 (JP, A) 6-277805 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/05 B22D 11/04 311 B22D 11/07 B22D 11/115

Claims (1)

(57) [Claims] 1. A continuous casting method for molten metal in which a high-frequency coil is arranged inside a mold and a high-frequency magnetic field is applied to a meniscus portion to perform casting, wherein at least one high-frequency coil is provided on each of the meniscuses on both short sides of the mold. A continuous casting method for molten metal, comprising separately arranging, moving a high-frequency coil following movement of a short side of a mold, and casting while applying a high-frequency magnetic field from the high-frequency coil to a meniscus portion.