KR101302525B1 - Method for Manufacturing Cast Slab - Google Patents

Abstract

The present invention relates to a method for manufacturing a cast steel, and more particularly, to a method for manufacturing a cast steel that can increase the equiaxed crystallization rate in a slab by performing electromagnetic stirring at a predetermined intensity at a specific position of the cast steel in which there is molten steel. The present invention can increase the equiaxed crystal in the slab by performing the first electromagnetic stirring and the second electromagnetic stirring of a predetermined strength at a specific position of the cast steel in the conventional tundish molten steel superheat range and casting speed It is possible to provide a method for producing cast steel. In addition, the present invention increases the equiaxed crystallization rate in the slab by performing the first electromagnetic stirring and the second electromagnetic stirring of a certain strength at a specific position of the cast steel to minimize the operating conditions such as casting speed and tundish molten steel temperature, while non-directional It is possible to provide a method for manufacturing a cast steel that can prevent leasing coupling during processing of cold-rolled steel sheet material.

Cast steel, electromagnetic, stirring, equiaxed crystal, leasing

Description

Method for Manufacturing Cast Steels {Method for Manufacturing Cast Slab}

The present invention relates to a method for manufacturing a cast steel, and more particularly, to a method for manufacturing a cast steel that can increase the equiaxed crystallization rate in a slab by performing electromagnetic stirring at a predetermined intensity at a specific position of the cast steel in which there is molten steel.

In general, the solidification structure of the metal affects the properties and materials of the final product. Therefore, it is necessary to control the solidification structure of the metal in the manufacture of the metal. For example, when the solidification structure of the stainless steel sheet and the electrical steel sheet is not properly controlled, a ridging defect occurs in which streaks having irregularities appear in the rolling direction of the steel sheet during deformation or processing of the steel sheet. This ridging defect not only damages the appearance of the steel sheet but also causes deterioration of electrical properties in the case of electrical steel sheet.

In particular, the non-oriented electrical steel sheet is widely used for the motor core, the steel sheet produced by hot rolling and cold rolling the non-oriented electrical steel sheet is subjected to deep processing or cold working, such as bending (bending) If the shape of the bending (ridging) is formed along the rolling direction, the appearance of the product is significantly damaged and there is a problem that the crack occurs during the molding process. Such leasing occurs when the coarse columnar structure generated during continuous casting is not sufficiently destroyed in the hot rolling process, and the coarse aggregate structure (band-like structure) remains. At this time, in the case of manufacturing the cast by continuous casting to suppress the occurrence of ridging or band (phase) structure, the casting method according to the prior art is a low-temperature casting method for casting by lowering the tundish molten steel superheat to increase the equiaxed crystallization rate; The non-solidified molten steel in the cast steel being cast was cast by an electromagnetic stirring method of electromagnetic stirring.

In the low temperature casting method according to the prior art, the difference between the temperature of the molten steel and the solidification temperature of the cast alloy in the tundish (hereinafter, molten steel superheat (ΔT)) in order to prevent the coagulation nuclei from re-dissolving the molten steel temperature inside the slab to increase the equiaxed crystallization rate in the slab. Lower the molten steel temperature in the cast steel, or when the molten steel temperature is high in the tundish, the casting speed was lowered to control the temperature inside the cast steel. However, in this case, if the molten steel overheating degree (ΔT) is less than 10 degrees Celsius, the lubricating ability of the mold powder decreases during the playing process, causing problems of interposition defects in the casting cast, and the nozzles clogged during casting, causing the casting to stop. There is a risk of operation accidents such as clogging. In addition, the method of lowering the casting speed may not be able to smoothly control the time between nozzle clogging and converter steel, secondary refining, and continuous casting processes due to a decrease in the tundish molten steel temperature.

In addition, the electromagnetic stirring method according to the prior art generates a swirl flow in the molten steel of the solidification interface, when the columnar tablet grown in the mold reaches the region affected by electromagnetic stirring, the tip portion of the columnar tablet is separated by electromagnetic stirring And cut. At this time, the cut grains of the columnar tablets move to the inside of the cast steel to act as a coagulation nucleus. Under these conditions, equiaxed crystals form when coagulated nuclei grow without re-dissolution, and columnar tablets form when these coagulated nuclei re-dissolve. However, the electromagnetic stirring method according to the prior art has a problem in that the electromagnetic stirring is performed immediately after the cast steel is formed, and if there is an unsolidified molten steel in the cast steel after the region in which the electromagnetic stirring is affected, the solidification core is re-dissolved and regrows into the columnar tablet. In addition, when the magnetic stirring is performed at the end of the solidification of the cast steel, the columnar well mainly grows until the electromagnetic stirring affects the molten steel from the meniscus to the solidification end point of the cast steel under normal operating conditions. Therefore, the equiaxed crystallization rate which can be stably achieved is only 20% or less, and there is a problem not reaching the lower limit of 45%, which is the lower limit of the equiaxed crystallization ratio, which can obtain a steel sheet excellent in the lowering property by ordinary rolling.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a cast steel that can increase the equiaxed crystallization rate of the cast steel to prevent ridging defects.

The present invention is to prepare a molten steel to achieve the above object; Injecting the molten steel into a mold to perform continuous casting; Primary electromagnetic stirring of the liquid layer inside the coagulation cell between 2 and 5 meters of the bottom of the coagulation cell meniscus produced during the continuous casting; It provides a method for producing a cast piece comprising the step of secondary electromagnetic stirring the liquid layer inside the coagulation cell between the bottom 5 to 10 meters of the coagulation cell meniscus.

In this case, the step of primary electromagnetic stirring of the liquid layer may include the step of electromagnetic stirring of the liquid layer with an intensity of 200 to 2200 (N) or 600 to 800 (N). In addition, the second electromagnetic stirring step of the liquid phase, may include the step of electromagnetic stirring the strength of the liquid layer to 200 to 2200 (N) or 600 to 800 (N). At this time, it is effective that the first electromagnetic stirring step of the liquid phase and the same strength of the second electromagnetic stirring of the liquid layer.

The first electromagnetic stirring of the liquid layer and the second electromagnetic stirring of the liquid layer may include the electromagnetic stirring of the liquid layer in one direction of the width of the liquid layer. However, the present invention is not limited thereto, and the first electromagnetic stirring of the liquid layer and the second electromagnetic stirring of the liquid layer may include electromagnetic stirring of the liquid layer in both directions. At this time, the step of stirring the liquid layer in both directions of the liquid layer width may include the step of electromagnetic stirring the liquid layer in both directions of the liquid layer width, and may include the step of stopping the electromagnetic stirring. In this case, it is effective that the time ratio between the step of electromagnetic stirring the liquid layer in both directions of the liquid layer width and the step of stopping the electromagnetic stirring is 2 to 5 or 5 to 8.

In addition, the present invention may further include the step of cutting the coagulation cell to a predetermined length after the second electromagnetic stirring of the liquid layer, the coagulation cell is a non-oriented electrical steel sheet containing silicon (Si) It may include.

The present invention can increase the equiaxed crystal in the slab by performing the first electromagnetic stirring and the second electromagnetic stirring of a predetermined strength at a specific position of the cast steel in the conventional tundish molten steel superheat range and casting speed It is possible to provide a method for producing cast steel.

In addition, the present invention increases the equiaxed crystallization rate in the slab by performing the first electromagnetic stirring and the second electromagnetic stirring of a certain strength at a specific position of the cast steel to minimize the operating conditions such as casting speed and tundish molten steel temperature, while non-directional It is possible to provide a method for manufacturing a cast steel that can prevent leasing coupling during processing of cold-rolled steel sheet material.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know. Like reference numerals refer to like elements throughout.

1 is a schematic cross-sectional view of a continuous casting apparatus according to the present invention.

As shown in FIG. 1, the continuous casting apparatus according to the present invention includes a ladle turret (not shown) and a ladle 100 installed in the ladle turret and storing molten steel 700. ), A tundish for receiving secondary injection of the molten steel 700 stored in the ladle 100, and a mold 300 for forming the molten steel 700 stored in the tundish 200 as a cast steel 710. ), A conveying roller 400 for conveying the cast steel 710 formed in the mold 300, and an electromagnetic stirring device 500 for stirring the cast steel 710. At this time, the molten steel 700 filled in the ladle 100 is injected into the tundish 200, and the nozzle 110 formed of a cylindrical refractory brick and the molten steel 700 stored in the tundish 200 are poured into the mold 300. Injecting may include a immersion nozzle 210 formed of a cylindrical refractory brick and a cutter 600 for cutting a continuously cast cast piece 710 to a predetermined length. In addition, the present embodiment will be described with an example of continuous casting of non-oriented electrical steel sheet containing 2% or more silicon (Si). In addition, in the present embodiment, for convenience of description, the solidification cell discharged by cooling the surface of the mold 300 is defined as a slab 710, but the slab 710 is not formed inside the solidification cell until it is cut to a predetermined length. There is a liquid layer, the electromagnetic stirring device 500 agitates the liquid layer inside the coagulation cell.

The ladle turret is for installing the ladle 100, and is generally manufactured to be rotatable, and the ladle 100 is installed at an upper portion thereof. At this time, the ladle turret should be provided with a ladle 100 installation space for installing the ladle 100, the ladle 100 installation space may be changed according to the number of ladles (100).

The ladle 100 is for accommodating the molten steel 700 in which impurities are removed and chemical components are adjusted. As shown in the figure, the ladle 100 is preferably hollow and has an open upper container shape. 700 may be stored. At this time, the lower portion of the ladle 100 may be provided with a nozzle for injecting the molten steel accommodated in the ladle 100 to the tundish 200, for this purpose, ladle 100 corresponding to the area where the nozzle is to be provided The area may be open. Of course, such a nozzle 110 may be opened and closed automatically and manually, and thus, the molten steel stored in the ladle 100 may be stored in the ladle 100 or injected into the tundish 200. have.

The tundish 200 is for injecting the molten steel 700 injected from the ladle 100 into the mold 300 and may be manufactured in a hollow container shape. In this case, as shown, the nozzle 110 connected to the ladle 100 may be connected to the upper portion of the tundish 200, and the molten steel 700 accommodated in the tundish 200 may be connected to the lower portion of the tundish 200. ) May be provided with an immersion nozzle 210 for injecting into the mold 300. In this case, the immersion nozzle 210 may also be opened and closed automatically and manually in the same manner as the nozzle 110 described above, thereby adjusting the amount of molten steel 700 injected into the mold 300.

The mold 300 is to form the molten steel 700 introduced through the immersion nozzle 210 in the tundish 200 as the cast steel 710, and cools the molten steel 700 introduced from the immersion nozzle 210. It is preferable to be installed so as to be close to the periphery of the molten steel 700 flowing from the immersion nozzle (210). At this time, in order to cool the molten steel 700 introduced from the immersion nozzle 210, it is effective that a cooling mechanism is provided inside the mold 300. Accordingly, as the molten steel flows into the mold 300, the mold is cooled ( Cast piece 710 having a cross section corresponding to the cross section of 300 may be cast. Meanwhile, a transfer roller 400 may be provided below the mold 300 based on the casting direction, and the transfer roller 400 may be installed on the top and bottom surfaces of the cast piece 710 based on a plane. It is preferable.

Electromagnetic stirring device 500 is for stirring the molten steel in the cast steel 710, the rotary induction type (rotary induction type) to make the circumferential movement of the molten steel around the casting direction, and to stir in parallel with the casting direction It may include a linear induction type, a helicoidal type that is a mixture of a ring induction method and a linear induction method. This embodiment will be described taking an example of an annular induction type electromagnetic stirring device. Of course, the present invention may use a linear induction type and a spiral type electromagnetic stirring device as well as an annular induction type electromagnetic stirring device. In this case, the continuous casting apparatus according to the present invention may include two annular induction type electromagnetic stirring device 500, that is, the first electromagnetic stirring device 510 and the second electromagnetic stirring device 520.

The first electromagnetic stirring device 510 is for first stirring the slab 710 formed in the mold 300, and may be positioned below the mold 300 based on the casting direction. In the continuous casting apparatus according to the present invention, the molten steel 700 is primarily cooled in the mold 300 to form the cast steel 710, and then the secondary casting of the cast steel 710 is performed at the feed roller 400. At this time, the primary cooled slab 710 becomes a completely solidified slab 710 during the secondary cooling, the inside of the slab 710 during the secondary cooling is in a molten steel state not completely solidified state exist. At this time, the first electromagnetic stirring device 510 is provided on the conveying roller 400 subjected to the secondary cooling, and agitates the molten steel inside the cast steel 710. The present embodiment has been described that the first electromagnetic stirring device 510 is provided in the transfer roller 400, but is not limited to this, the first electromagnetic stirring device 510 according to the present invention is a mold based on the casting direction It is effective to be provided between meniscus bottom 300, for example between 2 and 5 meters from the meniscus. In addition, the first electromagnetic stirring device 510 may be operated such that molten steel in the cast steel 710 rotates in one direction, and may be operated so that molten steel in the cast steel 710 alternately rotates in one direction and the other direction.

The second electromagnetic stirring device 520 is for secondary stirring the slab 710 formed in the mold 300, and the lower portion of the mold 300 on the basis of the casting direction in the same way as the first electromagnetic stirring device 510 Can be located. At this time, the second electromagnetic stirring device 520 is preferably provided at a position farther from the mold 300 than the first electromagnetic stirring device 510, the second electromagnetic stirring device 520 is a mold ( It is effective to be provided between the bottom of the meniscus in 300), for example between 5 and 10 m from the meniscus. In this case, the second electromagnetic stirring device 520 may also be operated such that the molten steel in the cast steel 710 rotates in one direction, similar to the first electromagnetic stirring device 510, and the molten steel in the cast steel 710 may be rotated in one direction and the other direction. It can be operated to rotate alternately. As described above, the electromagnetic stirring device 500 according to the present invention is located at the lower portion of the mold 300 and is installed in a strand electromagnetic stirrer method that can improve equiaxed crystallinity, internal crack reduction, and center segregation. effective.

Next will be described with reference to the drawings and tables cast slab manufactured using a continuous casting apparatus according to the present invention having the above-described structure.

Figure 2 is a graph showing the correlation between the intensity of the electromagnetic stirring and the equiaxed rate, Table 1 shows the relationship between the intensity of the electromagnetic stirring and the equiaxed rate.

Referring to FIGS. 1 and 2 and Table 1, when the electromagnetic stirring is not performed, the equiaxed crystallization rate of the cast steel 710 is 12.3%, and when the magnetic stirring is performed at an intensity of 200 to 300 (N), the casting steel 710 The equiaxed crystallization rate of is 20.5%, and the equiaxed crystallization rate of the slab 710 is 32% when electromagnetic stirring is performed at an intensity of 600 to 800 (N). In addition, when electromagnetic agitation is performed at a strength of 1800 to 2200 (N), the equiaxed crystallization rate of the cast steel 710 is 35%. As the intensity of the agitation is increased, the equiaxed crystallinity of the cast steel 710 also increases. In addition, except that the electromagnetic stirring was not performed, the equiaxed crystals of 11.5% and 3% were increased while increasing the strength of electromagnetic stirring by about three times, and the electromagnetic stirring was performed at an intensity of 1800 to 2200 (N). In this case, about 3 equiaxed crystals increased compared with the case where electromagnetic stirring was not performed. As such, as the intensity of electromagnetic agitation increases, the equiaxed crystal rate also increases, and it can be seen that the equiaxed crystal rate is highest when the intensity of electromagnetic agitation is 1800 to 2200 (N).

<Table 1>

Stirring Strength (N) 0 (not stirring) 200-300 600 to 800 1800-2200 Equivalence rate (%) 12.3 20.5 32 35

3 is a graph showing the correlation between the electromagnetic stirring position and the equiaxed rate, and Table 2 shows the correlation between the electromagnetic stirring position and the equiaxed rate. At this time, the first electromagnetic stirring device 510 performs electromagnetic stirring at an intensity of 600 to 800 (N), and the second electromagnetic stirring device 520 performs electromagnetic stirring at an intensity of 400 to 500 (N).

Referring to FIGS. 1, 3, and 2, when the electromagnetic stirring is not performed, an isometric rate of 12.3% is shown, and when only the upper portion of the cast steel 710, that is, the first electromagnetic stirring device 510 is operated, 32 The equiaxed percentage is shown. In addition, when the lower portion of the cast steel 710, that is, only the second electromagnetic stirring device 520 is operated, it exhibits an equiaxed rate of 35.1%, and when the first and second electromagnetic stirring devices 520 are operated, 45.1%. The equiaxed rate is shown. At this time, when both the first and second electromagnetic stirring apparatus 520 were operated, the lower limit of 45%, which is the lower limit of the equiaxed crystal ratio, to obtain a steel plate excellent in the lowering property by ordinary rolling. That is, it is advantageous to increase the equiaxed crystallization by stirring the lower portion than the upper portion of the cast steel 710 based on the casting direction, and stirring the upper and lower portions of the cast steel 710 to obtain the highest equiaxed crystallization rate. have.

<Table 2>

Stirring Position Without stirring First electromagnetic stirring device 2nd electromagnetic stirring device First and second electromagnetic stirring device Equivalence rate (%) 12.3 32 35.1 45.1

4 is a graph showing the correlation between the stirring method and the slab 710 widthwise equiaxed rate, and Table 3 shows the correlation between the stirring method and the slab 710 widthwise isometric rate. At this time, the upper portion of the stirring position means the first electromagnetic stirring device 510, the lower means the second electromagnetic stirring device 520. In addition, the one-way mode is a case where the electromagnetic agitation is continuously performed in one direction, and the bidirectional mode is a case where the electromagnetic agitation is alternately performed in the left direction and the right direction of the slab 710 width. In this case, in the bidirectional mode, the experiment was conducted under two conditions in which the ratio of the electromagnetic stirring operation time and the non-operation time was changed. In the bidirectional mode 1, the ratio of the operation time and the non-operating time of the electromagnetic stirring apparatus 500 was 2: 1. To 5: 1, and the bidirectional mode 2 has a ratio of the operating time and the non-operating time of the electromagnetic stirring device 500 to 5: 1 to 8: 1. In addition, the central and edge equiaxed coefficients represent equiaxed coefficients according to the widthwise position of the cast piece 710.

Referring to FIGS. 1 and 4 and Table 3, the equiaxed crystallization rate at the center of the cast steel 710 is continuously equalized only in one direction. The lower limit was found to be 45.1%, and the edge of the cast 710 had an equiaxed crystal rate of 25.4%. However, the equiaxed crystal ratio of the edge of the cast steel 710 is reduced by 20%, which shows a difference between the center and the edge of the cast steel 710 having a high equiaxed crystal coefficient.

In the bidirectional mode 1, the equiaxed crystallization rate of the center of the cast steel 710 is 29.8% and the edge equiaxed crystallinity of the cast steel 710 is 29.4%. However, the equiaxed crystal ratio of the center and the edge of the cast 710 is about 29%, which is 45% or less, showing a low equiaxed crystal coefficient.

In case of the bidirectional mode 2, the isometric equivalence of the cast iron 710 is 47.1%, and the edge isometric equilibrium of the cast steel 710 is 36.4%. It did not appear to be large.

That is, in the bidirectional mode than the one-way mode, it is possible to ensure a more uniform equiaxed rate along the width direction of the slab 710. In addition, when the operation time of the electromagnetic stirring device 500 in the bidirectional mode is less than five times less than the non-operation time, the result is that the central equiaxed coefficient of the slab 710 is lower than in the one-way mode, but the operation of the electromagnetic stirring device 500 operates. When the time is more than five times the non-operation time, it is possible to obtain a higher equiaxed crystal rate than the one-way mode at the center and the edge of the cast (710).

<Table 3>

Agitation method One-way mode Bidirectional mode 1 Bidirectional mode 2 Equivalence rate (%) center 45.1 29.8 47.1 edge 25.4 29.4 36.4

FIG. 5 is a graph showing the correlation between equiaxed constants and leasing defects of continuous casting casts, and Table 4 shows a correlation between equiaxed constants and leasing defects of continuous casting casts. At this time, the one-way mode and the bi-directional mode, the top and bottom, the center and the edge of Table 4 is the same as the conditions of Tables 1 to 3 described above.

1 and 5 and Table 4, it can be seen that the leasing height is reduced when the electromagnetic stirring in the bidirectional mode than when performing the electromagnetic stirring in one direction mode. That is, when the electromagnetic agitation is performed in the bidirectional mode than the electromagnetic agitation in the one-way mode, the equiaxed crystallinity is high, and the leasing height is also low.

<Table 4>

Test Number Agitation method Stirring Position Agitation strength
(N) Equiaxed
(%) Leasing Height
(탆) One No electromagnetic stirring 12.3 32 2 One-way mode Top 200-300 20.5 31 3 One-way mode Top 600 to 800 32 - 4 One-way mode Top 1800-2200 35 26 5 One-way mode bottom 400 to 500 35.1 - 6 One-way mode Top 1800-2200 45.1 (center)
25.4 (edge) 21 bottom 400 to 500 7 Bidirectional mode 1 Top 1800-2200 29.8 (center)
29.4 (edge) - bottom 400 to 500 8 Bidirectional mode 2 Top 1800-2200 47.1 (center)
36.4 (edge) - bottom 400 to 500

Next, a method for manufacturing a cast steel according to the present invention will be described with reference to the drawings. Duplicate descriptions will be omitted or briefly described below.

6 is a flowchart illustrating a method for manufacturing a cast steel according to the present invention.

1 and 6, a method of manufacturing a cast steel according to the present invention, preparing a molten steel (S ₁ ), and injecting the prepared molten steel into a mold to form a cast (S ₂ ) and the cast steel 1 Primary electromagnetic stirring step (S ₃ ), and the secondary electromagnetic stirring step (S ₄ ). At this time, although not shown, it may include a step (S ₅ ) of cutting the slab to a predetermined length and the step (S ₆ ) of transporting the cut slab to the collecting box. At this time, as described above, the step of electromagnetic stirring of the cast means to stir the liquid phase of the solidification cell and the liquid layer inside the solidification cell.

In preparing the molten steel (S ₁ ), separately prepared molten steel 700 is injected into the ladle 100. In this case, in order to improve the characteristics of the cast steel 710, an additional material may be added to the molten steel 700 in which the ladle 100 is accommodated. In addition, the molten steel 700 accommodated in the ladle 100 is injected into the tundish 200 through a nozzle provided in the ladle 100, and the molten steel 700 injected into the tundish 200 is a tundish. It is injected into the mold 300 through the immersion nozzle 210 provided in the (200). In this case, the amount of molten steel 700 injected into the mold 300 may be adjusted using the immersion nozzle 210.

Forming the cast steel by injecting the prepared molten steel in the mold (S ₂ ) is injected into the molten steel 700 injected through the immersion nozzle 210 to the mold 300 and cooled to form a cast 710. At this time, the mold 300 provided in the lower portion of the immersion nozzle 210 may be provided with a cooling mechanism, for example, a water cooling cooling mechanism, through which the cast steel 710 having a cross section corresponding to the cross section of the mold 300. ) May be discharged to the bottom of the mold (300). Of course, the cast steel 710 discharged to the lower portion of the mold 300 may be transferred through the transfer roller 400. At this time, the slab 710 includes a coagulation cell and a liquid layer inside the coagulation cell.

The primary electromagnetic stirring step (S ₃ ) of the slab is a primary electromagnetic stirring at a predetermined position the cast piece 710 is discharged to the lower portion of the mold 300. At this time, the first electromagnetic stirring is effective to be carried out in the region of the cast 710 located between 2 to 5m in the downward direction from the solidification cell meniscus of the cast 710 in the mold 300 based on the casting direction. For this purpose, the first electromagnetic stirring device 510 for performing the first electromagnetic stirring is preferably located between 2 to 5m in the downward direction from the meniscus of the cast piece 710. In addition, primary electromagnetic stirring may be performed only in one direction such that the molten steel in the cast steel 710, that is, the liquid layer is rotated in one direction. Of course, the present invention is not limited thereto, and as described above, the molten steel in the cast steel 710 may be alternately rotated to the left or right of the cast steel 710 in the width direction, that is, in the liquid layer width direction. At this time, the primary electromagnetic stirring may be carried out with an intensity of 200 to 2200 (N), it is effective to be carried out to 600 to 800 (N). In addition, when electromagnetic stirring is performed in both directions, the first electromagnetic stirring device 510 may be periodically operated and non-operated. In this case, the ratio of the operating time and the non-operating time of the first electromagnetic stirring device 510 may be less than five or more than five. When the ratio of the operating time and the non-operating time is less than 5, the ratio of the operating time and the non-operating time of the first electromagnetic stirring device 510 is 2: 1 to 5: 1, and when the ratio of the operating time and the non-operating time is 5 or more, 1 It is effective that the ratio of the operating time and the non-operation time of the electromagnetic stirring device 510 is 5: 1 to 8: 1.

The second electromagnetic stirring step (S ₄ ) of the slab is a secondary electromagnetic stirring of the primary electromagnetic stirred slab 710. At this time, the secondary electromagnetic stirring is preferably performed in a region farther from the position for performing the primary electromagnetic stirring on the basis of the casting direction. Accordingly, the secondary electromagnetic stirring is effective to be carried out in the region of the cast 710 located between 2 to 5 m in the downward direction from the meniscus of the cast 710 in the mold 300 based on the casting direction, The first electromagnetic stirring device 510 for performing primary electromagnetic stirring is preferably located between 2 to 5 m in the downward direction at the meniscus of the cast steel 710. In addition, the secondary electromagnetic stirring may also be performed in one direction so that the molten steel in the cast steel 710 rotates in one direction similarly to the primary electromagnetic stirring, and the one direction may be the same as or different from the direction of the primary electromagnetic stirring. Further, the molten steel in the cast steel 710 may be implemented in both directions so that the molten steel can be rotated alternately to the left or right of the cast steel 710 width direction. At this time, the conditions for performing the secondary electromagnetic stirring, that is, the ratio between the strength of the electromagnetic stirring and the operating time and the non-operating time of the second electromagnetic stirring device 520 is preferably the same as the conditions for performing the primary electromagnetic stirring. However, the present invention is not limited thereto, and the conditions of the secondary electromagnetic agitation may be changed in a range in which the primary electromagnetic agitation is performed. Of course, the secondary electromagnetic agitation after the primary electromagnetic agitation may be omitted. As described above, the present invention can increase the equiaxed crystal rate in the cast steel 710 by performing electromagnetic stirring on the cast steel 710 in which molten steel exists.

Cutting the slab to a predetermined length (S ₅ ) is a second electromagnetic stirring is solidified to the inside to cut the slab 710 transferred through the conveying roller 400 to a predetermined length, and to transfer the cut slab to the collecting cabinet Step S ₆ transfers the slab 710 cut to a predetermined length, for example by a table roller, to the collecting box.

As described above, the present invention performs the primary electromagnetic stirring and the secondary electromagnetic stirring of a predetermined intensity at a specific position of the cast steel 710 in which the molten steel is present in the conventional tundish molten steel superheat range and casting speed. You can increase the equiaxed rate. In addition, the present invention increases the equiaxed crystal rate in the cast 710 by performing the first electromagnetic stirring and the second electromagnetic stirring of a predetermined strength at a specific position of the cast steel 710, the operation conditions such as casting speed and tundish molten steel temperature While minimizing the constraints, it is possible to prevent leasing coupling when processing non-oriented cold-rolled steel sheet material.

Although described above with reference to the drawings and embodiments, those skilled in the art can be variously modified and changed within the scope of the invention without departing from the spirit of the invention described in the claims below. I can understand.

1 is a schematic cross-sectional view of a continuous casting device according to the present invention.

2 is a graph showing the correlation between the intensity of electromagnetic stirring and the equiaxed rate;

3 is a graph showing the correlation between the electromagnetic stirring position and the equiaxed rate.

4 is a graph showing the correlation between the stirring method and the slab width direction isometric constant.

Fig. 5 is a graph showing the correlation between equiaxed constants and leasing defects of continuous casting casts.

6 is a flow chart for explaining a method for manufacturing a cast steel according to the present invention.

<Explanation of symbols for the main parts of the drawings>

100: ladle 110: nozzle

200: tundish 210: immersion nozzle

300: mold 400: feed roller

500: electromagnetic stirring device 510: first electromagnetic stirring device

520: second electromagnetic stirring device 600: cutting machine

700: molten steel 710: cast steel

Claims (10)

Preparing molten steel; Injecting the molten steel into a mold to perform continuous casting; Primary electromagnetic stirring of the liquid layer inside the coagulation cell at the bottom of the coagulation cell meniscus generated during the continuous casting; And Performing a second electromagnetic stirring of the liquid layer inside the coagulation cell at a position farther from the mold than the first electromagnetic stirring position; Primary and secondary electromagnetic stirring of the liquid layer comprises electromagnetic stirring in both directions of the liquid layer width, Stirring in both directions of the width of the liquid layer, electromagnetic stirring in both directions of the width of the liquid layer, and the method of manufacturing a cast steel comprising the step of stopping the electromagnetic stirring. The method according to claim 1, Primary electromagnetic stirring of the liquid layer, Method for producing a cast, characterized in that the liquid layer comprises the step of electromagnetic stirring to the strength of 200 to 2200 (N). The method according to claim 1 or 2, The second electromagnetic stirring step of the liquid layer, Method of producing a cast, characterized in that it comprises the step of electromagnetic stirring the liquid layer to the strength of 200 to 2200 (N). The method of claim 3, Primary electromagnetic stirring of the liquid layer and the strength of the secondary electromagnetic stirring the liquid layer is the method of manufacturing a cast. The method according to claim 1, The first electromagnetic stirring step is carried out between the bottom 2 to 5 meters of the coagulation cell meniscus, The secondary electromagnetic stirring step is the manufacturing method of the cast, characterized in that proceeding between the bottom 5 to 10 meters of the coagulation cell meniscus. The method according to claim 1, The first electromagnetic stirring step or the second electromagnetic stirring step, the method of manufacturing a cast steel, characterized in that it comprises the step of electromagnetic stirring the liquid layer to the strength of 600 to 800 (N). The method according to claim 1, Method of manufacturing a cast steel, characterized in that the time ratio of the step of electromagnetic stirring the liquid layer in both directions of the liquid layer width and the step of stopping the electromagnetic stirring. The method according to claim 1, Method of producing a cast steel, characterized in that the time ratio of the step of electromagnetic stirring the liquid layer in both directions of the liquid layer width and the step of stopping the electromagnetic stirring. The method according to claim 1, After the second electromagnetic stirring of the liquid layer, The method for manufacturing a cast steel, characterized in that it further comprises the step of cutting the coagulation cell solidified to the liquid layer to a predetermined length. The method according to claim 1, The solidification cell is a method of manufacturing a cast steel, characterized in that it comprises a non-oriented electrical steel sheet containing silicon (Si).

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