JP6036144B2 - Continuous casting method - Google Patents

Description

  The present invention relates to a continuous casting equipment and a continuous casting method for controlling the flow of molten steel in a mold using a magnetic field.

  In recent years, quality requirements for high-grade sheet steel products such as automotive steel plates and steel plates for cans have become stricter, and steel slab slabs (hereinafter simply referred to as “slab slabs”) manufactured by continuous casting machines, which are the materials of these high-grade thin steel plate products. There is a demand for higher quality) (also referred to as “slab”). One of the qualities required for slab slabs is that the amount of inclusions on the slab surface layer is small. Inclusions trapped in the surface layer of the slab slab are [1] Deoxidation products generated in the deoxidation process of molten steel with Al, etc., suspended in the molten steel, [2] Tundish and immersion nozzle There are Ar gas bubbles blown into the molten steel, and [3] a mold powder spread on the molten steel surface in the mold and suspended in the molten steel. Since all of these become surface defects at the stage of a thin steel plate product, it is important to reduce the amount captured by the slab surface layer.

  In continuous casting operations, it is necessary to improve productivity at the same time. In order to improve productivity, it is necessary to increase the casting speed, that is, increase the amount of molten steel per unit time injected into the mold. As one of the problems in that case, there is a problem that the discharge speed of the molten steel from the immersion nozzle installed in the mold increases, and the flow speed of the molten steel in the mold increases more than necessary.

  In continuous casting of slab slabs, an immersion nozzle is usually installed at the center of the mold long side width direction, and the molten steel discharged into the mold from the discharge holes on both the left and right sides of the immersion nozzle is directed to the mold short side. The molten steel flow collides with the solidified shell on the short side of the mold. The molten steel flow that collides with the solidified shell on the short side of the mold branches in two directions, and the upward molten steel flow (upward reversal flow) flows in the molten steel surface in the mold (hereinafter also referred to as “meniscus”). The flow is directed from the short side of the mold toward the immersion nozzle. When the molten steel flow velocity at the meniscus becomes too fast, the mold powder added to the meniscus is caught in the molten steel and is captured by the solidified shell, resulting in a surface defect of the thin steel sheet product. On the other hand, the molten steel flow that moves downward after colliding with the solidified shell (downward reversal flow) carries the deoxidized product in the molten steel to the deep part of the molten steel in the mold, and the deoxidized product that could not float up is trapped in the solidified shell. And cause surface defects in thin steel sheet products. As the casting speed increases, both the upward and downward reversal flows increase, and the frequency of surface defects in the steel sheet product increases.

  Moreover, the molten steel flow in the mold changes with time due to the adhesion of alumina to the submerged nozzle discharge hole, the submerged nozzle or the like even if the casting conditions are the same. In particular, when the amount of alumina deposited on the left and right discharge holes of the immersion nozzle is different, the balance of the molten steel discharge flow rate on the left and right of the immersion nozzle is lost, and the discharge flow rate from the side with the smaller amount of alumina adhesion increases. The phenomenon in which the difference between the discharge flow rates of the molten steel on the left and right of the immersion nozzle is referred to as the “diffusion phenomenon”. On the side where the molten steel flow in the mold becomes asymmetrical due to this drift phenomenon, The problem arises that the flow velocity is extremely increased.

  In order to solve these problems, the following techniques have been proposed. For example, in Patent Document 1, magnetic poles whose magnetic core width is at least one times the width of the slab slab are arranged at the upper and lower portions of the submerged nozzle discharge hole, respectively, and a static magnetic field generated from the magnetic poles is used. There has been proposed a continuous casting method in which a braking force is applied to a discharge flow of molten steel supplied into a mold from an immersion nozzle.

  For molten steel that moves in a static magnetic field, no matter which direction the molten steel moves, the braking force in the direction opposite to the moving direction acts electromagnetically. Is slowed down. Of the static magnetic fields, a static magnetic field generated from a direct current electromagnet by a direct current is called a direct current static magnetic field.

  Further, in Patent Document 2, in the continuous casting of a slab slab in which a DC static magnetic field in the same direction in the thickness direction is applied over the entire width of the mold to control the flow of molten steel in the mold, the vicinity of the discharge hole of the immersion nozzle On the other hand, Patent Document 3 proposes that a slab slab is formed by applying a DC static magnetic field in the same direction in the thickness direction over the entire width of the mold. In contrast to Patent Document 2, a technique has been proposed in which a DC static magnetic field is applied so that the magnetic flux density in the vicinity of the mold short side is smaller than that in the vicinity of the center in the slab width direction.

JP-A-2-284750 JP 2003-117636 A JP-A-10-263766

  However, the above prior art has the following problems.

  That is, in Patent Document 1, when applying a static magnetic field, the magnetic flux density in the width direction of the slab slab is made uniform, and for this reason, the discharge hole is used to brake the upward reversal flow caused by the discharge flow from the immersion nozzle. When the upper static magnetic field is strengthened, the upward reversal flow is damped, but at the center of the slab width direction where the influence of the discharge flow is small, the molten steel flow velocity is extremely reduced, and the cleaning effect by the molten steel flow is lost, leading to the solidified shell. There is a concern that the trapping of deoxidation products and Ar gas bubbles will increase. Conversely, if the static magnetic field above the discharge hole is weakened to ensure the molten steel flow velocity at the center of the slab width direction, braking of the upward reversal flow becomes insufficient.

  In Patent Document 2 and Patent Document 3, DC static magnetic fields having different magnetic flux densities in the slab width direction can be applied, but the magnetic flux density is changed independently at each position in the slab width direction from the magnetic pole structure. Therefore, when the casting speed, the slab width, and the like change, the DC static magnetic field cannot be applied under the optimum application conditions. In particular, when a drift phenomenon occurs, a DC static magnetic field with a non-uniform magnetic flux density cannot be applied to the left and right of the mold width direction depending on the degree of the drift, and braking control corresponding to the drift phenomenon is not possible. Can not.

  The present invention has been made in view of the above circumstances, and its object is to determine the center position in the width direction of the mold when continuously casting by applying a DC static magnetic field over the entire width direction of the slab slab. The magnetic flux density can be adjusted independently at the left and right of the mold width direction as a boundary, and not only the deoxidation product, Ar gas bubbles and mold powder can be prevented from being trapped in the solidified shell, but also a drift phenomenon occurs. In this case, it is to provide a continuous casting equipment and a continuous casting method capable of applying a DC static magnetic field having a non-uniform magnetic flux density on the left and right of the mold width direction.

The gist of the present invention for solving the above problems is as follows.
[1] A pair of upper magnetic poles that are opposed to each other across the mold long side, the center of the magnetic pole is located above the ejection hole of the immersion nozzle, and the center of the magnetic pole is located below the ejection hole of the immersion nozzle A pair of lower magnetic poles facing each other across the long side of the mold is provided on the back side of the long side of the mold, a DC static magnetic field is applied from the lower magnetic pole to the entire width of the slab slab, and slab casting is performed from the upper magnetic pole. A continuous casting facility for applying a DC static magnetic field over the entire width of the slab and an AC moving magnetic field over the entire width of the slab slab, wherein the DC electromagnet for applying the DC static magnetic field of the upper magnetic pole is a mold A continuous casting facility, which is divided into four in the width direction, and is configured such that the magnetic flux density applied from each of the divided DC electromagnets can be changed independently.
[2] When continuously casting molten steel using the continuous casting equipment described in [1] above, a magnetic flux density of a DC static magnetic field applied from the lower magnetic pole is defined as a magnetic flux density A (Tesla), and the four upper magnetic poles. Among the DC electromagnets divided into two, the magnetic flux density of the DC static magnetic field applied from the two DC electromagnets on both ends is the magnetic flux density B (Tesla), and the center part of the DC electromagnets divided into four upper magnetic poles When the magnetic flux density of the DC static magnetic field applied from the two DC magnets on the side is defined as magnetic flux density C (Tesla), the magnetic flux density A, magnetic flux density B, and magnetic flux density C are the following formulas (1) and (2): The continuous casting method characterized by adjusting and applying each magnetic flux density so that it may satisfy | fill simultaneously.
0.4 ≦ magnetic flux density C / magnetic flux density A ≦ 0.9 (1)
0.3 ≦ magnetic flux density B / magnetic flux density C ≦ 0.8 (2)
[3] The molten steel flow velocity in the mold width direction of the molten steel in the mold at the position of the upper magnetic pole is measured, and when the drift phenomenon in the mold is confirmed from the measured molten steel flow velocity, the molten steel flow is divided into the four The continuous casting method according to the above [2], wherein the current value supplied to the direct current electromagnet is controlled to eliminate the drift phenomenon in the mold.

  According to the present invention, the molten steel discharge flow discharged from the discharge hole of the immersion nozzle with a DC static magnetic field applied from the lower magnetic pole, and the downward reversal flow that branches off when the molten steel discharge flow collides with the solidified shell on the short side of the mold. Ascending reversal flow in which the molten steel discharge flow collides with the solidified shell on the short side of the mold and branches by a DC static magnetic field that is braked and applied by adjusting the magnetic flux density from each of the DC magnets divided into four upper magnetic poles. The molten steel flow velocity of the meniscus is braked, and an appropriate molten steel flow can be imparted to the meniscus by the AC moving magnetic field applied from the upper magnetic pole, so that the deoxidation product, Ar gas bubbles and mold powder to the slab surface layer portion It is possible to suppress the trapping and to stably produce a clean and high quality slab slab. Even if a drift phenomenon occurs in the mold, the drift phenomenon in the mold is eliminated by applying a DC static magnetic field having a different magnetic flux density from the DC magnet divided into four upper magnetic poles. It is possible to make the molten steel flow uniform.

1 is a schematic side view of a continuous casting mold used in the present invention. It is the horizontal cross-sectional schematic diagram in the upper magnetic pole position provided with the direct-current electromagnet comprised with one electromagnet used for the mold width direction used for the comparison. FIG. 2 is a schematic horizontal sectional view at the position of the lower magnetic pole shown in FIG. 1. It is a horizontal section schematic diagram in the upper magnetic pole position used by the present invention.

  Hereinafter, the present invention will be described in detail.

  The inventors of the present invention have an upper magnetic pole whose center of the magnetic pole is located above the discharge hole of the immersion nozzle and a lower magnetic pole whose center of the magnetic pole is located below the discharge hole of the immersion nozzle. Using a continuous casting mold provided on the back side, a DC static magnetic field and an AC moving magnetic field are applied superimposed from the upper magnetic pole, and at the same time, a DC static magnetic field is applied from the lower magnetic pole to continuously cast molten steel. Magnetic flux density of DC static magnetic field applied from upper magnetic pole for the purpose of stably producing clean and high quality slab slabs with less deoxidation products, Ar gas bubbles and mold powder trapping Was examined.

  A schematic side view of the continuous casting mold used is shown in FIG. The mold 1 has a configuration in which a pair of mold short sides 3 are sandwiched between a pair of opposed mold long sides 2 so that the mold short sides 3 face each other in the length direction of the mold long side 2. By moving along, the width of the slab slab to be cast, that is, the mold width is changed. An immersion nozzle 4 for injecting molten steel into the mold is installed at the approximate center in the width direction of the mold 1, and one discharge hole 5 facing the mold short side 3 is provided below the immersion nozzle 4. The molten steel is provided as a discharge flow (referred to as “molten steel discharge flow”) directed from the discharge hole 5 toward the mold short side 3 and injected into the mold. The discharge direction of the discharge holes 5 is downward or upward, and normally, a discharge angle of about 5 to 50 degrees downward is provided.

  A pair of upper magnetic poles 6 that are opposed to each other with the mold long side 2 interposed therebetween are arranged with the center position of the magnetic poles above the upper end position of the discharge hole 5. The upper magnetic pole 6 is configured so that a DC static magnetic field and a linear AC moving magnetic field can be superimposed and applied over the entire width of the slab. In addition, a pair of lower magnetic poles 9 that are opposed to each other with the mold long side 2 interposed therebetween are arranged with the center position of the magnetic poles below the lower end position of the discharge hole 5. The lower magnetic pole 9 is configured so that a DC static magnetic field can be applied over the entire width of the slab.

  The meniscus position (molten steel surface position) in the mold is an upper position about 150 to 350 mm away from the upper end position of the discharge hole 5 (this distance varies depending on the specifications of the continuous casting machine and operational restrictions). The molten steel in the meniscus portion is agitated so as to rotate in the same horizontal direction by the AC moving magnetic field applied from 6, and the molten steel discharge flow from the submerged nozzle 4 is caused by the short mold by the DC static magnetic field applied from the upper magnetic pole 6. The upward reversal flow that collides with the solidified shell on the side and branches upward is decelerated upon receiving the braking force. Further, the upward reversal flow turns and the meniscus molten steel flow directed from the mold short side toward the immersion nozzle is also decelerated by receiving a braking force by the DC static magnetic field applied from the upper magnetic pole 6. That is, in the meniscus, the braking force by the DC static magnetic field and the stirring force by the AC moving magnetic field act, and the molten steel flow of the meniscus is controlled by controlling these strengths.

  On the other hand, the lower magnetic pole 9 is positioned below the molten steel discharge flow from the immersion nozzle 4. Therefore, the molten steel discharge flow from the immersion nozzle 4 receives the braking force from the lower magnetic pole 9 and decelerates. Further, the downward reversal flow in which the molten steel discharge flow from the immersion nozzle 4 collides with the solidified shell on the short side of the mold and branches downward also receives the braking force by the lower magnetic pole 9 and decelerates.

  In the continuous casting mold 1 configured as described above, for comparison, first, as a DC electromagnet for applying a DC static magnetic field from the upper magnetic pole 6, one electromagnet conventionally used in the mold width direction is used. A test using a DC electromagnet comprised of FIG. 2 is a schematic horizontal sectional view at the position of the upper magnetic pole 6 provided with a DC electromagnet composed of one electromagnet in the mold width direction used for comparison. FIG. 3 is a schematic horizontal sectional view at the position of the lower magnetic pole 9 shown in FIG. The lower magnetic pole 9 shown in FIG. 3 is for applying a DC static magnetic field.

  As shown in FIG. 2, the upper magnetic pole 6 used for comparison includes an AC moving magnetic field generating coil 8 for applying an AC moving magnetic field, which is disposed close to the mold long side 2, and this AC moving magnetic field. A DC electromagnet 7 'for applying a DC static magnetic field, which is disposed on the outer periphery of the generating coil 8, is configured. In the DC electromagnet 7 ′ shown in FIG. 2 and the lower magnetic pole 9 shown in FIG. 3, the magnetic flux density changes according to the DC current value to be supplied. However, the magnetic flux density can be changed independently at each position in the mold width direction. Can not.

  When the upper magnetic pole 6 was used, the molten steel flow velocity distribution in the mold was investigated by numerical calculation and an actual 1/4 size test apparatus using a low melting point alloy (Bi, Pb, Sn, Cd alloy: melting point 70 ° C.). . As a result, it was confirmed that there was a region with a low surface flow velocity of the low melting point alloy in the vicinity of the short side of the mold in the slab width direction.

  In addition, as a result of investigating the defect occurrence distribution of the slab slab cast using the mold 1 in which the upper magnetic pole 6 shown in FIG. 2 is disposed, the area where the slab defect exists is a test of 1/4 size of the actual machine. It was found to be consistent with the “slow flow area” in the device. This is because, as a result of various considerations, the DC static magnetic field applied from the upper magnetic pole 6 is too strong in the vicinity of the mold short side, so a low flow velocity region is generated in the vicinity of the mold short side, and the deoxidation product is generated in that region. And Ar gas bubbles were captured by the solidified shell.

  On the other hand, as a result of reducing the magnetic flux density of the DC static magnetic field from the upper magnetic pole 6 in order to prevent the occurrence of a low flow velocity region near the mold short side, the generation of the low flow velocity region near the mold short side is eliminated. It was found that the surface flow velocity at the center part in the slab width direction becomes too fast, and the quality of the center part in the slab width direction deteriorates due to the entrainment of mold powder.

  Based on these results, the present inventors did not change the lower magnetic pole 9 and equally divided the DC electromagnet of the upper magnetic pole 6 into four in the mold width direction with respect to the maximum width of the mold. The method of independently controlling was investigated. FIG. 4 is a schematic horizontal sectional view at the position of the upper magnetic pole 6 in which the DC electromagnets 7 equally divided in the mold width direction used in the present invention are arranged. As shown in FIG. 4, a DC electromagnet 7 is constituted by four DC electromagnets 7a, 7b, 7c, and 7d having the same length in the mold width direction.

  When the mold 1 having the upper magnetic pole 6 shown in FIG. 4 is used, both end portions of the DC electromagnet 7 divided into four parts in the above-described actual machine 1/4 size test apparatus using the low melting point alloy. By making the magnetic flux density of the DC static magnetic field applied from the two DC electromagnets 7a and 7d on the side smaller than the magnetic flux density of the DC static magnetic field applied from the two DC electromagnets 7b and 7c on the center side, The low flow velocity region in the vicinity of the short side was eliminated, and the phenomenon that the surface flow velocity at the center part in the slab width direction was increased could be suppressed.

  Furthermore, the present inventors have repeated numerical calculations and experiments to optimize the ratio between the magnetic flux density of the DC static magnetic field applied from the upper magnetic pole 6 and the magnetic flux density of the DC static magnetic field applied from the lower magnetic pole 9 shown in FIG. Thus, it was confirmed that high quality slab slabs could be manufactured stably.

  That is, the DC static magnetic field applied from the lower magnetic pole 9 is divided into the magnetic flux density A (Tesla) and the upper magnetic pole 6, and the DC static magnets applied from the two DC electromagnets 7a and 7d on both ends. The magnetic flux density of the DC static magnetic field applied from the two DC electromagnets 7b and 7c on the central part side of the magnetic flux density B (Tesla) and the upper magnetic pole 6 divided into four magnetic flux densities C (Tesla). ), The magnetic flux density A, the magnetic flux density B, and the magnetic flux density C are adjusted and applied so that the following equations (1) and (2) are satisfied simultaneously. It was found that the molten steel flow can be maintained under suitable conditions.

0.4 ≦ magnetic flux density C / magnetic flux density A ≦ 0.9 (1)
0.3 ≦ magnetic flux density B / magnetic flux density C ≦ 0.8 (2)
When this condition is satisfied, it is possible to prevent the deoxidation product, Ar gas bubbles, and mold powder from being trapped in the solidified shell.

  When the magnetic flux density C / magnetic flux density A is less than 0.4, the molten steel flow velocity at the center of the mold width is high, and the entrainment of mold powder increases, while the magnetic flux density C / magnetic flux density A is 0.9. In the case of exceeding, the molten steel flow at the upper magnetic pole position is insufficient, and the trapping of the deoxidized product and Ar gas bubbles in the solidified shell increases. On the other hand, when the magnetic flux density B / magnetic flux density C is less than 0.3, the DC static magnetic field on the short side of the mold becomes too weak, the molten steel flow speed on the short side of the mold is high, and the mold powder is caught. When the magnetic flux density B / magnetic flux density C exceeds 0.8, the molten steel flow velocity on the short side of the mold decreases, and the trapping of the deoxidized product and Ar gas bubbles in the solidified shell increases.

  Furthermore, the inventors of the upper magnetic pole 6 shown in FIG. 4 use the characteristic that the DC static magnetic field applied from the upper magnetic pole 6 can be controlled independently in the slab width direction. We investigated whether this drift phenomenon could be eliminated when a phenomenon (a phenomenon in which the flow rate of molten steel between the left and right immersion nozzles differed and the flow of molten steel became asymmetrical between the left and right in the mold) occurred.

  In the test equipment of 1/4 size actual machine using the low melting point alloy mentioned above, it is assumed that a drift phenomenon occurs due to narrowing of one flow path of the discharge hole of the immersion nozzle due to the adhesion of alumina. The test which changed the opening area of the discharge hole of the right and left of a nozzle was done. While measuring the surface flow velocity of the low melting point alloy in the mold, the magnetic flux density of the four divided DC electromagnets 7a, 7b, 7c, and 7d is set so that the magnetic flux density on the side where the surface flow velocity of the low melting point alloy is faster is increased. It was confirmed that the surface flow velocity on the left and right sides in the mold width direction can be controlled almost symmetrically by adjusting.

  That is, the molten steel flow velocity in the mold width direction of the molten steel in the mold at the position where the upper magnetic pole 6 including the DC electromagnet 7 divided into four is measured, and the drift phenomenon in the mold is confirmed from the measured molten steel flow velocity. In this case, it was confirmed that the drift phenomenon in the mold was eliminated by controlling the DC current value supplied to the DC electromagnets 7a, 7b, 7c, 7d divided into four.

  In continuous casting of steel, a technique is employed in which a plurality of temperature measuring elements are arranged across the width direction of the back side of the long side of the mold and the molten steel flow velocity is measured based on the mold temperature measured by the temperature measuring elements. (See, for example, Japanese Patent Application Laid-Open No. 2000-246413), it is possible to grasp the drift phenomenon in the mold by using this technique.

  As described above, according to the present invention, the molten steel discharge flow discharged from the discharge hole 5 of the immersion nozzle 4 by the DC static magnetic field applied from the lower magnetic pole 9 and the molten steel discharge flow are applied to the solidified shell on the short side of the mold. The molten steel discharge flow is generated by a DC static magnetic field applied by adjusting the magnetic flux density from the DC electromagnets 7a, 7b, 7c, and 7d divided into four parts of the upper magnetic pole 6 while braking the descending reverse flow that collides and branches. The upward reversal flow that branches off by colliding with the solidified shell on the short side of the mold and the molten steel flow velocity of the meniscus are braked. Further, an appropriate molten steel flow is applied to the meniscus by the AC moving magnetic field applied from the AC moving magnetic field generating coil 8 of the top pole 6 Therefore, it is possible to inhibit the deoxidation product, Ar gas bubbles, and mold powder from being trapped on the surface of the slab, and to stably produce a clean, high-quality slab slab. Fruit It is. Also, even when a drift phenomenon occurs in the mold, the drift phenomenon in the mold is eliminated by applying a DC static magnetic field having a different magnetic flux density from each of the four divided DC electromagnets 7a, 7b, 7c, and 7d. It is possible to make the molten steel flow in the mold uniform.

  In the above description, the case where the DC electromagnets 7a, 7b, 7c, 7d divided into four parts have the same length in the mold width direction is described as an example, but the DC electromagnets 7a, 7b, 7c, divided into four parts are described as examples. It is not necessary to equalize the length in the mold width direction of 7d. In the slab continuous casting machine, as described above, the width of the cast slab slab is determined by moving the mold short side 3 on the inner surface of the mold long side 2. In the example described above, when the cast slab slab has the maximum width, the lengths in the mold width direction applied by the DC electromagnets 7a, 7b, 7c, and 7d are approximately equal. When casting a slab slab narrower than the maximum width, the range applied by the DC electromagnets 7b and 7c is not changed, but the range applied by the DC electromagnets 7a and 7d is narrowed. In order to solve this problem, the length of the DC electromagnets 7b and 7c in the mold width direction may be narrowed to about ½ of the DC electromagnets 7a and 7d. In this case, the length of the DC electromagnets 7b and 7c in the mold width direction is about 1/6 of the entire mold width. The boundary between the DC electromagnet 7b and the DC electromagnet 7c needs to be the center position of the mold 1.

  In a slab continuous casting machine capable of casting a slab slab having a width of 1200 to 1800 mm and a thickness of 250 mm, an ultra-low carbon steel having a carbon concentration of 0.003 mass% or less was manufactured. The casting amount of the molten steel was 4 to 6 ton / min, and the immersion nozzle used was an immersion nozzle having a pair of discharge holes facing the short side of the mold in the vicinity of the lower end thereof.

  The AC magnetic field generating coil for the upper magnetic pole has a maximum magnetic flux density of 0.08 Tesla, and the DC magnet divided into four upper magnetic poles has a maximum magnetic flux density of 0.25 Tesla. A DC electromagnet having a maximum magnetic flux density of 0.35 Tesla was used as the magnetic pole. Further, in a test conducted for comparison in which the DC magnet of the upper magnetic pole was not divided, a DC electromagnet having a maximum magnetic flux density of 0.35 Tesla was used.

  The cast slab was rolled into a thin steel plate product, and surface defect inspection was performed on the thin steel plate product. Table 1 shows the results of the surface defect inspection in the thin steel sheet product together with the casting condition and the magnetic field application condition. The result of the surface defect inspection is displayed as an index based on the surface defect occurrence rate in Comparative Example 3, and indicates that the larger the numerical value, the higher the defect occurrence rate.

  As shown in Table 1, it was confirmed that Examples 1 to 18 of the present invention had a lower surface defect occurrence rate than Comparative Examples 1 to 6. Among Invention Examples 1 to 18, Invention Examples 1 to 12 in which the magnetic flux density C / the magnetic flux density A and the magnetic flux density B / the magnetic flux density C satisfy the expressions (1) and (2) at the same time are the invention examples. It was confirmed that the surface defect occurrence rate was lower than in Examples 12-18.

  In this way, by applying the present invention, it is possible to suppress the capture of deoxidation products, Ar gas bubbles, and mold powder to the slab surface layer portion, and a clean, high-quality slab slab can be stably produced. It was confirmed that it was manufactured.

DESCRIPTION OF SYMBOLS 1 Mold 2 Mold long side 3 Mold short side 4 Immersion nozzle 5 Discharge hole 6 Upper magnetic pole 6
7 DC electromagnet 8 AC moving magnetic field generating coil 9 Lower magnetic pole

Claims (2)

A mold in which the center of the magnetic pole is positioned above the discharge hole of the immersion nozzle, a pair of upper magnetic poles facing each other across the long side of the mold, and the center of the magnetic pole is positioned below the discharge hole of the immersion nozzle A pair of lower magnetic poles facing each other across the long side are provided on the back of the long side of the mold, a DC static magnetic field is applied from the lower magnetic pole to the full width of the slab cast, and the full width of the slab cast from the upper magnetic pole. A continuous casting facility that applies a DC static magnetic field across and an AC moving magnetic field over the entire width of the slab cast,
The DC electromagnet for applying the DC static magnetic field of the upper magnetic pole is divided into four in the width direction of the mold, and the magnetic flux density applied from the DC electromagnet is independently changed in each divided DC electromagnet. When continuously casting molten steel using the continuous casting equipment configured as possible, the magnetic flux density of the DC static magnetic field applied from the lower magnetic pole is divided into the magnetic flux density A (Tesla) and the upper magnetic pole. The magnetic flux density of the DC static magnetic field applied from the two DC electromagnets on both ends of the DC electromagnets is set to the magnetic flux density B (Tesla), and the DC magnet on the center side of the DC electromagnet divided into four upper magnetic poles. When the magnetic flux density of the DC static magnetic field applied from the two DC electromagnets is defined as the magnetic flux density C (Tesla), the magnetic flux density A, the magnetic flux density B, and the magnetic flux density C simultaneously satisfy the following formulas (1) and (2). Each to be satisfied Continuous casting method characterized by applying to adjust the magnetic flux density.
0.4 0 ≦ magnetic flux density C / magnetic flux density A ≦ 0.9 0 (1)
0.3 0 ≦ magnetic flux density B / magnetic flux density C ≦ 0.8 0 (2)   When the molten steel flow velocity in the mold width direction of the molten steel in the mold at the position of the upper magnetic pole is measured, and a drift phenomenon in the mold is confirmed from the measured molten steel flow velocity, the DC electromagnet divided into the four parts The continuous casting method according to claim 1, wherein a current value supplied to the mold is controlled to eliminate a drift phenomenon in the mold.

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