JP2020078815A - Continuous casting method - Google Patents

Abstract

To provide a new and improved continuous casting method that can stably secure quality of a casted piece for high-tensile steel even if improving productivity of the casted piece.SOLUTION: In the continuous casting method in which casted pieces for high-tensile steel are continuously casted, an alternate-current magnetic field is applied to molten steel in a casting mold using an electromagnetic agitation core arranged outside a long-side surface of an upper part of the casting mold, while a static magnetic field is applied to the molten steel using an electromagnetic brake core, arranged outside a long-side surface of a lower part of the casting mold, whose plurality of magnetic poles oppose to the long side surface, where magnetic flux densities of the alternate-current magnetic field by the electromagnetic agitation core are set to 0.05T or more and 0.2T or less and magnetic flux densities of the static magnetic field by the electromagnetic brake core are set to 0.1T or more and 0.4T or less, and an immersion nozzle is arranged at a position opposing to a space between the plurality of magnetic poles.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a continuous casting method.

  In continuous casting, molten steel once stored in the tundish is poured from above into the mold through a dipping nozzle, where the outer peripheral surface is cooled, and the solidified slab is pulled out from the lower end of the mold to continuously cast it. Is done. The solidified portion of the outer peripheral surface of the cast piece is called a solidified shell.

  Here, the molten steel contains gas bubbles of an inert gas (for example, Ar gas) that is supplied together with the molten steel to prevent clogging of the discharge hole of the immersion nozzle, non-metallic inclusions, etc. If these impurities remain in the slab, the quality of the product may be deteriorated. Generally, the specific gravity of these impurities is smaller than the specific gravity of the molten steel, so that it is often floated and removed in the molten steel during continuous casting. Therefore, when the casting speed is increased (that is, the throughput is increased), the floating separation of the impurities is not sufficiently performed, and the quality of the cast piece tends to deteriorate. Thus, in continuous casting, there is a trade-off relationship between the productivity and the quality of the slab, that is, if the productivity is pursued, the quality of the slab deteriorates, and if the quality of the slab is prioritized, There is a relationship that decreases the sex.

  By the way, high-strength steel, which is a type of steel material produced from molten steel slabs, is used for various automobile parts such as automobile exterior materials and suspensions. The quality required for such a high-strength steel is becoming stricter year by year, and in addition to the above-mentioned internal quality affected by impurities, high quality is also required for the surface quality. High-strength steel contains many alloy components. Therefore, when continuously casting a slab for high-strength steel, the slab is likely to crack for the following reasons. That is, since molten steel contains a large amount of alloy components, solidification of molten steel proceeds with peritectic reaction. Here, the peritectic reaction is a reaction in which a brittle δ phase is first precipitated in the liquid phase, and the interface between the δ phase and the liquid phase is transformed into the γ phase. The transformation from the δ phase to the γ phase is accompanied by volume contraction. Therefore, a part of the solidified shell undergoes volume contraction due to such a peritectic reaction, and such volume contraction may cause separation from the mold. Then, since the part away from the mold is less likely to be deprived of heat from the mold, it is less likely to be cooled. Therefore, the thickness of the solidified shell becomes thin in this portion. That is, non-uniform solidification of the solidified shell may occur. When such non-uniform solidification occurs, various stresses (thermal stress, transformation stress) generated during solidification contraction of molten steel increase, and the stress concentrates on the thin portion of the solidification shell. As a result, cracking occurs in the thin portion of the solidified shell. Further, molten steel solidifies through a brittle solid-liquid coexisting state. Since the region in the solid-liquid coexisting state, that is, the solid-liquid coexisting region is fragile, cracking occurs even with a small stress. Since the molten steel contains a large amount of alloy components, the temperature range of the solid-liquid coexisting state is wide. That is, the time during which the solid-liquid coexisting region exists is long and cracks are likely to occur. For example, the solidified shell has a thin portion that is in a solid-liquid coexisting state, and cracks easily occur at this portion.

  If the slab is rolled while the cracks in the solidified shell remain, the cracks cause surface defects and the surface quality deteriorates. Therefore, it is necessary to cut the cracks at the stage of casting. However, in this process, the yield or work efficiency is reduced. Further, if the cracks expand during continuous casting, the shell may break and breakout may occur.

  Cracking of the solidified shell occurs due to uneven solidification of the solidified shell. This is because the non-uniform solidification of the solidified shell causes a large stress, and this stress concentrates on the thin portion of the solidified shell, causing cracking. The non-uniform solidification of the solidified shell tends to be promoted as the temperature variation of the molten steel in the mold (that is, the variation of the molten steel temperature distribution) or the variation of the molten metal level increases.

  Therefore, in continuous casting of slabs for high-strength steel, there is a tendency that the productivity is sacrificed in order to ensure quality. That is, the discharge flow ejected from the immersion nozzle has a great influence on the temperature fluctuation and the molten metal level fluctuation of the molten steel. Specifically, the greater the force of the discharge flow, the greater the difference between the temperature near the immersion nozzle and the temperature near the mold (that is, the greater the temperature fluctuation), and the greater the fluctuation in the molten metal level. For this reason, the flow velocity of the discharge flow ejected from the immersion nozzle is reduced (that is, the casting speed is reduced) to suppress the temperature variation and molten metal level variation of the molten steel. In view of such circumstances, in continuous casting of a slab for high-strength steel, there has been a demand for a technique for improving the productivity while ensuring the quality of the slab.

  As described above, it is known that the quality of the slab for high-strength steel is greatly affected by the temperature fluctuation and molten metal level fluctuation of the molten steel in the mold during continuous casting. Then, such temperature fluctuations and molten metal level fluctuations of the molten steel are affected by the flow state of the molten steel in the mold. Therefore, by appropriately controlling the flow of the molten steel in the mold, it may be possible to realize high-speed stable operation, that is, improve productivity, while maintaining the desired quality of the ingot.

  In order to control the flow of molten steel in a mold, a technique using an electromagnetic force generator that applies an electromagnetic force to the molten steel in the mold has been developed. In this specification, the group of members around the mold including the mold and the electromagnetic force generator is also referred to as mold equipment for convenience.

  Specifically, an electromagnetic brake device and an electromagnetic stirring device are widely used as the electromagnetic force generator. Here, the electromagnetic brake device is a device that applies a static magnetic field to the molten steel to generate a braking force in the molten steel and suppress the flow of the molten steel. On the other hand, the electromagnetic stirrer generates an electromagnetic force called Lorentz force in the molten steel by applying a dynamic magnetic field to the molten steel, and gives the molten steel a flow pattern that swirls in the horizontal plane of the mold. It is a device that does.

  The electromagnetic brake device is generally provided so as to generate a braking force in molten steel that weakens the force of the discharge flow ejected from the immersion nozzle. Here, the discharge flow from the immersion nozzle collides with the inner wall of the mold, and thus, the upward flow (that is, the direction in which the molten metal surface exists) and the downward flow (that is, the direction in which the slab is pulled out) ) Forms a descending flow toward. Therefore, the force of the upward flow is weakened by weakening the force of the discharge flow by the electromagnetic brake device, and fluctuations in the molten steel level can be suppressed. Furthermore, the upward flow becomes a flow in the width direction (for example, the long side or the short side direction) near the meniscus, and this flow in the width direction (that is, reverse flow) may disturb the stirring flow (swirl flow) by the electromagnetic stirring device. There is. That is, there is a possibility that the electromagnetic stirring flow is obstructed and the effect of electromagnetic stirring is canceled. Since the electromagnetic brake device can reduce the force of such an upward flow, the effect of electromagnetic stirring can be more effectively exhibited. Further, since the force of the discharge flow colliding with the solidified shell is also weakened, the effect of suppressing breakout due to remelting of the solidified shell can be exerted. Further, since the force of the discharge flow is weakened, it can be expected to suppress the temperature fluctuation of the molten steel. As described above, the electromagnetic brake device is often used for the purpose of high-speed stable casting. That is, by using the electromagnetic brake device, it is expected that the temperature variation and molten metal level variation of the molten steel can be suppressed even if the momentum of the discharge flow is increased, so that the uneven solidification of the solidification shell can be expected to be suppressed. Further, according to the electromagnetic brake device, since the flow velocity of the downward flow formed by the discharge flow is suppressed, the floating separation of impurities in the molten steel is promoted, and the internal quality (hereinafter also referred to as the internal quality) of the cast piece is improved. It is possible to obtain the effect of improving.

  On the other hand, a disadvantage of the electromagnetic brake device is that the flow velocity of the molten steel at the interface of the solidified shell becomes low, so that impurities may be trapped in the solidified shell and the surface quality may deteriorate. Further, since it is difficult for the upward flow formed by the discharge flow to reach the surface of the molten metal, the temperature of the molten metal lowers, causing skinning, which may cause internal defects.

  The electromagnetic stirring device imparts a predetermined flow pattern to the molten steel as described above, that is, generates a stirring flow in the molten steel. This promotes the flow of molten steel at the interface of the solidified shell, so that the impurities such as Ar gas bubbles and non-metallic inclusions described above are suppressed from being trapped in the solidified shell, and the surface quality of the slab is improved. Can be improved. Further, since the temperature of the molten steel is made uniform by stirring, it is expected that the temperature fluctuation of the molten steel can be suppressed. Therefore, the use of the electromagnetic stirrer can be expected to suppress the temperature fluctuation of the molten steel even if the force of the discharge flow is increased, and thus the suppression of non-uniform solidification of the solidified shell can be expected. On the other hand, the disadvantage of the electromagnetic stirrer is that when the stirring flow collides with the inner wall of the mold, an upward flow and a downward flow occur similarly to the discharge flow from the immersion nozzle described above, so that the upward flow is on the molten metal surface. It may be mentioned that the powder may be entrained and the descending flow may cause impurities to flow downward in the mold, thereby deteriorating the quality of the slab.

  As described above, the electromagnetic brake device and the electromagnetic stirrer have respective advantages and disadvantages from the viewpoint of ensuring the quality of the slab. Therefore, for the purpose of improving both the surface quality and the internal quality of the slab, the mold equipment provided with both the electromagnetic brake device and the electromagnetic stirring device for the mold, and a plurality of electromagnetic stirring devices for the mold were provided. Techniques for continuous casting have been developed using casting equipment.

  For example, Patent Document 1 discloses a mold facility in which an electromagnetic stirrer is provided above the mold (more specifically, near the meniscus) and an electromagnetic brake device is provided below the mold. According to Patent Document 1, with such a configuration, the surface quality of the slab can be improved by the electromagnetic stirrer, and the intrusion of inclusions into the slab, which can be remarkable when high-speed casting is performed by the electromagnetic brake device, is reduced. It is described that the effect of obtaining (that is, improving the internal quality) is obtained. Further, for example, Patent Document 2 discloses a mold facility in which two stages of electromagnetic stirring devices are provided in the vertical direction. According to Patent Document 2, the surface quality of the slab can be improved by the electromagnetic stirrer in the upper stage that applies electromagnetic force to the molten steel in the vicinity of the meniscus, and the lower stage that applies electromagnetic force in the discharge flow from the immersion nozzle. It is described that the effect of improving the quality of the slab can be obtained by the electromagnetic stirrer. Further, Patent Document 3 describes a method of continuously casting a slab for high-strength steel. In this method, a static magnetic field is applied below the immersion nozzle, and an alloy containing Ti, Nb, or V is added while electromagnetically stirring the upstream side of the magnetic field.

JP-A-6-226409 JP, 2000-61599, A Japanese Unexamined Patent Publication No. 8-257702

  However, in the mold equipment disclosed in Patent Document 1, the lower end of the electromagnetic brake device is located below the mold. Since the electromagnetic force (braking force) generated by the electromagnetic brake acts according to the flow velocity of the molten steel, the electromagnetic force acting on the molten steel at this installation position is greater than when the electromagnetic brake device is installed near the discharge hole of the immersion nozzle. It is feared that will become very small. That is, the effect of improving the internal quality of the slab by the electromagnetic brake device at the time of high-speed casting, which is described in Patent Document 1, may be limited. Regarding this point, the inventors conducted a numerical analysis simulation and the like under the assumption of general casting conditions (such as a slab size and product type and the position of the dipping nozzle), and as a result examined, electromagnetic waves were placed at the position described in Patent Document 1. When the casting speed is increased to improve productivity when the brake device is installed, the intrusion of inclusions can be suitably prevented only at a casting speed of up to about 1.6 m/min. It has been newly found that when the value exceeds 1.6 m/min, it is difficult to effectively prevent the intrusion of inclusions.

  Further, in the mold equipment disclosed in Patent Document 2, the force of the discharge flow is reduced by applying an upward force to the discharge flow by the electromagnetic stirring device without using the electromagnetic brake device. However, since the electromagnetic force generated by the electromagnetic stirring acts regardless of fluctuations in the flow rate of the discharge flow, it is considered difficult to stably control the flow rate of the discharge flow by the electromagnetic stirring device. As a result of the study by the present inventors, when trying to control the flow of molten steel in the mold using the mold equipment described in Patent Document 2, due to the difficulty of controlling the discharge flow by the electromagnetic stirring device described above, It has been newly found that there is a problem that the flow of the molten steel is likely to be unstable and the quality of the slab tends to fluctuate.

  Further, when the present inventor examined mold equipment as disclosed in Patent Documents 1 and 3, when performing continuous casting of a slab for high-strength steel using the mold equipment, casting of high-strength steel was performed. It has been found that there is a range of magnetic flux densities suitable for the strip. That is, by driving the mold equipment within such a range of the magnetic flux density, it is possible to suppress the temperature fluctuation and molten metal level fluctuation of the molten steel. However, Patent Documents 1 and 3 make no mention of a range of magnetic flux density suitable for a slab for high-strength steel. Therefore, with the techniques disclosed in Patent Documents 1 and 3, it is not possible to suppress the temperature fluctuation and molten metal level fluctuation of the molten steel, and there is a possibility that the internal quality and surface quality of the high-strength steel may deteriorate.

  Further, the electromagnetic brake devices disclosed in Patent Documents 1 and 3 have a single magnetic pole. That is, in Patent Documents 1 and 3, a single magnetic pole is provided outside the long side surface of the mold, and the magnetic pole extends over both ends in the width direction (that is, the length direction of the long side surface). .. The magnetic field generated from such a magnetic pole has a characteristic that the magnetic flux density becomes maximum in the central portion in the width direction of the magnetic pole. On the other hand, the immersion nozzle is often arranged at a position facing the central portion in the width direction of the magnetic pole. Therefore, when the magnetic flux density of the magnetic field generated from the electromagnetic brake device is increased, the magnetic flux density around the immersion nozzle becomes extremely high. For this reason, the braking force due to the static magnetic field becomes excessive near the discharge holes of the immersion nozzle, and the discharge flow is likely to rise in the vicinity of the nozzle without spreading in the width direction. As described above, this upward flow becomes a flow in the width direction near the meniscus, and this flow in the width direction (that is, the reverse flow) may disturb the stirring flow by the electromagnetic stirring device. In other words, the flow in the width direction may interfere with the electromagnetic stirring flow and cancel the effect of electromagnetic stirring. Therefore, when the magnetic flux density by the electromagnetic brake device is increased, the uneven flow in the mold is rather promoted and the effect of electromagnetic stirring may be canceled. That is, the effect of the electromagnetic stirring and the effect of the electromagnetic brake cancel each other out, and as a result, the quality of the cast piece may deteriorate. Specifically, the temperature fluctuation and molten metal level fluctuation of the molten steel are promoted, and as a result, the non-uniform solidification of the solidified shell may be promoted.

  As described above, there is still room for study on the continuous casting method that can improve the productivity while ensuring the quality of the slab for high-strength steel. Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to stably cast a slab for high-strength steel even if the productivity is improved. It is an object of the present invention to provide a new and improved continuous casting method capable of ensuring the quality of pieces.

  In order to solve the above problems, according to an aspect of the present invention, C: 0.05% by mass or more and 0.5% by mass or less, Si: 0.005% by mass or more and 2.0% by mass or less, Mn: 0.3 mass% or more and 2.5 mass% or less, P: 0.01 mass% or more and 0.05 mass% or less, S: 0.015 mass% or less, N: 0.005 mass% or less A continuous casting method for continuously casting molten steel containing, while applying an AC magnetic field to the molten steel in the mold using an electromagnetic stirring core installed on the outside of the long side of the upper mold, outside the long side of the lower mold The static magnetic field is applied to the molten steel by using the electromagnetic brake core that is installed at the multiple magnetic poles facing the long side surface, and the magnetic flux density of the alternating magnetic field by the electromagnetic stirring core is 0.05T or more and 0.2T or less. A static casting magnetic field having a magnetic flux density of 0.1 T or more and 0.4 T or less and disposing an immersion nozzle at a position facing a space between a plurality of magnetic poles is provided.

  Here, the molten steel further includes, as optional components, Ti: 0.003 mass% or more and 0.2 mass% or less, Nb: 0.003 mass% or more and 0.1 mass% or less, V: 0.002 mass% or more. 0.1 mass% or less, Cr: 0.1 mass% or more and 0.8 mass% or less, Cu: 0.1 mass% or more and 0.6 mass% or less, Mo: 0.05 mass% or more and 0.6 mass% or less Hereinafter, B: 0.0004% by mass or more and 0.005% by mass or less may be included any one or more selected from the group of elements.

  Further, the height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core may satisfy the relationship shown in the following mathematical expression (101).

  Further, the height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core may satisfy the relationship shown in the following mathematical expression (103).

  As described above, according to the present invention, it is possible to ensure the quality of the slab in continuous casting even if the productivity of the slab for high-strength steel is improved. Specifically, it is possible to suppress temperature fluctuations and molten metal level fluctuations of molten steel during continuous casting. As a result, the uneven solidification of the solidified shell can be suppressed, and the occurrence of cracks can be suppressed.

It is a side sectional view showing roughly an example of 1 composition of a continuous casting machine concerning this embodiment. It is sectional drawing in the YZ plane of the mold equipment which concerns on this embodiment. It is sectional drawing in the AA cross section shown in FIG. 2 of casting equipment. It is sectional drawing in the BB cross section shown in FIG. 3 of casting equipment. It is sectional drawing in CC cross section shown in FIG. 3 of casting equipment. It is a figure for demonstrating the direction of the electromagnetic force given to molten steel by an electromagnetic brake device. It is a figure which shows the relationship between a casting speed (m/min) and the distance (mm) from a molten steel molten metal surface when the thickness of a solidification shell becomes 4 mm or 5 mm. It is a graph figure which shows the relationship between core height ratio H1/H2 and a pinhole index in case the casting speed is 1.4 m/min obtained by the numerical analysis simulation. It is a graph figure which shows the relationship between core height ratio H1/H2 and a pinhole index in case the casting speed is 2.0 m/min obtained by the numerical analysis simulation. It is a graph figure which shows the relationship between a casting speed and an internal quality index obtained by numerical analysis simulation.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, constituent elements having substantially the same functional configuration are designated by the same reference numerals, and a duplicate description will be omitted.

  It should be noted that in the drawings shown in this specification, the size of some of the constituent members may be exaggerated for the sake of explanation. The relative size of each member illustrated in each drawing does not always accurately represent the magnitude relationship between the actual members.

  In the continuous casting, the present inventors improve productivity while securing the quality of the slab by stabilizing the flow of molten steel in the mold by using a mold facility that combines an electromagnetic brake device and an electromagnetic stirring device. I tried to let you. However, these devices have not been able to easily obtain the advantages of both devices by simply installing both devices. For example, as described above, the excessive upward flow generated by the electromagnetic brake device may hinder the electromagnetic stirring flow, and these devices also have the effect of canceling each other's effects. Therefore, in continuous casting using both the electromagnetic brake device and the electromagnetic stirrer, the quality (surface quality and internal quality) of the slab often deteriorates as compared with the case where these devices are used alone.

  Therefore, the inventors repeatedly performed numerical analysis simulations and actual machine tests, and as a result of diligent studies, as a result, in the continuous casting using the electromagnetic brake device and the electromagnetic stirrer, more effectively exhibit the effect of improving the quality of the slab. In order to ensure the quality of the slab even when productivity is improved, it is important to properly define the configuration and installation position of these devices. Came to. Furthermore, when performing continuous casting of a slab for high-strength steel, there is a suitable range for the magnetic flux density of the electromagnetic stirring flow device and the electromagnetic brake device. The present embodiment will be described below.

(1. Structure of continuous casting machine)
A configuration of a continuous casting machine and a continuous casting method according to a preferred embodiment of the present invention will be described with reference to FIG. FIG. 1 is a side sectional view schematically showing a configuration example of a continuous casting machine according to this embodiment.

  As shown in FIG. 1, the continuous casting machine 1 according to the present embodiment is an apparatus for continuously casting a molten steel 2 using a continuous casting mold 110 to produce a slab 3 or other slab. The continuous casting machine 1 includes a mold 110, a ladle 4, a tundish 5, a dipping nozzle 6, a secondary cooling device 7, and a cast piece cutting machine 8.

  The ladle 4 is a movable container for transporting the molten steel 2 from the outside to the tundish 5. The ladle 4 is arranged above the tundish 5, and the molten steel 2 in the ladle 4 is supplied to the tundish 5. The tundish 5 is arranged above the mold 110, stores the molten steel 2, and removes inclusions in the molten steel 2. The immersion nozzle 6 extends downward from the lower end of the tundish 5 toward the mold 110, and its tip is immersed in the molten steel 2 in the mold 110. The immersion nozzle 6 continuously supplies the molten steel 2 from which inclusions have been removed by the tundish 5 into the mold 110.

  The mold 110 has a rectangular tubular shape corresponding to the width and thickness of the slab 3, and includes, for example, a pair of long-side mold plates (corresponding to a long-side mold plate 111 shown in FIG. 2 described later). The mold plate (corresponding to the short-side mold plate 112 shown in FIGS. 4 to 6 described later) is assembled so as to sandwich it from both sides. The long-side mold plate and the short-side mold plate (hereinafter, may be collectively referred to as a mold plate) are, for example, water-cooled copper plates provided with water passages through which cooling water flows. The mold 110 cools the molten steel 2 that is in contact with the mold plate to manufacture the cast slab 3. As the cast slab 3 moves downward in the mold 110, the solidification of the unsolidified portion 3b inside proceeds, and the thickness of the solidified shell 3a of the outer shell gradually increases. The cast piece 3 including the solidified shell 3a and the unsolidified portion 3b is pulled out from the lower end of the mold 110.

  In the following description, the up-down direction (that is, the direction in which the cast piece 3 is pulled out from the mold 110) is also referred to as the Z-axis direction. Further, two directions orthogonal to each other in a plane (horizontal plane) perpendicular to the Z-axis direction are also referred to as an X-axis direction and a Y-axis direction, respectively. Further, the X-axis direction is defined as a direction parallel to the long side of the mold 110 in the horizontal plane, and the Y-axis direction is defined as a direction parallel to the short side of the mold 110 in the horizontal plane. In the following description, when expressing the size of each member, the length of the member in the Z-axis direction is also referred to as the height, and the length of the member in the X-axis direction or the Y-axis direction. Is sometimes referred to as width.

  Here, although illustration is omitted in FIG. 1 to avoid complication of the drawing, in the present embodiment, the electromagnetic force is applied to the outer surface of the long side mold plate of the mold 110 (that is, the outer side of the long side surface). A generator is installed. The electromagnetic force generation device includes an electromagnetic stirring device and an electromagnetic brake device. In the present embodiment, continuous casting is performed while driving the electromagnetic force generator, so that it is possible to perform casting at a higher speed while ensuring the quality of the slab. The configuration of the electromagnetic force generator, the installation position with respect to the mold 110, and the like will be described later with reference to FIGS. 2 to 5.

  The secondary cooling device 7 is provided in the secondary cooling zone 9 below the mold 110, and cools the cast slab 3 drawn from the lower end of the mold 110 while supporting and transporting the slab 3. The secondary cooling device 7 includes a plurality of pairs of support rolls (for example, support rolls 11, pinch rolls 12 and segment rolls 13) arranged on both sides of the slab 3 in the thickness direction, and cooling water for the slab 3. And a plurality of spray nozzles (not shown) for ejecting.

  The support rolls provided in the secondary cooling device 7 are arranged in pairs on both sides of the slab 3 in the thickness direction, and function as a support/conveying unit that conveys the slab 3 while supporting it. By supporting the slab 3 from both sides in the thickness direction by the support rolls, breakout and bulging of the slab 3 during solidification in the secondary cooling zone 9 can be prevented.

  The support roll 11, the pinch roll 12, and the segment roll 13, which are support rolls, form a transport path (pass line) for the cast slab 3 in the secondary cooling zone 9. This pass line is vertical just below the mold 110, then curved in a curvilinear manner and finally horizontal, as shown in FIG. In the secondary cooling zone 9, a portion where the pass line is vertical is referred to as a vertical portion 9A, a curved portion is referred to as a curved portion 9B, and a horizontal portion is referred to as a horizontal portion 9C. The continuous casting machine 1 having such a pass line is called a vertical bending type continuous casting machine 1. The present invention is not limited to the vertical bending type continuous casting machine 1 as shown in FIG. 1, but can be applied to various other continuous casting machines such as a curved type or a vertical type.

  The support roll 11 is a non-drive type roll provided in the vertical portion 9A immediately below the mold 110, and supports the slab 3 immediately after being pulled out from the mold 110. Since the solidified shell 3a of the cast slab 3 immediately after being pulled out from the mold 110 is in a thin state, it is necessary to support it at a relatively short interval (roll pitch) in order to prevent breakout and bulging. Therefore, as the support roll 11, it is desirable to use a roll having a small diameter that can reduce the roll pitch. In the example shown in FIG. 1, three pairs of support rolls 11 having small diameter rolls are provided on both sides of the slab 3 in the vertical portion 9A at a relatively narrow roll pitch.

  The pinch roll 12 is a drive type roll that is rotated by a drive unit such as a motor, and has a function of pulling out the slab 3 from the mold 110. The pinch rolls 12 are arranged at appropriate positions in the vertical portion 9A, the curved portion 9B, and the horizontal portion 9C, respectively. The slab 3 is pulled out from the mold 110 by the force transmitted from the pinch roll 12 and is conveyed along the pass line. The arrangement of the pinch rolls 12 is not limited to the example shown in FIG. 1, and the arrangement position may be set arbitrarily.

  The segment roll 13 (also referred to as a guide roll) is a non-drive type roll provided in the curved portion 9B and the horizontal portion 9C, and supports and guides the slab 3 along the pass line. The segment roll 13 depends on the position on the pass line, and on either the F surface (Fixed surface, the lower left surface in FIG. 1) or the L surface (Loose surface, the upper right surface in FIG. 1) of the slab 3. They may be arranged with different roll diameters and roll pitches depending on whether they are provided.

  The slab cutting machine 8 is arranged at the end of the horizontal portion 9C of the pass line and cuts the slab 3 conveyed along the pass line into a predetermined length. The cut plate-shaped slab 14 is conveyed by the table roll 15 to the equipment for the next step.

  The overall configuration of the continuous casting machine 1 according to the present embodiment has been described above with reference to FIG. In the present embodiment, the electromagnetic force generator described above is installed in the mold 110, and continuous casting may be performed using the electromagnetic force generator. Other than the electromagnetic force generator in the continuous casting machine 1. The configuration may be similar to a typical conventional continuous casting machine. Therefore, the configuration of the continuous casting machine 1 is not limited to that shown in the figure, and any configuration of the continuous casting machine 1 may be used.

(2. Electromagnetic force generator)
(2-1. Configuration of electromagnetic force generator)
With reference to FIGS. 2 to 5, the configuration of the electromagnetic force generation device installed on the mold 110 described above will be described in detail. 2 to 5 are diagrams showing a configuration example of the mold equipment according to the present embodiment.

  FIG. 2 is a cross-sectional view on the YZ plane of the mold equipment 10 according to the present embodiment. FIG. 3 is a cross-sectional view of the mold equipment 10 taken along the line AA shown in FIG. FIG. 4 is a cross-sectional view of the mold facility 10 taken along the line BB shown in FIG. FIG. 5 is a cross-sectional view of the mold equipment 10 taken along the line C-C shown in FIG. 3. Since the mold equipment 10 has a configuration symmetrical with respect to the center of the mold 110 in the Y-axis direction, in FIGS. 2, 4 and 5, only the portion corresponding to one long side mold plate 111 is shown. Shows. Further, in FIGS. 2, 4 and 5, the molten steel 2 in the mold 110 is also shown in order to facilitate understanding.

  Referring to FIG. 2 to FIG. 5, the mold equipment 10 according to the present embodiment includes two molds on the outer side surface (that is, the outer side of the long side surface) of the long side mold plate 111 of the mold 110 via the backup plate 121. The water boxes 130 and 140 and the electromagnetic force generator 170 are installed and configured.

  As described above, the mold 110 is assembled such that the pair of long side mold plates 111 sandwich the pair of short side mold plates 112 from both sides. The mold plates 111 and 112 are made of copper plates. However, the present embodiment is not limited to this example, and the mold plates 111 and 112 may be formed of various materials generally used as a mold of a continuous casting machine.

  Here, in the present embodiment, continuous casting of a steel slab is targeted, and its slab size is, for example, width (that is, length in the X-axis direction) of about 800 to 2300 mm, or about 1000 to 1800 mm, and thickness (that is, , Y-axis direction) about 150 to 300 mm, or about 200 to 270 mm. That is, the mold plates 111 and 112 also have a size corresponding to the size of the cast piece. That is, the long side mold plate 111 has a width in the X-axis direction that is at least longer than the width of the slab 3 (for example, 800 to 2300 mm), and the short side mold plate 112 has a thickness of the slab 3 (for example, 200 to 300 mm). ) Has the same width in the Y-axis direction as

  Further, as will be described later in detail, in the present embodiment, in order to more effectively obtain the effect of improving the quality of the cast slab 3 by the electromagnetic force generator 170, the length in the Z-axis direction is made as long as possible. The mold 110 is constructed. Generally, when solidification of the molten steel 2 proceeds in the mold 110, the slab 3 may be separated from the inner wall of the mold 110 due to solidification shrinkage, which may result in insufficient cooling of the slab 3. Are known. Therefore, the length of the mold 110 is limited to about 1000 mm at the longest from the surface of the molten steel. In the present embodiment, in consideration of such circumstances, the length in the Z-axis direction is sufficiently larger than 1000 mm so that the length from the molten steel surface to the lower ends of the mold plates 111 and 112 is about 1000 mm. Thus, the mold plates 111 and 112 are formed.

  The backup plates 121 and 122 are made of, for example, stainless steel, and are provided to cover the outer surfaces of the mold plates 111 and 112 in order to reinforce the mold plates 111 and 112 of the mold 110. Hereinafter, for the sake of distinction, the backup plate 121 provided on the outer surface of the long side template plate 111 is also referred to as the long side backup plate 121, and the backup plate 122 provided on the outer surface of the short side template plate 112 is short. Also referred to as the side backup plate 122.

  Since the electromagnetic force generator 170 applies an electromagnetic force to the molten steel 2 in the mold 110 via the long side backup plate 121, at least the long side backup plate 121 is made of a non-magnetic material (for example, non-magnetic stainless steel). Etc.). However, the magnetic flux of the electromagnetic brake device 160 is provided at a portion of the long side backup plate 121 that faces an end portion 164 of an iron core (core) 162 (hereinafter, also referred to as an electromagnetic brake core 162) of the electromagnetic brake device 160 described later. In order to secure the density, magnetic soft iron 124 is embedded.

  The long side backup plate 121 is further provided with a pair of backup plates 123 extending in a direction perpendicular to the long side backup plate 121 (that is, the Y-axis direction). As shown in FIGS. 3 to 5, the electromagnetic force generator 170 is installed between the pair of backup plates 123. Thus, the backup plate 123 can define the width (that is, the length in the X-axis direction) of the electromagnetic force generator 170 and the installation position in the X-axis direction. In other words, the mounting position of the backup plate 123 is determined so that the electromagnetic force generator 170 can apply the electromagnetic force to a desired range of the molten steel 2 in the mold 110. Hereinafter, for the sake of distinction, the backup plate 123 is also referred to as a width direction backup plate 123. Similarly to the backup plates 121 and 122, the widthwise backup plate 123 is also made of stainless steel, for example.

  The water boxes 130 and 140 store cooling water for cooling the mold 110. In the present embodiment, as shown in the figure, one water box 130 is installed in a region of a predetermined distance from the upper end of the long side template plate 111, and the other water box 140 is a region of a predetermined distance from the lower end of the long side template plate 111. To install. As described above, by providing the water boxes 130 and 140 on the upper part and the lower part of the mold 110, respectively, it is possible to secure a space for installing the electromagnetic force generation device 170 between the water boxes 130 and 140. Hereinafter, for the sake of distinction, the water box 130 provided on the upper side of the long side template plate 111 is also referred to as an upper water box 130, and the water box 140 provided on the lower side of the long side template plate 111 is also referred to as a lower water box 140.

  A water channel (not shown) through which cooling water passes is formed inside the long side template plate 111 or between the long side template plate 111 and the long side backup plate 121. The water channel extends to the water boxes 130 and 140. By a pump (not shown), the cooling water flows from the one water box 130, 140 toward the other water box 130, 140 (for example, from the lower water box 140 toward the upper water box 130) through the water channel. As a result, the long side mold plate 111 is cooled, and the molten steel 2 inside the mold 110 is cooled via the long side mold plate 111. Although not shown, a water box and a water channel are similarly provided for the short side mold plate 112, and the short side mold plate 112 is cooled by flowing cooling water.

  The electromagnetic force generation device 170 includes an electromagnetic stirring device 150 and an electromagnetic braking device 160. As illustrated, the electromagnetic stirring device 150 and the electromagnetic brake device 160 are installed in the space between the water boxes 130 and 140. In the space, the electromagnetic stirring device 150 is installed above and the electromagnetic brake device 160 is installed below. That is, the electromagnetic stirring device 150 is installed outside the long side surface of the upper part of the mold, and the electromagnetic brake device 160 is installed outside the long side surface of the lower part of the mold. The heights of the electromagnetic stirring device 150 and the electromagnetic braking device 160, and the installation positions of the electromagnetic stirring device 150 and the electromagnetic braking device 160 in the Z-axis direction are described below (details of installation position of 2-2. electromagnetic force generating device). ) Will be described in detail.

  The electromagnetic stirring device 150 applies an electromagnetic field to the molten steel 2 in the mold 110 to apply an electromagnetic force to the molten steel 2. The electromagnetic stirrer 150 is driven so as to apply the electromagnetic force in the width direction (that is, the X-axis direction) of the long side template plate 111 on which it is installed to the molten steel 2. In FIG. 4, the direction of the electromagnetic force applied to the molten steel 2 by the electromagnetic stirrer 150 is schematically shown by a thick line arrow. Here, the electromagnetic stirrer 150 provided on the long-sided mold plate 111 (that is, the long-sided mold plate 111 facing the long-sided mold plate 111 shown in the drawing) is the long side on which the electromagnetic stirring device 150 is installed. It is driven along the width direction of the mold plate 111 so as to apply an electromagnetic force in a direction opposite to the illustrated direction. In this way, the pair of electromagnetic stirring devices 150 are driven so as to generate a stirring flow (swirl flow) in the horizontal plane. According to the electromagnetic stirring device 150, by generating such a stirring flow, the molten steel 2 at the interface of the solidified shell is made to flow, and a cleaning effect of suppressing trapping of air bubbles and inclusions in the solidified shell 3a is obtained. The surface quality of the piece 3 can be improved. Furthermore, since the temperature of the molten steel 2 is made uniform by stirring the molten steel 2, the temperature fluctuation of the molten steel 2 is suppressed. As a result, uneven solidification of the solidified shell is suppressed, and thus cracking of the slab is suppressed. That is, the surface quality of the slab is improved.

  The detailed configuration of the electromagnetic stirring device 150 will be described. The electromagnetic stirring device 150 is configured by a case 151, an iron core (core) 152 (hereinafter, also referred to as an electromagnetic stirring core 152) stored in the case 151, and a conductive wire wound around the electromagnetic stirring core 152. And a plurality of coils 153.

  The case 151 is a hollow member having a substantially rectangular parallelepiped shape. The size of the case 151 is such that the electromagnetic stirring device 150 can apply an electromagnetic force to a desired range of the molten steel 2, that is, the coil 153 provided inside is arranged at an appropriate position with respect to the molten steel 2. It can be appropriately determined so as to obtain. For example, the width W4 of the case 151 in the X-axis direction, that is, the width W4 of the electromagnetic stirrer 150 in the X-axis direction applies an electromagnetic force to the molten steel 2 in the mold 110 at any position in the X-axis direction. In order to obtain, it is decided to be larger than the width of the slab 3. For example, W4 is about 1800 mm to 2500 mm. Further, in the electromagnetic stirrer 150, an electromagnetic force is applied to the molten steel 2 from the coil 153 through the side wall of the case 151, so that the material of the case 151 is, for example, non-magnetic stainless steel or FRP (Fiber Reinforced Plastics). ) And the like, which are non-magnetic and can secure strength.

  The electromagnetic stirring core 152 is a solid member having a substantially rectangular parallelepiped shape, and is installed in the case 151 such that its longitudinal direction is substantially parallel to the width direction of the long-side mold plate 111 (that is, the X-axis direction). To be done. The electromagnetic stirring core 152 is formed, for example, by stacking electromagnetic steel plates.

  A coil 153 is formed by winding a conductive wire around the X-axis direction as a central axis around the electromagnetic stirring core 152. As the conductive wire, for example, a copper wire having a cross section of 10 mm×10 mm and a cooling water channel having a diameter of about 5 mm is used. When a current is applied, the conductor is cooled using the cooling water channel. The surface of the conductive wire is insulated with an insulating paper or the like, and can be wound in layers. For example, the one coil 153 is formed by winding the conductive wire in about 2 to 4 layers. Coils 153 having the same configuration are provided in parallel with each other at a predetermined interval in the X-axis direction.

  An AC power supply (not shown) is connected to each of the coils 153. An AC magnetic field is applied from the electromagnetic stirring core 152 to the molten steel 2 in the mold by the AC power source. Specifically, by applying a current to the coils 153 so that the phases of the currents in the adjacent coils 153 are appropriately deviated, an electromagnetic force that causes a stirring flow can be applied to the molten steel 2. The driving of the AC power supply can be appropriately controlled by a control device (not shown) including a processor or the like operating according to a predetermined program. The controller appropriately controls the amount of current applied to each of the coils 153, the timing of applying the current to each of the coils 153, and the like, and can control the strength of the electromagnetic force applied to the molten steel 2. As a method of driving the AC power supply, various known methods used in a general electromagnetic stirring device may be applied, and therefore detailed description thereof will be omitted here.

  The width W1 of the electromagnetic stirring core 152 in the X-axis direction is set so that the electromagnetic stirring device 150 can apply an electromagnetic force to a desired range of the molten steel 2, that is, the coil 153 is at an appropriate position with respect to the molten steel 2. It can be appropriately determined so that it can be arranged. For example, W1 is about 1800 mm.

  The electromagnetic brake device 160 applies an electromagnetic force to the molten steel 2 by applying a static magnetic field to the molten steel 2 in the mold 110. Here, FIG. 6 is a diagram for explaining the direction of the electromagnetic force applied to the molten steel 2 by the electromagnetic brake device 160. FIG. 6 schematically shows a cross section of the configuration near the mold 110 in the XZ plane. Further, in FIG. 6, the positions of the electromagnetic stirring core 152 and the end portion 164 of the electromagnetic brake core 162, which will be described later, are schematically shown by broken lines.

  As shown in FIG. 6, the immersion nozzle 6 may be provided with a pair of discharge holes at positions facing the short side template plate 112. Molten steel 2 is discharged into the mold 110 through these discharge holes. The discharge flow of the molten steel 2 advances toward the short side and collides with the shell formed on the short side. After that, the discharge flow forms an upward flow in the upward direction (that is, the direction in which the molten metal surface exists) and a downward flow in the downward direction (that is, the direction in which the slab is pulled out). The electromagnetic brake device 160 is driven so as to apply to the molten steel 2 an electromagnetic force in a direction that suppresses the flow (discharging flow) of the molten steel 2 from the discharge hole of the immersion nozzle 6. In FIG. 6, the direction of the discharge flow is simulated by thin arrows, and the direction of the electromagnetic force applied to the molten steel 2 by the electromagnetic brake device 160 is simulated by thick arrows. According to the electromagnetic brake device 160, the downward flow is suppressed by generating the electromagnetic force in the direction of suppressing the discharge flow, and the effect of promoting the floating separation of the bubbles and inclusions is obtained, and the slab 3 is obtained. The internal quality of can be improved. Furthermore, since the force of the discharge flow is weakened, the temperature fluctuation of the molten steel 2 is suppressed. Further, since the momentum of the upward flow due to the discharge flow is weakened, fluctuations in the molten metal level are suppressed. Therefore, the uneven solidification of the solidified shell is suppressed, and the surface quality of the slab is improved.

  The detailed configuration of the electromagnetic brake device 160 will be described. The electromagnetic brake device 160 includes a case 161, an electromagnetic brake core 162, a part of which is stored in the case 161, and a plurality of conductive wires wound around a portion of the electromagnetic brake core 162 inside the case 161. Coil 163 of

  The case 161 is a hollow member having a substantially rectangular parallelepiped shape. The size of the case 161 is such that the electromagnetic brake device 160 can apply an electromagnetic force to a desired range of the molten steel 2, that is, the coil 163 provided inside is arranged at an appropriate position with respect to the molten steel 2. It can be appropriately determined so as to obtain. For example, the width W4 of the case 161 in the X-axis direction, that is, the width W4 of the electromagnetic braking device 160 in the X-axis direction can apply an electromagnetic force to the molten steel 2 in the mold 110 at a desired position in the X-axis direction. Thus, the width is determined to be larger than the width of the slab 3. In the illustrated example, the width W4 of the case 161 is substantially the same as the width W4 of the case 151. However, the present embodiment is not limited to such an example, and the width of the electromagnetic stirring device 150 and the width of the electromagnetic braking device 160 may be different.

  Further, in the electromagnetic brake device 160, an electromagnetic force is applied to the molten steel 2 from the coil 163 through the side wall of the case 161, so that the case 161 is similar to the case 151, for example, non-magnetic stainless steel or FRP. It is formed of a material that is non-magnetic and that can ensure strength.

  The electromagnetic brake core 162 is a solid member having a substantially rectangular parallelepiped shape, and a pair of end portions 164 on which the coil 163 is provided, and a solid member having a substantially rectangular parallelepiped shape and having the pair of end portions 164. And a connecting portion 165 for connecting. The electromagnetic brake core 162 is provided with a pair of end portions 164 so as to project from the connecting portion 165 in the Y-axis direction and toward the long side template plate 111. The position where the pair of end portions 164 is provided is a position where electromagnetic force is desired to be applied to the molten steel 2, that is, the discharge flows from the pair of discharge holes of the immersion nozzle 6 pass through the regions where the magnetic field is applied by the coil 163. Can be provided in such a position (see also FIG. 6). The electromagnetic brake core 162 is formed, for example, by stacking electromagnetic steel plates.

  A coil 163 is formed by winding a conductive wire around the end 164 of the electromagnetic brake core 162 with the Y-axis direction as the central axis. The structure of the coil 163 is similar to the coil 153 of the electromagnetic stirring device 150 described above. For each end 164, a plurality of coils 163 are provided in parallel with each other at a predetermined interval in the Y-axis direction.

  A DC power supply (not shown) is connected to each of the coils 163. By applying a DC current to each coil 163 by the DC power supply, an electromagnetic force that weakens the force of the discharge flow can be applied to the molten steel 2. That is, each end 164 serves as a magnetic pole, one end 164 serves as an N pole, and the other end 164 serves as an S pole. Therefore, the two magnetic poles face the long side surface. Further, the immersion nozzle 6 is arranged at a position facing the space 164a between the two magnetic poles (see FIG. 6). Since a similar electrode brake core 162 is arranged on the other long side, a total of two pairs of magnetic poles are arranged. Further, the driving of the DC power supply can be appropriately controlled by a control device (not shown) including a processor or the like operating according to a predetermined program. The amount of current applied to each coil 163 is appropriately controlled by the control device, and the strength of the electromagnetic force applied to the molten steel 2 can be controlled. As a method for driving the DC power supply, various known methods used in a general electromagnetic brake device may be applied, and therefore detailed description thereof will be omitted here.

  The width W0 of the electromagnetic brake core 162 in the X-axis direction, the width W2 of the end portion 164 in the X-axis direction, and the distance W3 between the end portions 164 in the X-axis direction with respect to the desired range of the molten steel 2 by the electromagnetic stirring device 150. Can be appropriately determined so that the electromagnetic force can be applied by the magnetic field, that is, the coil 163 can be arranged at an appropriate position with respect to the molten steel 2. For example, W0 is about 1600 mm, W2 is about 500 mm, and W3 is about 350 mm.

  Here, for example, the electromagnetic brake devices disclosed in Patent Documents 1 and 3 have a single magnetic pole. A single magnetic pole is provided outside the long side surface of the mold, and the magnetic pole extends over both ends in the width direction (that is, the length direction of the long side surface). The magnetic field generated from such a magnetic pole has a characteristic that the magnetic flux density becomes maximum in the central portion in the width direction of the magnetic pole. Therefore, when the magnetic flux density of the magnetic field generated from the electromagnetic brake device is increased, the magnetic flux density around the immersion nozzle becomes extremely high. For this reason, the braking force due to the static magnetic field becomes excessive near the discharge holes of the immersion nozzle, and the discharge flow is likely to rise in the vicinity of the nozzle without spreading in the width direction. As described above, this upward flow becomes a flow in the width direction near the meniscus, and this flow in the width direction (that is, the reverse flow) may disturb the stirring flow by the electromagnetic stirring device. As a result, the effect of the electromagnetic stirring and the effect of the electromagnetic brake cancel each other out, and there is a possibility that the quality of the cast piece may deteriorate. Specifically, the temperature fluctuation and molten metal level fluctuation of the molten steel are promoted, and as a result, the non-uniform solidification of the solidified shell may be promoted.

  On the other hand, in the present embodiment, as described above, the electromagnetic brake device 160 is configured to have the two end portions 164, that is, to have the two magnetic poles. Further, the immersion nozzle 6 is arranged at a position facing the space 164a between the two magnetic poles. With this configuration, for example, when the electromagnetic brake device 160 is driven, these two magnetic poles function as an N pole and an S pole, respectively, and are located near the approximate center of the mold 110 in the width direction (that is, the X axis direction). The application of the current to the coil 163 can be controlled by the control device so that the magnetic flux density of the region becomes lower than the magnetic flux densities of the other regions. Therefore, since the braking force due to the static magnetic field can be reduced in the vicinity of the discharge hole of the immersion nozzle, it is possible to suppress the generation of excessive upflow. As a result, the effect of electromagnetic stirring is less likely to be impaired by the electromagnetic brake, and the effect of electromagnetic braking and the effect of electromagnetic stirring can be further enhanced. Therefore, it is possible to meet a wider range of casting conditions. Furthermore, since the effect of electromagnetic stirring can be obtained more effectively, the temperature fluctuation is further suppressed. Further, fluctuations in the molten metal surface and fluctuations in temperature due to the upward flow are suppressed. Therefore, non-uniform solidification of the solidified shell is suppressed, which in turn improves the surface quality of the slab.

  In the illustrated configuration example, the electromagnetic brake device 160 is configured to have two magnetic poles, but the present embodiment is not limited to this example. The electromagnetic braking device 160 may have more than two ends 164 and may be configured to have more than two magnetic poles. In this case, by appropriately adjusting the amount of current applied to the coil 163 of each end 164, it is possible to control the application of the electromagnetic force to the molten steel 2 related to the electromagnetic brake in more detail. Even when there are three or more magnetic poles, it is preferable to arrange the immersion nozzle 6 at a position facing the space between the magnetic poles.

(2-2. Details of installation position of electromagnetic force generator)
The heights of the electromagnetic stirring device 150 and the electromagnetic braking device 160, and the installation positions of the electromagnetic stirring device 150 and the electromagnetic braking device 160 in the Z-axis direction will be described.

  In the electromagnetic stirrer 150 and the electromagnetic brake device 160, it can be said that the higher the height of the electromagnetic stirrer core 152 and the electromagnetic brake core 162, respectively, the higher the performance of applying the electromagnetic force. For example, the performance of the electromagnetic brake device 160 is determined by the cross-sectional area (height H2 in the Z-axis direction×width W2 in the X-axis direction) of the end 164 of the electromagnetic brake core 162 in the XZ plane and the applied DC current. It depends on the value and the number of turns of the coil 163. Therefore, when both the electromagnetic stirrer 150 and the electromagnetic brake device 160 are installed on the mold 110, the installation positions of the electromagnetic stirrer core 152 and the electromagnetic brake core 162, more specifically, the electromagnetic stirrer in a limited installation space. How to set the height ratio of the core 152 and the electromagnetic brake core 162 is very important from the viewpoint of more effectively exhibiting the performance of each device in order to improve the quality of the cast slab 3. ..

  Here, as disclosed in Patent Documents 1 and 3 above, conventionally, a method of using both an electromagnetic stirring device and an electromagnetic brake device in continuous casting has been proposed. However, in practice, even if both the electromagnetic stirrer and the electromagnetic brake device are combined, the quality of the slab often deteriorates as compared with the case where the electromagnetic stirrer or the electromagnetic brake device is used alone. .. This does not mean that the advantages of both devices can be easily obtained by simply installing both devices, and the advantages of each device may cancel each other out depending on the configuration and installation position of each device. Because you get it. If the respective merits are canceled out, the temperature fluctuation of the molten steel and the fluctuation of the molten metal surface are promoted, which may promote the non-uniform solidification of the solidified shell. In the above-mentioned Patent Documents 1 and 3, the specific device configuration is not specified, and the heights of the iron cores of both devices are not specified. That is, it cannot be said that the conventional method can sufficiently obtain the effect of improving the quality of the cast product by providing both the electromagnetic stirring device and the electromagnetic brake device.

  On the other hand, in the present embodiment, as described below, appropriate heights of the electromagnetic stirring core 152 and the electromagnetic brake core 162 are ensured so that the quality of the slab 3 can be ensured even in high-speed casting. Stipulate the ratio of. This makes it possible to improve the productivity while ensuring the quality of the slab 3.

  Here, the casting speed in continuous casting varies greatly depending on the slab size and product type, but is generally about 0.6 to 2.3 m/min, and continuous casting exceeding 1.6 m/min is called high speed casting. Be seen. Conventionally, for automobile exterior materials and the like which are required to have high quality, it is difficult to secure quality by high speed casting such that the casting speed exceeds 1.6 m/min. /Min is a general casting speed.

  Therefore, in the present embodiment, in view of the above circumstances, for example, even in high-speed casting where the casting speed exceeds 1.6 m/min, it is equal to or more than the case where continuous casting is performed at a slower casting speed than in the past. Securing the quality of the slab 3 is set as a specific target. Hereinafter, the height ratios of the electromagnetic stirring core 152 and the electromagnetic brake core 162 in this embodiment that can satisfy the target will be described in detail.

  As described above, in the present embodiment, in order to secure a space for installing the electromagnetic stirring device 150 and the electromagnetic brake device 160 in the central portion of the mold 110 in the Z-axis direction, the water box 130 is provided above and below the mold 110, respectively. , 140 are arranged. Here, even if the electromagnetic stirring core 152 is located above the molten steel surface, the effect cannot be obtained. Therefore, the electromagnetic stirring core 152 should be installed below the molten steel level. Further, in order to effectively apply a magnetic field to the discharge flow, the electromagnetic brake core 162 is preferably located near the discharge hole of the immersion nozzle 6. When the water boxes 130 and 140 are arranged as described above, since the discharge holes of the immersion nozzle 6 are located above the lower water box 140, the electromagnetic brake core 162 is also installed above the lower water box 140. Should be. Therefore, the height H0 of the space (hereinafter, also referred to as an effective space) in which the effect is obtained by installing the electromagnetic stirring core 152 and the electromagnetic brake core 162 is the height from the molten steel surface to the upper end of the lower water box 140 ( See FIG. 2).

  In this embodiment, in order to make the most effective use of the effective space, the electromagnetic stirring core 152 is installed so that the upper end of the electromagnetic stirring core 152 is substantially at the same height as the molten steel surface. At this time, the height of the electromagnetic stirring core 152 of the electromagnetic stirring device 150 is H1, the height of the case 151 is H3, the height of the electromagnetic brake core 162 of the electromagnetic braking device 160 is H2, and the height of the case 161 is H4. Then, the following mathematical expression (1) is established. Here, the height H1 of the electromagnetic stirring core 152 is the length from the upper end to the lower end of the electromagnetic stirring core 152 (that is, the length in the Z-axis direction (distance in the casting direction)), and the height H3 of the case 151 is The length from the upper end to the lower end of the case 151 (that is, the length in the Z-axis direction). The height of the electromagnetic brake core 162 is the length from the upper end to the lower end of the electromagnetic brake core 162 (that is, the length in the Z-axis direction), and the height H4 of the case 161 is the length from the upper end to the lower end of the case 161. (That is, the length in the Z-axis direction).

  In other words, the ratio H1/H2 between the height H1 of the electromagnetic stirring core 152 and the height H2 of the electromagnetic brake core 162 (hereinafter, also referred to as core height ratio H1/H2) is satisfied while satisfying the above formula (1). Need to be specified. The heights H0 to H4 will be described below.

(About the height H0 of the effective space)
As described above, in the electromagnetic stirring device 150 and the electromagnetic braking device 160, it can be said that the larger the height of the electromagnetic stirring core 152 and the electromagnetic brake core 162, respectively, the higher the performance of applying the electromagnetic force. Therefore, in the present embodiment, the mold equipment 10 is configured so that the height H0 of the effective space is as large as possible so that both devices can exhibit their performance more. Specifically, in order to increase the height H0 of the effective space, the length of the mold 110 in the Z-axis direction may be increased. On the other hand, as described above, in consideration of the cooling property of the slab 3, it is desirable that the length from the molten steel surface to the lower end of the mold 110 is about 1000 mm or less. Therefore, in the present embodiment, in order to maximize the height H0 of the effective space while ensuring the cooling property of the slab 3, the mold 110 is set so that the distance from the molten steel surface to the lower end of the mold 110 is about 1000 mm. Form.

  Here, if it is attempted to configure the lower water box 140 so as to store a sufficient amount of water to obtain a sufficient cooling capacity, the height of the lower water box 140 needs to be at least about 200 mm based on past operation results and the like. Becomes Therefore, the height H0 of the effective space is about 800 mm or less.

(About the heights H3 and H4 of the electromagnetic stirrer and electromagnetic brake device cases)
As described above, the coil 153 of the electromagnetic stirrer 150 is formed by winding 2 to 4 layers of conductive wire having a cross-sectional size of about 10 mm×10 mm around the electromagnetic stirrer core 152. Therefore, the height of the electromagnetic stirring core 152 including the coil 153 is about H1+80 mm or more. Considering the space between the inner wall of the case 151 and the electromagnetic stirring core 152 and the coil 153, the height H3 of the case 151 is about H1+200 mm or more.

  Similarly, in the electromagnetic brake device 160, the height of the electromagnetic brake core 162 including the coil 163 is about H2+80 mm or more. Considering the space between the inner wall of the case 161, the electromagnetic brake core 162, and the coil 163, the height H4 of the case 161 is about H2+200 mm or more.

(H1+H2 range)
Substituting the values of H0, H3, and H4 described above into the above equation (1), the following equation (2) is obtained.

  That is, the electromagnetic stirring core 152 and the electromagnetic brake core 162 need to be configured such that the sum H1+H2 of their heights is about 500 mm or less. Hereinafter, an appropriate core height ratio H1/H2 will be examined so that the effect of improving the quality of the slab 3 can be sufficiently obtained while satisfying the above formula (2).

(About core height ratio H1/H2)
In the present embodiment, an appropriate range of the core height ratio H1/H2 is set by defining the range of the height H1 of the electromagnetic stirring core 152 so that the effect of electromagnetic stirring can be obtained more reliably.

  As described above, in the electromagnetic stirring, by flowing the molten steel 2 at the interface of the solidified shell, a cleaning effect of suppressing the capture of impurities in the solidified shell 3a can be obtained, and the surface quality of the slab 3 can be improved. it can. On the other hand, the thickness of the solidified shell 3a in the mold 110 increases as the mold 110 moves downward. Since the effect of electromagnetic stirring is exerted on the unsolidified portion 3b inside the solidified shell 3a, the height H1 of the electromagnetic stirring core 152 secures the surface quality of the slab 3 up to what thickness. It can be determined by what is needed.

  Here, in a product having a strict surface quality, a process of grinding the surface layer of the cast slab 3 by several millimeters is often performed. This grinding depth is about 2 mm to 5 mm. Therefore, in such a variety requiring a strict surface quality, even if electromagnetic stirring is performed in the mold 110 in a range where the thickness of the solidified shell 3a is smaller than 2 mm to 5 mm, impurities are reduced by the electromagnetic stirring. The surface layer of the slab 3 will be removed by the subsequent grinding process. In other words, the effect of improving the surface quality of the cast slab 3 cannot be obtained unless electromagnetic stirring is performed within the range in which the thickness of the solidified shell 3a is 2 mm to 5 mm or more in the mold 110.

  It is known that the solidified shell 3a gradually grows from the surface of the molten steel and its thickness is represented by the following mathematical expression (3). Here, δ is the thickness (m) of the solidified shell 3a, k is a constant depending on the cooling capacity, x is the distance from the molten steel surface (m), and Vc is the casting speed (m/min).

  From the formula (3), the relationship between the casting speed (m/min) and the distance from the molten steel surface (mm) when the thickness of the solidified shell 3a was 4 mm or 5 mm was obtained. The result is shown in FIG. FIG. 7 is a diagram showing the relationship between the casting speed (m/min) and the distance (mm) from the molten steel surface when the thickness of the solidified shell 3a is 4 mm or 5 mm. In FIG. 7, the horizontal axis represents the casting speed, the vertical axis represents the distance from the molten steel surface, and the solidification shell 3a has a thickness of 4 mm and the solidification shell 3a has a thickness of 5 mm. The relationship is plotted. In the calculation for obtaining the results shown in FIG. 7, k=17 was set as a value corresponding to a general template.

  For example, from the results shown in FIG. 7, when the thickness of the ground metal is less than 4 mm and the molten steel 2 may be electromagnetically stirred within the range of the thickness of the solidified shell 3a up to 4 mm, the height of the electromagnetic stirring core 152 may be increased. It can be seen that when H1 is 200 mm, the effect of electromagnetic stirring can be obtained in continuous casting at a casting speed of 3.5 m/min or less. When the thickness to be ground is smaller than 5 mm and the molten steel 2 may be electromagnetically stirred within the range where the thickness of the solidified shell 3a is up to 5 mm, if the height H1 of the electromagnetic stirring core 152 is 300 mm, the casting speed is It can be seen that the effect of electromagnetic stirring can be obtained in continuous casting at 3.5 m/min or less. The value of "3.5 m/min" of the casting speed corresponds to the maximum casting speed that is possible in operation and equipment in a general continuous casting machine.

  Here, as described above, in the present embodiment, for example, even in high-speed casting where the casting speed exceeds 1.6 m/min, a slab equivalent to that obtained when continuous casting is performed at a slower casting speed than in the past The goal is to ensure quality of 3. In order to obtain the effect of electromagnetic stirring even when the thickness of the solidified shell 3a becomes 5 mm when the casting speed exceeds 1.6 m/min, from FIG. 7, the height H1 of the electromagnetic stirring core 152 is at least about 150 mm. You can see that we have to do this.

  From the results of the above examination, in the present embodiment, for example, in continuous casting at a relatively high casting speed of 1.6 m/min, the effect of electromagnetic stirring is obtained even when the thickness of the solidified shell 3a becomes 5 mm. In addition, the electromagnetic stirring core 152 is configured such that the height H1 of the electromagnetic stirring core 152 is about 150 mm or more.

  Regarding the height H2 of the electromagnetic brake core 162, as described above, the performance of the electromagnetic brake device 160 is higher as the height H2 is larger. Therefore, from the above formula (2), when H1+H2=500 mm, the range of H2 corresponding to the range of the height H1 of the electromagnetic stirring core 152 may be obtained. That is, the height H2 of the electromagnetic brake core 162 is about 350 mm.

  From the values of the height H1 of the electromagnetic stirring core 152 and the height H2 of the electromagnetic brake core 162, the core height ratio H1/H2 in the present embodiment is, for example, the following mathematical expression (4).

  In summary, in the present embodiment, even if the casting speed exceeds 1.6 m/min, it is necessary to secure the quality of the cast slab 3 which is equal to or higher than that in the case where continuous casting is performed at a lower casting speed than the conventional one. When the target is set, for example, the electromagnetic stirring core 152 and the electromagnetic brake core 162 are set so that the height H1 of the electromagnetic stirring core 152 and the height H2 of the electromagnetic brake core 162 satisfy the mathematical expression (4). Composed.

  A preferable upper limit value of the core height ratio H1/H2 can be defined by the minimum value that the height H2 of the electromagnetic brake core 162 can take. The smaller the height H2 of the electromagnetic brake core 162, the larger the core height ratio H1/H2. However, if the height H2 of the electromagnetic brake core 162 is too small, the electromagnetic brake does not function effectively, and the slab produced by the electromagnetic brake is reduced. This is because the effect of improving the quality of No. 3, in particular, the internal quality cannot be obtained. The minimum value of the height H2 of the electromagnetic brake core 162 at which the effect of the electromagnetic brake can be sufficiently exerted differs depending on the casting conditions such as the slab size and product type and the casting speed. Therefore, the minimum value of the height H2 of the electromagnetic brake core 162, that is, the upper limit value of the core height ratio H1/H2 is a numerical value simulating the casting conditions in the actual operation as shown in Examples 1 to 3 below. It can be specified based on analysis simulation and actual machine test.

  The configuration of the mold equipment 10 according to the present embodiment has been described above. In the above description, when obtaining the relationship shown in the mathematical expression (4), these relationships were obtained from the mathematical expression (2) as H1+H2=500 mm. However, the present embodiment is not limited to this example. As described above, it is preferable that H1+H2 is as large as possible in order to maximize the performance of the apparatus. Therefore, in the above example, H1+H2=500 mm. On the other hand, in consideration of workability when installing the water boxes 130, 140, the electromagnetic stirrer 150, and the electromagnetic brake device 160, for example, it may be preferable that a gap be present between these members in the Z-axis direction. .. In this way, when other factors such as workability are emphasized, H1+H2=500 mm does not necessarily have to be set. May be set.

  Further, in the above description, when the casting speed exceeds 1.6 m/min, as a condition for obtaining the effect of electromagnetic stirring even when the thickness of the solidified shell 3a becomes 5 mm, as shown in FIG. The minimum value of the height H1 of about 150 mm was obtained, and 0.43, which is the value of the core height ratio H1/H2 at this time, was set as the lower limit value of the core height ratio H1/H2. However, the present embodiment is not limited to this example. When the target casting speed is set higher, the lower limit of the core height ratio H1/H2 may also change. That is, the minimum value of the height H1 of the electromagnetic stirring core 152 is obtained from FIG. 7 so that the effect of electromagnetic stirring can be obtained even when the thickness of the solidified shell 3a is 5 mm at the casting speed targeted in the actual operation. The core height ratio H1/H2 corresponding to the value of H1 may be set as the lower limit value of the core height ratio H1/H2.

  As an example, considering workability and the like, H1+H2=450 mm, and even at a higher casting speed of 2.0 m/min, the quality of the cast slab 3 which is equal to or higher than that when continuous casting is performed at a lower casting speed of the related art is achieved. The condition of the core height ratio H1/H2 in the case of securing the target will be calculated. First, from FIG. 7, when the casting speed is 2.0 m/min or more, the condition for obtaining the effect of electromagnetic stirring even when the thickness of the solidified shell 3a becomes 5 mm is obtained. Referring to FIG. 7, when the casting speed is 2.0 m/min, the solidified shell has a thickness of 5 mm at a position where the distance from the molten steel surface is about 175 mm. Therefore, in consideration of the margin, the minimum value of the height H1 of the electromagnetic stirring core 152 that can obtain the effect of electromagnetic stirring even when the thickness of the solidified shell 3a is 5 mm is required to be about 200 mm. At this time, since H1+H2=450 mm to H2=250 mm, the condition required for the core height ratio H1/H2 is represented by the following mathematical expression (5).

  That is, in the present embodiment, in the case of aiming to secure the quality of the cast slab 3 which is equal to or higher than that in the case where continuous casting is performed at a lower casting speed of the related art even at the casting speed of 2.0 m/min, The electromagnetic stirring core 152 and the electromagnetic brake core 162 may be configured to satisfy at least the above mathematical expression (5). The upper limit of the core height ratio H1/H2 may be specified based on the numerical analysis simulation simulating the casting conditions in the actual operation and the actual machine test as described above.

  As described above, in the present embodiment, it is possible to secure the quality (surface quality and internal quality) of the slab that is equal to or higher than that of the conventional continuous casting at a lower speed even when the casting speed is increased. The range of the core height ratio H1/H2 can be changed according to the specific value of the target casting speed and the specific value of H1+H2. Therefore, when setting an appropriate range of the core height ratio H1/H2, the target casting speed and H1+H2 of H1+H2 should be considered in consideration of the casting conditions during actual operation, the configuration of the continuous casting machine 1, and the like. The value may be appropriately set, and an appropriate range of the core height ratio H1/H2 at that time may be appropriately obtained by the method described above.

  Considering the examples described below, it is preferable that H1/H2 satisfy the relationship shown in the following expression (101), and more preferably the following expression (103).

(3. Continuous casting method)
Next, a continuous casting method using the above continuous casting machine 1 will be described. In this embodiment, the continuous casting machine 1 is used to continuously cast a slab for high-strength steel. High-strength steel is a steel material having a tensile strength of 490 MPa or more, for example, but is not limited to this. Here, the tensile strength is a value measured according to JIS Z2241 "Metallic material tensile test method". That is, the molten steel 2 is C: 0.05% by mass or more and 0.5% by mass or less, Si: 0.005% by mass or more and 2.0% by mass or less, Mn: 0.3% by mass or more and 2.5% by mass or less. Hereinafter, an element group including P: 0.01% by mass or more and 0.05% by mass or less, S: 0.015% by mass or less, and N: 0.005% by mass or less is included. Further, the molten steel 2 has, as optional components, Ti: 0.003 mass% or more and 0.2 mass% or less, Nb: 0.003 mass% or more and 0.1 mass% or less, V: 0.002 mass% or more and 0.1% or less. 1 mass% or less, Cr: 0.1 mass% or more and 0.8 mass% or less, Cu: 0.1 mass% or more and 0.6 mass% or less, Mo: 0.05 mass% or more and 0.6 mass% or less, B: It may contain any one or more selected from the element group consisting of 0.0004% by mass or more and 0.005% by mass or less. Here, the mass% of each component means the mass% with respect to the total mass of the molten steel 2. The balance of molten steel is iron and inevitable impurities.

(C: 0.05% by mass or more and 0.5% by mass or less)
C is an element necessary to secure the strength of the high-strength steel, and is added to molten steel 2 in an amount of 0.05 mass% or more in order to obtain the effect. On the other hand, if the C content exceeds 0.5 mass %, the weldability is significantly deteriorated, so the C content is set to 0.5 mass% or less.

(Si: 0.005 mass% or more and 2.0 mass% or less)
Since Si has the effect of strengthening the steel, it is added to the molten steel 2 depending on the required strength of the high-strength steel. The Si content is 0.005 mass% or more. On the other hand, if the Si content is too high, the formability deteriorates, so the Si content is set to 2.0% by mass or less.

(Mn: 0.3 mass% or more and 2.5 mass% or less)
Since Mn has a function of strengthening steel, 0.3 mass% or more is added to the molten steel 2 depending on the required strength of the high-strength steel. On the other hand, if the Mn content is too large, the formability is deteriorated and the alloy cost becomes high. Therefore, the Mn content is set to 2.5 mass% or less.

(P: 0.01% by mass or more and 0.05% by mass or less)
Since P has the effect of strengthening the steel, it is added to the molten steel 2 according to the required strength of the high-strength steel. The content of P is 0.01% by mass or more. On the other hand, if the content of P is too large, embrittlement occurs due to the segregation of grain boundaries, so the content of P is set to 0.05% by mass or less.

(S: 0.015 mass% or less)
S is present in steel as an impurity. If the S content is too large, it causes embrittlement, so the smaller the content, the better. If the S content exceeds 0.015%, the embrittlement becomes remarkable. Therefore, the content of S is set to 0.015 mass% or less.

(N: 0.005 mass% or less)
N is preferable because it lowers the moldability, and when the content of N exceeds 0.005 mass %, the effect of N becomes remarkable. Therefore, the content of N is set to 0.005 mass% or less.

(Ti: 0.003 mass% or more and 0.2 mass% or less)
Ti has the effect of increasing the strength of high-strength steel by combining with C and precipitating as carbide. Therefore, 0.003 mass% or more may be added to the molten steel 2 if necessary. On the other hand, if the Ti content exceeds 0.2 mass %, Ti easily reacts with the powder during continuous casting to become foreign matter. Therefore, the Ti content is 0.2 mass% or less.

(Nb: 0.003 mass% or more and 0.1 mass% or less)
Nb has the effect of increasing the strength of high-strength steel by precipitating as NbC. Therefore, 0.003 mass% or more may be added to the molten steel 2 if necessary. On the other hand, when the content of Nb exceeds 0.1% by mass, the yield strength is increased and the elongation is decreased, so that the formability is deteriorated. Therefore, the content of Nb is set to 0.1% by mass or less.

(V: 0.002 mass% or more and 0.1 mass% or less)
V has the effect of increasing the strength of high-strength steel by combining with C and precipitating as carbide. Therefore, 0.002 mass% or more may be added to the molten steel 2 if necessary. On the other hand, when the V content exceeds 0.1% by mass, surface cracking of the cast becomes significant. Therefore, the content is 0.1 mass% or less.

(Cr: 0.1% by mass or more and 0.8% by mass or less)
Cr has the effect of increasing the strength of high-strength steel. Therefore, 0.1 mass% or more may be added to the molten steel 2 if necessary. On the other hand, if the Cr content exceeds 0.8 mass %, the effect becomes saturated. Therefore, the content of Cr is set to 0.8% by mass or less.

(Cu: 0.1% by mass or more and 0.6% by mass or less)
Cu has the effect of increasing the strength of high-strength steel. Therefore, 0.1 mass% or more may be added to the molten steel 2 if necessary. On the other hand, since Cu is a rare metal, the Cu content is set to 0.6 mass% or less from the viewpoint of cost.

(Mo: 0.05% by mass or more and 0.6% by mass or less)
Mo has the effect of increasing the strength of high-strength steel. Therefore, 0.05 mass% or more may be added to the molten steel 2 if necessary. On the other hand, since Mo is a rare metal, the Mo content is set to 0.6 mass% or less from the viewpoint of cost.

(B: 0.0004 mass% or more and 0.005 mass% or less)
Solid solution B has the effect of increasing the strength of high-strength steel. Therefore, 0.0004 mass% or more may be added to the molten steel 2 if necessary. On the other hand, when the B content is 0.005% by mass or more, surface cracking of the slab becomes significant. Therefore, the content of B is set to 0.005 mass% or less.

  When performing continuous casting, the magnetic flux density of the alternating magnetic field by the electromagnetic stirring device 150 (that is, the electromagnetic stirring core 152) (hereinafter, also simply referred to as “electromagnetic stirring strength”) is set to 0.05 T or more and 0.2 T or less. When the electromagnetic stirring strength is less than 0.05 T, the stirring flow is insufficient and the molten steel temperature cannot be made uniform. Therefore, uneven solidification of the solidified shell is promoted, and cracks may occur. When the electromagnetic stirring strength is larger than 0.2T, the fluctuation of the molten metal surface due to the stirring flow becomes large. Therefore, uneven solidification of the solidified shell is promoted, and cracks may occur. From this, it is appropriate that the electromagnetic stirring strength is 0.05 T or more and 0.2 T or less. Unless otherwise specified, the unit "T" of the electromagnetic stirring strength and the electromagnetic brake strength, which will be described later, means Tesla.

  On the other hand, the magnetic flux density of the static magnetic field by the electromagnetic brake device 160 (that is, the electromagnetic brake core 162) (hereinafter, also simply referred to as “electromagnetic brake strength”) is set to 0.1 T or more and 0.4 T or less. When the electromagnetic brake strength is less than 0.1T, the discharge flow is not sufficiently braked, and the molten metal level changes due to the upward flow generated on the short side. Therefore, uneven solidification of the solidified shell is promoted, and cracks may occur. When the electromagnetic brake strength is greater than 0.4T, the braking force is excessive and the discharge flow is concentrated in the vicinity of the nozzle, so that the shell thickness near the nozzle may be thin. That is, the discharge flow promotes non-uniform solidification of the solidified shell in the width direction of the slab, which may cause cracking. Further, since the discharge flow is excessively damped, an upward flow is formed at the center in the width direction. Due to this upward flow, the fluctuation of the molten metal level becomes large. Therefore, uneven solidification of the solidified shell is promoted, and cracks may occur. From this, it is appropriate that the electromagnetic brake strength is 0.1 T or more and 0.4 T or less.

  Here, the electromagnetic stirring strength and the electromagnetic brake strength are the magnetic flux densities of the core center portion (that is, the center portions of the electromagnetic stirring core 152 and the electromagnetic brake core 162) measured in the cold state in which the molten steel does not exist in the mold 110. .. Since the magnetic field generated by the electromagnetic stirring core 152 is an alternating magnetic field, the maximum value of the temporal change in magnetic flux density is taken as the value of electromagnetic stirring strength. Note that the correlation between the electromagnetic stirring strength and the electromagnetic brake strength and the application conditions (current, frequency) to the electromagnetic stirring device 150 and the electromagnetic brake device 160 can be specified in advance, so in actual operation, the application conditions to each device can be changed. By adjusting, the electromagnetic stirring strength and the electromagnetic brake strength may be adjusted.

  Continuous casting may be performed in the same manner as the conventional continuous casting method except for the above operating conditions. As shown in Examples described later, according to the continuous casting method according to the present embodiment, even if the productivity of the slab for high-strength steel is enhanced, the quality of the slab is stably ensured. Is possible. As described above, the molten steel 2 may contain one or more of Nb, Ti, and V. In this case, NbC, TiN, VN, or the like intervenes in the crystal grain boundaries of the slab. A lot of things are deposited. When such inclusions precipitate at the crystal grain boundaries, stress may concentrate at the crystal grain boundaries and cracks may occur. It should be noted that such cracking occurs when strain is applied in the embrittlement temperature range of steel. Therefore, when the molten steel 2 contains one or more of Nb, Ti, and V, the slab temperature during bending and straightening may be adjusted during secondary cooling. Thereby, cracking can be suppressed.

  A numerical analysis simulation was performed in order to confirm that the surface quality of the slab can be ensured even if the casting speed is increased by applying the mold equipment 10 according to the present embodiment to continuous casting. In the numerical analysis simulation, a calculation model imitating the mold equipment 10 in which the electromagnetic force generator 170 according to the present embodiment described with reference to FIGS. The behavior of the molten steel and Ar gas bubbles was calculated. The conditions of the numerical analysis simulation are as follows. In addition, also in Example 2, a numerical analysis simulation was performed under the same conditions.

(Conditions for numerical analysis simulation)
Width W1 of the electromagnetic stirring core of the electromagnetic stirring device: 1900 mm
Current application condition of electromagnetic stirring device: 680 A, 3.0 Hz
Number of windings of coil of electromagnetic stirrer: 20 turns Width of electromagnetic brake core of electromagnetic brake device W2: 500 mm
Distance W3 between the electromagnetic brake cores of the electromagnetic brake device: 350 mm
Current application condition of electromagnetic brake device: 900A
Number of turns of coil of electromagnetic brake device: 120 turns Casting speed: 1.4 m/min or 2.0 m/min
Mold width: 1600 mm
Mold thickness: 250 mm
Blow-in amount of Ar gas: 5 NL/min

In the evaluation of the surface quality, a fluid simulation is performed under the above conditions, the flow rate of molten steel in the molten steel of the continuous casting machine 1, the solidification rate of the molten steel, and the distribution of Ar gas bubbles are calculated and trapped in the solidified shell. Ar gas bubbles were evaluated. Specifically, the probability P _g of Ar gas bubbles being trapped in the solidified shell was calculated by the function shown in the following mathematical expression (6). Here, C ₀ is a constant and U is the molten steel flow velocity at the solidification interface.

Further, the rate η _{g at} which the Ar gas bubbles were captured by the solidified shell at this time was calculated using the following mathematical expression (7). Here, n _g is the number density of the Ar gas bubbles in the solidified shell interface, the R _s is the solidification speed of the solidified shell.

Then, the number density S _g of Ar gas bubbles in the solidified shell was calculated using the following mathematical expression (8). Here, U _s is the moving speed of the solidified shell in the drawing direction of the cast piece.

The number density S _g of Ar gas bubbles in the solidified shell calculated from the above formula (8) is time-averaged, and the number of Ar gas bubbles with a diameter of 1 mm captured within a range of 4 mm from the surface layer of the slab is pinned. It was calculated as a Hall index. It can be said that the smaller the pinhole index, the higher the surface quality of the slab. For details of the method for evaluating the surface quality of a cast piece by the numerical analysis simulation described above, reference can be made to JP-A-2015-157309, which is a prior application by the applicant of the present application.

  In the evaluation of the surface quality, the height H1 of the electromagnetic stirring core 152 and the height H2 of the electromagnetic brake core 162 are set to H1+H2=500 mm in consideration of the relationship shown in the above formula (2). The simulation was performed with eight combinations shown in Table 1 below.

  In addition, for comparison, as an example of the conventional continuous casting method, the surface quality of the slab when only the electromagnetic stirring device 150 is installed was also evaluated. The conventional continuous casting method used as the evaluation target corresponds to the continuous casting method using the mold equipment 10 shown in FIGS. 2 to 5 from which the electromagnetic brake device 160 is removed. Moreover, in the calculation of the conventional continuous casting method, the height H1 of the electromagnetic stirring core 152 was fixed at 250 mm. Regarding the conventional continuous casting method, the pinhole index is calculated by the same method as the above-described calculation method except that the electromagnetic brake device 160 is not installed and the height H1 of the electromagnetic stirring core 162 is fixed at 250 mm. did.

  Numerical analysis simulation results for surface quality are shown in FIGS. 8 and 9. FIG. 8 is a graph showing the relationship between the core height ratio H1/H2 and the pinhole index obtained by the numerical analysis simulation when the casting speed is 1.4 m/min. FIG. 9 is a graph showing the relationship between the core height ratio H1/H2 and the pinhole index, obtained by the numerical analysis simulation, when the casting speed is 2.0 m/min. In FIGS. 8 and 9, the horizontal axis represents the core height ratio H1/H2 and the vertical axis represents the pinhole index, and the relationship between the two is plotted. Further, in FIG. 8 and FIG. 9, the value of the pinhole index in the above-mentioned conventional continuous casting method is shown by a broken straight line parallel to the horizontal axis.

  Referring to FIG. 8, when the casting speed is 1.4 m/min, the pinhole index in the conventional continuous casting method is about 40. On the other hand, in the continuous casting method according to the present embodiment, when the core height ratio H1/H2 is 0.82 or more, a pinhole index equal to or less than that of the conventional continuous casting method is obtained. In particular, when the core height ratio H1/H2 becomes 1.0 or more, the pinhole index becomes lower than that in the conventional continuous casting method. The pinhole index decreases as the core height ratio H1/H2 increases. That is, it is considered that as the height H1 of the electromagnetic stirring core 152 becomes larger than the height H2 of the electromagnetic brake core 162, the pinhole index decreases and the surface quality of the cast slab 3 improves.

  Referring to FIG. 9, when the casting speed is increased to 2.0 m/min, the pinhole index in the conventional continuous casting method deteriorates to about 80. On the other hand, in the continuous casting method according to the present embodiment, when the core height ratio H1/H2 is about 0.70 to about 2.70, the pinhole index decreases to the same level as or lower than that of the conventional continuous casting method. To do. Especially, when the core height ratio H1/H2 is about 1.0 to about 1.5, the pinhole index is reduced to about 40, and the casting speed is increased to 2.0 m/min. However, it can be seen that even with the conventional continuous casting method, it is possible to obtain the same surface quality as in the case where continuous casting is performed at a casting speed of 1.4 m/min.

  From the above results, under the casting conditions corresponding to the above numerical analysis simulation conditions, if the core height ratio H1/H2 is set to any value between about 0.70 and about 2.70, at least the casting speed 1. It has been found that in continuous casting at 4 m/min to 2.0 m/min, it is possible to secure the surface quality of the slab that is equal to or higher than that of the conventional continuous casting method. In particular, if the core height ratio H1/H2 is set to about 1.0 to about 1.5, even if the casting speed is increased to 2.0 m/min, a lower speed than the conventional one (specifically, It was found that it is possible to secure the surface quality of the slab that is equal to or higher than that of the continuous casting method at a casting speed of 1.4 m/min).

A numerical analysis simulation was performed in order to confirm that the internal quality of the slab can be ensured even if the casting speed is increased by applying the mold facility 10 according to the present embodiment to continuous casting. Regarding the internal quality, a value similar to the above-described simulation method used for evaluating the surface quality was evaluated by the same simulation method as that used for evaluating the surface quality, but the value of alumina, which is a typical impurity inclusion in the slab, remaining in the slab. Specifically, assuming a vertical bending type continuous casting machine 1, the behavior of alumina particles during continuous casting is analyzed by simulation, and it is considered that the alumina particles settled below the vertical portion remain in the slab as they are. The number of alumina particles in a predetermined volume of the slab was calculated as the internal quality index. At this time, the vertical length of the continuous casting machine 1 was set to 3 m. The diameter of the alumina particles was 0.4 mm, and the specific gravity of the alumina particles was 3990 kg/m ³ . It can be said that the smaller the quality index, the higher the quality of the slab.

  In the evaluation of the internal quality, regarding the height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core, H1+H2=450 mm as shown in the following table in consideration of the relationship shown in the above mathematical expression (2). The simulation was performed with four combinations shown in 2.

  In addition, regarding the internal quality, for comparison, the internal quality in the case where only the electromagnetic stirring device 150 was installed was also evaluated as an example of a conventional continuous casting method. As the conventional continuous casting method used as the evaluation target, the one in which the electromagnetic brake device 160 is removed in the mold equipment 10 according to the present embodiment shown in FIGS. It is a continuous casting method. Further, the height H1 of the electromagnetic stirring core 152 of the electromagnetic stirring device 150 is fixed to 250 mm.

  FIG. 10 shows the result of numerical analysis simulation for the inner quality. FIG. 10 is a graph showing the relationship between the casting speed and the internal quality index, which is obtained by the numerical analysis simulation. In FIG. 10, the horizontal axis represents the casting speed and the vertical axis represents the internal quality index. The relationship between the casting speed and the internal quality index corresponding to the core height ratios H1/H2 shown in Table 2 above is plotted. is doing. Moreover, in FIG. 10, the result by the above-mentioned conventional continuous casting method is also plotted together.

  Referring to FIG. 10, in the conventional continuous casting method, the internal quality index at a general casting speed of 1.4 m/min is about 40, and the internal quality index significantly increases as the casting speed increases. (Ie, the internal quality of the slab is significantly deteriorated as the casting speed is increased).

  On the other hand, in the continuous casting method according to the present embodiment, when the core height ratio H1/H2 is 1.5 or less, the internal quality index is 40 even if the casting speed is increased to about 2.0 m/min. It is suppressed to be smaller than that of the conventional continuous casting method, and it is possible to obtain a better internal quality than in the case where the casting speed is 1.4 m/min in the conventional continuous casting method. Even when the core height ratio H1/H2 is 2.0, the internal quality index is about 60 when the casting speed is 2.4 m/min, and the casting speed is 1.6 m/min in the conventional continuous casting method. It is possible to secure the same internal quality as in the case of min. From the above results, the core height ratio H1/H2 is set to 2.0 or less, and more preferably 1.5 or less in order to secure the internal quality of the cast slab that is equal to or lower than the conventional value even if the casting speed is high. do it.

  From the above results, under the casting conditions corresponding to the numerical analysis simulation conditions, if the core height ratio H1/H2 is set to any value of about 1.5 or less, continuous casting at a casting speed of 2.0 m/min In the above, it was found that it is possible to secure the internal quality of the slab that is equal to or lower than that of the conventional continuous casting method at a casting speed of 1.4 m/min. Further, if the core height ratio H1/H2 is set to any value of about 2.0 or less, in continuous casting at a casting speed of 2.4 m/min, conventional continuous casting at a casting speed of 1.6 m/min will be performed. It has been found that it is possible to secure the internal quality of the slab that is equal to or less than the method.

  In order to further confirm the effect of this embodiment, an actual machine test was conducted. In the actual machine test, the electromagnetic force generator 170 according to the present embodiment described with reference to FIGS. 2 to 5 is installed in the continuous casting machine actually used for the operation, and the continuous casting machine 1 is used. , The core height ratio H1/H2, and the casting speed were variously changed, and continuous casting was actually performed. The mold 110 is a copper water-cooled type (water-cooled copper mold), has a height (the length from the upper end to the lower end of the mold) of 900 mm, and has a rectangular cross section. The continuous casting machine 1 was a vertical bending type. The specific water amount for secondary cooling was set to 1.5 to 2.5 L/kg-steel. The amount of argon gas blown into the immersion nozzle 6 was set to 7 NL/min. The upper end of the electromagnetic stirring core 152 was placed 100 mm from the upper end of the mold, and the upper end of the electromagnetic brake core 162 was placed 150 mm from the lower end of the electromagnetic stirring core. Then, the surface quality and internal quality of the cast slab were examined by visual inspection and ultrasonic flaw detection, respectively. Specifically, the surface of the slab was ground smoothly so as to allow flaw detection (about 1-2 mm), and bubble defects and inclusion defects existing on the surface were visually inspected. Also, in the ultrasonic flaw detection, bubble defects and inclusion defects were detected from the echo of the ultrasonic waves directed from the surface of the slab toward the center of thickness. Further, for comparison, continuous casting was also performed for the conventional continuous casting method in which only an electromagnetic stirring device was installed, and the quality of the cast piece was investigated by the same method. The conventional continuous casting method is a continuous casting method using the mold equipment 10 according to the present embodiment shown in FIGS. 2 to 5 from which the electromagnetic brake device 160 is removed, as in the case of the numerical analysis simulation described above. .. Further, the casting speed in the conventional continuous casting method was 1.4 m/min, and the height H1 of the electromagnetic stirring core 152 of the electromagnetic stirring device 150 was 200 mm.

  As for the immersion nozzle, both in the present embodiment and in the conventional continuous casting method, the discharge hole used had a downward angle of 45°, and the depth from the molten steel surface at the upper end of the discharge hole was 270 mm.

  The results are shown in Table 3 below. In Table 3, with respect to the quality of the slab, when the quality (that is, the number of defects) obtained is better than that of the conventional continuous casting method on the basis of the quality of the conventional continuous casting method, "○", If a quality comparable to the conventional continuous casting method (that is, the number of defects is similar) is obtained, it is “△”, and a quality worse than that of the conventional continuous casting method (that is, the number of defects is large). ) Is obtained, it is expressed by adding "x".

  In this example, even when the casting speed was increased to 2.0 m/min, it was superior to the conventional continuous casting method at a lower speed (specifically, the casting speed was 1.6 m/min). The range of the core height ratio H1/H2 that can secure the quality (surface quality and internal quality) of the cast piece was investigated. From the results shown in Table 3, under the casting conditions corresponding to the actual machine test, the casting speed was 2.0 m/min by setting the value of the core height ratio H1/H2 to about 0.80 to about 2.33. It has been found that it is possible to ensure a better quality of the slab than that of the conventional continuous casting method at a lower speed even when it is increased. In other words, from the results of this example, the present invention is applied, and the value of the core height ratio H1/H2 is set to about 0.80 to about 2.33, while ensuring the quality of the slab, It was shown that it is possible to increase the casting speed to 2.0 m/min and improve the productivity. Similarly, from the results shown in Table 3, under the casting conditions corresponding to the actual machine test, by setting the value of the core height ratio H1/H2 to about 1.00 to about 2.00, the casting speed was It has been found that even when the speed is increased to 2.2 m/min, it becomes possible to secure the quality of the ingot which is superior to the conventional continuous casting method at a lower speed.

  In Example 4, an actual machine test was performed on a continuous casting method for high-strength steel. In the actual machine test, the electromagnetic force generator 170 according to the present embodiment described with reference to FIGS. 2 to 5 is installed in the continuous casting machine which is actually used for the operation, and the continuous casting machine 1 is used. The high-strength steel was continuously cast by changing the electromagnetic stirring strength and the electromagnetic brake strength. Here, the mold is a copper water-cooled type (water-cooled copper mold) and has a rectangular cross section with a height (the length from the upper end to the lower end of the mold) of 900 mm. The type of the continuous casting machine 1 was a vertical bending type. The mass% of C is 0.12 to 0.17 mass%, the mass% of Si is 0.1 to 0.2 mass%, the mass% of Mn is 0.5 to 0.8 mass%, and the mass% of P is 0.02-0.025%, S mass% is 0.007-0.009 mass%, N mass% is 0.002-0.0035 mass%, Ti mass% is 0.01%-0. The molten steel used was 0.02 mass%, Nb mass% was 0.01 to 0.02 mass%, and the balance was iron and unavoidable impurities. The specific water amount of the secondary cooling was set to 1.5 to 2.5 L/kg-steel. The amount of argon gas blown into the immersion nozzle was 7 NL/min. The upper end of the electromagnetic stirring core 152 was arranged at a position 100 mm from the upper end of the mold 110, and the height H1 of the electromagnetic stirring core 152 was set to 250 mm. The upper end of the electromagnetic brake core 162 was arranged at a position of 500 mm from the upper end of the mold 110, and the height H2 of the electromagnetic brake core 162 was 200 mm. Therefore, the core height ratio H1/H2 is 250/200=1.25, which satisfies the condition of Expression (101).

  Furthermore, the slab after continuous casting was visually observed in the cold, and the presence or absence of cracks on the surface of the slab was investigated. If there is no crack, ◎, if there is a minor crack that does not cause a flaw during rolling, ○, if there is a crack that causes a flaw during rolling but is maintainable, △; Classified as.

(Invention Example 1)
Invention Example 1 is the basis of the following invention examples and comparative examples. In Inventive Example 1, the cast piece thickness and cast piece width were set to 250 mm thickness and 1250 mm width, which are general sizes in a continuous casting machine for thin plates. The casting speed was set to 1.5 m/min when fluctuations in the molten metal surface began to affect the surface cracks of the slab. The electromagnetic stirring strength and the electromagnetic brake strength were set on the basis of the flow analysis (the numerical analysis simulation shown in Example 1; the conditions were the same as in Example 1) performed in advance, and fluctuations in the molten metal level and temperature in the mold were determined. The electromagnetic stirring strength of 0.1 T and the electromagnetic brake strength of 0.15 T, which are the conditions to be small, were set. The number of electromagnetic brake cores (that is, the number of magnetic poles facing the long side surface) is two (two per one side of the long side surface, that is, two pairs on both sides) that can effectively reduce the static magnetic field strength near the discharge hole. ). All of these conditions were within the range of the present embodiment, and there was no surface crack of the slab.

(Invention Example 2)
In Invention Example 2, the slab width was made larger than that in Invention Example 1, and the electromagnetic stirring and the electromagnetic brake strength were the same as in Invention Example 1. The condition of Inventive Example 2 is a condition in which the fluctuation of the molten metal surface becomes large as the throughput increases, but there was no surface cracking of the cast slab.

(Invention Example 3)
In Invention Example 3, the electromagnetic stirring strength and the electromagnetic brake strength were both increased within the range of the present embodiment as compared with Invention Example 1. In Invention Example 3, the fluctuations in the molten metal surface due to electromagnetic stirring and the fluctuations in temperature due to the electromagnetic brake were slightly larger than those in Invention Example 1, and slight cracks were observed, but at a level that does not affect rolling.

(Invention Example 4)
In Invention Example 4, the electromagnetic stirring strength and the electromagnetic brake strength were both reduced within the range of the present embodiment as compared with Invention Example 1. In Invention Example 4, the fluctuation of the molten metal surface was slightly increased due to the influence of the discharge flow and slight cracks were seen, but the level was not affected by rolling.

(Invention Example 5)
Inventive Example 5 has a higher casting speed than Inventive Example 1. Further, the electromagnetic stirring strength and the electromagnetic brake strength were increased within the range of this embodiment. Although the throughput was increased in Inventive Example 5, the level fluctuation and the temperature fluctuation were suppressed by increasing the electromagnetic stirring strength and the electromagnetic brake strength, and no surface crack was observed.

(Invention Example 6)
In Invention Example 6, the casting speed and the slab width were increased as compared with Invention Example 1. Further, the electromagnetic stirring strength and the electromagnetic brake strength were increased within the range of this embodiment. In the invention example 6, the throughput is increased, but since the electromagnetic stirring strength and the electromagnetic brake strength are high as in the invention example 5, the fluctuation of the molten metal surface and the fluctuation of the temperature are suppressed, and the surface crack is observed. There wasn't.

(Invention Example 7)
In Invention Example 7, the casting speed was further increased as compared with Invention Example 1. In Inventive Example 7, since the throughput greatly increased, the influence of the melt level fluctuation due to the discharge flow was slightly present, but the surface cracking was slight and the level did not affect the rolling.

(Invention Example 8)
In Invention Example 8, the width of the slab was larger than that of Invention Example 1, and the casting speed was further increased. In Inventive Example 8, since the throughput was greatly increased, slight cracks were seen due to the influence of the melt level fluctuation due to the discharge flow, as in Inventive Example 7, but the level was not affected by rolling.

(Comparative Example 1)
In Comparative Example 1, only the electromagnetic stirring device 150 was installed in the mold. That is, the electromagnetic brake device 160 was not installed in the mold. In Comparative Example 1, the fluctuation of the molten metal surface due to the discharge flow was large and many cracks were generated.

(Comparative example 2)
In Comparative Example 2, the electromagnetic stirrer 150 and the electromagnetic brake device 160 were installed in the mold 110. However, the electromagnetic brake core 162 is a pair on both sides. That is, the unipolar electromagnetic brake core 162 is installed on each long side surface. In Comparative Example 2, since the magnetic field in the central portion in the width direction was large, the discharge flow was excessively braked and an upward flow was formed in the central portion in the width direction. As a result, the fluctuation of the molten metal surface became large and cracking occurred.

(Comparative example 3)
In Comparative Example 3, the electromagnetic stirrer 150 and the electromagnetic brake device 160 were installed in the mold. However, the electromagnetic stirring strength was set to 0.04T, which is less than the range of this embodiment. Therefore, the stirring force was insufficient and the temperature fluctuation was not sufficiently suppressed, so that cracking occurred.

(Comparative example 4)
In Comparative Example 4, the electromagnetic stirring device 150 and the electromagnetic braking device 160 were installed in the mold, and the electromagnetic stirring strength was set to a value within the range of this embodiment. However, the electromagnetic brake strength was set to 0.08T, which is smaller than the range of this embodiment. In Comparative Example 4, since the electromagnetic brake strength was smaller than the range of this embodiment, braking of the discharge flow was insufficient, and many surface cracks occurred due to fluctuations in the molten metal level.

(Comparative example 5)
In Comparative Example 5, the electromagnetic stirring strength was set to 0.3 T, which is higher than the range of this embodiment. In Comparative Example 5, as a result of the stirring flow being too strong and the fluctuation in the molten metal surface becoming large, many cracks occurred.

(Comparative example 6)
In Comparative Example 6, the electromagnetic stirring strength was 0.25T, which was lower than that of Comparative Example 5, but it was still higher than the range of this embodiment. For this reason, the stirring flow was rather strong and surface cracking occurred due to fluctuations in the molten metal level.

(Comparative Example 7)
In Comparative Example 7, the electromagnetic brake strength was set to 0.5T, which is larger than the range of this embodiment. In Comparative Example 7, as in Comparative Example 2, the discharge flow was excessively damped, and an upward flow was formed at the center in the width direction. As a result, the fluctuation of the molten metal surface became large and cracking occurred.

  The results are summarized in Table 4. Inventive Examples 1 to 8 had good casting quality, but Comparative Examples 1 to 7 had problems in casting quality.

(4. Supplement)
Although the preferred embodiments of the present invention have been described above in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

1 Continuous casting machine 2 Molten steel 3 Slab 3a Solidified shell 3b Unsolidified part 4 Ladle 5 Tundish 6 Immersion nozzle 10 Mold equipment 110 Mold 111 Long side mold plate 112 Short side mold plate 121, 122, 123 Backup plate 130 Upper water box 140 Lower Water Box 150 Electromagnetic Stirring Device 151 Case 152 Electromagnetic Stirring Core 153 Coil 160 Electromagnetic Brake Device 161 Case 162 Electromagnetic Brake Core 163 Coil 164 End 165 Connection Part 170 Electromagnetic Force Generator

Claims (4)

C: 0.05% by mass or more and 0.5% by mass or less, Si: 0.005% by mass or more and 2.0% by mass or less, Mn: 0.3% by mass or more and 2.5% by mass or less, P: 0. A continuous casting method for continuously casting a molten steel containing an element group consisting of 01 mass% or more and 0.05 mass% or less, S: 0.015 mass% or less, and N: 0.005 mass% or less,
While applying an AC magnetic field to the molten steel in the mold using the electromagnetic stirring core installed on the outside of the long side of the upper part of the mold, it is installed on the outside of the long side of the lower part of the mold, and a plurality of magnetic poles are provided on the long side. Applying a static magnetic field to the molten steel using opposing electromagnetic brake cores,
The magnetic flux density of the AC magnetic field by the electromagnetic stirring core is 0.05T or more and 0.2T or less, and the magnetic flux density of the static magnetic field by the electromagnetic brake core is 0.1T or more and 0.4T or less,
A continuous casting method, wherein an immersion nozzle is arranged at a position facing a space between the plurality of magnetic poles.   The molten steel further contains, as optional components, Ti: 0.003 mass% or more and 0.2 mass% or less, Nb: 0.003 mass% or more and 0.1 mass% or less, V: 0.002 mass% or more and 0.1% or less. 1 mass% or less, Cr: 0.1 mass% or more and 0.8 mass% or less, Cu: 0.1 mass% or more and 0.6 mass% or less, Mo: 0.05 mass% or more and 0.6 mass% or less, B: The continuous casting method according to claim 1, further comprising at least one selected from an element group consisting of 0.0004 mass% or more and 0.005 mass% or less. 3. The continuous casting method according to claim 1, wherein the height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core satisfy the relationship represented by the following mathematical expression (101).

The height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core satisfy the relationship shown in the following mathematical formula (103), The continuous according to any one of claims 1 to 3, Casting method.

Images