JP7256386B2 - Continuous casting method - Google Patents

Description

The present invention relates to a continuous casting method.

In continuous casting, molten steel temporarily stored in a tundish is poured into the mold from above through an immersion nozzle, where the outer peripheral surface is cooled and solidified, and the cast slab is pulled out from the bottom of the mold for continuous casting. is done. The solidified portion of the outer peripheral surface of the slab is called a solidified shell.

Here, the molten steel contains gas bubbles of inert gas (for example, Ar gas) supplied together with the molten steel to prevent clogging of the discharge hole of the immersion nozzle, and non-metallic inclusions. If these impurities remain in the cast slab, it will cause the quality of the product to deteriorate. Since the specific gravity of these impurities is generally smaller than that of molten steel, they often float and are removed in molten steel during continuous casting. Therefore, if the casting speed is increased (that is, the throughput is increased), this impurity will not be sufficiently floated off, and the quality of the slab will tend to deteriorate. Thus, in continuous casting, there is a trade-off relationship between productivity and slab quality. There is a relationship that reduces sexuality.

By the way, high-alloy steel products produced from cast slabs of molten steel tend to develop surface cracks in the slabs during bending or straightening of the slabs in a vertical bending type continuous casting machine. For example, electrical steel, which is a type of high-alloy steel, is used in a variety of applications, such as transformers and motors. Si and Al are added to such an electrical steel in a larger amount than normal steel in order to reduce iron loss of the electrical steel. If a large amount of these elements are added to the steel material, the high temperature embrittlement of the steel material (slab) becomes significant.

The high-temperature embrittlement of the slab becomes remarkable when the surface temperature of the slab is lowered. Therefore, as a general countermeasure against surface cracks, a method of reducing the amount of secondary cooling spray water during casting is known. According to this method, the surface temperature of the slab can be increased during casting, so surface cracks can be reduced.

However, as described above, a large amount of Si may be added to cast slabs for high-alloy steel. Since Si is also a ferrite former, the slab contains a large amount of ferrite, which has a lower strength than austenite. This reduces the strength of the solidified shell. Therefore, when the amount of secondary cooling spray water is reduced, bulging due to the static pressure of molten steel occurs more remarkably than in normal steel. Here, bulging is roughly a phenomenon in which a slab transported in a continuous casting machine expands between rolls. Due to such expansion of the slab, the molten steel surface fluctuates greatly, which leads to deterioration of the quality of the slab.

Deterioration of slab quality due to fluctuations in the molten steel level will be described in more detail. Depression tends to occur in the slab in the mold due to increased fluctuations in the molten steel level. Here, a depression is roughly a fine dent which arises in the surface of a slab. Furthermore, fluctuations in the molten metal surface tend to disturb the oscillation marks. Here, the oscillation mark is roughly a pattern formed on the surface of the slab due to the vibration of the mold (the mold often oscillates in a continuous casting machine). Distortion of the oscillation marks makes it easier for the above-described depression to occur.

When depression occurs in the slab in the mold, the depressed portion is less likely to come into contact with the mold, resulting in a higher slab temperature. As a result, the crystal grains on the surface of the cast slab tend to coarsen in the mold, increasing the susceptibility to cracking. That is, surface cracks are likely to occur in the slab within the mold. In addition, the oscillation marks may be formed excessively deep, and in this case also surface cracks are likely to occur in the cast slab. Furthermore, uneven patterns called ridging tend to occur on the surface of the slab. Therefore, the quality of the slab deteriorates.

Therefore, conventionally, in addition to reducing the amount of secondary cooling spray water described above, the casting speed is suppressed to suppress fluctuations in the molten metal surface. Furthermore, cracks in the cast slab are dealt with by cutting the portion where surface cracks have occurred.

Japanese Patent No. 3391660 JP-A-2002-153947

However, since these countermeasures reduce the casting speed, the productivity of the slab is reduced. Furthermore, cutting alone could not sufficiently remove surface cracks. For this reason, the quality of the slab could not be sufficiently improved. In view of these circumstances, there has been a demand for a technique for further improving productivity while ensuring the quality of slabs in continuous casting of slabs for high alloy steel.

As described above, surface cracking and grain coarsening of the slab in the mold are considered to be affected by non-uniform heat removal behavior in the mold due to disturbance of oscillation marks and depression. In other words, the depressed portion is less likely to come into contact with the mold, so heat is less likely to be removed, and the slab temperature increases. As a method for suppressing surface cracks and coarsening of crystal grains of the slab, in addition to the above-described reduction in casting speed, changing the oscillation conditions, changing the powder, and the like are conceivable. However, changing the oscillation conditions can lead to breakouts and should be done more carefully. Furthermore, the preferable conditions vary depending on the composition of the steel material and the like. For these reasons, it is very difficult to suppress the surface cracking of the slab and the coarsening of the crystal grains due to fluctuations in the oscillation conditions. In addition to the same phenomenon as changing the oscillation conditions, changing the powder may cause deterioration in quality due to entrainment of the powder in the cast slab depending on how the composition is selected. Therefore, both methods require a lot of time and effort.

On the other hand, surface cracks and grain coarsening of slabs are primarily caused by an increase in melt surface fluctuation. Therefore, if it is possible to suppress fluctuations in the molten steel level, it is thought that the problems of surface cracks in cast slabs and coarsening of crystal grains can be solved. Therefore, the present inventors have conceived of using both an electromagnetic stirrer and an electromagnetic brake to suppress fluctuations in the molten metal surface in the mold. In this specification, a group of members around the mold including the mold and the electromagnetic force generator is also referred to as mold equipment for convenience.

Here, the electromagnetic brake device is a device that suppresses the flow of the molten steel by applying a static magnetic field to the molten steel to generate a braking force in the molten steel. On the other hand, the electromagnetic stirrer applies a dynamic magnetic field to the molten steel to generate an electromagnetic force called Lorentz force in the molten steel, giving the molten steel a swirling flow pattern in the horizontal plane of the mold. It is a device that

An electromagnetic brake device is generally provided so as to generate a braking force in molten steel that weakens the force of a discharge flow ejected from an immersion nozzle. Here, the discharge flow from the submerged nozzle collides with the inner wall of the mold, so that there is an upward flow directed upward (that is, the direction in which the molten steel surface exists) and a downward flow (that is, the direction in which the slab is pulled out). ) to form a downward flow. Therefore, by weakening the momentum of the discharge flow by the electromagnetic brake device, the momentum of the upward flow is weakened, and fluctuations in the molten steel surface can be suppressed. Furthermore, the ascending flow becomes a flow in the width direction (for example, in the direction of the long side or the short side) near the meniscus, and this flow in the width direction (that is, reverse flow) may disturb the stirring flow (swirling flow) by the electromagnetic stirrer. There is In other words, there is a possibility that the electromagnetically stirred flow will be blocked and the effect of the electromagnetically stirred will be counteracted. Since the electromagnetic brake device can weaken the force of such upward flow, the effect of electromagnetic stirring can be exhibited more effectively. In addition, since the impetus with which the discharge flow collides with the solidified shell is also weakened, an effect of suppressing breakout due to remelting of the solidified shell can be exhibited. Thus, the electromagnetic brake device is often used for the purpose of high-speed stable casting. In other words, by using the electromagnetic brake device, it can be expected that fluctuations in the surface of the molten steel can be suppressed even if the momentum of the discharge flow is increased. Furthermore, according to the electromagnetic brake device, since the flow velocity of the downward flow formed by the discharge flow is suppressed, the floatation separation of impurities in the molten steel is promoted, and the internal quality of the slab (hereinafter also referred to as internal quality) is improved. It is possible to obtain an improvement effect.

On the other hand, a disadvantage of the electromagnetic brake system is that the flow velocity of the molten steel at the interface of the solidified shell becomes low, so that impurities may be captured in the solidified shell, degrading the surface quality. In addition, since it becomes difficult for the ascending flow formed by the discharge flow to reach the surface of the molten steel, it is feared that skinning may occur due to a decrease in the temperature of the surface of the molten steel, which may cause internal defects.

The electromagnetic stirrer 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, thereby suppressing the above-mentioned impurities such as Ar gas bubbles and non-metallic inclusions from being captured in the solidified shell, thereby improving the surface quality of the slab. can be improved. On the other hand, a 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 are generated in the same manner as the discharge flow from the submerged nozzle described above. There is a case where the internal quality of the cast slab is deteriorated by entraining powder and the downward flow sweeping away impurities to the lower side of the mold.

By the way, if the electromagnetic stirring device and the electromagnetic braking device are simply installed in the continuous casting machine and operated, the effect is not obtained by the amount of operation. Furthermore, in the case of having equipment for both and applying them simultaneously, the effects of both may not be added, but rather may cancel each other out. In particular, since the conventional electromagnetic brake device has a single magnetic pole, the magnetic flux density is maximized at the central portion in the width direction of the installed core. For this reason, when the magnetic flux strength is increased, an extreme braking force acts in the vicinity of the discharge hole of the submerged nozzle, which may even increase the fluctuation of the molten metal surface in the mold.

Patent Documents 1 and 2 disclose techniques for installing only an electromagnetic stirrer or only an electromagnetic brake in a continuous casting machine. However, these techniques cannot sufficiently solve the problems described above. Specifically, in Patent Document 1, when continuously casting a unidirectional electromagnetic steel slab, a mold with an electromagnetic stirrer built into the long side of the mold is used to electromagnetically stir the molten steel in the mold. Techniques for reducing the depth of the ration mark to 1.5-2 mm or less have been disclosed. This technology reduces the occurrence of edge cracks during hot rolling. However, under these conditions, cracks still occur depending on the slab, so it can be said that the conditions are insufficient. In addition, since only an electromagnetic stirrer is used, it is thought that as the casting speed increases, the molten metal surface fluctuates due to the reversal of the discharge flow, deepening the oscillation marks and increasing the number of surface cracks.

Patent Literature 2 describes a technique of installing an electromagnetic brake device in a continuous casting machine for the purpose of suppressing bulging. However, in this technique, since no electromagnetic stirrer is installed, there may arise problems such as trapping of impurities in the solidified shell and generation of internal defects due to skinning. In addition, since the magnetic pole is a single pole in this technique, when the magnetic flux strength is increased, the magnetic flux density becomes excessive at the widthwise central portion of the core, and an extreme braking force acts in the vicinity of the submerged nozzle discharge hole. That is, an excessive upward flow is generated. In some cases, such an upward flow promotes fluctuations in the molten metal surface in the mold. Moreover, such an upward flow may impede the electromagnetically stirred flow.

The present invention has been made in view of the above problems, and an object of the present invention is to stably produce slabs even when the productivity of slabs for high alloy steel is improved. To provide a new and improved continuous casting method capable of ensuring quality.

In order to solve the above problems, according to one aspect of the present invention, C: 0.005% by mass or more and 0.1% by mass or less, Mn: 0.05% by mass or more and 3.0% by mass or less, Si: 0 A continuous casting method for continuously casting molten steel containing an element group consisting of 4% by mass or more and 4.0% by mass or less and Al: 0.01% by mass or more and 3.0% by mass or less, wherein the long side surface of the upper part of the mold While applying an alternating magnetic field to the molten steel in the mold using an electromagnetic stirring core installed outside, an electromagnetic brake core installed outside the long side surface of the lower mold and having multiple magnetic poles facing the long side surface is used. A static magnetic field is applied to the molten steel, the magnetic flux density of the alternating magnetic field by the electromagnetic stirring core is 0.05 T or more and 0.25 T or less, the magnetic flux density of the static magnetic field by the electromagnetic brake core is 0.1 T or more and 0.4 T or less, and the tundish An immersion nozzle that extends downward from the lower end of the mold toward the mold and is immersed in the molten steel in the mold is arranged in a position facing the space between the plurality of magnetic poles. An electromagnetic force is applied to the molten steel in a direction to suppress the flow of molten steel from the discharge hole, and the height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core satisfy the relationship shown in the following formula (101). A continuous casting method is provided, characterized in that :

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 formula (103).

As described above, according to the present invention, in continuous casting, it is possible to ensure the quality of slabs even when the productivity of slabs for high alloy steel is improved. Specifically, it is possible to suppress fluctuations in the molten steel surface during continuous casting. As a result, it is possible to suppress disturbance and depression of the oscillation marks caused by fluctuations in the molten steel surface, and it is possible to suppress surface cracking and coarsening of crystal grains of the slab in the mold. Therefore, the quality of the slab can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is a sectional side view which shows roughly one structural example of the continuous casting machine which concerns on this embodiment. FIG. 2 is a cross-sectional view along the YZ plane of the mold facility according to the present embodiment; FIG. 3 is a cross-sectional view of the mold facility taken along the line AA shown in FIG. 2; FIG. 4 is a cross-sectional view of the mold facility taken along the line BB shown in FIG. 3; FIG. 4 is a cross-sectional view of the mold facility along the CC cross section shown in FIG. 3; FIG. 4 is a diagram for explaining the direction of electromagnetic force applied to molten steel by an electromagnetic brake device; FIG. 4 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 is 4 mm or 5 mm. FIG. 5 is a graph showing the relationship between the core height ratio H1/H2 and the pinhole index when the casting speed is 1.4 m/min, obtained by numerical analysis simulation. FIG. 4 is a graph showing the relationship between the core height ratio H1/H2 and the pinhole index when the casting speed is 2.0 m/min, obtained by numerical analysis simulation. FIG. 4 is a graph showing the relationship between casting speed and internal quality index obtained by numerical analysis simulation.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

In addition, in each drawing shown in this specification, the sizes 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 necessarily represent the actual size relationship between the members accurately.

In continuous casting, the inventors of the present invention stabilize the flow of molten steel in the mold by using mold equipment that combines an electromagnetic brake device and an electromagnetic stirring device, thereby improving productivity while ensuring the quality of slabs. I tried to let However, these devices are not simply installed to obtain the advantages of both devices. For example, as described above, an excessive upward flow generated by an electromagnetic braking device may impede the electromagnetic stirring flow, and these devices also have the effect of canceling out each other's effects. Therefore, in continuous casting using both an electromagnetic brake device and an electromagnetic stirrer, there are many cases in which the slab quality (surface quality and internal quality) is worse than when these devices are used alone.

Therefore, the inventors repeatedly conducted numerical analysis simulations and actual machine tests, and as a result of earnest examination, the effect of improving the quality of slabs was more effectively exhibited in continuous casting using an electromagnetic brake device and an electromagnetic stirring device. In order to make it possible to ensure the quality of slabs even when productivity is improved, it is important to appropriately define the configuration and installation position of these devices. reached. Furthermore, when performing continuous casting of slabs for high-alloy steel, there is a preferred range for the magnetic flux density of the electromagnetic agitator and the electromagnetic brake. The present embodiment will be described below.

(1. Configuration 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 one configuration example of a continuous casting machine according to this embodiment.

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

The ladle 4 is a movable container for conveying the molten steel 2 to the tundish 5 from the outside. A ladle 4 is arranged above a tundish 5 and molten steel 2 in the ladle 4 is supplied to the tundish 5 . The tundish 5 is arranged above the mold 110 to store the molten steel 2 and remove 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 inside the mold 110 . The immersion nozzle 6 continuously supplies the molten steel 2 from which inclusions have been removed in the tundish 5 into the mold 110 .

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

In the following description, the vertical direction (that is, the direction in which the slab 3 is pulled out from the mold 110) is also referred to as the Z-axis direction. In addition, two mutually orthogonal directions in a plane (horizontal plane) perpendicular to the Z-axis direction are also referred to as the X-axis direction and the Y-axis direction, respectively. Further, the X-axis direction is defined as a direction parallel to the long sides of the mold 110 in the horizontal plane, and the Y-axis direction is defined as the direction parallel to the short sides of the mold 110 in the horizontal plane. In addition, 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 called width.

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

The secondary cooling device 7 is provided in the secondary cooling zone 9 below the mold 110 and cools the cast slab 3 pulled out from the lower end of the mold 110 while supporting and transporting it. 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) that spray the

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 supporting and conveying means for supporting and conveying the slab 3 . By supporting the slab 3 from both sides in the thickness direction with the support rolls, it is possible to prevent breakout and bulging of the slab 3 during solidification in the secondary cooling zone 9 . However, in this embodiment, the slab for high alloy steel is continuously cast. For this reason, high-temperature embrittlement of the cast slab becomes significant. In order to suppress surface cracks caused by such high-temperature embrittlement, the amount of secondary cooling spray water may be reduced. In this case, as described above, there is a concern that bulging may occur. Such bulging may cause fluctuations in the molten metal surface. However, in this embodiment, the electromagnetic stirring device and the electromagnetic braking device are used together, and the magnetic flux density of each device is appropriately adjusted. Furthermore, in the electromagnetic brake device, the magnetic flux density in the region near the center in the width direction (that is, the X-axis direction) of the mold 110 can be made lower than the magnetic flux density in other regions. As a result, it is possible to suppress fluctuations in the molten steel level, and as a result, it is possible to improve the quality of the slab. The details of the electromagnetic stirring device and the electromagnetic brake device will be described later.

Support rolls 11 , pinch rolls 12 , and segment rolls 13 that are support rolls form a conveying path (pass line) for the slab 3 in the secondary cooling zone 9 . This pass line is vertical immediately below the mold 110, then curves into a curve, and finally becomes horizontal, as shown in FIG. In the secondary cooling zone 9, a portion where the pass line is vertical is called a vertical portion 9A, a curved portion is called a curved portion 9B, and a horizontal portion is called a horizontal portion 9C. A 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 also be applied to other various types of continuous casting machines such as curved type or vertical type.

The support roll 11 is a non-driven roll provided in the vertical portion 9A directly below the mold 110, and supports the cast slab 3 immediately after being pulled out from the mold 110. As shown in FIG. Since the slab 3 immediately after being pulled out from the mold 110 has a thin solidified shell 3a, it needs to be supported at relatively short intervals (roll pitch) in order to prevent breakout and bulging. Therefore, as the support roll 11, it is desirable to use a small-diameter roll capable of shortening the roll pitch. In the example shown in FIG. 1, three pairs of support rolls 11 made of small-diameter rolls are provided at a relatively narrow roll pitch on both sides of the cast slab 3 in the vertical portion 9A.

The pinch rolls 12 are drive rolls that are rotated by drive means such as a motor, and have a function of pulling out the cast slab 3 from the mold 110 . The pinch rolls 12 are arranged at appropriate positions in the vertical section 9A, the curved section 9B and the horizontal section 9C. The cast slab 3 is pulled out from the mold 110 by the force transmitted from the pinch rolls 12 and 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 rolls 13 (also referred to as guide rolls) are non-driven rolls provided on the curved portion 9B and the horizontal portion 9C, and support and guide the slab 3 along the pass line. The segment roll 13 is positioned on the pass line and on either the F surface (fixed surface, lower left surface in FIG. 1) or the L surface (loose surface, upper right surface in FIG. 1) of the slab 3. Depending on whether they are provided, they may be arranged with different roll diameters and roll pitches.

The slab cutting machine 8 is arranged at the terminal 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 slab 14 in the form of a thick plate is transported to equipment for the next process by a table roll 15 .

The overall configuration of the continuous casting machine 1 according to the present embodiment has been described above with reference to FIG. Note that, in the present embodiment, the above-described electromagnetic force generator is installed in the mold 110, and continuous casting is performed using the electromagnetic force generator. 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 the illustrated one, and any configuration may be used as the continuous casting machine 1 .

(2. Electromagnetic force generator)
(2-1. Configuration of electromagnetic force generator)
2 to 5, the configuration of the electromagnetic force generator installed with respect to the mold 110 described above will be described in detail. 2 to 5 are diagrams showing one configuration example of the mold facility according to the present embodiment.

FIG. 2 is a cross-sectional view along the YZ plane of the mold facility 10 according to this embodiment. FIG. 3 is a cross-sectional view of the mold facility 10 taken along 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 facility 10 taken along line CC shown in FIG. In addition, since the mold facility 10 has a symmetrical configuration with respect to the center of the mold 110 in the Y-axis direction, only the part corresponding to one of the long-side mold plates 111 is shown in FIGS. showing. 2, 4 and 5 also show the molten steel 2 in the mold 110 for easy understanding.

Referring to FIGS. 2 to 5, the mold facility 10 according to the present embodiment has two mold plates 111 on the outer surface (that is, outside the long side surface) of the mold 110 via the backup plate 121. Water boxes 130 and 140 and an electromagnetic force generator 170 are installed.

As described above, the mold 110 is assembled such that the pair of long-side mold plates 111 sandwiches 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 such an example, and the mold plates 111 and 112 may be made of various materials generally used as molds for continuous casting machines.

Here, in this embodiment, continuous casting of steel slabs is targeted, and the 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, thickness (that is, , length in the Y-axis direction) is about 150 to 300 mm, or about 200 to 270 mm. That is, the mold plates 111 and 112 also have sizes corresponding to the size of the slab. 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 (eg, 800 to 2300 mm), and the short-side mold plate 112 has a thickness of the slab 3 (eg, 200 to 300 mm). ) in the Y-axis direction.

Further, although details will be described later, in the present embodiment, in order to more effectively obtain the effect of improving the quality of the slab 3 by the electromagnetic force generator 170, the length in the Z-axis direction is set to be as long as possible. A mold 110 is constructed. In general, when the molten steel 2 solidifies in the mold 110, the slab 3 separates 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 maximum length of the mold 110 is limited to about 1000 mm from the surface of the molten steel. In this 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. The mold plates 111 and 112 are formed as follows.

The backup plates 121 and 122 are made of stainless steel, for example, and are provided so as to cover the outer surfaces of the mold plates 111 and 112 of the mold 110 in order to reinforce the mold plates 111 and 112 . Hereinafter, for distinction, the backup plate 121 provided on the outer surface of the long-side mold 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 mold plate 112 is referred to as the short side plate. It is also called 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, a portion of the long-side backup plate 121 facing an end portion 164 of an iron core 162 (hereinafter also referred to as an electromagnetic brake core 162) of the electromagnetic brake device 160 described later has magnetic flux of the electromagnetic brake device 160. Soft iron 124 of a magnetic material is embedded in order to ensure density.

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, an electromagnetic force generator 170 is installed between the pair of backup plates 123. FIG. In this way, 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 electromagnetic force to a desired range of the molten steel 2 in the mold 110 . Hereinafter, the backup plate 123 is also referred to as a width direction backup plate 123 for distinction. The width direction backup plate 123 is also made of stainless steel, for example, like the backup plates 121 and 122 .

Water boxes 130 and 140 store cooling water for cooling mold 110 . In this embodiment, as shown in the figure, one water box 130 is installed in a region at a predetermined distance from the upper end of the long side mold plate 111, and the other water box 140 is installed in a region at a predetermined distance from the lower end of the long side mold plate 111. to be installed. By providing the water boxes 130 and 140 above and below the mold 110 in this manner, it is possible to secure a space between the water boxes 130 and 140 for installing the electromagnetic force generator 170 . Hereinafter, for distinction, the water box 130 provided above the long side mold plate 111 is also referred to as the upper water box 130, and the water box 140 provided below the long side mold plate 111 is also referred to as the lower water box 140.

Inside the long-side mold plate 111 or between the long-side mold plate 111 and the long-side backup plate 121, water channels (not shown) through which cooling water passes are formed. The waterway extends to water boxes 130 and 140 . A pump (not shown) causes cooling water to flow through the channel from one water box 130, 140 to the other water box 130, 140 (for example, from the lower water box 140 to the upper water box 130). Thereby, the long-side mold plate 111 is cooled, and the molten steel 2 inside the mold 110 is cooled through the long-side mold plate 111 . Although not shown, the short side mold plate 112 is similarly provided with a water box and a water channel, and the short side mold plate 112 is cooled by flowing cooling water.

The electromagnetic force generator 170 includes an electromagnetic stirrer 150 and an electromagnetic brake device 160 . As shown, the electromagnetic stirring device 150 and the electromagnetic braking device 160 are installed in the space between the water boxes 130,140. In the space, the electromagnetic stirring device 150 is installed above and the electromagnetic braking device 160 is installed below. In other words, the electromagnetic stirring device 150 is installed outside the long side of the upper part of the mold, and the electromagnetic brake device 160 is installed outside the long side of the lower part of the mold. The height 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 (2-2. Details of the installation position of the electromagnetic force generation device ) will be described in detail.

The electromagnetic stirrer 150 applies an electromagnetic force to the molten steel 2 in the mold 110 by applying a dynamic magnetic field. The electromagnetic stirrer 150 is driven so as to apply to the molten steel 2 an electromagnetic force in the width direction (that is, the X-axis direction) of the long-side mold plate 111 on which it is installed. In FIG. 4 , the direction of the electromagnetic force applied to the molten steel 2 by the electromagnetic stirring device 150 is schematically indicated by bold arrows. Here, the electromagnetic stirrer 150 provided on the long-side mold plate 111 not shown (that is, the long-side mold plate 111 facing the long-side mold plate 111 shown in the drawing) is installed on the long side 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 manner, the pair of electromagnetic stirring devices 150 are driven to generate a stirring flow (swirling flow) in the horizontal plane. According to the electromagnetic stirrer 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 is obtained that suppresses trapping of bubbles and inclusions in the solidified shell 3a. The surface quality of the piece 3 can be improved.

A detailed configuration of the electromagnetic stirring device 150 will be described. The electromagnetic stirring device 150 includes a case 151, an iron 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 stirrer 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 . can be determined as appropriate. 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. It is determined to be larger than the width of the slab 3 so as to obtain. For example, W4 is approximately 1800 mm to 2500 mm. 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. Therefore, the material of the case 151 is, for example, non-magnetic stainless steel or FRP (Fiber Reinforced Plastics). ), etc., which are non-magnetic and whose strength can be secured.

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 (that is, the X-axis direction) of the long-side mold plate 111. be done. The electromagnetic stirring core 152 is formed by laminating electromagnetic steel sheets, for example.

A coil 153 is formed by winding a conductive wire around the electromagnetic stirring core 152 with the X-axis direction as the central axis. As the conducting wire, for example, a copper wire having a cross section of 10 mm×10 mm and a cooling water channel with a diameter of about 5 mm is used. When current is applied, the conducting wire is cooled using the cooling water passage. The conducting wire has its surface layer insulated with insulating paper or the like, and can be wound in layers. For example, one coil 153 is formed by winding the conductive wire in two to four layers. Coils 153 having a similar configuration are arranged in parallel at predetermined intervals 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 adjacent coils 153 such that the phases of currents in the adjacent coils 153 are appropriately shifted, an electromagnetic force can be applied to the molten steel 2 to generate a churning flow. The driving of the AC power supply can be appropriately controlled by a control device (not shown) consisting of a processor or the like operating according to a predetermined program. The amount of current applied to each of the coils 153, the timing of applying current to each of the coils 153, and the like are appropriately controlled by the controller, and the strength of the electromagnetic force applied to the molten steel 2 can be controlled. As a method for driving this AC power source, various known methods used in general electromagnetic stirrers 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 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 is positioned appropriately with respect to the molten steel 2. can be determined as appropriate. For example, W1 is about 1800 mm.

The electromagnetic brake device 160 applies an electromagnetic force to the molten steel 2 in the mold 110 by applying a static magnetic field to the molten steel 2 . 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. As shown in FIG. FIG. 6 schematically shows a cross-section of the configuration near the mold 110 in the XZ plane. In addition, in FIG. 6, positions of the electromagnetic stirring core 152 and an end portion 164 of an electromagnetic brake core 162, which will be described later, are schematically indicated by dashed lines.

As shown in FIG. 6 , the submerged nozzle 6 may be provided with a pair of discharge holes at positions facing the short-side mold plate 112 . Molten steel 2 is discharged into the mold 110 from these discharge holes. The discharged stream of molten steel 2 advances toward the short side and collides with the shell formed on the short side. Thereafter, the discharged flow forms an ascending flow directed upward (that is, the direction in which the surface of the molten steel exists) and a downward flow directed downward (that is, the direction in which the slab is pulled out). The electromagnetic brake device 160 is driven so as to apply an electromagnetic force to the molten steel 2 in a direction to suppress the flow (discharge flow) of the molten steel 2 from the discharge hole of the submerged nozzle 6 . In FIG. 6, the direction of the discharge flow is simulatively indicated by thin arrows, and the direction of the electromagnetic force applied to the molten steel 2 by the electromagnetic brake device 160 is simulatively indicated by thick arrows. According to the electromagnetic brake device 160, by generating an electromagnetic force in the direction of suppressing such a discharge flow, the downward flow is suppressed, and the effect of promoting floating separation of air bubbles and inclusions is obtained. can improve the inner quality of Furthermore, since the momentum of the upward flow caused by the discharge flow is weakened, fluctuations in the surface of the molten steel are suppressed. Therefore, it is possible to suppress disturbance and depression of oscillation marks caused by fluctuations in the molten metal surface, and it is possible to suppress surface cracking and coarsening of crystal grains of the cast slab in the mold. Therefore, the quality of the slab can be improved.

A detailed configuration of the electromagnetic brake device 160 will be described. The electromagnetic brake device 160 is composed of a case 161, an electromagnetic brake core 162 partly stored in the case 161, and a conductive wire wound around a portion of the electromagnetic brake core 162 inside the case 161. and a 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 . can be determined as appropriate. For example, the width W4 of the case 161 in the X-axis direction, that is, the width W4 of the electromagnetic brake 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. , 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 this example, and the width of the electromagnetic stirring device 150 and the width of the electromagnetic braking device 160 may be different.

In addition, in the electromagnetic brake device 160, since the electromagnetic force is applied to the molten steel 2 from the coil 163 through the side wall of the case 161, the case 161, like the case 151, is made of, for example, non-magnetic stainless steel or FRP. , which is non-magnetic and whose strength can be ensured.

The electromagnetic brake core 162 is a substantially rectangular parallelepiped solid member having a pair of end portions 164 on which the coil 163 is provided, and a substantially rectangular solid member similarly having a pair of end portions 164 . and a connection portion 165 to be connected. The electromagnetic brake core 162 is provided with a pair of end portions 164 protruding from the connecting portion 165 in the direction of the Y-axis toward the long-side mold plate 111 . The position where the pair of ends 164 are provided is the position where it is desired to apply an electromagnetic force to the molten steel 2, that is, the discharge flow from the pair of discharge holes of the submerged nozzle 6 passes through the region where the magnetic field is applied by the coil 163. (See also FIG. 6). The electromagnetic brake core 162 is formed by laminating electromagnetic steel sheets, for example.

A coil 163 is formed by winding a conductive wire around an end portion 164 of the electromagnetic brake core 162 with the Y-axis direction as the central axis. The structure of the coil 163 is the same as the coil 153 of the electromagnetic stirring device 150 described above. A plurality of coils 163 are arranged in parallel at predetermined intervals in the Y-axis direction for each end 164 .

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 can be applied to the molten steel 2 to weaken the momentum of the discharge flow. That is, each end 164 becomes a magnetic pole, one end 164 becomes an N pole, and the other end 164 becomes an S pole. Therefore, the two magnetic poles are opposed to the long side surfaces. Furthermore, the submerged nozzle 6 is arranged at a position facing the space 164a between the two magnetic poles (see FIG. 6). A similar electrode brake core 162 is also arranged on the other long side, so that a total of two pairs of magnetic poles are arranged. Further, the driving of the DC power supply can be appropriately controlled by a controller (not shown) consisting of a processor or the like operating according to a predetermined program. The amount of current applied to each coil 163 can be appropriately controlled by the controller, and the strength of the electromagnetic force applied to the molten steel 2 can be controlled. As a method for driving this DC power supply, various known methods used in general electromagnetic brake devices 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 are set to the desired range of the molten steel 2 by the electromagnetic stirring device 150. can be appropriately determined so that the coil 163 can be arranged at an appropriate position with respect to the molten steel 2 . For example, W0 is approximately 1600 mm, W2 is approximately 500 mm, and W3 is approximately 350 mm.

Here, for example, the electromagnetic brake device disclosed in Patent Document 2 has a single magnetic pole. A single magnetic pole is provided on the outside of the long side of the mold and extends across both widthwise (that is, lengthwise of the long side) ends. The magnetic field generated from such a magnetic pole has the characteristic that the magnetic flux density is maximized at the center 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 submerged nozzle becomes extremely high. Therefore, in the vicinity of the ejection hole of the submerged nozzle, the braking force due to the static magnetic field becomes excessive, and the ejection flow tends to rise in the vicinity of the nozzle without spreading in the width direction. As described above, this ascending flow becomes a flow in the width direction near the meniscus, and this flow in the width direction (that is, reverse flow) may disturb the flow stirred by the electromagnetic stirrer. As a result, the effect of the electromagnetic stirring and the effect of the electromagnetic brake may cancel each other out, and the quality of the slab may deteriorate. Specifically, fluctuations in the surface of the molten steel are accelerated, and as a result, disturbance and depression of the oscillation marks due to the fluctuations in the surface of the molten steel may frequently occur.

On the other hand, in this embodiment, as described above, the electromagnetic brake device 160 is configured to have two ends 164, that is, to have two magnetic poles. Further, an immersion nozzle 6 is arranged at a position facing the space 164a between the two magnetic poles. According to such a configuration, for example, when the electromagnetic brake device 160 is driven, these two magnetic poles function as the N pole and the S pole, respectively, and the width direction of the mold 110 (that is, the X-axis direction) near the approximate center The application of current to the coil 163 can be controlled by the controller so that the magnetic flux density in one area is lower than that in other areas. Therefore, the braking force due to the static magnetic field can be reduced in the vicinity of the discharge hole of the submerged nozzle, thereby suppressing the occurrence of excessive upward flow. As a result, the effect of electromagnetic stirring is less likely to be impaired by the electromagnetic brake, and the effect of the electromagnetic brake and the effect of electromagnetic stirring can be further enhanced. Therefore, it becomes possible to respond to a wider range of casting conditions. Furthermore, since the effect of electromagnetic stirring can be obtained more effectively, temperature fluctuations are further suppressed. Furthermore, fluctuations in the surface of molten water and fluctuations in temperature caused by the upward flow are suppressed. Therefore, uneven solidification of the solidified shell is suppressed, and the surface quality of the slab is improved.

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 brake device 160 may be configured to have three or more ends 164 and have three or more magnetic poles. In this case, by appropriately adjusting the amount of current applied to the coil 163 of each end 164, the application of the electromagnetic force to the molten steel 2 associated with the electromagnetic brake can be controlled in more detail. That is, the number of magnetic poles may be appropriately adjusted according to the degree of upward flow generated in the vicinity of the submerged nozzle 6, and there is no particular upper limit. Even when there are three or more magnetic poles, it is preferable to arrange the submerged nozzle 6 at a position facing the space between the magnetic poles.

(2-2. Details of the installation position of the electromagnetic force generator)
The height 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 stirring device 150 and the electromagnetic braking device 160, it can be said that the greater the height of the electromagnetic stirring core 152 and the electromagnetic braking core 162, the higher the performance of applying the electromagnetic force. For example, the performance of the electromagnetic brake device 160 depends on the cross-sectional area (height H2 in the Z-axis direction×width W2 in the X-axis direction) of the end portion 164 of the electromagnetic brake core 162 in the XZ plane, and the applied DC current. value and the number of turns of coil 163 . Therefore, when both the electromagnetic stirring device 150 and the electromagnetic brake device 160 are installed in the mold 110, the installation positions of the electromagnetic stirring core 152 and the electromagnetic brake core 162, more How to set the ratio of the heights of the core 152 and the electromagnetic brake core 162 is very important from the viewpoint of effectively exhibiting the performance of each device for improving the quality of the slab 3. .

A method of using both an electromagnetic stirrer and an electromagnetic brake in continuous casting has been proposed. However, in practice, even if both the electromagnetic stirring device and the electromagnetic braking device are combined, there are many cases in which the quality of the slab is worse than when the electromagnetic stirring device or the electromagnetic braking device is used alone. . Simply installing both devices does not mean that the advantages of both devices can be easily obtained, and depending on the configuration and installation position of each device, the advantages of each device may cancel each other out. Because you get If the respective advantages cancel each other out, fluctuations in the surface of the molten steel will be accelerated, and in turn, there is a possibility that disturbance and depression of the oscillation marks due to the fluctuations in the surface of the molten steel will frequently occur. Therefore, it cannot be said that the effect of improving the quality of slabs can be sufficiently obtained simply by combining the electromagnetic stirring device and the electromagnetic braking device.

On the other hand, in the present embodiment, as described below, the electromagnetic stirring core 152 and the electromagnetic brake core 162 have appropriate heights 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 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. will be Conventionally, for automotive exterior materials, etc., which require high quality, it is difficult to ensure quality in high-speed casting where the casting speed exceeds 1.6 m / min, so 1.3 to 1.4 m /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 higher than the case where continuous casting is performed at a conventional slower casting speed. A specific goal is set to ensure the quality of the slab 3 . Hereinafter, the height ratio 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 this embodiment, in order to secure a space for installing the electromagnetic stirring device 150 and the electromagnetic braking device 160 in the central part of the mold 110 in the Z-axis direction, the water box 130 is provided above and below the mold 110, respectively. , 140 are placed. Here, even if the electromagnetic stirring core 152 is positioned above the surface of the molten steel, the effect cannot be obtained. Therefore, the electromagnetic stirring core 152 should be installed below the surface of the molten steel. Moreover, in order to effectively apply a magnetic field to the discharge flow, the electromagnetic brake core 162 is preferably positioned near the discharge hole of the submerged nozzle 6 . When the water boxes 130 and 140 are arranged as described above, the discharge hole of the submerged nozzle 6 is located above the lower water box 140, so the electromagnetic brake core 162 is also installed above the lower water box 140. should. Therefore, the height H0 of the space where the effect can be obtained by installing the electromagnetic stirring core 152 and the electromagnetic brake core 162 (hereinafter also referred to as the effective space) is the height from the molten steel surface to the upper end of the lower water box 140 ( See Figure 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 approximately the same height as the surface of the molten steel. 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 formula (1) is established. Here, the height H1 of the electromagnetic stirring core 152 is the length from the top end to the bottom end of the electromagnetic stirring core 152 (that is, the length in the Z-axis direction (casting direction distance)), and the height H3 of the case 151 is It 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 top end to the bottom 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 top end to the bottom end of the case 161. length (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 the core height ratio H1/H2) is Must be specified. Each of the heights H0 to H4 will be described below.

(Regarding height H0 of effective space)
As described above, in the electromagnetic stirring device 150 and the electromagnetic braking device 160, it can be said that the greater the height of the electromagnetic stirring core 152 and the electromagnetic braking core 162, the higher the performance of applying the electromagnetic force. Therefore, in this embodiment, the mold facility 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. Specifically, in order to increase the height H0 of the effective space, the length of the mold 110 in the Z-axis direction should be increased. On the other hand, as described above, it is desirable that the length from the surface of the molten steel to the lower end of the mold 110 is about 1000 mm or less in consideration of the cooling property of the slab 3 . Therefore, in the present embodiment, the mold 110 is arranged so that the distance from the surface of the molten steel to the lower end of the mold 110 is about 1000 mm in order to maximize the height H0 of the effective space while ensuring the cooling performance of the slab 3. Form.

Here, when trying to configure the lower water box 140 so as to store enough water to obtain a sufficient cooling capacity, the height of the lower water box 140 must be at least about 200 mm based on past operational results. becomes. Therefore, the height H0 of the effective space is approximately 800 mm or less.

(Regarding the heights H3 and H4 of the cases of the electromagnetic stirring device and the electromagnetic braking device)
As described above, the coil 153 of the electromagnetic stirring device 150 is formed by winding two to four layers of conductive wire with a cross-sectional size of about 10 mm×10 mm around the electromagnetic stirring 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, for the electromagnetic brake device 160, the height of the electromagnetic brake core 162 including the coil 163 is approximately H2+80 mm or more. Considering the space between the inner wall of the case 161 and the electromagnetic brake core 162 and coil 163, the height H4 of the case 161 is approximately H2+200 mm or more.

(Range that H1 + H2 can take)
Substituting the above values of H0, H3, and H4 into the above formula (1) yields the following formula (2).

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

(Regarding core height ratio H1/H2)
In this 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 in which the effect of electromagnetic stirring can be obtained more reliably.

As described above, in the electromagnetic stirring, by causing the molten steel 2 to flow at the interface of the solidified shell, the 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. can. On the other hand, the thickness of the solidified shell 3a inside the mold 110 increases toward the bottom of the mold 110 . 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 ensures the surface quality of the slab 3 to what thickness. It can be determined by the need.

Here, for a product with strict surface quality, a step of grinding the surface layer of the slab 3 after casting by several millimeters is often performed. This grinding depth is about 2 mm to 5 mm. Therefore, even if electromagnetic stirring is performed in the mold 110 where the thickness of the solidified shell 3a is smaller than 2 mm to 5 mm, the impurities are reduced by the electromagnetic stirring in the product that requires such strict surface quality. 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 slab 3 cannot be obtained unless electromagnetic stirring is performed in the mold 110 where the thickness of the solidified shell 3a is 2 mm to 5 mm or more.

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

The relationship between the casting speed (m/min) and the distance (mm) from the surface of the molten steel was obtained from the above formula (3) when the thickness of the solidified shell 3a was 4 mm or 5 mm. The results are 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 and the vertical axis represents the distance from the molten steel surface. plotting the relationship. In addition, in the calculation for obtaining the results shown in FIG. 7, k=17 was used as a value corresponding to a general template.

For example, from the results shown in FIG. 7, if the thickness to be ground is less than 4 mm and the thickness of the solidified shell 3a is up to 4 mm, the molten steel 2 can be electromagnetically stirred. 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. In the case where the thickness to be ground is less than 5 mm and the thickness of the solidified shell 3a is up to 5 mm, the molten steel 2 can be electromagnetically stirred. It can be seen that the effect of electromagnetic stirring is obtained in continuous casting at 3.5 m/min or less. The casting speed of "3.5 m/min" corresponds to the maximum casting speed possible in terms of operation and equipment in a general continuous casting machine.

Here, as described above, in the present embodiment, for example, even in high-speed casting in which the casting speed exceeds 1.6 m / min, the cast slab equivalent to the case of continuous casting at a conventional slower casting speed The goal is to ensure the quality of 3. When the casting speed exceeds 1.6 m/min, in order to obtain the effect of electromagnetic stirring even if the thickness of the solidified shell 3a is 5 mm, from FIG. I know I have to do more than that.

From the results of the above examination, in the present embodiment, for example, in continuous casting at a relatively high casting speed exceeding 1.6 m/min, the effect of electromagnetic stirring can be obtained even if the thickness of the solidified shell 3a is 5 mm. Secondly, 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 greater the height H2, the higher the performance of the electromagnetic brake device 160. Therefore, when H1+H2=500 mm, the range of H2 corresponding to the range of height H1 of the electromagnetic stirring core 152 can be obtained from the above formula (2). That is, the height H2 of the electromagnetic brake core 162 is approximately 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 this embodiment is given by, for example, the following formula (4).

In summary, in the present embodiment, even when the casting speed exceeds 1.6 m/min, it is intended to ensure the quality of the slab 3 equal to or higher than the case of continuous casting at a conventional lower casting speed. In the case of the target, for example, the electromagnetic stirring core 152 and the electromagnetic brake core 162 are arranged so that the height H1 of the electromagnetic stirring core 152 and the height H2 of the electromagnetic brake core 162 satisfy the above formula (4). Configured.

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. This is because the effect of improving the quality of 3, especially 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 fully exhibited varies depending on the casting conditions such as the slab size, type, and 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 that simulates the casting conditions in actual operation, as shown in Examples 1 to 3 below. It can be specified based on analytical simulations and actual machine tests.

The configuration of the mold facility 10 according to the present embodiment has been described above. In the above description, when obtaining the relationship shown in the above formula (4), these relationships were obtained by setting H1+H2=500 mm from the above formula (2). However, this embodiment is not limited to such an example. As described above, it is preferable that H1+H2 be as large as possible in order to exhibit the performance of the device, so in the above example, H1+H2=500 mm. On the other hand, in consideration of workability when installing the water boxes 130 and 140, the electromagnetic stirring device 150, and the electromagnetic braking device 160, for example, it may be preferable to have a gap between these members in the Z-axis direction. . When other factors such as workability are emphasized, H1+H2 is not necessarily 500 mm. For example, H1+H2=450 mm. may be set.

Further, in the above description, when the casting speed exceeds 1.6 m/min, even if the thickness of the solidified shell 3a is 5 mm, the conditions for obtaining the effect of electromagnetic stirring are shown in FIG. A minimum value of about 150 mm was obtained for the height H1 of the core, 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, this embodiment is not limited to such an example. If the target casting speed is set faster, the lower limit of the core height ratio H1/H2 may also change. In other words, the minimum value of the height H1 of the electromagnetic stirring core 152 that can obtain the effect of electromagnetic stirring even if the thickness of the solidified shell 3a is 5 mm at the target casting speed in actual operation is obtained from FIG. The core height ratio H1/H2 corresponding to the value of H1 may be set as the lower limit of the core height ratio H1/H2.

As an example, considering workability, etc., H1 + H2 = 450 mm, and even at a higher casting speed of 2.0 m / min, the quality of the slab 3 is equal to or higher than the case of continuous casting at a conventional lower casting speed. Let's try to find the conditions for the core height ratio H1/H2 when the goal is to ensure. First, from FIG. 7, the conditions for obtaining the effect of electromagnetic stirring even when the thickness of the solidified shell 3a is 5 mm when the casting speed is 2.0 m/min or more are obtained. Referring to FIG. 7, when the casting speed is 2.0 m/min, the thickness of the solidified shell becomes 5 mm at a position about 175 mm from the surface of the molten steel. Therefore, considering the margin, the minimum value of the height H1 of the electromagnetic stirring core 152 that can obtain the effect of electromagnetic stirring even if 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, H2=250 mm, so the condition required for the core height ratio H1/H2 is represented by the following formula (5).

That is, in the present embodiment, even at a casting speed of 2.0 m / min, if the goal is to ensure the quality of the slab 3 that is equal to or higher than the case where continuous casting is performed at a conventional lower casting speed, , the electromagnetic stirring core 152 and the electromagnetic brake core 162 may be configured to satisfy at least the above formula (5). As described above, the upper limit of the core height ratio H1/H2 may be defined based on numerical analysis simulations simulating casting conditions in actual operations, actual machine tests, and the like.

Thus, in the present embodiment, even when the casting speed is increased, it is possible to ensure 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. The range of the core height ratio H1/H2 can vary depending on the specific value of the target casting speed and the specific value of H1+H2. Therefore, when setting an appropriate range for the core height ratio H1/H2, the target casting speed and the ratio 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. Values may be appropriately set, and an appropriate range of the core height ratio H1/H2 at that time may be obtained as appropriate by the method described above.

Considering the examples described later, H1/H2 preferably satisfies the relationship shown in the following formula (101), and more preferably satisfies the following formula (103).

(3. Continuous casting method)
Next, a continuous casting method using the above-described continuous casting machine 1 will be described. In this embodiment, a continuous casting machine 1 is used to continuously cast slabs for high alloy steel. That is, the molten steel 2 has C: 0.1% by mass or less, Mn: 0.05% by mass or more and 3.0% by mass or less, Si: 0.4% by mass or more and 4.0% by mass or less, and Al: 0.01%. An element group consisting of not less than 3.0% by mass and not more than 3.0% by mass is included. Other elements may be included depending on the use of the high-alloy steel. Here, mass % of each component means mass % with respect to the total mass of the molten steel 2 .

(C: 0.1% by mass or less)
If the C content is too high, the formability of the steel deteriorates, so the C content is made 0.1% by mass or less. Although the lower limit of the C content is not particularly limited, the C content may be 0.005% by mass or more because if the content is too low, the strength of the steel material is lowered.

(Mn: 0.05% by mass or more and 3.0% by mass or less)
Mn is added to the molten steel 2 in an amount of 0.05% by mass or more because it has the effect of increasing the electrical resistance of the steel material and reducing iron loss. On the other hand, if the Mn content is too high, the γ phase tends to occur and the magnetic properties deteriorate.

(Si: 0.4% by mass or more and 4.0% by mass or less)
Si is added to the molten steel 2 in an amount of 0.4% by mass or more because Si has the effect of increasing the electric resistance of the steel material and reducing iron loss. On the other hand, if the Si content is too high, the magnetic flux density will decrease, so the Si content should be 4.0% by mass or less.

(Al: 0.01% by mass or more and 3.0% by mass or less)
Al is added to the molten steel 2 in an amount of 0.01% by mass or more because, like Si, Al has the effect of increasing electrical resistance and reducing iron loss. On the other hand, if the Al content is too high, the magnetic flux density will decrease, so the Al content is made 3.0% by mass or less.

When performing continuous casting, the magnetic flux density of the alternating magnetic field (hereinafter simply referred to as "electromagnetic stirring strength") by the electromagnetic stirring device 150 (that is, the electromagnetic stirring core 152) is set to 0.05T or more and 0.25T or less. If the electromagnetic stirring intensity is less than 0.05 T, the fluctuation of the molten steel surface due to stirring is not sufficiently suppressed, deepening the oscillation marks and causing surface cracks. In addition, since the stirring flow is insufficient, the entrapment of air bubbles and inclusions in the shell is not suppressed, resulting in increased rolling scratches. When the electromagnetic stirring density is greater than 0.25 T, the stirring flow becomes excessive, which increases the influence of the melt surface fluctuation and causes surface cracks. Furthermore, the molten powder present on the surface of the molten steel is remarkably entrained, degrading the quality of the cast slab. Therefore, the appropriate electromagnetic stirring strength is 0.05 T or more and 0.25 T or less. Unless otherwise specified, the unit "T" of the electromagnetic stirring strength and the electromagnetic braking strength described below means Tesla.

On the other hand, the magnetic flux density of the static magnetic field (hereinafter also simply referred to as "electromagnetic brake strength") by the electromagnetic brake device 160 (that is, the electromagnetic brake core 162) is set to 0.1T or more and 0.4T or less. If the electromagnetic brake strength is less than 0.1 T, the discharge flow is not sufficiently braked, and the rising flow generated on the short side causes the melt surface to fluctuate, degrading the quality of the slab. If the electromagnetic braking strength is greater than 0.4 T, the braking force becomes excessive, the molten steel concentrates in the vicinity of the submerged nozzle 6, and the molten steel surface fluctuates greatly, resulting in surface cracks. Therefore, the appropriate electromagnetic brake strength is 0.1T or more and 0.4T or less.

Under the condition that a conventional one-pole (single-pole) electromagnetic brake core is installed, if the strength of the electromagnetic brake is greater than 0.2 T, the molten steel concentrates near the submerged nozzle 6, and the molten steel surface fluctuates greatly. Occur. Therefore, when the electromagnetic brake device 160 has a plurality of magnetic poles as in the present embodiment, it is possible to improve the quality of the slab over a wider range of magnetic flux densities than the conventional single-pole type electromagnetic brake device.

Here, the electromagnetic stirring strength and the electromagnetic braking strength are the magnetic flux densities of the core center (that is, the center of the electromagnetic stirring core 152 and the electromagnetic brake core 162) measured when the mold 110 is in a cold state without molten steel. . Since the magnetic field generated by the electromagnetic stirring core 152 is an alternating magnetic field, the maximum value of the change in the magnetic flux density over time is taken as the value of the electromagnetic stirring strength. In addition, since the correlation between the electromagnetic stirring strength and the electromagnetic braking strength and the application conditions (current, frequency) to the electromagnetic stirring device 150 and the electromagnetic braking device 160 can be specified in advance, in actual operation, the application conditions to each device are determined. By adjusting, the strength of electromagnetic stirring and the strength of electromagnetic braking may be adjusted.

Continuous casting may be performed in the same manner as the conventional continuous casting method except for the operating conditions described above. As will be shown in the examples described later, according to the continuous casting method according to the present embodiment, even when the productivity of slabs for high-alloy steel is increased, it is possible to suppress fluctuations in the molten steel surface, and to achieve stable casting. It is possible to ensure the quality of the slab effectively.

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 facility 10 according to the present embodiment to continuous casting. In the numerical analysis simulation, a calculation model simulating the mold facility 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 for the numerical analysis simulation are as follows. In addition, Example 2 also performed the numerical analysis simulation on the same conditions.

(Conditions for numerical analysis simulation)
Width W1 of the electromagnetic stirring core of the electromagnetic stirring device: 1900 mm
Current application conditions for electromagnetic stirrer: 680 A, 3.0 Hz
Number of turns of coil of electromagnetic stirrer: 20 turns Width W2 of electromagnetic brake core of electromagnetic brake device: 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 coil turns of electromagnetic brake device: 120 turns Casting speed: 1.4 m/min or 2.0 m/min
Mold width: 1600mm
Mold thickness: 250 mm
Amount of Ar gas blown: 5 NL/min

In the evaluation of the surface quality, a fluid simulation was performed under the above conditions to calculate the flow velocity of the molten steel in the molten steel of the continuous casting machine 1, the solidification velocity of the molten steel, and the distribution of Ar gas bubbles trapped in the solidified shell. Ar gas bubbles were evaluated. Specifically, the probability _Pg that Ar gas bubbles are captured by the solidified shell was calculated using the function shown in the following formula (6). where _C0 is a constant and U is the molten steel flow velocity at the solidification interface.

Also, the speed _ηg at which Ar gas bubbles are captured by the solidified shell at this time was calculated using the following formula (7). Here, _ng is the number density of Ar gas bubbles at the solidified shell interface, and _Rs is the solidification rate of the solidified shell.

Then, the number density _Sg of Ar gas bubbles in the solidified shell was calculated using the following formula (8). Here, U _s is the moving speed of the solidified shell in the drawing direction of the slab.

The number density _Sg of Ar gas bubbles in the solidified shell calculated from the above formula (8) is averaged over time, and the number of Ar gas bubbles with a diameter of 1 mm captured within a range of 4 mm from the cast slab surface layer is pinpointed. Calculated as 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 cast slabs using the numerical analysis simulation described above, reference can be made to Japanese Patent Application Laid-Open No. 2015-157309, which is a prior application filed 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 were determined so that H1+H2=500 mm based on the relationship shown in the above formula (2). A simulation was performed with eight combinations shown in Table 1 below.

For comparison, as an example of a conventional continuous casting method, the surface quality of a slab was also evaluated when only the electromagnetic stirring device 150 was installed. The conventional continuous casting method to be evaluated corresponds to the continuous casting method using the mold facility 10 shown in FIGS. 2 to 5 from which the electromagnetic brake device 160 is removed. Further, in the calculation for the conventional continuous casting method, the height H1 of the electromagnetic stirring core 152 was fixed at 250 mm. For the conventional continuous casting method, the pinhole index is calculated by the same calculation method as described above, 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. bottom.

Numerical analysis simulation results for surface quality are shown in FIGS. 8 and 9. FIG. FIG. 8 is a graph showing the relationship between the core height ratio H1/H2 and the pinhole index when the casting speed is 1.4 m/min, obtained by numerical analysis simulation. FIG. 9 is a graph showing the relationship between the core height ratio H1/H2 and the pinhole index when the casting speed is 2.0 m/min, obtained by numerical analysis simulation. 8 and 9 plot the relationship between the core height ratio H1/H2 on the horizontal axis and the pinhole index on the vertical axis. In FIGS. 8 and 9, the values of the pinhole index in the conventional continuous casting method are indicated by dashed straight lines parallel to the horizontal axis.

Referring to FIG. 8, the pinhole index in the conventional continuous casting method is about 40 when the casting speed is 1.4 m/min. 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 lower than that of the conventional continuous casting method is obtained. In particular, when the core height ratio H1/H2 is 1.0 or more, the pinhole index becomes lower than that of the conventional continuous casting method. The pinhole index decreases as the value of 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 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 is reduced to the same level as that of the conventional continuous casting method. do. In particular, 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 a surface quality equivalent to that obtained by continuous casting at a casting speed of 1.4 m/min by a conventional continuous casting method can be obtained.

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 between about 0.70 and about 2.70, the casting speed is at least 1.00. It was found that in continuous casting at 4 m/min to 2.0 m/min, it is possible to ensure a slab surface quality 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, it is lower than the conventional speed (specifically, , and a casting speed of 1.4 m/min).

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, the same simulation method as that used for evaluating the surface quality described above was used to evaluate the value of alumina, which is a representative impurity inclusion of the slab, instead of Ar bubbles 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 assumed that the alumina particles that settle below the vertical part remain in the slab as they are. , the number of alumina particles in a given volume of the slab was calculated as an intrinsic quality index. At this time, the length of the vertical portion of the continuous casting machine 1 was set to 3 m. Also, the alumina particles had a diameter of 0.4 mm and a specific gravity of 3990 kg/m ³ . It can be said that the smaller the internal quality index, the higher the internal quality of the slab.

In the evaluation of the internal quality, the height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core were determined according to the following table so that H1 + H2 = 450 mm based on the relationship shown in the above formula (2) A simulation was performed with the four combinations shown in 2.

For comparison, the internal quality was also evaluated in the case where only the electromagnetic stirrer 150 was installed as an example of a conventional continuous casting method. In the conventional continuous casting method to be evaluated, the electromagnetic brake device 160 was removed from the mold facility 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 at 250 mm.

FIG. 10 shows the numerical analysis simulation results for the endoplasm. FIG. 10 is a graph showing the relationship between casting speed and internal quality index obtained by numerical analysis simulation. In FIG. 10, the casting speed is plotted on the horizontal axis and the internal quality index is plotted on the vertical axis, and the relationship between the casting speed and the internal quality index corresponding to the values of each core height ratio H1/H2 shown in Table 2 above is plotted. are doing. In addition, FIG. 10 also plots the results of the conventional continuous casting method described above.

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 increases significantly as the casting speed increases. (that is, the internal quality of the slab deteriorates significantly as the casting speed increases).

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. The casting speed is 1.4 m/min in the conventional continuous casting method, and a better internal quality can be obtained. Even when the core height ratio H1/H2 is 2.0, when the casting speed is 2.4 m/min, the internal quality index is about 60, and the casting speed in the conventional continuous casting method is 1.6 m/min. The internal quality equivalent to the case of min can be secured. From the above results, in order to ensure the quality of the cast slab equivalent to or lower than the conventional one even if the casting speed is increased, the core height ratio H1/H2 should be 2.0 or less, more preferably 1.5 or less. 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 , it is possible to ensure the internal quality of the slab 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, the continuous casting at the casting speed of 2.4 m/min can be compared with the conventional continuous casting at the casting speed of 1.6 m/min. It was found that it is possible to secure the slab internal quality equal to or lower than that of 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. , the core height ratio H1/H2, and the casting speed, were actually continuously cast. The mold 110 is a water-cooled copper mold (water-cooled copper mold) with a height of 900 mm (the length from the top end to the bottom end of the mold) and a rectangular cross section. The continuous casting machine 1 was of a vertical bending type. The specific amount of water for secondary cooling was 1.5 to 2.5 L/kg-steel. The amount of argon gas blown into the submerged nozzle 6 was 7 NL/min. The upper end of the electromagnetic stirring core 152 was positioned 100 mm from the upper end of the mold, and the upper end of the electromagnetic brake core 162 was positioned 150 mm from the lower end of the electromagnetic stirring core. Then, the surface quality and internal quality of the cast slab were examined visually and by ultrasonic flaw detection, respectively. Specifically, the cast slab surface was ground smooth (about 1 to 2 mm) so that flaw detection was possible, and the surface was visually inspected for bubble defects and inclusion defects. Also, in the ultrasonic inspection, bubble defects and inclusion defects were detected from the echo of ultrasonic waves from the surface of the slab toward the center of the thickness. For comparison, a conventional continuous casting method in which only an electromagnetic stirrer was installed was also continuously cast, and the quality of the cast slab was investigated by the same method. The conventional continuous casting method is a continuous casting method using the mold facility 10 according to the present embodiment shown in FIGS. . The casting speed in the conventional continuous casting method was set to 1.4 m/min, and the height H1 of the electromagnetic stirring core 152 of the electromagnetic stirring device 150 was set to 200 mm.

In both the present embodiment and the conventional continuous casting method, the submerged nozzle has a discharge hole facing downward at 45°, and the depth of the upper end of the discharge hole from the surface of the molten steel is set to 270 mm.

The results are shown in Table 3 below. In Table 3, regarding the quality of the slab, the quality in the conventional continuous casting method is used as a standard, and if the quality is better than that in the conventional continuous casting method (that is, fewer defects), "○", If the same quality as the conventional continuous casting method (that is, the number of defects is the same) is obtained, "△" is worse than the conventional continuous casting method (that is, the number of defects is large). ) is obtained, it is expressed by attaching “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, a casting speed of 1.6 m / min). The range of the core height ratio H1/H2 that can ensure the quality of the slab (surface quality and internal quality) was investigated. 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 0.80 to about 2.33, the casting speed was set to 2.0 m/min. It has been found that it is possible to ensure a better slab quality than conventional continuous casting methods at lower speeds, even when increasing to . In other words, from the results of this example, by applying the present invention and setting the value of the core height ratio H1/H2 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 can be increased. It has been found that even an increase to 2.2 m/min makes it possible to ensure a better slab quality than conventional continuous casting processes at lower speeds.

In Example 4, an actual machine test was conducted on a continuous casting method for high alloy steel. In the actual machine test, the electromagnetic force generator 170 according to the present embodiment described with reference to FIGS. , the strength of electromagnetic stirring, the strength of electromagnetic braking, etc. were variously changed to perform continuous casting of high-alloy steel. 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 top end to the bottom end of the mold) of 900 mm. The form of the continuous casting machine 1 was a vertical bending type. Further, C is 0.01% by mass, Mn is 0.5% by mass, Si is 2.0% by mass, P is 0.012% by mass, S is 0.0025% by mass, Al is 0.8% by mass, Molten steel with the remainder being iron and unavoidable impurities was used, and the specific amount of water for secondary cooling was set at 1.5-2.5 L/kg-steel. The amount of argon gas blown into the immersion nozzle was 7 NL/min. The position of the upper end of the electromagnetic stirring core 152 was set to 100 mm from the upper end of the mold 110, and the height (casting direction distance) H1 from the upper end to the lower end of the electromagnetic stirring core 152 was set to 250 mm. The position of the upper end of the electromagnetic brake core 162 was set to 500 mm from the upper end of the mold 110, and the height H2 from the upper end to the lower end of the electromagnetic brake core 162 was set to 200 mm. Therefore, the core height ratio H1/H2 is 250/200=1.25, which satisfies the condition of formula (101).

After continuous casting, the surface of the torch-cut slab was visually observed to count the number of depressions on the surface. Then, the depression index per surface area of the slab was calculated. It has been confirmed in advance that if the depression index is 0.1 pieces/m ² or less, flaws do not occur during rolling. Here, depressions having a depth of approximately 1 mm or more were counted as depressions.

(Invention Example 1)
Inventive Example 1 serves as a base for the following Inventive Examples and Comparative Examples. In Invention Example 1, the slab thickness (slab thickness) and slab width (slab width) were set to 250 mm thick and 1250 mm wide, which are common sizes for continuous casting machines for thin plates. The casting speed was set to 1.3 m/min, at which point the discharge flow from the submerged nozzle begins to adversely affect stirring. The strength of electromagnetic stirring and the strength of electromagnetic braking were set based on the flow analysis performed in advance (the numerical analysis simulation shown in Example 1. The conditions were also the same as in Example 1), and the flow of molten steel in the mold was uniform. The conditions were 0.15T and 0.3T. The number of electromagnetic brake cores (that is, the number of magnetic poles facing the long side surfaces) is set to two (two per long side surface, that is, two pairs on both sides) to reduce the static magnetic field strength near the discharge hole. . This condition is within the range of this embodiment, and the depression index is 0, which is good.

(Invention Example 2)
In invention example 2, the slab width was made larger than that of invention example 1, and the electromagnetic stirring and electromagnetic brake strength conditions were the same as in example 1. In Inventive Example 2, the melt surface fluctuated easily due to the increase in throughput, but the depression index was 0, which was good.

(Invention example 3)
In Invention Example 3, both the strength of the electromagnetic stirring and the electromagnetic brake were increased within the range of the present embodiment as compared with Invention Example 1. In Invention Example 3, similarly to Invention Example 1, depression did not occur, and no situation in which the effects of electromagnetic stirring and electromagnetic braking were canceled out was observed.

(Invention Example 4)
In Invention Example 4, both the strengths of the electromagnetic stirring and the electromagnetic brake were made smaller than those of Invention Example 1 within the range of the present embodiment. In Invention Example 4, although the depression index was slightly worse than that in Invention Example 1, it was at a level that did not affect the product.

(Invention example 5)
In invention example 5, the casting speed was increased compared to invention example 1. In Invention Example 5, the molten steel surface fluctuates easily due to the increase in throughput, but although the depression index is slightly worse than that of Invention Example 1, it is at a level that does not affect the product.

(Invention example 6)
In invention example 6, the casting speed and slab width were increased compared to invention example 1. Furthermore, the strength of the electromagnetic brake was increased within the range of the present embodiment as compared with Example 1 of the invention. In Invention Example 6, the increase in throughput tends to increase the melt surface fluctuation, but although the depression index was slightly worse than that of Invention Example 1, it was at a level that did not affect the product.

(Invention Example 7)
In Invention Example 7, the casting speed was further increased compared to Invention Example 1. In Invention Example 7, the increase in throughput tends to increase the melt surface fluctuation, but although the depression index was slightly worse than that of Invention Example 1, it was at a level that did not affect the product.

(Invention Example 8)
In invention example 8, compared with invention example 1, the slab width was increased and the casting speed was further increased. Furthermore, the strength of the electromagnetic brake was increased within the range of the present embodiment as compared with Example 1 of the invention. In Invention Example 8, the increase in throughput tends to increase the melt surface fluctuation, but although the depression index was slightly worse than that in Invention Example 1, it was at a level that did not affect the product.

(Comparative example 1)
In Comparative Example 1, only the electromagnetic stirrer 150 was installed in the mold. That is, the electromagnetic brake device 160 was not installed in the mold. In Comparative Example 1, the reversal flow of the discharge flow on the short side causes fluctuations in the molten metal surface, and the depression index deteriorates, failing the test.

(Comparative example 2)
In Comparative Example 2, an electromagnetic stirrer 150 and an electromagnetic brake 160 were installed in the mold 110 . However, the electromagnetic brake cores 162 are paired on both sides. In other words, a unipolar electromagnetic brake core 162 was installed on each long side. The electromagnetic brake strength of Comparative Example 2 is 0.2 T, which is smaller than the electromagnetic brake strength of Invention Example 1 and the like. However, in Comparative Example 2, the electromagnetic brake core 162 has a single pole. Therefore, in Comparative Example 2, compared to the case where two pairs of electromagnetic brake cores 162 are provided as in Example 1 of the present invention, etc., the magnetic field at the central portion in the width direction is large, and the discharge flow is excessively damped at the central portion in the width direction. It is thought that an upward flow of As a result, the molten metal level fluctuated greatly, and the depression index became a disqualifying level.

(Comparative Example 3)
In Comparative Example 3, an electromagnetic stirrer 150 and an electromagnetic brake 160 were installed in the mold. However, the electromagnetic stirring strength was set to 0.04 T, which is less than the range of this embodiment. For this reason, the stirring force was insufficient, and the molten steel was not provided with a stirring flow sufficient to suppress the fluctuation of the molten steel surface, and the depression index deteriorated to the level of disqualification.

(Comparative Example 4)
In Comparative Example 4, the electromagnetic stirring device 150 and the electromagnetic brake device 160 were installed in the mold, and the electromagnetic stirring strength was set to 0.15 T within the range of this embodiment. However, the electromagnetic brake strength was set to 0.08 T, which is smaller than the range of this embodiment. For this reason, in Comparative Example 4, the suppression of the reverse flow formed by the discharge flow was insufficient, causing fluctuations in the surface of the molten steel, and the depression index deteriorated, resulting in a disqualified level.

(Comparative Example 5)
In Comparative Example 5, the electromagnetic stirring device 150 and the electromagnetic brake device 160 were installed in the mold, and the electromagnetic stirring strength was set to 0.3 T, which is larger than the range of this embodiment. Therefore, in Comparative Example 5, the agitation was too strong, which caused fluctuations in the surface of the molten steel, resulting in a deterioration in the depression index and a failure level.

(Comparative Example 6)
In Comparative Example 6, the electromagnetic stirring device 150 and the electromagnetic brake device 160 were installed in the mold, and the electromagnetic stirring strength was set to 0.15 T within the range of this embodiment. However, the electromagnetic brake strength was set to 0.5 T, which is larger than the range of this embodiment. For this reason, molten steel accumulated in the vicinity of the submerged nozzle 6, and the fluctuation of the molten steel surface at the widthwise central portion of the slab became large, and the depression index deteriorated to the level of rejection.

Table 4 summarizes the results. Inventive Examples 1 to 8 had good casting quality, but Comparative Examples 1 to 6 had problems in casting quality.

(4. Supplement)
Although the preferred embodiments of the present invention have been described in detail above 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 belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

1 continuous casting machine 2 molten steel 3 cast piece 3a solidified shell 3b unsolidified portion 4 ladle 5 tundish 6 submerged 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 portion 165 connecting portion 170 electromagnetic force generator

Claims (2)

C: 0.005% by mass or more and 0.1% by mass or less, Mn: 0.05% by mass or more and 3.0% by mass or less, Si: 0.4% by mass or more and 4.0% by mass or less, Al: 0.01% A continuous casting method for continuously casting molten steel containing an element group consisting of 3.0% by mass or more and 3.0% by mass or less,
While applying an alternating magnetic field to the molten steel in the mold using an electromagnetic stirring core installed on the outside of the long side surface of the upper part of the mold, a plurality of magnetic poles are installed on the outside of the long side surface of the lower part of the mold, and a plurality of magnetic poles are arranged on the long side surface applying a static magnetic field to the molten steel using opposing electromagnetic brake cores;
The magnetic flux density of the alternating magnetic field by the electromagnetic stirring core is 0.05 T or more and 0.25 T or less, and the magnetic flux density of the static magnetic field by the electromagnetic brake core is 0.1 T or more and 0.4 T or less,
An immersion nozzle extending downward from the lower end of the tundish toward the mold and immersed in the molten steel in the mold is arranged at a position facing the space between the plurality of magnetic poles, and the electromagnetic brake core is used to applying an electromagnetic force to the molten steel in a direction to suppress the flow of the molten steel from the discharge hole provided in the immersion nozzle;
A continuous casting method , wherein the height H1 of the electromagnetic stirring core and the height H2 of the electromagnetic brake core satisfy the relationship shown in the following formula (101).

2. 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 formula (103).

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