JP2008055431A - Method of continuous casting for steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of continuous casting for steel, which method can prevent the contamination of mold powder and can carry out a cleaning and removing operation of deoxidation products from solidifying interfaces by using a movable magnetic field and a static magnetic field at the same time. <P>SOLUTION: When the continuous casting is carried out by pouring molten steel into a rectangular casting mold having the long sides and the short sides via a submerged nozzle 2, movable magnetic field generating devices 3 for moving magnetic fields in the direction of the width of a cast strip are arranged so as to oppose to the back surfaces of the long sides of the casting mold such that the projected plane of the movable magnetic field generating devices 3 to the movable magnetic field generating devices opposed to each other across the long sides of the casting mold overlap with at least a part of the locus of the molten steel flow discharged from the discharge port of the submerged nozzle to the short sides of the casting mold. The movable magnetic fields moving from the short sides toward the central side of the casting mold in the direction of the width or moving in the reversed direction are applied using the movable magnetic field generating devices, and at the same time, the static magnetic field generating devices 4 are arranged over the whole width of the cast strip at the position separated downward by a specified distance from the movable magnetic field generating devices, and the casting operation is carried out while applying the static magnetic fields over the whole width of the casting mold using the static magnetic field generating devices. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention applies a linear moving magnetic field to the discharge flow of molten steel discharged from a submerged nozzle into a mold and simultaneously applies a static magnetic field below the linear moving magnetic field to flow the unsolidified molten steel in the slab. The present invention relates to a continuous casting method of steel that is cast while controlling the temperature.

  In continuous casting of steel, the flow state of the molten steel in the mold, particularly the flow state near the molten steel surface, includes mold powder entrainment, generation of scum, adhesion of deoxidation products and inert gas bubbles to the solidification interface, etc. It is related and is known to have a great influence on slab quality. In order to produce a defect-free slab, it is important to control the flow of molten steel near the molten steel surface in the mold. To that end, a magnetic field was applied to the molten steel near the molten steel surface in the mold and applied. A method of optimizing the flow of molten steel in the vicinity of the molten steel surface in the mold by generating an induced current between the magnetic field and the moving molten steel and utilizing the electromagnetic force generated in the molten steel by the action of the induced current and the applied magnetic field, Traditionally done. In addition, said inert gas bubble is a bubble by the inert gas blown into an immersion nozzle in order to prevent alumina adhesion.

  One method of applying this magnetic field is to apply a static magnetic field. For example, in Patent Document 1, a static magnetic field generating magnetic pole over the entire mold width is disposed at a height position corresponding to the vicinity of the molten steel surface on the back side of the mold long side, and the casting speed, the discharge angle of the immersion nozzle, and the immersion nozzle immersion There has been proposed a method for controlling the flow velocity of the molten steel surface by changing the strength of the magnetic field applied according to the depth and the mold width, thereby preventing the entrainment of mold powder. On the other hand, a method of applying a moving magnetic field instead of a static magnetic field has been proposed. For example, in Patent Document 2, a moving magnetic field generator that is divided into two or more sections in the mold width direction on the back side of the mold long side is arranged so that a horizontal swirl flow is formed on the molten steel surface in the mold. A method has been proposed in which a magnetic field is applied, the flow rate of the molten steel surface is 0.1 to 0.6 m / sec, and cleaning is performed so that deoxidation products and inert gas bubbles are not trapped at the solidification interface.

Patent Document 2 is a method of directly controlling the flow rate of the molten steel surface in the mold by the moving magnetic field, but as another method using the moving magnetic field, the flow rate of the molten steel discharge flow from the immersion nozzle is decelerated by the moving magnetic field, Thus, a method for indirectly controlling the flow velocity of the molten steel surface in the mold has also been proposed. For example, in Patent Document 3, a moving magnetic field generator arranged on the back side of a long mold side causes a flow from the short side of the mold toward the submersible nozzle side with respect to a discharge flow from the submerged nozzle, that is, a discharge direction of molten steel from the submerged nozzle. A method has been proposed in which a moving magnetic field is applied in the opposite direction to decelerate the discharge flow from the immersion nozzle, thereby controlling the flow velocity in the vicinity of the molten steel surface within an appropriate range and preventing the entrainment of mold powder.
JP 7-314100 A JP-A-6-606 JP-A-9-192801

  However, the above prior art has the following problems.

  That is, in the method of applying a static magnetic field as in Patent Document 1, since the magnetic field works only on the moving molten steel and works only as a braking force, the effect of the static magnetic field is not exhibited in the stagnant region of the molten steel flow, There is a problem that the molten steel in the stagnation area cannot be activated.

  In the method of Patent Document 2 in which a swirling flow is formed on the surface of molten steel by a moving magnetic field, electromagnetic force acts in the moving direction of the magnetic field, so that control flexibility can be ensured, but when the casting speed is increased, the immersion nozzle The molten steel flow rate discharged from the molten steel increases, and the molten steel flow rate at the molten steel surface in the mold naturally increases. Therefore, when a moving magnetic field is applied so that a horizontal swirl flow is formed in this state, There is a problem that the molten steel flow velocity on the surface is further increased and mold powder entrainment occurs.

  The method of Patent Document 3 that controls the flow rate of the discharge flow by a moving magnetic field can prevent mold powder entrainment in a wide range of casting speeds and is an effective method for preventing mold powder entrainment. Since it is decelerated, there is a problem that the cleaning effect of deoxidation products and inert gas bubbles at the solidification interface is reduced.

  The present invention has been made in view of the above circumstances. The object of the present invention is to prevent the entrainment of mold powder and deoxidation by using a moving magnetic field and a static magnetic field in combination in continuous casting of steel using a magnetic field. It is an object of the present invention to provide a continuous casting method of steel that can simultaneously achieve cleaning and removal of products and inert gas bubbles from a solidification interface.

  The continuous casting method for steel according to the first invention for solving the above-described problems is a method of injecting molten steel into a rectangular mold having a mold long side and a mold short side through an immersion nozzle and continuously casting a magnetic field. The molten steel discharge flow until the projection surface of the moving magnetic field generating device whose moving direction is the slab width direction and the moving magnetic field generating device facing each other across the long mold side reaches the short side of the mold from the discharge hole of the immersion nozzle Is arranged relative to the back of the long side of the mold so as to overlap at least a part of the locus of the mold, and using the moving magnetic field generator, the direction from the short side of the mold toward the center of the mold width direction or the opposite direction At the same time that a moving magnetic field is applied to the moving magnetic field generator, a static magnetic field generating device that covers the entire width of the slab is disposed at a position spaced apart from the moving magnetic field generating device by a certain distance. Applying a static magnetic field to the entire area It is characterized in that the casting.

  The steel continuous casting method according to the second invention is characterized in that, in the first invention, the distance between the moving magnetic field generator and the static magnetic field generator is in the range of 200 to 1000 mm. .

  According to the present invention having the above-described configuration, the molten steel flow velocity at the molten steel surface in the mold is controlled by the moving magnetic field to a region where the mold powder does not entrain, and the molten steel discharge flow from the immersion nozzle collides with the mold short side. The downward flow formed later is blocked by a static magnetic field placed below the moving magnetic field, and the blocked downward flow becomes an upward flow along the solidification interface, so that the molten steel flow velocity at the solidification interface increases. Prevention of entrainment of powder and cleaning / removal of deoxidation products and inert gas bubbles from the solidification interface can be achieved at the same time, and it becomes possible to produce a slab that is much cleaner than before.

  The present invention is described in detail below. First, the examination results that led to the present invention will be described.

  In order to achieve the simultaneous prevention of mold powder entrapment and cleaning / removal of deoxidation products and inert gas bubbles from the solidification interface, the surface flow velocity of the molten steel surface in the mold is suppressed to the optimum range and the solidification interface is achieved. In order to increase the flow velocity of the molten steel in the vicinity, the flow conditions in the mold were determined by electromagnetic fluid simulation for the three types of magnetic field application, a moving magnetic field, a static magnetic field, and a combination of a moving magnetic field and a static magnetic field.

  FIG. 1 shows a flow velocity vector diagram obtained by magnetohydrodynamic simulation when a moving magnetic field is applied. FIG. 1 shows that the vertical center position of the moving magnetic field generator is 345 mm from the molten steel surface in the mold (corresponding to the lower end position of the immersion nozzle discharge hole), and the discharge flow of the molten steel discharged from the discharge hole of the immersion nozzle is FIG. 1A is a flow velocity vector diagram when a moving magnetic field in a direction from the mold short side to the mold width direction center side is applied to reduce the flow velocity of the discharge flow. FIG. FIG. 1B is a vector diagram in the central section of the slab thickness, and FIG. 1C is a vector diagram in the long side surface of the slab, that is, in the vicinity of the solidification interface. 1 (A), (B), and (C) show the flow velocity in the right half of the mold. Reference numeral 2 in the figure denotes an immersion nozzle, and reference numeral 6 denotes a mold short side. 1C, the upper part on the left side in the figure corresponds to the immersion nozzle 2, and the right side end part in the figure corresponds to the position of the inner wall surface of the mold short side 6.

  As shown in FIG. 1, the flow from the immersion nozzle is suppressed by the moving magnetic field to flow toward the short side of the mold and bypasses the flow toward the long side of the slab. It can be seen that the flow near the slab solidification interface is stronger. However, it can be seen that the flow in the vicinity of the slab solidification interface is mainly a downward flow, and the speed is not so high. On the molten steel surface in the mold, about 1/4 of the width of the slab is about 1/4 of the width of the slab, and on the short side of the mold, the flow is from the short side of the mold toward the immersion nozzle. It can be seen that on the immersion nozzle side from the vicinity, the flow is directed from the immersion nozzle toward the mold short side, and the flow is gentle as a whole. That is, although the flow near the molten steel surface is slow and the entrainment of the mold powder is difficult to occur, the flow near the solidification interface is slow and there is a possibility of capturing deoxidation products and inert gas bubbles. . It can also be seen that the flow in the vicinity of the solidification interface is mainly downward, and there is a possibility that deoxidized products and inert gas bubbles may penetrate deep into the slab unsolidified layer.

  FIG. 2 shows a flow velocity vector diagram obtained by magnetohydrodynamic simulation when a static magnetic field is applied. FIG. 2 shows that the center position in the vertical direction of the static magnetic field generator is set to a position of 1110 mm from the molten steel surface in the mold (corresponding to a position 765 mm below the lower end position of the submerged nozzle discharge hole). FIG. 2 (A) is a vector diagram at the molten steel surface, FIG. 2 (B) is a vector diagram in the thickness central section of the slab, and FIG. 2 (C) is a flow velocity vector diagram when a magnetic field is applied. It is a vector figure in the long side surface of a slab, ie, the solidification interface vicinity. FIG. 2 also shows the flow velocity in the right half of the mold as in FIG. 1. In FIG. 2, reference numeral 2 is an immersion nozzle, and reference numeral 6 is a short side of the mold. FIGS. 2 (B) and 2 (C) Then, the upper part on the left side in the figure corresponds to the immersion nozzle 2, and the right side end part in the figure corresponds to the inner wall surface position of the mold short side 6.

  As shown in FIG. 2, when a static magnetic field is applied below the immersion nozzle, the electromagnetic force does not directly affect the discharge flow from the immersion nozzle, but the downward flow is blocked by the static magnetic field application position, Since the flow of the molten steel is formed above the position where the static magnetic field is applied, the flow velocity in the vicinity of the molten steel surface increases. Therefore, although it is inappropriate for the entrainment of the mold powder, the flow rate at the solidification interface increases, so that it is a preferable flow for cleaning / removing deoxidation products and inert gas bubbles.

  FIG. 3 shows a flow velocity vector diagram obtained by an electromagnetic fluid simulation when a moving magnetic field is applied to the upper part and a static magnetic field is applied to the lower part. FIG. 3 shows that the vertical center position of the moving magnetic field generator is 345 mm from the molten steel surface in the mold (corresponding to the lower end position of the immersion nozzle discharge hole), and the vertical center position of the static magnetic field generator is the molten steel in the mold. At a position of 1110 mm from the molten metal surface (corresponding to a position 765 mm below the lower end position of the immersion nozzle discharge hole), the molten steel discharged from the discharge hole of the immersion nozzle is directed from the mold short side to the mold width direction center side. FIG. 3A is a flow velocity vector diagram when a static magnetic field is applied over the entire width direction of the slab at the same time as applying the moving magnetic field in the slab direction. FIG. 3A is a vector diagram at the molten steel surface, FIG. ) Is a vector diagram in the thickness central cross section of the slab, and FIG. 3C is a vector diagram in the long side surface of the slab, that is, in the vicinity of the solidification interface. FIG. 3 also shows the flow velocity in the right half of the mold as in FIG. 1. Reference numeral 2 in the figure is the immersion nozzle, and reference numeral 6 is the short side of the mold. FIGS. 3 (B) and 3 (C) Then, the upper part on the left side in the figure corresponds to the immersion nozzle 2, and the right side end part in the figure corresponds to the inner wall surface position of the mold short side 6.

  As shown in FIG. 3, the discharge flow is braked by application of a moving magnetic field and the flow velocity at the molten steel surface in the mold is suppressed, and the downward flow is blocked by application of a static magnetic field. Then you can see how the upward flow is formed.

  From these results, a moving magnetic field is applied to the discharge flow from the immersion nozzle to control the discharge flow velocity, and at the same time, a static magnetic field is applied across the entire slab width direction below the moving magnetic field. The molten steel flow velocity at the surface is controlled within an appropriate range, the molten steel flow velocity at the solidification interface is increased, the mold powder is prevented from being caught on the molten steel surface, and the deoxidation products and inert gas bubbles are washed and removed at the solidification interface. It was found that this was achieved at the same time.

  The present invention has been made on the basis of the results of this study. The projection surface of the moving magnetic field generating device in which the moving direction of the magnetic field is the slab width direction and the moving magnetic field generating device facing each other across the mold long side is an immersion nozzle. It is arranged relative to the back of the long side of the mold so that it overlaps at least part of the trajectory of the molten steel discharge flow from the discharge hole to the short side of the mold, and from the short side of the mold using the moving magnetic field generator Applying a moving magnetic field that moves in the direction toward the center of the mold width direction or in the opposite direction, and at the same time, a static magnetic field generator across the entire slab width at a position spaced apart from the moving magnetic field generator by a fixed distance And casting while applying a static magnetic field to the entire mold width direction using the static magnetic field generator.

  Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 4 is a schematic perspective view of a flow control device and a mechanism in the case of applying a moving magnetic field that moves in the mold width direction (X-axis direction) from the mold short side toward the immersion nozzle side in the mold center. These are the schematic front views of the casting_mold | template part of the slab continuous casting machine used when implementing this invention.

  4 and 5, a mold 1 having a rectangular horizontal inner surface space is constituted by the opposed mold long sides 5 and the opposed mold short sides 6 provided inside the mold long sides 5. The inner space of the mold 1 formed by being surrounded by the mold long side 5 and the mold short side 6 is substantially at the center position of the tundish (not shown) disposed at a predetermined position above the mold 1. An attached immersion nozzle 2 is inserted. A pair of discharge holes 7 for discharging the molten steel 8 in the direction of the mold short side 6 is provided below the immersion nozzle 2.

  On the back of the mold long side 5, a total of four linear type moving magnetic field generators 3 divided into two on the left and right in the width direction of the mold long side 5 with the immersion nozzle 2 as a boundary sandwich the mold long side 5. Arranged relative to each other. In this case, the linear-type moving magnetic field generator 3 is configured so that the projection surfaces of the linear-type moving magnetic field generators facing each other across the mold long side 5 reach the mold short side 6 from the discharge hole 7 of the immersion nozzle 2. It arrange | positions so that it may overlap with at least one part of the locus | trajectory of the discharge flow 9 of the molten steel 8. FIG. That is, the linear moving magnetic field generator is applied so that the moving magnetic field generated from the opposing linear moving magnetic field generator 3 is applied to at least a part of the discharge flow 9 from the discharge hole 7 to the mold short side 6. 3 is arranged. Each linear moving magnetic field generator 3 is connected to an AC power source (not shown), and the AC power source is connected to a control device (not shown) for controlling the moving direction, frequency, and magnetic field strength of the magnetic field. The magnetic field strength, frequency, and magnetic field moving direction applied from the linear moving magnetic field generator 3 are respectively determined by the power supplied from the AC power source based on the magnetic field moving direction, frequency, and magnetic field strength input from the control device. It is controlled individually.

  A static magnetic field generator 4 is disposed below the linear moving magnetic field generator 3 so as to face the entire slab width direction across the long side surface of the slab. That is, it arrange | positions so that the static magnetic field which penetrates in the thickness direction of a slab can be applied over the slab width direction whole region. The static magnetic field generator 4 is connected to a direct current power source (not shown), and the direct current power source is connected to a control device (not shown) for controlling the magnetic field strength, and the magnetic field strength input from the control device is adjusted. The magnetic field strength applied from the static magnetic field generator 4 is controlled by the electric power supplied from the DC power source. Although the static magnetic field generator 4 can also be comprised with a permanent magnet, since an intensity | strength of a magnetic field can be changed arbitrarily, an electromagnet type is preferable.

  In FIG. 5, the static magnetic field generator 4 is disposed between the guide rolls 13 adjacent to each other in the casting direction and disposed in the secondary cooling zone, but is disposed in the gap between the mold 1 and the guide roll 13. Alternatively, it may be arranged on the back surface of the mold long side 5. However, it is preferable to arrange the linear moving magnetic field generator 3 so that the center position in the casting direction and the center position in the casting direction of the static magnetic field generator 4 are within a range of 200 to 1000 mm. Since the linear type moving magnetic field generator 3 is arranged according to the position of the discharge flow 9, the static magnetic field generator 4 may be determined according to the arrangement position of the linear type moving magnetic field generator 3.

  When the center position in the casting direction of the linear moving magnetic field generator 3 and the static magnetic field generator 4 is less than 200 mm, the molten steel flow dammed by the static magnetic field generator 4 affects the flow of the molten steel surface 10 in the mold. As a result, it becomes difficult to control the flow rate to be optimal for prevention of mold powder entrainment. On the other hand, when the center position in the casting direction exceeds 1000 mm, the flow velocity of the molten steel at the installation position of the static magnetic field generator 4 is attenuated, and the upward flow due to the flow blocked by the static magnetic field generator 4 is decelerated. This is not preferable because the desired flow rate of the solidification interface cannot be obtained.

  The continuous casting method of this invention is implemented as follows using the slab continuous casting machine comprised in this way.

  Molten steel 8 melted in a primary refining furnace such as a converter or an electric furnace or a secondary refining furnace such as an RH vacuum degassing apparatus is injected into the mold 1 from the tundish through the immersion nozzle 2. The molten steel 8 is injected into the mold as a discharge flow 9 from the discharge hole 7 toward the mold short side 6. The molten steel 8 injected into the mold is cooled by the mold 1 to form a solidified shell 11. If a predetermined amount of molten steel 8 is injected into the mold, a pinch roll (not shown) installed in the secondary cooling zone below the mold 1 with the discharge hole 7 immersed in the molten steel 8 in the mold. Is driven, the outer shell is made into a solidified shell 11, and drawing of a slab having unsolidified molten steel 8 inside is started. After the start of drawing, casting is performed while controlling the position of the molten steel surface 10 to a substantially constant position in the mold. Mold powder 12 is added on the molten steel surface 10 in the mold. The mold powder 12 melts to prevent oxidation of the molten steel 8 and flows between the solidified shell 11 and the mold 1 to exert an effect as a lubricant.

  During this casting, a moving magnetic field is applied from the linear moving magnetic field generator 3 and a static magnetic field is applied from the static magnetic field generator 4.

As shown in FIG. 4, the linear moving magnetic field generator 3 has a plurality of electromagnetic coils (not shown in FIG. 5) arranged side by side in the width direction. By shifting, a so-called linear type moving magnetic field is generated. FIG. 4 shows a state in which the magnetic field moves from the mold short side 6 toward the immersion nozzle 2 in the center of the mold 1. In FIG. 4, F _X represents the electromagnetic force acting on the discharge flow 9 of the molten steel 8. represents, V _X represents the moving speed of the moving magnetic field, B _Y represents a magnetic flux density of the moving magnetic field. The moving speed V _{X of the} magnetic field is expressed by the following equation (1) from the pole pitch τ and the frequency f of the electromagnetic coil. The pole pitch of the electromagnetic coil is the distance from the S pole to the N pole.

From Lenz's law, the generated induced current J _Z is expressed by the following equation (2). In Equation (2), σ is the electric conductivity of the molten steel, V _X is the moving speed of the moving magnetic field, and _BY is the magnetic flux density of the moving magnetic field.

The electromagnetic force F _X is expressed by the following equation (3), and the electromagnetic force F _X acts in the same direction as the moving direction of the magnetic field.

That is, by setting the moving direction of the moving magnetic field and the electromagnetic force F _X at that time, the molten steel flow in the mold can be controlled by the linear moving magnetic field generator 3.

In the present invention, there are two types of application patterns of the moving magnetic field applied by the linear type moving magnetic field generator 3 shown in FIGS. 6 and 7, when the casting speed is fast and the molten steel flow in the mold 1 is to be decelerated. As shown in FIG. 6, the magnetic field is moved from both mold short sides 6 toward the immersion nozzle 2 to decelerate the discharge flow 9 of the molten steel 8 discharged from the immersion nozzle 2 by the electromagnetic force F _X. also, slow casting speed, when it is desired to accelerate the flow of molten steel in the mold 1, as shown in FIG. 7, by moving the magnetic field from the immersion nozzle 2 in the direction of the mold short side 6, immersed by the electromagnetic force F _X The discharge flow 9 of the molten steel 8 discharged from the nozzle 2 is accelerated. 6 and 7 are diagrams showing the moving direction of the magnetic field from directly above the mold 1, and the arrows in the drawings indicate the moving direction of the magnetic field.

  On the other hand, the downward flow of the discharge flow 9 decelerated or accelerated by the moving magnetic field toward the lower side of the mold enters the region where the static magnetic field is applied by the static magnetic field generator 4. In the static magnetic field, an induced current is generated in the moving molten steel, and an electromagnetic force opposite to the moving direction acts on the molten steel by the induced current and the static magnetic field. That is, an electromagnetic force acts so as to stop the flow of molten steel.

  The downward flow that has entered the region to which the static magnetic field is applied may be slowed down by the static magnetic field, but turns into an upward flow so that it bypasses the static magnetic field region or repels the static magnetic field region. . This upward flow increases the molten steel flow velocity in the vicinity of the solidified shell 11 over the entire mold width direction. As a result, the cleaning effect of the deoxidized product and the inert gas bubbles at the interface between the solidified shell 11 and the molten steel 8 is increased, the adhesion of the deoxidized product and the inert gas bubbles is suppressed, and the deoxidized product and the inert gas bubbles are suppressed. A solidified shell 11 having very few active gas bubbles can be obtained.

  That is, in the present invention, the molten steel flow velocity on the molten steel surface 10 is controlled to an appropriate range by the linear moving magnetic field generator 3 installed at the position of the discharge hole 7 of the immersion nozzle 2, and the linear moving magnetic field generator 3 With the static magnetic field generator 4 installed below, the molten steel flow velocity in the vicinity of the solidified shell 11 is increased, so that the mold powder 12 is not caught in the solidified shell 11 in the vicinity of the molten steel surface 10 and solidified. It is possible to stably produce a clean and high-quality steel slab slab with very little deoxidation product and inert gas bubbles adhering to the shell 11.

  In order to confirm the effect of the present invention, a cast test of aluminum killed steel was performed using a slab continuous casting machine shown in FIG. In the test, the slab was cast with a thickness of 220 mm, a width of 1600 mm, and a casting speed during steady casting of 2.3 m / min. The immersion nozzle used is a so-called “with pool” two-hole nozzle in which the bottom of the nozzle hole has a concave shape, and is an immersion nozzle having a discharge angle of 25 degrees downward and a nozzle inner diameter of 90 mm. The moving magnetic field generator is a three-phase AC linear moving magnetic field generator, and is installed so that the center position of the electromagnetic coil is 345 mm away from the molten steel surface in the mold (corresponding to the lower end position of the immersion nozzle discharge hole). The static magnetic field generator was an electromagnet and was installed such that the center position of the electrode was 1110 mm away from the molten steel surface in the mold. The moving magnetic field generator was applied with a strength of 0.12 Tesla (T), and the moving direction of the magnetic field was applied from the short side of the mold to the immersion nozzle, and the static magnetic field generator was applied with a strength of 0.4 T.

  The test was performed under conditions in which neither a moving magnetic field nor a static magnetic field was applied (condition 1), only a static magnetic field was applied (condition 2), only a moving magnetic field was applied (condition 3), or a moving magnetic field and a static magnetic field were applied. The test was carried out at the four levels (Condition 4).

  During casting, under conditions 1, 3 and 4, the molten steel flow velocity near the molten steel surface in the mold and the molten steel flow velocity at the solidification interface near the molten steel surface in the mold were measured. The molten steel flow velocity in the vicinity of the molten steel surface changes depending on the molten steel flow velocity with the lower end portion immersed in the molten steel surface with a refractory immersion rod supported on the molten steel surface in a rotatable manner. It was calculated from the inclination angle of the dip rod. The molten steel flow velocity at the solidification interface was calculated by the heat transfer equation based on the temperature measurement value of the thermocouple embedded in the mold.

  FIG. 8 shows the measurement result of the molten steel flow velocity near the molten steel surface, and FIG. 9 shows the measurement result of the molten steel flow velocity at the solidification interface. In FIG. 8 and FIG. 9, the mold width direction position on the horizontal axis starts from the mold center (zero), the left side is displayed as negative (minus), and the right side is displayed as positive (plus). Moreover, the molten steel flow velocity of FIG. 8 displays the flow in which the position in the width direction of the horizontal axis is directed from the negative side to the positive side as positive, and displays the flow in the opposite direction as negative. The molten steel flow in FIG. 9 is displayed as an absolute value regardless of the flow direction.

  Under condition 1 where no magnetic field was applied, the flow velocity in the vicinity of the molten steel surface in the mold was fast, and fluctuations in the molten metal surface were large, and stable molten metal surface control was difficult. On the other hand, it was found that the molten steel flow side of the solidification interface was fast, and the deoxidation product and inert gas bubbles were highly effective for cleaning and removing.

  In condition 2 where only a static magnetic field was applied, the behavior was almost the same as in condition 1, the flow velocity in the vicinity of the molten steel surface in the mold was high, and the molten metal surface fluctuation was large, and stable molten metal surface control was difficult.

  Under condition 3 in which only the moving magnetic field was applied, the flow velocity in the vicinity of the molten steel surface in the mold was suppressed, the variation in the molten metal surface was small, and it was found that the entrainment of mold powder was small. However, as shown in FIG. 9, the flow velocity at the solidification interface was the slowest among the four levels tested, and it was confirmed that the effect of cleaning and removing deoxidized products and inert gas bubbles was small.

  In condition 4 where a moving magnetic field and a static magnetic field were applied, the flow velocity in the vicinity of the molten steel surface in the mold was suppressed in the same manner as in condition 3, and the molten metal surface fluctuation was small, and it was found that the entrainment of mold powder was small. Further, the flow velocity at the solidification interface was increased as compared with Condition 3, and it was confirmed that the effect of cleaning and removing the deoxidized product and the inert gas bubbles was ensured.

  The cast slab slab was rolled into a thin steel plate, and the thin steel plate was examined for defects caused by mold powder and deoxidation products by an ultrasonic flaw detection test. As a result, under conditions 1 and 2, a considerable number of defects due to the mold powder occurred. On the other hand, in the condition 3 and the condition 4, the defect caused by the mold powder was not detected. Moreover, in condition 4, the micro defect considered to be derived from a deoxidation product was reduced by about 60% compared to condition 3.

  From the above results, it was confirmed that the present invention can simultaneously achieve the prevention of mold powder entrainment and the cleaning / removal of the deoxidized product from the solidification interface, and the production of a clean slab is possible. .

It is the flow velocity vector figure calculated | required by the electromagnetic fluid simulation when a moving magnetic field is applied. It is the flow velocity vector figure calculated | required by the electromagnetic fluid simulation when a static magnetic field is applied. It is the flow velocity vector figure calculated | required by the magnetohydrodynamic simulation when applying a combination of a moving magnetic field and a static magnetic field. It is a schematic perspective view of the flow control apparatus and mechanism in the case of applying the moving magnetic field which moves toward the immersion nozzle side of the mold center from the mold short side. It is a schematic front view of the casting_mold | template part of the slab continuous casting machine used when implementing this invention. It is a figure which shows the application pattern of a moving magnetic field when decelerating the discharge flow discharged from an immersion nozzle. It is a figure which shows the application pattern of a moving magnetic field when accelerating the discharge flow discharged from an immersion nozzle. It is a figure which shows the measurement result of the molten steel flow velocity of the molten steel surface vicinity. It is a figure which shows the measurement result of the molten steel flow velocity in a solidification interface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold 2 Immersion nozzle 3 Linear type | mold moving magnetic field generator 4 Static magnetic field generator 5 Mold long side 6 Mold short side 7 Discharge hole 8 Molten steel 9 Discharge flow 10 Molten steel surface 11 Solidified shell 12 Mold powder 13 Guide roll

Claims (2)

  When injecting molten steel into a rectangular mold having a long mold side and a short mold side through a dipping nozzle and continuously casting, a moving magnetic field generator in which the moving direction of the magnetic field is the slab width direction is used. Arranged relative to the back of the long side of the mold so that the projection surface of the moving magnetic field generator facing each other overlaps at least part of the trajectory of the molten steel discharge flow from the discharge hole of the immersion nozzle to the short side of the mold The moving magnetic field generator is used to apply a moving magnetic field that moves in the direction from the short side of the mold toward the center of the mold width direction or in the opposite direction, and at the same time, a certain distance downward from the moving magnetic field generator. A continuous casting of steel, characterized in that a static magnetic field generator over the entire width of the slab is disposed at a position separated by a distance, and casting is performed while applying a static magnetic field throughout the mold width direction using the static magnetic field generator. Method.   The method for continuous casting of steel according to claim 1, wherein a distance between the moving magnetic field generator and the static magnetic field generator is in a range of 200 to 1000 mm.

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