JP4254576B2 - Steel continuous casting apparatus and continuous casting method - Google Patents

Description

  The present invention relates to a technique for producing a high-quality slab by controlling a flow by applying a moving magnetic field to molten steel in continuous casting of steel in which molten steel is supplied to a mold using an immersion nozzle.

  In continuous casting of steel, it is known that the molten steel flow state in the mold, particularly the flow in the vicinity of the molten steel surface, affects the slab quality in relation to the entrainment of mold powder and the biting. In order to produce defect-free slabs, molten steel flow control technology in the mold is important.

  Conventionally, a method of applying a magnetic field to molten steel in a mold to optimize the flow has been performed. As a method for applying a magnetic field, for example, there is a method in which a coil is placed opposite to the back surfaces of both long sides and a DC static magnetic field is applied. Patent Document 1 proposes a method in which a DC static magnetic field is applied over the entire width of the mold, and the applied strength is defined by the casting speed, nozzle discharge hole angle, discharge hole area, nozzle immersion depth, and mold width. However, the method of applying a static magnetic field as in Patent Document 1 has a problem that the flow stagnation region cannot be activated efficiently because the static magnetic field always acts as a braking force on the molten steel flow.

  Patent Document 2 proposes a method in which a moving magnetic field generating coil is arranged in the long side direction of the mold to form a swirling stirring flow in the horizontal direction so that inclusions are not captured by the solidified shell. This method is a method in which the molten steel in the mold is positively stirred and inclusions mixed in the molten steel are not solidified on the slab surface layer, but there is also a risk that powder or the like is newly mixed by stirring.

  In contrast, Patent Document 3 discloses a moving magnetic field generator of a linear moving magnetic field type, in which a magnetic field moves from a short side toward an immersion nozzle at the center of the mold. Is set so that at least one cycle of the action of the linear moving magnetic field is received while the molten steel flow from the discharge hole passes through the magnetic field action region, and the upper limit of the frequency is the attenuation of the magnetic field (skin effect) In consideration of the above, it is assumed that the influence of the magnetic field reaches the molten steel inside the mold sufficiently. Patent Document 4 states that the above-mentioned Patent Document 3 is developed and both the magnetic flux density and the frequency are increased or decreased to obtain an appropriate flow.

  In Patent Documents 3 and 4, the moving magnetic field is controlled on the assumption that molten steel flows from the discharge hole toward the short side of the mold, but at the time of casting a wide material in recent years, from low speed casting to high speed casting. It is difficult to control the flow sufficiently. That is, in particular, in the case of a wide material, the flow rate of molten steel to be supplied from the immersion nozzle increases, so that the flow rate of molten steel from the immersion nozzle increases. Increasing the flow rate increases the dynamic pressure, and there is a problem that a negative pressure is generated in the vicinity of the immersion nozzle, and there is a high possibility that the molten powder is entrained from the meniscus.

Furthermore, recently, a method of combining a static magnetic field and a moving magnetic field has been proposed (for example, Patent Document 5). By combining various types of magnetic fields in this way, control according to the situation becomes possible. However, with this technology, the control logic becomes complicated, and there are concerns that the equipment will become larger and the power consumption will increase.
JP 7-314100 A Japanese Patent Publication No.58-49172 Japanese Patent Laid-Open No. 5-23804 Japanese Patent Laid-Open No. 10-5945 JP 2003-164948 A

  The present invention has been made in view of such circumstances, and even when it is difficult to optimize the flow of molten steel in the past, such as when the width of the mold is wide, without performing complicated control, the mold during casting It is an object of the present invention to provide an electromagnetic flow control device for continuous casting of steel and a method of continuous casting of steel capable of appropriately controlling the flow of molten steel.

  In order to solve the above problems, the present invention provides a rectangular mold having a long side and a short side, and a mold in the mold width direction along the long side of the mold in the mold, and injects molten steel into the mold. A continuous casting apparatus for steel comprising: an immersion nozzle; and an electromagnetic flow control device for controlling a flow of molten steel in the mold by forming a moving magnetic field whose moving direction is a mold width direction along the long side, The electromagnetic flow control device includes a plurality of electromagnetic coils arranged so as to face each other on both sides in the mold width direction, a power source that supplies power to the electromagnetic coils, and a waveform control that controls a waveform of a magnetic field generated from the electromagnetic coils. The waveform control unit is configured such that the waveform of the magnetic field generated from the electromagnetic coil corresponding to the central part in the mold width direction is a rectangular function waveform, and the waveform of the magnetic field generated from the electromagnetic coil corresponding to the mold short side is The waveform is trigonometric To provide a continuous casting apparatus of steel, characterized by waveform controlled to be shaped.

  The present invention also provides a plurality of electromagnetic coils by injecting molten steel into a rectangular continuous casting mold having a long side and a short side from an immersion nozzle provided in the mold width direction center along the long side of the mold. By an electromagnetic flow control device that controls the flow of molten steel in the mold by forming a moving magnetic field in which the moving direction is the mold width direction along the long side. A continuous casting method of steel that casts while controlling the flow of molten steel in the mold, and generates a magnetic field having a rectangular function waveform from an electromagnetic coil corresponding to the central portion in the mold width direction, and corresponds to the mold short side. There is provided a continuous casting method for steel, characterized in that a magnetic field having a trigonometric function waveform is generated from an electromagnetic coil and cast.

  In the present invention, the waveform control of the magnetic field can be performed by controlling at least the waveform of the current supplied to the electromagnetic coil in the mold width direction to a rectangular function waveform. The pole pitch of the electromagnetic coil is preferably 100 to 1200 mm, the intensity of the magnetic field generated from the electromagnetic coil is preferably 0.2 T or less, and the frequency of the magnetic field is preferably 0.5 to 6 Hz.

  According to the present invention, a plurality of electromagnetic coils are arranged on both sides in the mold width direction so as to oppose each other, and a moving magnetic field is formed in which the moving direction is the mold width direction along the long side. When performing continuous casting using an electromagnetic flow control device that controls the flow of the mold, a magnetic field having a rectangular function waveform is generated from the electromagnetic coil corresponding to the central portion in the mold width direction, and the electromagnetic wave corresponding to the short side of the mold is generated. Since a magnetic field with a trigonometric function waveform is generated from the coil, at the center in the mold width direction near the immersion nozzle, the flow of the molten steel is suppressed by the static magnetic field due to the rectangular function waveform magnetic field. In the vicinity of the short side of the mold, the effect of the moving magnetic field activates the flow at the solidification interface and promotes inclusions in the solidified shell. Suppression Is, it is possible to ensure the cleanliness of the solidification interface. Therefore, the molten steel flow in the mold can be appropriately controlled, and a high-quality slab can be manufactured.

Embodiments of the present invention will be described below.
First, referring to FIG. 1, an electromagnetic flow control device of a type in which a magnetic field applied to molten steel moves in a direction along the long side of the mold (mold width direction), which is used for molten steel flow control in continuous casting of steel, and An outline of the molten steel flow control mechanism will be described. Note that the subscripts X, Y, and Z of physical quantities shown in the following expressions in the following description indicate those in the X, Y, and Z directions in FIG.

  As shown in FIG. 1, this type of electromagnetic flow control device 10 is generally arranged at a position where a discharge flow is discharged from an immersion nozzle 3 in a rectangular mold 2 having a long side 2a and a short side 2b. A plurality of electromagnetic coils 1 are arranged side by side (in the width direction) along the long side 2a of the rectangular mold 2, and by shifting the phase of the current flowing through the adjacent coils, a so-called linear type A moving magnetic field is generated. In addition, the code | symbol 3 of FIG. 1 is an immersion nozzle.

The moving speed of the magnetic field can be expressed by the following equation (1) by the pole pitch (distance from the S pole to the N pole) τ of the coil 1 and the frequency f of the magnetic field generated from the electromagnetic coil 1. In the following equations, the subscripts X, Y, and Z of each physical quantity indicate those in the X, Y, and Z directions in FIG.
V _x = 2τf (1)
Further, the applied magnetic field B _y as shown in Figure 1, is applied in a direction passing through the mold 2 in the direction of the short side, therefore, from the Lorentz's law, the induced current is to be expressed by the following equation (2) it can.
J _z = σV _x B _y (2)
Furthermore, the electromagnetic force can be expressed by the following equation (3), which indicates that the electromagnetic force works mainly in the same direction as the moving direction of the magnetic field.
F _x = J _z B _y = 2τσfB _y ² (3)

  In such an electromagnetic flow control device 10, when the casting speed is high and it is desired to suppress the flow of molten steel in the mold 2, the magnetic field is moved from the short side 2 b side of the mold 2 toward the immersion nozzle 3 and discharged. It acts to suppress (decelerate) the flow. On the other hand, when the casting speed is low, such as when the pan is replaced, the magnetic field is moved from the immersion nozzle 3 toward the short side 2b to accelerate the discharge flow from the immersion nozzle 3 and activate the flow of molten steel in the mold 2. The effect of promoting heat supply can be exhibited. Alternatively, the magnetic field movement direction is reversed between the front surface and the rear surface of the long side 2a of the mold 2 so that the magnetic field rotates, and the cleaning effect by swirling the molten steel can be obtained.

  FIG. 2 shows a schematic diagram of a flow pattern in a mold that has been generally observed. 2A is a horizontal sectional view of the mold, and FIG. 2B is a vertical sectional view. In this case, the molten steel flow velocity is substantially uniform in the width direction, and the intended molten steel flow is obtained by moving the magnetic field in the direction from the short side 2b of the mold 2 toward the immersion nozzle 3 with respect to the discharge flow 4. A braking effect is obtained. Reference numeral 5 is a mold powder, and 6 is a solidified shell. FIG. 3 shows an image of the action of the molten steel flow braking effect of the electromagnetic flow control device in this case. As shown in this figure, the molten steel flow velocity is decelerated by the moving magnetic field regardless of the position.

  However, it is known that a flow pattern as shown in FIG. 4 also appears depending on the balance of casting conditions (casting width, argon gas flow rate blown into the molten steel flow from the immersion nozzle, casting speed). 4A is a horizontal sectional view of the mold, and FIG. 4B is a vertical sectional view. In particular, such a flow pattern is often observed when casting is performed using a wide mold which is implemented as a measure for improving productivity in recent years. In such a case, the heat supply to the short side of the mold is insufficient, and unmelted mold powder is mixed into the molten steel, or troubles such as a bite occur. In order to avoid this, it is customary to use the acceleration mode in which the magnetic field is moved from the immersion nozzle side to the mold short side, but in the case of casting a wide material, the flow rate of the molten steel to be supplied from the immersion nozzle Therefore, the flow rate of molten steel from the immersion nozzle is increased, the dynamic pressure is increased, and a negative pressure is generated in the vicinity of the immersion nozzle, so that the possibility of the entrainment of the molten powder from the meniscus increases.

  Therefore, in the present invention, in the electromagnetic flow control device, a magnetic field having a rectangular function waveform is generated from the electromagnetic coil corresponding to the central part in the mold width direction near the immersion nozzle, and the electromagnetic coil corresponding to the short side of the mold To generate a magnetic field with a trigonometric waveform. As a result, at the center in the mold width direction near the immersion nozzle, the magnetic field of the rectangular function waveform acts as a static magnetic field to suppress the flow of the molten steel and eliminate the negative pressure at the immersion nozzle. Entrainment of molten powder is suppressed. On the other hand, in the vicinity of the short side of the mold, the flow at the solidification interface is activated by the effect of the moving magnetic field, and the promotion of inclusions in the solidification shell is suppressed, ensuring cleanliness at the solidification interface. It is possible to prevent remelting of the solidified shell on the short side of the mold at the time of high speed casting due to the effect of suppressing the flow of molten steel.

  Next, a specific apparatus configuration for realizing such control will be described. FIG. 5 is a horizontal sectional view showing the continuous casting apparatus according to the first embodiment of the present invention. Similar to FIG. 1 described above, an immersion nozzle 3 is arranged at the center of a rectangular mold 2 having a long side 2a and a short side 2b. And the electromagnetic flow control apparatus 10a is arrange | positioned in the position where a discharge flow is discharged from the immersion nozzle 3 of the casting_mold | template 2. FIG. Similar to the electromagnetic flow control device 10 described with reference to FIG. 1, the electromagnetic flow control device 10 a is disposed at a position where a discharge flow is discharged from the immersion nozzle 3 of the mold 2, and the plurality of electromagnetic coils 1 are rectangular. It is installed side by side along the two long sides 2a of the mold 2 (in the width direction), and a so-called linear type moving magnetic field is generated by shifting the phase of the current flowing through the adjacent coils. ing. The plurality of electromagnetic coils 1 on both sides are respectively attached to the yoke 7 and integrated. The number of electromagnetic coils 1 on one side is twelve, and twelve coils are similarly arranged on the other side, and the electromagnetic coils on both sides are provided facing each other. In addition, the arrow in a figure has shown the direction of the magnetic field in a certain moment.

  Power is supplied to these electromagnetic coils 1 from the three-phase AC power supply 11 so that the phases of the adjacent electromagnetic coils 1 are shifted by 120 °. A current value control unit 12 that controls a current value supplied to the electromagnetic coil 1 is provided on the power supply line from the power source 11 to the electromagnetic coil 1. As shown in the figure, when the electromagnetic coil 1 is marked with symbols A to L from the left side, a normal trigonometric current waveform is applied to the feeding lines of the electromagnetic coils 1 of D, E, and F as a rectangular function system. An inverter 13 for changing the waveform to the above-described waveform is provided, and an inverter 14 having a similar function is also provided for the feeding lines of the G, H, and I electromagnetic coils 1.

  In such an apparatus, the pole pitch of the electromagnetic coil 1 is preferably in the range of 100 to 1200 mm, more preferably 500 to 900 mm. The strength of the magnetic field generated from the electromagnetic coil 1 is preferably 0.2T or less, and more preferably 0.05 to 0.15T. Furthermore, the frequency of the magnetic field is preferably 0.5 to 6 Hz, and more preferably 0.5 to 2 Hz.

  In the electromagnetic flow control device 10a configured as described above, when molten steel stored in a tundish from a ladle (not shown) is injected into the mold 2 from the immersion nozzle 3, a current is supplied from the power source 11 to the electromagnetic coil 1. The flow of molten steel in the mold 2 is controlled by supplying and forming a moving magnetic field.

  At this time, a rectangular function system current waveform is supplied to the electromagnetic coil 1 existing in the center portion in the mold width direction indicated by D, E, F, G, H, and I by the inverters 13 and 14. A magnetic field having a rectangular function waveform as shown in FIG. On the other hand, the electromagnetic coil 1 present on the short side of the mold indicated by A, B, C, J, K, and L is supplied with a trigonometric current waveform from the power supply 11, and as shown in FIG. A trigonometric magnetic field is generated.

  For this reason, in the mold width direction center in the vicinity of the immersion nozzle 3, a magnetic field having a rectangular function waveform is applied, which becomes a static magnetic field, and the molten steel flows so as to eliminate the negative pressure at the immersion nozzle 3. In the vicinity of the mold short side 2b, a trigonometric waveform magnetic field is applied, the effect of the moving magnetic field is exerted, the flow at the solidification interface is activated, and the cleanliness at the solidification interface is improved. Can be secured.

  In addition, although the inverter was not provided in the electromagnetic coil 1 which exists in the casting_mold | template short side shown by A, B, C, J, K, and L, an inverter is provided and the magnetic field of the waveform of a desired trigonometric system is generated. You may do it. Further, the number of arrangement of the electromagnetic coils 1 is not limited to 12, and the applied current may be two-phase alternating current as well as three-phase alternating current as long as the phase of the applied current can be shifted by the adjacent electromagnetic coils. For example, the number of arrangement of electromagnetic coils is 10 and two-phase alternating current is used, and the adjacent electromagnetic coils are 90 ° out of phase.

  Here, a slab center of a slab having a width of 1800 mm and a thickness of 250 mm is formed from the immersion nozzle to the short side of the casting slab by the electromagnetic flow control device having the structure shown in FIG. 5 installed under continuous casting conditions of 2.5 m / min. A moving magnetic field was generated at a maximum magnetic field strength of 0.08 T and a frequency of 1 Hz. The length of the yoke was 2 m and the pole pitch was 0.5 m. As shown in FIG. 5, twelve electromagnetic coils through which a three-phase current having a phase difference of 120 degrees flows were arranged. A rectangular function waveform magnetic field is applied to the six coils in the central portion corresponding to half the width, and a trigonometric waveform magnetic field is applied to the six coils in the short side portion corresponding to ¼ width from both ends. Was applied for casting. As a result, defects due to entrainment of molten powder that occurred at 2.2 m / min under conventional casting conditions could be eliminated.

  In addition, casting experiments were performed with varying magnetic field strengths to ascertain the quality defect rate. Quality defects were measured by an optical inspection device provided on the exit side of the continuous casting machine. The result is shown in FIG. Here, the pole pitch is 250 mm and the frequency of the magnetic field is 1.5 Hz. If the strength of the magnetic field is weak, the quality improvement does not appear remarkably, but the effect can be confirmed from about 0.05T, and the quality defect rate is almost zero at 0.15T. However, 0.2T or more is not preferable because the facility becomes too large. Overall, it was confirmed that 0.05 to 0.15 T is preferable.

  Since the frequency of the magnetic field and the pole pitch ensure the cleanliness of the solidification interface by setting the speed of the moving magnetic field to about 0.5 m / s to 1.5 m / s, the desirable condition is that the frequency is from 0.5 Hz. 6 Hz, more preferably 0.5 Hz to 2 Hz, and a pole pitch of 100 mm to 1200 mm, more preferably 500 mm to 900 mm. By setting the frequency to 1.5 Hz with a pole pitch of 250 mm, the moving speed becomes 0.75 m / s. If the pole pitch is P and the frequency is F, then P × F is the moving speed of the magnetic field, and a good cast slab is manufactured by setting 0.5 <2 × P × F <1.5. I was able to. Of course, depending on the casting conditions, the same effect can be obtained even if casting is performed in the direction of magnetic field movement opposite to that of the present embodiment.

  According to the present invention, since it is possible to optimize the flow of molten steel in the mold, even when it is difficult to optimize the flow of molten steel conventionally, such as when the width of the mold is wide, the molten steel in the mold The flow can be appropriately controlled, and a high quality slab can be manufactured.

The schematic block diagram which shows the moving magnetic field generator of the type which the magnetic field applied to molten steel moves to the direction (mold width direction) along the long side of a casting_mold | template. The horizontal sectional view and the vertical sectional view which show the molten steel flow pattern in the mold generally observed conventionally. The image figure which shows the state at the time of applying the conventional electromagnetic flow control at the time of the flow pattern shown in FIG. The horizontal sectional view and vertical sectional view which show the molten steel flow pattern in a casting_mold | template easy to be observed when it casts using a wide casting_mold | template. The horizontal sectional view showing the continuous casting device concerning one embodiment of the present invention. The figure which shows the example of the magnetic field of the waveform of a rectangular function system. The figure which shows the example of the magnetic field of the waveform of a trigonometric function system. The graph which shows the relationship between the strength of a magnetic field, and a quality defect rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Electromagnetic coil 2; Mold 2a; Long side 2b; Short side 3; Immersion nozzle 4; Discharge flow 10, 10a; Electromagnetic flow control device 11: Three-phase alternating current power supply 12; Current value control part 13, 14;

Claims (6)

A rectangular mold having a long side and a short side, an immersion nozzle for injecting molten steel into the mold along the long side of the mold in the mold, and a moving direction on the long side A continuous casting apparatus for steel comprising an electromagnetic flow control device for controlling a flow of molten steel in a mold by forming a moving magnetic field that is a mold width direction along the mold,
The electromagnetic flow control device comprises:
A plurality of electromagnetic coils arranged to oppose each other on both sides in the mold width direction, a power supply for supplying power to the electromagnetic coils, and a waveform control unit for controlling the waveform of the magnetic field generated from the electromagnetic coils,
In the waveform control unit, the waveform of the magnetic field generated from the electromagnetic coil corresponding to the central portion in the mold width direction is a rectangular function waveform, and the waveform of the magnetic field generated from the electromagnetic coil corresponding to the mold short side is a trigonometric function waveform. A continuous casting apparatus for steel, wherein the waveform is controlled so as to have a waveform.   The said waveform control part controls the waveform of a magnetic field by controlling the waveform of the electric current supplied to the electromagnetic coil of the said mold width direction at least to a rectangular function type | system | group waveform, The steel of Claim 1 characterized by the above-mentioned. Continuous casting equipment.   The pole pitch of the electromagnetic coil is 100 to 1200 mm, the intensity of the magnetic field generated from the electromagnetic coil is 0.2 T or less, and the frequency of the magnetic field is 0.5 to 6 Hz. The continuous casting apparatus for steel according to 2. Molten steel is injected into a rectangular continuous casting mold having a long side and a short side from an immersion nozzle provided at the center of the mold width direction along the long side of the mold, and a plurality of electromagnetic coils are arranged in the mold width direction. The flow of molten steel in the mold is controlled by an electromagnetic flow control device that controls the flow of molten steel in the mold by forming a moving magnetic field in which the moving direction is the mold width direction along the long side. A continuous casting method of steel that is cast while controlling
Casting is performed by generating a rectangular function waveform magnetic field from the electromagnetic coil corresponding to the central portion of the mold width direction, and generating a trigonometric waveform magnetic field from the electromagnetic coil corresponding to the mold short side. Steel continuous casting method.   5. The steel continuous casting method according to claim 4, wherein the waveform control of the magnetic field is performed by controlling at least a waveform of a current supplied to the electromagnetic coil in the mold width direction to a rectangular function waveform. .   The pole pitch of the electromagnetic coil is 100 to 1200 mm, the strength of the magnetic field generated from the electromagnetic coil is 0.2 T or less, and the frequency of the magnetic field is 0.5 to 6 Hz. 5. The continuous casting method for steel according to 5.

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