TWI599417B - Continuous Casting of Steel Emboss Casting - Google Patents

Description

Continuous casting method for steel embryo casting

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a continuous casting process for producing high quality steel slabs having few non-metallic inclusions in the surface layer of a steel slab by controlling the flow of molten steel in the mold.

In recent years, the quality requirements of high-grade steel products such as steel sheets for automobile outer panels and steel sheets for cans have been stricter, and in the stage of steel slab casting, in other words, high quality of steel slabs has been required from the continuous casting stage. One of the required qualities of the steel slab is, for example, a non-metallic inclusion in the surface layer of the steel slab (in the following description, simply referred to as "inclusion").

The inclusions trapped in the surface layer of the steel slab are exemplified by the following.

(a) A deoxidation product suspended in a molten steel when the molten steel deoxidation step is performed by an element such as aluminum.

(b) A fine oxide contained in the inside of the bubble of the argon gas blown into the molten steel by the casting tank or the immersion nozzle.

(c) A suspension or the like formed by the mold powder added to the molten steel soup surface in the mold being wound into the molten steel.

The above inclusions all form surface defects at the stage of the steel product, and therefore it is important to minimize the amount of inclusions caught by the surface layer of the steel slab. Further, if the argon gas bubbles caught in the surface layer of the steel slab are broken and the surface of the steel slab is broken, the inside of the bubble is oxidized by heating by a heating furnace or the like, and the oxidized portion becomes a surface defect.

Conventionally, in order to prevent defects such as deoxidation products, argon bubbles, and mold powder in the molten steel from being caught by the solidified cast piece outer casing, there has been a proposal that the molten steel in the continuous casting mold is used. Flow, maintain the proper state of practice.

For example, the technique disclosed in Patent Document 1 uses a continuous casting method having a pair of discharge nozzles that are symmetrically arranged with respect to the vertical axis of the immersion nozzle, wherein the immersion nozzle is impregnated. The depth, the maximum flow velocity of the discharge flow at the width of the mold 1/4, and the discharge angle of the discharge hole are defined, and the discharge direction of the discharge flow from the immersion nozzle and the angle formed by the long side of the mold are adjusted: The horizontal plane is 3~7°. The angle between the discharge direction of the discharge flow and the long side of the mold is adjusted to be 3 to 7°, so that at least a part of the discharge flow is intended to contact the solidified cast piece outer casing on the long side of the mold, thereby The flow rate of the spit outflow is attenuated.

[Previous Technical Literature]

[Patent Literature]

Patent Document 1: Japanese Patent No. 4285345

Patent Document 2: Japanese Patent No. 5,742,992

However, the above-mentioned conventional techniques have the following problems.

In other words, with the stricter quality requirements of steel sheets for automobile exterior panels in recent years, defects caused by the intrusion of fine bubbles and mold powder, which are not considered to be problems in the past, are also considered as problems. According to the traditional method, such strict quality requirements cannot be fully met. In particular, the alloyed hot-dip galvanized steel sheet is heated and then heated to diffuse the iron component of the base material steel sheet to the galvanized layer. Therefore, the surface properties of the base material steel sheet are good for the quality of the alloyed hot-dip galvanized layer. Have a great impact. That is, if the surface layer of the base metal sheet has the defects of bubble or mold powder, even a small defect may cause the thickness of the galvanized layer to be uneven, and this portion will appear striped on the surface of the steel sheet. Defects, so it can not be used in the use of steel plates for automotive exterior panels for quality requirements.

Patent Document 1 attempts to control the flow of molten steel in a mold by adjusting the immersion depth and shape of the immersion nozzle discharge hole and the discharge direction from the immersion nozzle. In general, in order to suppress adhesion of inclusions (mainly Al ₂ O ₃ ) to the inner wall of the immersion nozzle, between the casting tank outlet hole and the immersion nozzle discharge hole, an argon gas such as argon gas or nitrogen gas is blown. . The insufflation of such a gas is considered to have a very large influence on the behavior of the spouting jet, and the molten steel throughput certainly has a great influence on the behavior of the spouting jet. If the gas injection amount and the molten steel throughput are not controlled within a suitable range, but only the design of the immersion nozzle is adjusted, the flow control effect obtained is insufficient, and it cannot be applied to a steel plate for an automobile outer panel or the like. The quality of the steel requires strict manufacturing.

The present invention has been made in view of the above problems, and an object thereof is to provide not only a discharge position of a molten steel from an immersion nozzle, an immersion nozzle shape, a molten steel throughput, and a flow rate of blowing an blunt gas. It is also possible to control the continuous casting method of the high-quality steel blank cast piece by controlling the discharge direction of the dipping nozzle to a suitable direction to control the flow of the molten steel in the mold. Further, a continuous casting method for high-quality steel slabs capable of producing less inclusions is provided for various electromagnetic flow control technologies in the mold, suggesting a suitable immersion nozzle discharge direction.

The technical features of the present invention for solving such technical problems are as follows.

[1] A continuous casting method for a steel slab, which is a continuous casting method in which a immersion nozzle is disposed in a casting mold for continuous casting, and molten steel is supplied to the immersion nozzle to cast the molten steel. The immersion nozzle has one pair of discharge holes arranged symmetrically with respect to the vertical axis thereof, and the immersion depth of the immersion nozzle (the distance from the molten steel soup surface in the mold to the upper end of the discharge hole) is set to 180 mm. Above and not reached 300mm; the molten steel discharge angle of the discharge hole facing downward from the horizontal direction is set in the range of 15 to 35°; the flow rate A of the blunt gas which is blown into the discharge hole from the casting groove outflow hole to the discharge hole The ratio A/P of (NL/min) to the molten steel throughput P (ton/min) is set in the range of 2.0 to 3.5 NL/ton, and the discharge direction of the above-described immersion nozzle is set to be passed through the aforementioned immersion nozzle. The center of the vertical axis, and the reference plane parallel to the long side surface of the mold, is inclined within the range of the following formula (1), θ-6≦α≦θ+10. . . Number (1)

In the equation (1), when the continuous casting mold is viewed from the upper side, the α is the inclination angle (°) with respect to the reference surface in the discharge direction of the immersion nozzle; θ is the continuous casting mold. When viewed from the upper side, the angle formed by the straight line from the center of the vertical axis of the immersion nozzle toward the contact point between the long side of the mold and the short side of the mold and the reference plane (an acute angle) is determined by the following formula (2) ) defined angle (°), tan θ = (D / 2) / (W / 2). . . Number (2)

In the formula (2), D is the thickness (mm) of the continuously cast steel blank cast piece; W is the width (mm) of the continuously cast steel blank cast piece.

[2] The continuous casting method for a steel slab according to [1], wherein the α is determined after the change of the width of the mold in continuous casting or continuous casting, if the α does not satisfy the aforementioned formula ( In the case of 1), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (1).

[3] The continuous casting method of a steel slab according to [1], which is disposed on a back surface of a long side of the mold, and is disposed opposite to the upper magnetic pole and the pair of lower portions via the long side of the mold. a magnetic pole, wherein a position of the discharge hole is set between a position of a maximum value of a DC static magnetic field applied by the upper magnetic pole and a position of a maximum value of a DC static magnetic field applied by the lower magnetic pole, and the upper magnetic pole is used The lower magnetic pole applies a DC static magnetic field to brake the molten steel flow. If the intensity of the DC static magnetic field applied by the upper magnetic pole is 1500 Gs or more and less than 2500 Gs (Gauss; 1 Gs = 10 ^-4 T), the foregoing The discharge direction of the immersion nozzle is inclined with respect to the reference plane, and the above formula (1) is replaced by the following formula (3); if the intensity of the DC static magnetic field is 2500 Gs or more and less than 3500 Gs, The range in which the discharge direction of the immersion nozzle is inclined with respect to the reference plane is replaced by the following formula (4), θ ≦ α ≦ θ + 5. . . Equation (3)

θ+6≦α≦θ+10. . . Equation (4).

[4] The continuous casting method for steel slabs according to [3], wherein the measurement of the aforementioned α is performed after continuous change of the mold width in continuous casting or continuous casting, if the strength of the DC static magnetic field is 1500 Gs. When the above α is less than 2500 Gs, and the above α does not satisfy the above formula (3), the discharge direction of the immersion nozzle is changed to obtain the relationship according to the above formula (3), and the intensity of the DC static magnetic field is 2500 Gs. If the above α does not reach 3500 Gs, and the aforementioned α does not conform to the above formula (4), The discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (4).

[5] The continuous casting method of the steel slab according to [1], which is provided on the back side of the long side of the mold, and is provided with a linear moving magnetic field generating device in which the moving direction of the magnetic field is the width direction of the mold, The molten steel flow discharged from the immersion nozzle imparts a braking force to the moving magnetic field from the short side of the mold toward the immersion nozzle side, or is applied from the immersion nozzle side in order to impart an acceleration force to the molten steel flow. The flow is controlled toward the moving magnetic field on the short side of the mold, and the range of the discharge direction of the immersion nozzle is inclined with respect to the reference surface, and the above formula (5) is replaced by the following formula (5). θ+2≦α≦θ+7. . . Equation (5).

[6] The continuous casting method for a steel slab according to [5], wherein the α is determined after the change of the width of the mold in continuous casting or continuous casting, if the α does not satisfy the aforementioned formula ( In the case of 5), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (5).

[7] The continuous casting method for a steel slab according to [1], wherein the back surface of the long side of the mold is disposed to face a pair of magnetic poles with respect to a long side of the mold, and is applied from the magnetic pole The alternating moving magnetic field is used to perform the cyclotron stirring in the horizontal direction of the molten steel, except that the intensity of the alternating magnetic moving magnetic field is set in the range of 300 to 1000 Gs, if the intensity X (Gs) of the alternating magnetic moving magnetic field is continuously cast Width of steel slab When the ratio X/W (Gs/mm) of W (mm) is 0.30 or more and less than 0.45, the discharge direction of the immersion nozzle is set to the upstream side of the swirling flow formed by the alternating magnetic field. And the range (1) is replaced by the following formula (6) in a range inclined with respect to the reference plane, and if the ratio X/W (Gs/mm) is 0.45 or more and less than 0.55, In the range in which the reference plane is inclined, the above formula (1), θ-3≦α≦θ is replaced by the following formula (7). . . Number (6)

≦-6≦α≦θ-4. . . Equation (7).

[8] The continuous casting method for steel slabs according to [7], wherein the above-mentioned α is measured after continuous change of the mold width in continuous casting or continuous casting, if the ratio X/W (Gs/) When the mm is 0.30 or more and less than 0.45, and the above α does not satisfy the above formula (6), the discharge direction of the immersion nozzle is changed to obtain the relationship according to the above formula (6); if the ratio X/ When W (Gs/mm) is 0.45 or more and less than 0.55, and the above-mentioned α does not satisfy the above formula (7), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (7). .

[9] The continuous casting method for a steel slab according to [1], which is disposed on a back surface of a long side of the mold, and is disposed opposite to the upper magnetic pole and the pair of lower portions via the long side of the mold. a magnetic pole, wherein a position of the discharge hole is provided between a position at which a maximum value of a DC static magnetic field applied by the upper magnetic pole and a maximum value of a DC static magnetic field applied by the lower magnetic pole are overlapped from the upper magnetic pole Applying a DC static magnetic field and an AC moving magnetic field, and using the AC moving magnetic field applied by the upper magnetic pole to form a swirling flow of the molten steel rotating in the horizontal direction in the molten steel soup surface in the mold, and using the DC applied by the upper magnetic pole The static magnetic field brakes the molten steel flow, and uses the DC static magnetic field applied by the lower magnetic pole to brake the molten steel flow, except that the intensity of the aforementioned alternating moving magnetic field is set at 500 to 900 Gs (Gauss; 1 Gs = 10 ^-4) In the range of T), the intensity of the DC static magnetic field applied by the upper magnetic pole is set in the range of 2000 to 3300 Gs, and the DC static magnetic field applied by the lower magnetic pole is set. The intensity is set in the range of 3,000 to 4,500 Gs, and the ratio X/W (Gs/mm) of the intensity X (Gs) of the AC moving magnetic field to the width W (mm) of the continuously cast steel slab is controlled. The discharge direction of the immersion nozzle is set to be on the upstream side of the swirling flow of the molten steel formed by the alternating-current moving magnetic field, and is inclined with respect to the reference surface, at 0.30 or more and less than 0.55.

[10] The continuous casting method of a steel slab according to [9], wherein the discharge direction of the immersion nozzle is set if the ratio X/W (Gs/mm) is 0.30 or more and less than 0.45. In the range in which the reference plane is inclined with respect to the reference plane, the above formula (1) is replaced by the following formula (8); if the ratio X/W (Gs/mm) is 0.45 or more and less than 0.55, the foregoing The discharge direction of the immersion nozzle is inclined with respect to the reference plane, and the above formula (1) is replaced by the following formula (9), θ-2 ≦ α ≦ θ + 5. . . Number (8)

Θ-5≦α≦θ+2. . . Equation (9).

[11] The continuous casting method for steel slabs as described in [10], After the change of the mold width in continuous casting or continuous casting is completed, the above α is measured, and if the ratio X/W (Gs/mm) is 0.30 or more and less than 0.45, and the aforementioned α does not satisfy the above formula (8) In the case of changing the discharge direction of the immersion nozzle, the relationship of the above formula (8) is obtained. If the ratio X/W (Gs/mm) is 0.45 or more and less than 0.55, the α does not satisfy the above number. In the case of the formula (9), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (9).

According to the present invention, in addition to controlling the shape of the immersion nozzle, the throughput of the molten steel, the flow rate of the blown air, and the like, it is controlled within a suitable range, and the discharge direction of the immersion nozzle is also adjusted to an appropriate direction, thereby being adapted. The flow of molten steel in the mold is controlled to achieve high quality steel slab casting. Further, for various electromagnetic flow control conditions in the mold, by controlling the discharge direction of the appropriate immersion nozzle, it is possible to produce a high-quality steel slab having less inclusions.

1‧‧‧Continuous casting mold

2‧‧‧Molded long side

3‧‧‧Molded short side

4‧‧‧Dip nozzle

5‧‧‧Spit hole

6‧‧‧Upper magnetic pole

7‧‧‧lower magnetic pole

8‧‧‧Fused steel

9‧‧‧ Solidified cast shell

10‧‧‧Molded steel noodle soup in mold

11‧‧‧Spit out

12‧‧‧AC moving magnetic field generating coil

13‧‧‧DC static magnetic field generating coil

14‧‧‧DC static magnetic field generating coil

15‧‧‧ whirlpool

16‧‧‧ Reverse flow

17‧‧‧Low flow rate field

18‧‧‧ eddy current

19‧‧‧ Downstream

20‧‧‧Continuous casting mold

30‧‧‧Continuous casting mold

40‧‧‧Continuous casting mold

42‧‧‧Linear moving magnetic field generating device

50‧‧‧Continuous casting mold

52‧‧‧ magnetic pole

Fig. 1 is a schematic cross-sectional view showing an example of a continuous casting mold as viewed from the long side of the mold.

Fig. 2 is a schematic cross-sectional view showing a state of a discharge flow from an immersion nozzle in a continuous casting mold.

Fig. 3 is a schematic view showing a state in which the discharge direction of the immersion nozzle is inclined and the casting is performed from the vertical upper side.

Fig. 4 is a schematic cross-sectional view showing a mold for continuous casting which is different from Fig. 1 .

Fig. 5 is a schematic cross-sectional view when the fourth figure is viewed from the upper side.

Fig. 6 is a schematic cross-sectional view showing a mold for continuous casting which is different from the first and fourth drawings.

Fig. 7 is a schematic cross-sectional view when the sixth figure is viewed from the upper side.

Fig. 8 is a schematic cross-sectional view showing a mold for continuous casting different from the first, fourth, and sixth drawings.

Fig. 9 is a schematic cross-sectional view showing the eighth figure from the vertical upper side.

Fig. 10 is a schematic view showing the flow direction of the molten steel in the mold under casting conditions perpendicular to the short side of the mold.

Fig. 11 is a schematic view showing a state in which the direction of the discharge is inclined and the casting is performed from the vertical upper side.

Fig. 12 is a schematic cross-sectional view showing a mold for continuous casting which is different from Fig. 1, Fig. 4, Fig. 6, and Fig. 8.

Fig. 13 is a schematic cross-sectional view showing a portion of the upper magnetic pole of Fig. 12.

Fig. 14 is a schematic cross-sectional view showing a portion of the lower magnetic pole of Fig. 12.

Fig. 15 is a view showing the flow direction of the molten steel in the mold under the casting condition perpendicular to the short side of the mold, with the discharge direction from the immersion nozzle being set.

Fig. 16 is a schematic view showing a state in which the discharge direction of the immersion nozzle is inclined toward the upstream side of the swirling flow when the casting direction is performed.

Fig. 17 is a flowchart showing an example of a process of changing the inclination angle α of the discharge direction.

Fig. 18 is a flow chart showing another example different from Fig. 17.

Fig. 19 is a flow chart showing another example different from Fig. 17 and Fig. 18.

Fig. 20 is a flow chart showing another example different from Fig. 17 to Fig. 19.

Fig. 21 is a flow chart showing another example different from Fig. 17 to Fig. 20.

Fig. 22 is a flow chart showing an example in which the various processes of Figs. 17 to 21 are separately used depending on the casting conditions.

Fig. 23 is a diagram showing the relationship between "α-θ" and "product defect index" of Examples 19 to 38 of the present invention, and the static magnetic field strength of 2500 (Gs) is used as a boundary.

Fig. 24 is a graph showing the relationship between "α-θ" and "product defect index" in Examples 39 to 49 of the present invention.

Fig. 25 is a diagram showing the relationship between "α-θ" and "product defect index" of Examples 50 to 71 of the present invention, with a ratio of X/W of 0.45 as a boundary.

Figure 26 is a diagram showing the relationship between "α-θ" and "product defect index" of Examples 83 to 106 of the present invention, and the ratio of X/W is 0.45. The map displayed by the area.

Hereinafter, the present invention will be described in detail through embodiments of the invention. 1 is an example of a continuous casting mold 20 which can be applied to the continuous casting method of the present embodiment, and is a cross-sectional view when the continuous casting mold 20 is viewed from the long side of the mold. The continuous casting mold 20 for a steel slab is composed of a pair of opposed mold long sides 2 and a pair of opposed mold short sides 3 combined. In the inner space of the mold surrounded by the long sides of the pair of molds and the short sides of the pair of molds, the immersion nozzle 4 is disposed, and the molten steel 8 is injected into the inner space of the mold from the discharge hole 5 of the immersion nozzle 4. Continuous casting of the molten steel 8 is performed. The discharge hole 5 is disposed on the side wall of the immersion nozzle 4 in a bilaterally symmetrical manner with respect to the vertical axis of the immersion nozzle 4 . The molten steel 8 injected from the discharge hole 5 is discharged in the direction of the short side 3 of the right and left molds by forming a discharge flow. The molten steel 8 injected into the inner space of the mold is cooled by contact with the long side 2 of the mold and the short side 3 of the mold, and a solidified cast piece casing 9 is formed on the contact surface which is in contact with the long side 2 of the mold and the short side 3 of the mold. The solidified cast piece casing 9 is used as a casing, and a steel slab of molten steel 8 which has not been solidified inside is continuously drawn downward to be formed into a steel slab. At this time, a mold powder (not shown) which functions as a lubricant, a heat retaining agent, an oxidation preventive agent, or the like is added to the molten steel noodle soup 10 in the mold. Further, in order to prevent the inclusions from adhering to the inner surface of the immersion nozzle 4, argon is blown between the casting tank outflow holes (not shown) to the discharge holes 5 of the immersion nozzle 4. Gas, nitrogen, etc.

The flow behavior in the mold under the casting conditions shown in Fig. 1 is calculated by numerical calculation, 1/1 water model device of the actual machine, and low-melting alloy (Bi-Pb-Sn-Cd alloy; melting point) The flow rate measurement was performed on a 1/4-size test casting apparatus of an actual machine of about 70 ° C), and it was confirmed several times in succession. At this time, in particular, focusing on the flow behavior of the discharge stream 11, it is attempted to quantify the proper normalization conditions for the flow in the mold.

Fig. 2 is a schematic cross-sectional view showing a state of a discharge flow from an immersion nozzle in a continuous casting mold. It can be seen that the immersion depth of the immersion nozzle 4 (the distance from the molten steel soup surface in the mold to the upper end of the discharge hole) is 180 mm or more and less than 300 mm, and the discharge hole 5 is melted downward from the horizontal direction. When the steel discharge angle is set in the range of 15 to 35°, the flow rate A (NL/min) of the indulgent gas which is blown between the discharge holes 5 of the immersion nozzle 4 from the outflow hole of the casting groove is melted and melted. When the ratio A/P of the steel throughput P (ton/min) is controlled within the range of 2.0 to 3.5 (NL/ton), as shown in Fig. 2(a), the discharge flow 11 is short in reaching the mold. Immediately after the side, the discharge flow 11 tends to float toward the meniscus side. That is, it can be seen that since the blunt gas is blown into the discharge hole 5 of the immersion nozzle 4, the discharge flow 11 exhibits a lift up. From this, it can be seen that the blunt gas flow ratio with respect to the throughput of the molten steel, that is, the A/P value, the immersion depth of the immersion nozzle 4, and the balance between the discharge angle and the discharge angle can be appropriately controlled. Control: The flow of the discharge stream 11 is discharged. Further, as shown in Fig. 2(b), if the blunt gas flow rate A with respect to the molten steel throughput P is too large, the discharge flow 11 is subjected to a lift up effect and will float upward. It can be known that the floating of the advanced discharge stream 11 will promote the change of the meniscus, and it is easy to wind the mold powder. On the other hand, as shown in Fig. 2(c), it can also be seen that if the blunt gas flow rate A with respect to the molten steel throughput P is too small, the discharge flow 11 is less likely to float and directly hits the short side of the mold 3 On the other hand, there is a concern that the casting leakage occurs, and the supply of the molten steel on the meniscus side becomes unstable. Therefore, the heat supply to the meniscus is insufficient, and there is a possibility that the molten powder of the mold powder is poorly melted. In addition, these innovations are in the range of casting widths of 1000 to 2000 (mm), each of the discharge holes 1 is 4000 to 10000 (mm ² ), and the molten steel throughput is 3.0 to 8.0 (ton/min). Since it has been confirmed, as long as it is a casting condition within such a range, the flow behavior of the discharge flow 11 can be stably controlled.

Next, the inventors of the present invention paid attention to the investigation of the discharge direction of the discharge flow 11. As a result, it has been found that, in addition to the above-described control of the upward movement of the discharge flow 11 as described above, if the discharge direction is controlled within a suitable angle range toward the corner portion of the mold, it can be in the meniscus (Meniscus By obtaining a moderate flow rate, it is possible to suppress that bubbles and minute inclusions and powders which cause surface defects are caught in the solidified cast piece casing 9, whereby surface defects can be reduced.

Fig. 3 is a schematic view showing a state in which the direction in which the immersion nozzle is ejected obliquely is viewed from the upper side to perform casting. As shown in Fig. 3, it is assumed that "the line passing through the center of the vertical axis of the immersion nozzle 4 and extending toward the contact point (the corner portion of the mold) of the long side 2 of the mold and the short side 3 of the mold" and "the parallel side with the long side of the mold" are assumed. And through the vertical of the immersion nozzle 4 The angle (sharp angle) formed by the reference plane of the center of the shaft is θ (°), and θ is used: the thickness D (mm) of the cast steel slab and the width W (mm) of the cast steel slab It is defined by the following formula (2) (in the following description, the angle θ is also referred to as "diagonal direction angle θ"). Therefore, the diagonal direction angle θ varies depending on the size of the cross section of the steel slab.

Tan θ = (D / 2) / (W / 2). . . Number (2)

In addition, as shown in Fig. 3, when the casting direction of the immersion nozzle 4 is tilted and the casting mold 20 for continuous casting is viewed from the upper side, the inclination of the discharge direction of the immersion nozzle 4 with respect to the reference surface is observed. The angle is treated as α(°).

The present inventors have found a finding that, in addition to properly controlling the flow behavior of the discharge flow 11, if the inclination angle α with respect to the reference plane is set within the range of the following formula (1), A steel slab with a few surface defects is obtained. That is, by controlling the inclination angle α within the range of the formula (1), it is possible to obtain a suitable flow velocity at which the surface defect factor can be excluded.

≦-6≦α≦θ+10. . . Number (1)

Further, if the inclination angle α is smaller than θ-6, a suitable flow velocity cannot be obtained. Further, if the inclination angle α is larger than θ + 10, the discharge flow 11 will directly collide with the long-side solidified cast piece casing 9, and therefore, the risk of occurrence of casting leakage becomes large.

Therefore, by adopting the continuous casting method of the present embodiment, it is possible to manufacture a good steel blank cast piece without using an expensive electromagnetic flow coil device. Further, in the present embodiment, the steel blank slab in the range of 220 to 300 (mm) is used, and the continuous casting of the present embodiment can be applied as long as it is a steel slab having a thickness within the range. method.

Next, the inventors of the present invention have investigated the most suitable inclination angle α with respect to the reference surface in the case of using various electromagnetic flow control methods in the mold.

Fig. 4 is a schematic cross-sectional view showing a mold for continuous casting which is different from the above. In addition, Fig. 5 is a schematic cross-sectional view when the fourth figure is viewed from the upper side. The continuous casting mold 30 for a steel slab is provided for the continuous casting mold 20 shown in Fig. 1 and the opposite side of the long side 2 of the mold. The upper magnetic pole 6 and the pair of lower magnetic poles 7. As shown in Fig. 5, each of the upper magnetic poles 6 and the lower magnetic poles 7 is provided with a DC static magnetic field generating coil 13 for applying a DC static magnetic field. The DC static magnetic field generating coil 13 is arranged to be equal to or larger than the width of the cast steel slab.

The molten steel flow of the molten steel noodle 10 in the mold is braked (decelerated) by the DC static magnetic field applied from the DC static magnetic field generating coil 13 of the upper magnetic pole 6. Similarly, by the DC static magnetic field applied from the DC static magnetic field generating coil 13 of the lower magnetic pole 7, the molten steel flow system in the discharge flow 11 that is intended to pass downward through the DC static magnetic field generating coil 13 is braked. (slow down). Further, the discharge hole 5 of the immersion nozzle 4 is It is provided between "the position of the maximum value of the DC static magnetic field applied by the upper magnetic pole 6" and "the position of the maximum value of the DC static magnetic field applied by the lower magnetic pole 7".

When such electromagnetic flow control is performed, the molten steel flow system is braked by the static magnetic field, so that the mold powder can be prevented from being caught. On the other hand, in order to suppress the bubbles and minute inclusions from being caught in the solidified cast piece casing 9, it is necessary to impart a moderate flow velocity to the molten steel flow. The inventors of the present invention have continuously strived to repeat the results of the review, and found a finding that, in response to the intensity of the DC static magnetic field of the upper magnetic pole 6, there is indeed an inclination angle α of the appropriate discharge direction. That is, it can be known that if the intensity of the DC static magnetic field applied by the upper magnetic pole 6 is 1500 Gs or more and less than 2500 Gs (Gauss; 1 Gs = 10 ^-4 T), the discharge direction of the immersion nozzle 4 is set to: By the center of the vertical axis of the immersion nozzle 4, and with respect to the reference plane parallel to the long side surface of the mold, the inclination is maintained in the range of the following formula (3), and if the DC static magnetic field is applied by the upper magnetic pole 6, When the strength is 2,500 Gs or more and less than 3,500 Gs, if it is maintained within the range of the following formula (4), a good steel slab can be obtained. This is because if the intensity of the DC static magnetic field is 2500 Gs or more and the strength is less than 3500 Gs, by setting the inclination angle α to such a large angle as shown in the formula (4), The flow rate at which the molten steel flow is matched to the braking effect caused by the static magnetic field.

≦≦α≦θ+5. . . Equation (3)

θ+6≦α≦θ+10. . . Equation (4)

Fig. 6 is a schematic cross-sectional view of a casting mold for continuous casting different from the above Surface map. In addition, Fig. 7 is a schematic cross-sectional view when the sixth figure is viewed from the upper side. The continuous casting mold 40 for a steel slab is the one for the continuous casting mold 20 shown in Fig. 1, and the opposite side of the long side 2 of the mold is provided on the back side of the long side 2 of the mold. The linear magnetic field generating device 42 is moved. The moving direction of the magnetic field of the linear moving magnetic field generating device 42 is along the width direction of the mold. When the braking force is applied to the discharge flow 11 discharged from the immersion nozzle 4 provided in the mold to control the flow in the mold, as shown in Fig. 7(a), the orientation is from the short side of the mold. 3, a moving magnetic field is applied in the direction of the immersion nozzle 4; when an acceleration force is applied to the discharge flow 11 to control the flow in the mold, as shown in Fig. 7(b), the direction is: from the immersion nozzle 4 A moving magnetic field is applied in the direction of the short side 3 of the mold. It is understood that the flow control method is characterized in that the discharge flow 11 is given a braking force or an acceleration force, and the discharge flow 11 can be controlled in a convenient state at any time, but basically the center of the immersion nozzle 4 is formed. The symmetrical molten steel flow, therefore, in the portion where the left and right molten steel flows interfere with each other, an area where the flow velocity is small will occur. The present inventors have also found a finding that even in this case, it is possible to suppress the inclination angle α of the discharge direction of the immersion nozzle 4 with respect to the reference surface to an appropriate value. Air bubbles and minute inclusions are trapped in the solidified cast piece casing 9. As a result of various experiments and investigations, it is known that, in the case of the flow control method in the mold to which the moving magnetic field is applied, the discharge direction of the immersion nozzle 4 is set to be the center of the vertical axis passing through the immersion nozzle, and When it is inclined in the range of the following formula (5) with respect to the reference plane parallel to the long side surface of the mold, A good quality steel slab can be obtained.

θ+2≦α≦θ+7. . . Equation (5)

In other words, it is considered that even if it is easy to form a molten steel flow in a bilaterally symmetrical mold, if the discharge direction of the immersion nozzle is directed to the inclination angle shown by the formula (5), the molten steel flow can be imparted. Moderate flow rate.

Fig. 8 is a schematic cross-sectional view showing a mold for continuous casting which is different from the above. Further, Fig. 9 is a schematic cross-sectional view when the eighth figure is viewed from the upper side. In the continuous casting mold 50, the continuous casting mold 20 shown in Fig. 1 is placed on the back surface of the long side 2 of the mold, and is provided with a pair of magnetic poles 52 opposed to each other via the long side 2 of the mold. . In the magnetic pole 52, as shown in Fig. 9, an AC moving magnetic field generating coil 12 to which an AC moving magnetic field can be applied is provided. The magnetic pole 52 is moved in a direction in which the magnetic field is applied, and is a moving magnetic field in the width direction of the mold, and a swirling flow in the horizontal direction is given to the molten steel 8 in the mold to control the flow of the molten steel flow. In the flow control method, the discharge direction from the immersion nozzle 4 is set to be symmetrical in the direction of the short side 3 of the mold, and the molten steel flow in the mold is explained. The flow.

Fig. 10 is a view showing the flow rate of the molten steel in the casting mold under the casting conditions in which the discharge direction is set to be perpendicular to the short side of the mold. In Fig. 10, reference numeral 15 denotes a molten steel noodle soup 10 formed by an alternating magnetic field and a swirling flow in a single direction in a clockwise or counterclockwise direction in the vicinity thereof; :threw up The outflow 11 collides with the solidified cast piece casing 9 on the short side 3 side of the mold, and then flows vertically upward, and then, in the mold, the molten steel noodle 10 flows from the short side of the mold toward the impregnation nozzle side; Indicates: low flow velocity field; 18 series indicates: eddy current due to the impact of the swirling flow 15 and the reverse flow 16; 19 indicates that the discharge flow 11 hits the solidified cast piece shell on the short side of the mold, and then flows downward toward the vertical flow. flow. Further, in Fig. 10, although the low flow velocity region 17 and the eddy current 18 are indicated on only the short side of the mold on one side, the low flow velocity region 17 and the eddy current also occur on the short side of the mold on the other side. 18. Further, it has been confirmed that, as shown in Fig. 10, the flow rate of the molten steel is extremely low next to the short side 3 of the mold in the width direction of the long side 2 of the mold in the downstream region of the swirling flow 15 caused by the alternating moving magnetic field. Flow rate field 17. From the results of the investigation of the defect distribution of the steel product cast by the continuous casting machine under such casting conditions, it was confirmed that the field in which the defects of the steel product existed coincides with the occurrence position of the low flow velocity field 17.

Further, the inventors of the present invention, after various investigations, found a finding that, beside the short side 3 of the mold, there will be: the swirling flow 15 caused by the alternating magnetic field and the short side of the spouting stream 11 The reverse flow 16 caused by the solidified cast piece casing 9 strikes and interferes to produce a low flow velocity field 17, in which bubbles and inclusions are trapped, thereby becoming a defect in the final steel product. Moreover, a concept has also been found in which the swirling flow 15 collides with the reverse flow 16 to cause the eddy current 18, and the mold powder is caught by the eddy current 18 and captured in the solidified cast piece casing 9, which is molded. Powder may also become a steel product Defects. The present inventors have continuously reviewed the solutions to these problems. As described above, the defects of the steel product resulting from the inclusion of inclusions, bubbles, and mold powder are caused by the collision and interference of the swirling flow 15 caused by the alternating magnetic field and the reverse flow 16 of the discharge stream 11. The low flow rate field 17 is formed and the eddy current 18 is generated. Therefore, the present inventors have found a finding that even in the flow control mode in which the alternating magnetic field is applied to cause the swirling flow 15 in the horizontal direction, the discharge direction of the dipping nozzle 4 is set to be: If the reference surface is kept inclined, it is possible to prevent the swirling flow 15 from colliding and disturbing with the reverse flow 16.

Fig. 11 is a schematic view showing a state in which the direction in which the discharge direction is kept inclined and the casting is performed from the vertical upper side. According to various flow investigation experiments, it is known that, as shown in Fig. 11, the discharge direction of the immersion nozzle 4 is set such that it is important to keep the inclination toward the upstream side of the swirling flow 15 caused by the alternating magnetic field. of. Further, the inventors of the present invention have learned from the flow investigation experiment that the intensity of the alternating magnetic field is set in the range of 300 to 1000 Gs, and the intensity X (Gs) of the alternating magnetic field and the continuously cast steel embryo. When the ratio X/W (Gs/mm) of the width W (mm) of the slab is 0.30 or more and less than 0.45, the discharge direction of the immersion nozzle 4 is set to pass through the center of the vertical axis of the immersion nozzle 4. And with respect to the reference plane parallel to the long side surface of the mold, toward the upstream side of the swirling flow formed by the alternating magnetic field, is inclined in the range of the following formula (6); the intensity X of the moving magnetic field in the alternating current (Gs The ratio of the width W (mm) of the continuously cast steel slab is X/W (Gs/mm) is 0.45. When the above is less than 0.55, the discharge direction of the immersion nozzle 4 is set so as to pass through the center of the vertical axis of the immersion nozzle 4, and is formed toward the magnetic field by the alternating current with respect to the reference plane parallel to the long side surface of the mold. On the upstream side of the swirling flow, if it is inclined within the range of the following formula (7), a good steel blank cast piece can be obtained.

Θ-3≦α≦θ. . . Number (6)

≦-6≦α≦θ-4. . . Equation (7)

When a DC static magnetic field is applied to the molten steel 8 shown in Fig. 4, and when a braking force or an acceleration force is applied to the discharge flow 11 shown in Fig. 6, basically, the molten steel flow in the mold is Since it is symmetrical to the left and right, in order to provide an appropriate swirling flow rate, the discharge direction of the immersion nozzle 4 is preferably set to a large inclination toward the long side 2 side of the mold. On the other hand, in the case where the swirling flow agitation is given by the electromagnetic flow control shown in Fig. 8, the angle of inclination is sufficient to suppress the collision and dry winding of the reverse flow 16 and the swirling flow 15, so It is preferable to use a small inclination angle α as shown in the formula (6) and the formula (7). Further, if the inclination angle α is too large, the flow rate of the molten steel beside the solidified cast piece casing 9 will be too fast, which will hinder the growth of the solidified cast piece casing 9, and may cause operational troubles such as causing a blow out. It is not appropriate, therefore.

Fig. 12 is a schematic cross-sectional view showing a mold 1 for continuous casting different from the above, and the symbol 1 indicates: a mold for continuous casting; 2 indicates a long side of the mold; 3 indicates a short side of the mold; and 4 indicates: Immersion nozzle; 5 series means: discharge hole of the immersion nozzle; 6 series means: upper magnetic pole; 7 series means: lower magnetic pole; 8 series means: molten steel; It means: solidified cast piece outer casing; 10 series means: molten steel noodle soup in the mold; 11 series shows: discharge flow from the immersion nozzle.

The continuous casting mold 1 is composed of a pair of opposed mold long sides 2 and a pair of opposed mold short sides 3, and is surrounded by a pair of mold long sides 2 and a pair of mold short sides 3. In the inner space of the mold, the immersion nozzle 4 is disposed, and the molten steel 8 is injected into the inner space of the mold from the discharge hole 5 of the immersion nozzle 4 to carry out continuous casting of the molten steel 8. The discharge hole 5 is disposed on the side wall of the immersion nozzle 4 in a bilaterally symmetrical manner with respect to a straight line passing through the center of the immersion nozzle 4, and the molten steel 8 injected from the discharge hole 5 becomes the discharge flow 11 and faces the right and left sides of the mold. Spit in the direction of 3. The molten steel 8 injected into the inner space of the mold will be cooled by contact with the long side 2 of the mold and the short side 3 of the mold, and a solidified cast shell 9 will be formed at the contact surface with the long side 2 of the mold and the short side 3 of the mold. The solidified cast piece casing 9 is an outer casing, and the steel blank in which the inside of the molten steel 8 which has not been solidified is continuously drawn downward, and is formed into a steel blank cast piece. At this time, a mold powder (not shown) which functions as a lubricant, a heat retaining agent, an oxidation inhibitor, or the like is added to the molten steel noodle soup 10 in the mold.

Fig. 13 is a schematic cross-sectional view showing a portion of the upper magnetic pole of Fig. 12. Further, Fig. 14 is a schematic cross-sectional view showing a portion of the lower magnetic pole of Fig. 12; The continuous casting mold 1 used in the present embodiment is disposed on the back surface of the long side 2 of the mold, and is disposed with a pair of upper magnetic poles 6 and a pair of lower magnetic poles 7 opposed to each other via the long side 2 of the mold. The upper magnetic pole 6 is provided with an alternating current moving magnetic field generating coil 12 for applying an alternating current moving magnetic field and for applying a direct current static magnetic field as shown in FIG. The DC static magnetic field generating coil 13 is provided. On the other hand, as shown in Fig. 14, the lower magnetic pole 7 is provided with a DC static magnetic field generating coil 14 for applying a DC static magnetic field. The arrangement length of the AC moving magnetic field generating coil 12, the DC static magnetic field generating coil 13, and the DC static magnetic field generating coil 14 is equal to or greater than the width of the cast steel blank cast piece.

According to the alternating current moving magnetic field applied by the alternating magnetic field generating coil 12 of the upper magnetic pole 6, the molten steel in the mold will form a swirling flow of the molten steel 8 which is rotated in the horizontal direction, and, depending on the direct current static magnetic field generated by the upper magnetic pole 6, The DC static magnetic field applied by the coil 13 will be braked (decelerated) by the molten steel flow of the molten steel noodle 10 in the mold. Similarly, according to the DC static magnetic field applied by the DC static magnetic field generating coil 14 of the lower magnetic pole 7, the molten steel flow which is directed downward through the position of the DC static magnetic field generating coil 14 in the discharge flow 11 will be braked. (slow down). Further, the discharge hole 5 of the immersion nozzle 4 is provided at "the position of the maximum value of the DC static magnetic field applied by the upper magnetic pole 6" and "the position of the maximum value of the DC static magnetic field applied by the lower magnetic pole 7". between.

Fig. 15 is a view showing the flow direction of the molten steel in the mold under the casting condition perpendicular to the short side of the mold, with the discharge direction from the immersion nozzle being set. The present inventors have used the continuous casting mold 1 shown in Fig. 12 to apply a DC static magnetic field and an AC moving magnetic field to the upper magnetic pole 6, and to apply a DC static magnetic field to the lower magnetic pole 7, and to: The discharge direction of the discharge hole 5 of the immersion nozzle 4 was set to be parallel to the long side surface of the mold, and the flow state of the discharge flow 11 in the mold under the casting condition perpendicularly to the short side 3 of the mold was investigated.

The flow velocity distribution in the mold under such casting conditions was calculated by numerical calculation and a quarter-size test of an actual machine using a low melting point alloy (Bi-Pb-Sn-Cd alloy; melting point about 70 ° C) The flow rate measurement by the casting apparatus was repeatedly confirmed. As a result, it was confirmed that, as shown in Fig. 15, the downstream flow region of the swirling flow 15 caused by the alternating magnetic field, that is, the short side 3 of the mold in the width direction of the long side 2 of the mold was produced. The flow rate of the molten steel becomes smaller in the low flow rate field 17 . In Fig. 15, reference numeral 15 denotes a swirling flow which is formed by an alternating current moving magnetic field and which is rotated in a single direction of the molten steel noodle soup 10 in the mold and its vicinity in the clockwise direction or the counterclockwise direction; : The discharge flow 11 collides with the solidified cast piece shell on the short side of the mold, and then flows vertically upward, and then, in the mold, the molten steel noodle 10 flows from the short side of the mold toward the impregnation nozzle side; : low flow rate field; 18 series means: eddy current generated by the swirling flow 15 colliding with the reverse flow 16; 19 is a downward flow flowing downwardly directly after the discharge flow 11 collides with the solidified cast piece shell on the short side of the mold. . Further, in Fig. 15, although the low flow velocity region 17 and the eddy current 18 are indicated on only the short side of the mold on one side, the nitrogen flow field 17 and the eddy current 18 are generated on the short side of the mold on the other side.

In addition, from the investigation results of the defect distribution of the steel product cast by the continuous casting machine of the actual machine under such casting conditions, it was also confirmed that the field in which the defect of the steel product exists and the occurrence of the low flow rate field 17 described above The position is the same.

The inventors, etc., after various investigations, found A novelty is that, in the vicinity of the short side of the mold, the swirling flow 15 caused by the alternating magnetic field and the discharge flow 11 from the discharge hole 5 collide with the reverse flow 16 caused by the short-side solidified cast shell, because this The two flows collide and interfere with each other to create a low velocity field 17 where bubbles and inclusions are trapped into this low velocity field 17 and become a defect in the final steel product. In addition, a finding has been found that the swirling flow 15 and the reverse flow 16 collide to generate a vortex 18, and the mold powder is drawn into the vortex 18 and captured by the solidified cast shell, which may also become a steel product. Defects.

The inventors of the present invention constantly strive to review the solutions to these problems. As described above, the defects of the steel product caused by inclusions, bubbles, and mold powder are caused by the reverse flow 16 of the swirling flow 15 caused by the AC moving magnetic field and the discharge flow 11 from the discharge hole 5. The low velocity fields 17 and eddy currents 18 caused by collisions and disturbances are caused. Therefore, the inventors of the present invention have focused on how to avoid the method in which the swirling flow 15 and the reverse flow 16 collide and dry, and as a result, find a finding that the discharge from the dipping nozzle 4 is performed. The discharge direction of the flow 11 is shifted from the direction perpendicular to the short side 3 of the mold.

In general, the discharge hole 5 of the immersion nozzle 4 is often disposed so as to be discharged toward the short side surface of the mold, and is disposed in a direction parallel to the long side surface of the mold, and is intentionally provided to keep the inside and outside of the mold. The symmetry of the molten steel flow. However, the condition for imparting the swirling flow 15 to the molten steel 8 in the mold by the alternating moving magnetic field of the present invention is employed. In the following, it is considered that the symmetry of the left and right sides of the mold is maintained, and the discharge direction of the discharge port 5 of the immersion nozzle 4 is determined in consideration of the axis symmetry centering on the immersion nozzle 4 . In principle, it is more appropriate.

Fig. 16 is a schematic view showing a state in which the discharge direction of the immersion nozzle is inclined toward the upstream side of the swirling flow as viewed from the upper side. According to the numerical analysis and the test casting apparatus using the low-melting alloy, the results of reviewing the discharge direction from the immersion nozzle 4 under various conditions have found a novelty that the intensity of the alternating magnetic field of the upper magnetic pole 6 is moved. Set the range of 500 to 900 (Gs), set the intensity of the DC static magnetic field of the upper magnetic pole 6 to the range of 2000 to 3300 (Gs), and set the intensity of the DC static magnetic field of the lower magnetic pole 7 to 3000 to 4500. Within the range of Gs), the ratio X/W (Gs/mm) of the AC moving magnetic field strength X (Gs) of the upper magnetic pole 6 to the width W (mm) of the continuously cast steel blank is controlled to be 0.30 or more. When it is less than 0.55, as shown in Fig. 16, the discharge direction of the immersion nozzle 4 is set so as to be inclined toward the upstream side of the swirling flow 15 formed by the alternating magnetic field, and the swirling flow 15 can be avoided. The collision and interference with the reverse flow 16 does not produce the low velocity field 17 and the vortex 18, and the desired molten steel flow in the mold can be obtained.

Further, if the ratio of X/W is less than 0.30, the flow velocity of the swirling flow 15 with respect to the width of the steel slab is too small, so that a sufficient effect cannot be obtained even if the discharge direction of the immersion nozzle 4 is kept inclined. In addition, it is also considered to be: if the ratio of X/W is 0.55 or more In this case, it is possible to ensure a sufficient flow velocity of the swirling flow 15 with respect to the width of the steel slab, and it is possible to suppress the disadvantages of the low flow velocity region 17 due to the collision with the reverse flow 16 and, therefore, the immersion nozzle The effect obtained by setting the discharge direction of 4 to be inclined will become smaller. Further, if the ratio of X/W is excessively increased, the swirling flow 15 becomes too strong, and the mold powder is entangled, so that defects due to the mold powder to be wound may occur, which is not preferable. Further, it is also considered that, in the case where the flow velocity of the swirling flow 15 is sufficiently fast enough, if the discharge direction is inclined, the swirling flow 15 will become too strong, resulting in a thinning of the thickness of the solidified cast piece casing 9, and there will be It is not appropriate to cause a cause such as a casting leakage phenomenon that hinders the stability of the operation.

In addition, the present inventors have continuously reviewed and experimented repeatedly, focusing on the ratio X/W of the intensity X (Gs) of the alternating moving magnetic field to the width W (mm) of the cast steel slab, and thus found that The relationship between the best spitting directions.

It can be seen that when the ratio of the alternating magnetic field strength X to the ratio X/W of the slab width W (Gs/mm) is 0.30 or more and less than 0.45, the discharge direction is set to: through the immersion nozzle It is preferable to set the inclination angle α of the discharge axis direction of the reference plane parallel to the long side surface of the mold to the center of the vertical axis of 4, and to set it within the range of the following formula (8). The reason for this is considered to be that since the AC moving magnetic field strength X with respect to the width W of the steel slab is relatively small, the inclination angle α must be increased, and the swirling flow 15 and the counter on the downstream side of the swirling flow 15 are more actively avoided. The flow 16 is subject to collision and interference.

Θ-2≦α≦θ+5. . . Number (8)

Further, it is also known that when the ratio of X/W (Gs/mm) is 0.45 or more and less than 0.55, the discharge direction is set to pass through the center of the vertical axis of the immersion nozzle 4, and will be relative to The inclination angle α of the discharge direction of the reference surface parallel to the long side surface of the mold is preferably set within the range of the following formula (9). This is because the AC moving magnetic field intensity X with respect to the width W of the steel slab is relatively large. Therefore, by setting the inclination angle α to be small to keep the discharge direction inclined, the downstream side of the swirling flow 15 can be avoided. The swirling flow 15 collides with the reverse flow 16 and interferes with the risk of the stability of the work such as the casting leakage phenomenon as described above.

Θ-5≦α≦θ+2. . . Number (9)

Further, the inclination angle α of the discharge direction of the immersion nozzle 4 can be set in the continuous casting, in addition to the setting before the start of continuous casting, or by using an apparatus that can change the inclination angle α of the discharge direction. In the continuous casting using the apparatus, each time the casting conditions such as the width of the mold are changed, α and θ are successively measured so as to be in accordance with the formula (1) or from the formula (3) to the formula (9). A better effect can be obtained by changing the discharge direction of the immersion nozzle 4 in such a manner that the inclination angle α of the magnitude relationship between α and θ is expressed.

Fig. 17 is a flowchart showing an example of a process of changing the inclination angle α of the discharge direction. Here, use Figure 17 to illustrate the change The treatment of the inclination angle α of the discharge direction of the immersion nozzle 4 is further performed. The processing shown in Fig. 17 is confirmed every predetermined time: the immersion depth of the immersion nozzle 4 is 180 mm or more and less than 300 mm, and the molten steel discharge angle from the horizontal direction of the discharge hole is 15~ 35°, whether the ratio A/P of the flow rate A (NL/min) and the molten steel throughput P (ton/min) between the outflow hole and the discharge hole of the casting tank is between 2.0 and 3.5 NL/ton. Within the scope of this, if this condition is met, processing begins. In addition, the processing can be carried out using, for example, a device (hereinafter referred to as "angle adjustment device") having a drive mechanism capable of changing the discharge direction as disclosed in Patent Document 2. In the present embodiment, the angle adjustment device will be described as a main body that changes the inclination angle α of the discharge direction.

In the processing shown in Fig. 17, the angle adjusting means first judges whether or not the continuous casting apparatus is in the constant casting (step S101). In the present embodiment, the term "constant casting" means that "the casting speed is changed during the casting, and the mold width is not changed, and the flow rate of the blunt gas is not changed. The state of the immersion nozzle 4 is not changed in the state in which the immersion depth of the immersion nozzle 4 is changed.

When the angle adjusting device determines that the continuous casting device is not in the constant casting (step S101: No), the processing shown in Fig. 17 is ended. The angle adjusting device is configured such that when the continuous casting device is in a constant casting (step S101: Yes), the angle adjusting device performs the measurement of the inclination angles α and θ, and determines whether the inclination angle α conforms to the formula (1) (step S102). Angle adjustment device, determining the tilt angle α If the expression (1) is satisfied (step S102: Yes), the processing shown in Fig. 17 is ended. On the other hand, when the angle adjustment device determines that the inclination angle α does not satisfy the formula (1) (step S102: No), the inclination angle α conforming to the equation (1) is set again (step S103). The angle adjusting device changes the discharge direction of the immersion nozzle 4 so as to become the reset inclination angle α (step S104), and then ends the processing shown in Fig. 17.

In this manner, the angle adjusting device changes the discharge of the immersion nozzle 4 so that the inclination angle α conforms to the formula (1) every predetermined time by the processing shown in FIG. direction. In this way, even if there is some unknown reason that the inclination angle α becomes no longer in accordance with the formula (1), the discharge direction of the immersion nozzle 4 can be changed by the angle adjusting device to achieve the inclination angle α. The relationship of the formula (1) can be satisfied, and therefore, it is possible to prevent the steel slab containing inclusions from being continuously produced.

Fig. 18 is a flow chart showing an example different from the foregoing. Another treatment for changing the inclination angle α of the discharge direction of the immersion nozzle 4 will be described using FIG. In the processing shown in Fig. 18, in addition to the start condition of the processing shown in Fig. 17, on the back surface of the long side 2 of the mold, a pair of upper magnetic poles 6 opposed to each other across the long side of the mold are disposed. The pair of lower magnetic poles 7 are disposed between the "position of the maximum value of the DC static magnetic field applied by the upper magnetic pole 6" and "the position of the maximum value of the DC static magnetic field applied by the lower magnetic pole 7". When the intensity of the static magnetic field is 1500 Gs or more and less than 3500 Gs, the treatment is started.

In the process shown in Figure 18, the angle adjustment device is first It is judged whether or not the continuous casting apparatus is in a constant casting (step S201). When the angle adjusting device determines that the continuous casting device is not in the constant casting (step S201: No), the processing shown in Fig. 18 is ended. The angle adjusting device is a case where the continuous casting device is in a constant casting (step S201: Yes), and the angle adjusting device determines whether the intensity of the direct current static magnetic field falls within the range of 1500 ≦ Gs < 2500 (step S202). When the angle adjusting device determines that the intensity of the DC static magnetic field falls within the range of 1500 ≦Gs<2500 (step S202: Yes), the inclination angles α and θ are measured, and it is judged whether or not the inclination angle α conforms to the formula (3). Relationship (step S203).

When the angle adjustment device determines that the inclination angle α is in accordance with the equation (3) (step S203: Yes), the processing shown in Fig. 18 is ended. On the other hand, when the angle adjustment device determines that the inclination angle α does not satisfy the formula (3) (step S203: No), the inclination angle α conforming to the equation (3) is set again (step S204). The angle adjusting device changes the discharge direction of the immersion nozzle 4 so as to conform to the reset inclination angle α (step S205), and then ends the processing shown in Fig. 18.

On the other hand, when the angle adjusting means determines that the intensity of the DC static magnetic field does not fall within the range of 1500 ≦ Gs < 2500, but falls within the range of 2500 ≦ Gs < 3500 (step S202: No), The inclination angles α and θ are measured, and it is judged whether or not the inclination angle α conforms to the relationship of the formula (4) (step S206). When the angle adjusting means determines that the inclination angle α conforms to the formula (4) (step S206: Yes), the processing shown in Fig. 18 is ended. On the other hand, when the angle adjusting device determines that the tilt When the inclination angle α does not satisfy the formula (4) (step S206: No), the inclination angle α in accordance with the equation (4) is set again (step S207). The angle adjusting device changes the discharge direction of the immersion nozzle 4 so as to conform to the reset inclination angle α (step S208), and then ends the processing shown in Fig. 18.

Fig. 19 is a flow chart showing another example different from the foregoing. The other processing of changing the inclination angle α of the discharge direction of the immersion nozzle 4 will be described using FIG. The processing shown in Fig. 19 is performed in addition to the start condition of the processing shown in Fig. 17, in the case where the moving direction of the magnetic field is set to the linear moving magnetic field generating device 42 in the width direction of the mold. Process it.

In the processing shown in Fig. 19, the angle adjusting means first judges whether or not the continuous casting apparatus is in a constant casting (step S301). When the angle adjusting device determines that the continuous casting device is not in the constant casting (step S301: No), the processing shown in Fig. 19 is ended. The angle adjusting device, when the continuous casting device has become a constant casting (step S301: Yes), the angle adjusting device measures the inclination angles α and θ, and determines whether the inclination angle α conforms to the relationship of the formula (5) ( Step S302). When the angle adjusting means determines that the inclination angle ? has satisfied the formula (5) (step S302: Yes), the processing shown in Fig. 19 is ended. On the other hand, when it is judged that the inclination angle α does not satisfy the formula (5) (step S302: No), the angle adjustment device sets the inclination angle α in accordance with the equation (5) (step S303). The angle adjusting device changes the discharge direction of the immersion nozzle 4 so that the reset inclination angle α can be formed. (Step S304), then the processing shown in Fig. 19 is ended.

Fig. 20 is a flow chart showing another example different from the foregoing. The other treatment for changing the inclination angle α of the discharge direction of the immersion nozzle 4 will be described using FIG. In the process shown in Fig. 20, in addition to the start condition of the process shown in Fig. 17, a pair of magnetic poles 52 are provided on the back surface of the long side 2 of the mold, and the strength in the range of 300 to 1000 Gs is applied from the magnetic pole. The alternating moving magnetic field is started when the ratio X/W of the intensity of the alternating moving magnetic field to the width of the steel slab is 0.30 or more and less than 0.55.

In the processing shown in Fig. 20, the angle adjusting means first judges whether or not the continuous casting apparatus is in a constant casting (step S401). When the angle adjusting device determines that the continuous casting device is not in the constant casting (step S401: No), the processing shown in Fig. 20 is ended. In the case where the continuous casting apparatus has become a constant casting (step S401: Yes), the angle adjusting means determines whether the ratio of X/W is 0.30 or more and less than 0.45 (step S402). When the angle adjusting device determines that the ratio of X/W is 0.30 or more and does not reach 0.45 (step S402: Yes), the inclination angles α and θ are measured, and it is judged whether or not the inclination angle α conforms to the formula (6). Relationship (step S403).

When the angle adjusting means determines that the inclination angle ? corresponds to the equation (6) (step S403: Yes), the processing shown in Fig. 20 is ended. On the other hand, when the angle adjustment device determines that the inclination angle α does not satisfy the formula (6) (step S403: No), the inclination angle α in accordance with the equation (6) is set again (step S404). Angle adjustment device The discharge direction of the immersion nozzle 4 is changed so that the inclination angle α is set again (step S405), and the process shown in FIG. 20 is completed.

On the other hand, the angle adjusting device determines that the ratio of X/W is not 0.30 or more and less than 0.45. When it is 0.45 or more and less than 0.55 (step S402: No), the inclination angles α and θ are measured, and it is judged whether or not the inclination angle α satisfies the relationship of the formula (7) (step S406).

When the angle adjustment device determines that the inclination angle α conforms to the equation (7) (step S406: Yes), the processing shown in Fig. 20 is ended. On the other hand, when the angle adjustment device determines that the inclination angle α does not satisfy the formula (7) (step S406: No), the inclination angle α conforming to the equation (7) is set again (step S407). The angle adjusting device changes the discharge direction of the immersion nozzle 4 so that the reset inclination angle α can be formed (step S408), and then ends the processing shown in Fig. 20.

Fig. 21 is a flow chart showing another example different from the foregoing. The other processing of changing the inclination angle α of the discharge direction of the immersion nozzle 4 will be described using Fig. 21 . In the process shown in Fig. 21, in addition to the start condition of the process shown in Fig. 17, a pair of upper magnetic poles 6 and one facing each other across the long side of the mold are disposed on the back side of the long side of the mold. The lower magnetic pole 7 is disposed so as to overlap the position where the discharge hole is disposed at the maximum value of the DC static magnetic field applied by the upper magnetic pole 6 and the maximum value of the DC static magnetic field applied by the lower magnetic pole 7: The AC moving magnetic field of the intensity in the range of 500 to 900 Gs applied by the magnetic pole 6, and the DC static magnetic field of the intensity in the range of 2000 to 3300 Gs, The DC static magnetic field of the intensity in the range of 3000 to 4500 Gs applied by the lower magnetic pole 7 starts when the ratio of the intensity of the AC moving magnetic field to the X/W of the width of the steel slab is 0.30 or more and less than 0.55. Process it.

In the process shown in Fig. 21, the angle adjusting means determines whether or not the continuous casting device is in a constant casting (step S501). When the angle adjusting device determines that the continuous casting device is not in the constant casting (step S501: No), the processing shown in Fig. 21 is ended. When the angle adjusting device is in the constant casting (step S501: Yes), the angle adjusting device determines whether the ratio of X/W is 0.30 or more and less than 0.45 (step S502). When the angle adjusting device determines that the ratio of X/W is 0.30 or more and does not reach 0.45 (step S502: Yes), the inclination angles α and θ are measured, and it is judged whether or not the inclination angle α conforms to the relationship of the formula (8) ( Step S503).

When the angle adjusting device determines that the tilt angle α corresponds to the equation (8) (step S503: Yes), the processing shown in Fig. 21 is ended. On the other hand, when the angle adjusting device determines that the inclination angle α does not satisfy the formula (8) (step S503: No), the inclination angle α in accordance with the equation (8) is set again (step S504). The angle adjusting device changes the discharge direction of the immersion nozzle 4 so that the reset inclination angle α can be formed (step S505), and then ends the processing shown in Fig. 21.

On the other hand, when the angle adjusting device determines that the ratio of X/W is not 0.30 or more and does not reach 0.45, but is 0.45 or more and less than 0.55 (step S502: No), the inclination angles α and θ are measured, and And it is judged whether or not the inclination angle α satisfies the relationship of the formula (9) (step S506).

When the angle adjusting device determines that the inclination angle α conforms to the formula (9) (step S506: Yes), the processing shown in Fig. 21 is ended. On the other hand, when the angle adjustment device determines that the inclination angle α does not satisfy the formula (9) (step S506: No), the inclination angle α in accordance with the equation (9) is set again (step S507). The angle adjusting device changes the discharge direction of the immersion nozzle 4 so that the reset inclination angle α can be formed (step S508), and then the processing shown in Fig. 21 is ended.

Fig. 22 is a flow chart showing an example of various processes of Figs. 17 to 21 in accordance with casting conditions. In the example shown in Fig. 22, the angle adjusting device performs the checking of the casting conditions every predetermined time, and separately uses the processes described in Figs. 17 to 21 depending on the casting conditions. When the angle adjusting device determines that the immersion depth of the immersion nozzle 4 is 180 mm or more and less than 300 mm, the molten steel discharge angle of the discharge hole from the horizontal direction to the lower side is 15 to 35°, and is blown into the flow from the casting groove. The ratio A/P of the flow rate A (P/ton) of the blunt gas between the hole and the discharge hole to the molten steel throughput P (ton/min) falls within the range of 2.0 to 3.5 NL/ton. In the case of the condition A", the process of changing the inclination angle α in the discharge direction shown in Fig. 17 is executed.

Further, the angle adjusting device determines that the pair of upper magnetic poles 6 and the pair of lower magnetic poles 7 that face each other with the long side of the mold are disposed on the back side of the long side of the mold in addition to the condition A, and the discharge hole is formed. Positioned at the maximum value of the DC static magnetic field applied by the upper magnetic pole 6 When the position of the maximum value of the DC static magnetic field applied by the lower magnetic pole 7 is between 1500 Gs or more and the intensity of the static magnetic field is less than 3500 Gs, the condition B is as shown in FIG. The process of changing the inclination angle α of the discharge direction.

In addition, when the angle adjustment device determines that the condition C is in addition to the condition A, the so-called "condition C" in which the moving direction of the magnetic field is along the linear direction of the mold width is "condition C" The process of changing the inclination angle α of the discharge direction shown in Fig. 19 is performed.

Further, the angle adjusting device determines that "the magnetic pole 52 is provided on the back side of the long side in addition to the condition A, and the alternating magnetic field of the intensity in the range of 300 to 1000 Gs is applied from the magnetic pole 52, and the intensity of the alternating magnetic field is applied. In the case of the so-called "condition D" in which the ratio X/W of the width of the steel slab is 0.30 or more and less than 0.55", the process of changing the inclination angle α in the discharge direction shown in Fig. 20 is executed.

Further, the angle adjusting device determines that "in addition to the condition A, a pair of upper magnetic poles 6 and a pair of lower magnetic poles 7 that face each other across the long side of the mold are disposed on the back side of the long side of the mold, and the discharge holes are formed. Between the position where the maximum value of the DC static magnetic field applied by the upper magnetic pole 6 and the maximum value of the DC static magnetic field applied by the lower magnetic pole 7 are placed, the upper magnetic pole 6 is overlapped and applied in the range of 500 to 900 Gs. The intensity of the AC moving magnetic field and the DC static magnetic field of the intensity in the range of 2000 to 3300 Gs, the DC static magnetic field of the intensity in the range of 3000 to 4500 Gs is applied by the lower magnetic pole 7, and the strength of the AC moving magnetic field and the strength of the steel embryo casting When the ratio X/W of the width is 0.30 or more and the condition E is less than 0.55", the processing of changing the inclination angle α in the discharge direction shown in Fig. 21 is executed.

Therefore, the angle adjusting device according to the present embodiment performs the process of changing the tilt angle α corresponding to the casting condition every predetermined time, and determines that the tilt angle α does not correspond to the casting condition. In the case of the equations (1) and (3) to (9), the discharge direction of the immersion nozzle 4 is changed to conform to the equation. In this way, even if the inclination angle α does not satisfy the equations (3) to (9) for some reason, the angle adjustment device can be used to change the discharge direction of the immersion nozzle 4 to achieve compliance. According to the relationship of the equations, it is possible to prevent the steel slabs containing inclusions from being continuously produced.

As described above, by using the continuous casting method of the present embodiment, in addition to the intensity of the DC static magnetic field and the intensity of the AC moving magnetic field applied by the upper magnetic pole and the lower magnetic pole, the optimum range can be set and can be derived from The discharge direction of the immersion nozzle is inclined toward the upstream side of the swirling flow generated by the alternating current moving magnetic field, so that low flow velocity fields and eddy currents due to mutual collision and interference between the swirling flow and the reverse flow can be avoided, and inclusions can be produced. High quality steel slabs with few materials.

[Example 1]

A casting test of aluminum (deoxidized) killed molten steel of about 300 (ton) was carried out using a steel continuous casting machine having the continuous casting mold 20 shown in Fig. 1. The thickness of the cast steel slab is 250 (mm), wide The degree is 1000~2000 (mm), and the molten steel injection flow rate is 3.0~8.0 (ton/min). The molten steel discharge angle of the discharge hole of the two-hole type immersion nozzle used (the horizontal state is regarded as the angle is zero) is 15 (°) downward, and the immersion depth of the immersion nozzle (from the molten steel noodle soup in the mold) The distance from the upper end of the discharge hole is 180 (mm) or more and less than 300 (mm). The shape of the discharge hole of the immersion nozzle is a square having a length of 80 (mm) on each side, and the inner diameter of the immersion nozzle is 80 (mm). Further, argon gas was used for the blow-in air from the immersion nozzle. The discharge direction of the discharge flow from the immersion nozzle has two directions, one is a direction parallel to the long side of the mold (direction perpendicular to the short side of the mold), and the other is a direction inclined with respect to the reference surface.

For the cast steel slabs, the steel slabs are sequentially processed: hot rolling, cold rolling, alloying hot galvanizing, and the surface of the alloyed galvanized steel sheet is continuously measured using an on line surface defect meter. Defects, and from the measured results, by observing the appearance of the defects and performing SEM analysis, ICP analysis, and the like, it is determined that the steel defects (defects caused by the inclusions of the steel slabs), The number of defects per 100 (m) length of the alloyed hot-dip galvanized steel sheet (also referred to as "product defect index") was evaluated. Table 1 shows the results of investigations on casting conditions and product defect indexes of Inventive Examples 1 to 18 and Comparative Examples 1 to 18.

Table 1 shows the diagonal direction angle θ calculated from the thickness D of the cast slab and the width W of the cast piece, and the inclination angle α of the discharge flow at the time of casting. In addition, the diagonal direction angle θ is calculated by rounding off the second decimal place. Further, the numerical value of "α-θ" described in Table 1 is a numerical value obtained by rounding off the first decimal place.

It can be seen that in the inventive examples 1 to 18, because in addition to being molten steel The ratio A/P of the throughput to the argon flow rate is set to fall within the range of 2.0 to 3.5 (NL/ton), and "α-θ" is also set within the range of -6 to 10 (°). The product defect index is very low, only 0.26~0.29 (pieces/100m). That is, it can be known that by setting the inclination angle α (°) within a range of “θ-6” or more and “θ+10” or less, a suitable flow velocity of the molten steel flow can be imparted, and the product defect index can be lowered. .

On the other hand, in Comparative Examples 1 to 6, the discharge direction was not inclined, and thus the product defect index was high and reached 0.61 to 0.68 (pieces/100 m). Further, the inclination angles α of Comparative Examples 7 to 9 were smaller than those of Examples 1 to 18 of the present invention, and the product defect index in this case was also high to 0.63 to 0.67 (pieces/100 m). The reason for this is presumed: it is because the inclination angle α is too small to give a suitable flow rate of the molten steel flow.

The inclination angles α of Comparative Examples 10 to 12 were larger than those of Examples 1 to 18 of the present invention. In this case, the product defect index is reduced to 0.27 to 0.29 (pieces/100 m). However, from the investigation results of the cast sheet profile, it has been found that the growth thickness of the cast shell in the mold is thin. There is a possibility that the occurrence of casting leakage phenomenon hinders the stability of the work.

The ratio A/P of the molten steel throughput P to the argon flow rate A of Comparative Examples 13 to 18 falls outside the range of 2.0 to 3.5 (NL/ton). In this case, the product defect index is high and reaches 0.61 to 0.68. (one / 100m). The reason for this is presumed: it is because the discharge jet cannot be controlled, and the effect of setting the discharge direction to be inclined cannot be exhibited.

Further, although not described in the present embodiment, it is additionally confirmed that even if the thickness of the cast steel slab is In the range of 220 to 300 (mm), the same effect as that of the steel blank cast piece described in the present embodiment can be obtained. In addition, it was confirmed that the same tendency was obtained in the range in which the molten steel discharge angle of the immersion nozzle fell within the range of 15 to 35 (°). In addition, the shape of the discharge hole of the immersion nozzle and the inner diameter of the immersion nozzle are not limited to the conditions described in the present embodiment, and may be any extent as long as it is within the range that can be considered by those skilled in the art.

[Embodiment 2]

A casting test of aluminum (deoxidized) killed molten steel of about 300 (ton) was carried out using a steel continuous casting machine having a continuous casting mold 30 having an upper magnetic pole 6 and a lower magnetic pole 7 shown in Fig. 4 . The cast steel slab has a thickness of 250 (mm), a width of 1800 (mm), and a molten steel injection flow rate of 5.0 to 8.0 (ton/min). The discharge angle of the discharge hole of the two-hole type immersion nozzle used is 15 (°) downward, and the immersion depth of the immersion nozzle (the distance from the molten steel soup surface in the mold to the upper end of the discharge hole) is 180 (mm). Above and less than 300 (mm). The shape of the discharge hole of the immersion nozzle is a square having a length of 80 (mm) on each side, and the inner diameter of the immersion nozzle is 80 (mm). Further, argon gas was used as the blunt gas blown from the immersion nozzle. The ratio A/P of the molten steel throughput P to the argon flow rate A is set to fall within the range of 2.0 to 3.5 (NL/ton).

The discharge direction of the discharge flow from the immersion nozzle has two directions, one is a direction parallel to the long side of the mold (direction perpendicular to the short side of the mold), and the other is a direction inclined with respect to the reference surface.

For the cast steel slab cast, it is implemented in order: Hot rolling, cold rolling, alloying hot-dip galvanizing treatment, using the on line surface defect meter to continuously measure the surface defects of the alloyed hot-dip galvanized steel sheet, and then observing the defects from the measured results The appearance and the SEM analysis, ICP analysis, etc., to determine the defects of the steelmaking (defects caused by the inclusions of the steel slab), and then the length of each 100 (m) of the alloyed hot-dip galvanized steel sheet The number of defects in the middle (also known as the "product defect index") is used for evaluation. Table 2 shows the results of investigations on casting conditions and product defect indexes of Inventive Examples 19 to 38 and Comparative Examples 19 to 32. Similarly in Table 2, the diagonal direction angle θ is calculated by rounding off the second decimal place. Further, the numerical value of the diagonal direction angle θ described in Table 2 is a value obtained by rounding off the second decimal place. Further, the value of "α-θ" is a value obtained by rounding off the first decimal place. Fig. 23 is a view showing the relationship between "α-θ" and "product defect index" of Examples 19 to 38 of the present invention, and the static magnetic field strength of 2500 (Gs) is used as a boundary.

In Examples 19 to 28 of the present invention, the DC static magnetic field strength was set to 1500 (Gs) or more and less than 2500 (Gs). It can be seen from Fig. 23 that in this case, by setting "α-θ" in the range of 0 to 5 (°), the defect index of the product can be made lower and reach 0.21 to 0.24 (pieces/100 m). ). In other words, when the DC static magnetic field strength is set to 1500 (Gs) or more and less than 2500 (Gs), the inclination angle α (°) is set to fall below "θ" and " It is preferable to be in the range of θ + 5" or less.

Further, in Examples 29 to 38 of the present invention, the DC static magnetic field strength was set to 2500 (Gs) or more and less than 3500 (Gs). It can be known that in this case, by setting "α-θ" to fall within the range of 6 to 10 (°), the defect index of the product can be made lower to 0.21 to 0.24 (pieces/100 m). ). In other words, it can be seen that when the DC static magnetic field strength is set to 2500 (Gs) or more and less than 3500 (Gs), the inclination angle α (°) is set to fall below "θ + 6". It is preferable to use a range of "θ+10" or less.

In Comparative Examples 19 to 23 and Comparative Examples 26 to 30, the inclination angle α was set to be smaller than "θ-6". In this case, the product defect index is increased by 0.51 to 0.54 (pieces/100 m). Further, in Comparative Examples 24 to 25 and Comparative Examples 31 to 32, the inclination angle α was set to be larger than "θ + 10". In this case, the product defect index is reduced to 0.22 to 0.25 (pieces per 100 m). However, from the investigation results of the cast sheet profile, it has been found that the growth thickness of the cast shell in the mold is thinner, and There is a possibility of hindering the stability of the work such as the occurrence of casting leakage.

In addition, although not described in the present embodiment, it is additionally confirmed that even if the cast steel slab has a thickness of 220 to 300 (mm) and a casting width of 1000 to 2000 (mm), molten steel In the range of the throughput of 3.0 to 8.0, the same effect as that of the steel slab cast described in the present embodiment can be obtained. In addition, it was confirmed that the same tendency was obtained in the range in which the molten steel discharge angle of the immersion nozzle fell within the range of 15 to 35 (°). In addition, the shape of the discharge hole of the immersion nozzle and the inner diameter of the immersion nozzle are not limited to the conditions described in the present embodiment, and may be any extent as long as it is within the range that can be considered by those skilled in the art.

[Example 3]

Used: equipped with a pair of straight lines as shown in Figure 6 The steel preform continuous casting machine for the continuous casting mold 40 of the moving magnetic field generating device 42 was subjected to a casting test for casting aluminum (deoxidized) killed molten steel of about 300 (ton). The cast steel slab has a thickness of 250 (mm), a width of 1600 (mm), and a molten steel injection flow rate of 5.0 to 6.0 (ton/min). The discharge angle of the discharge hole of the two-hole type immersion nozzle used is 25 (°) downward, and the immersion depth of the immersion nozzle (the distance from the molten steel soup surface in the mold to the upper end of the discharge hole) is 180 (mm). Above and less than 300 (mm). The shape of the discharge hole of the immersion nozzle is a square having a length of 70 (mm) on each side, and the inner diameter of the immersion nozzle is 70 (mm). The blunt gas blown from the immersion nozzle used argon gas. Further, the ratio A/P of the molten steel throughput P to the argon flow rate A is set in the range of 2.0 to 3.5 (NL/ton). The alternating magnetic field is applied by the magnetic pole, and casting is performed under the condition that the molten steel discharge flow is braked.

For the cast steel slabs, the steel slabs are sequentially processed: hot rolling, cold rolling, alloying hot galvanizing, and the surface of the alloyed galvanized steel sheet is continuously measured using an on line surface defect meter. Defects, and from the measured results, by observing the appearance of the defects and performing SEM analysis, ICP analysis, and the like, it is determined that the steel defects (defects caused by the inclusions of the steel slabs), The number of defects per 100 (m) length of the alloyed hot-dip galvanized steel sheet (also referred to as "product defect index") was evaluated. Table 3 shows the results of investigations on the casting conditions and the product defect index of Examples 30 to 49 of the present invention. Similarly in Table 3, the diagonal direction angle θ is calculated by rounding off the second decimal place. Also, the diagonal direction angles shown in Table 3 The value of θ is the value obtained by rounding off the second decimal place. Further, the value of "α-θ" is a value obtained by rounding off the first decimal place. Fig. 24 is a graph showing the relationship between "α-θ" and "product defect index" in Examples 39 to 49 of the present invention.

In addition, although it is not described in Table 3, it is confirmed that the same flow control method is used, but the impregnation nozzle discharge hole is not inclined but is directed to the short side, and the product defect index is increased. It reaches 0.51~0.56 (pieces/100m).

In the inventive examples 39 to 44, "α-θ" was set in the range of 2 to 7 (°). As shown in Fig. 24, in this case, the product defect index is reduced to 0.22 to 0.24 (pieces/100 m). In other words, when the linear moving magnetic field generating device is provided and the flow is controlled while braking the molten steel flow, the inclination angle α (°) is set to be "θ + 2" or more and "θ + 7" is within the following range.

On the other hand, in the present invention examples 45 to 47, "α-θ" is set in the range of -6 to 0 (°). In this case, the product defect index is slightly increased to 0.27~0.29 (pieces/100m). The reason is presumed It is the result that the flow rate of the molten steel flow is slightly reduced, but these examples are also sufficiently good quality steel embryos. Further, in Examples 48 to 49 of the present invention, "α-θ" was set in the range of 8 to 10 (°). In this case, the product defect index is slightly increased to 0.27 to 0.28 (pieces/100 m). The reason for this is presumed to be that the flow rate to the molten steel flow is slightly increased, thereby contributing to the fact that the mold powder is entrapped, but these examples are also sufficiently good quality steel embryos. In addition, as a result of investigating the profile of the slabs of these steel slabs, it is also possible to see that the growth thickness of the solidified slab shell in the mold is slightly thinner, but it does not reach a situation that may hinder the stability of the work. degree.

Further, although not described in the present embodiment, it has been confirmed that even when the molten steel discharge flow from the immersion nozzle is accelerated, the same tendency is obtained. Moreover, it has been confirmed separately: in the case where the thickness of the cast steel slab is 220 to 300 (mm), the casting width is 1000 to 2000 (mm), and the molten steel throughput is in the range of 3.0 to 8.0. The same effects as those of the examples described in the examples can be obtained. Further, it was confirmed that the same tendency was obtained in the range in which the molten steel discharge angle of the immersion nozzle was 15 to 35 (°). In addition, the shape of the discharge hole of the immersion nozzle and the inner diameter of the immersion nozzle are not limited to the conditions described in the present embodiment, and may be any extent as long as it is within the range that can be considered by those skilled in the art.

[Example 4]

A steel slab continuous casting machine having a continuous casting mold 50 having a pair of magnetic poles 52 as shown in Fig. 8 is used for casting. Casting test of 300 (ton) aluminum (deoxidized) killed molten steel. The cast steel slab has a thickness of 260 (mm), a width of 1600 (mm), and a molten steel injection flow rate of 5.0 to 6.0 (ton/min). The discharge angle of the discharge hole of the two-hole type immersion nozzle used is 25 (°) downward, and the immersion depth of the immersion nozzle (the distance from the molten steel soup surface in the mold to the upper end of the discharge hole) is 180 (mm). Above and less than 300 (mm). The shape of the discharge hole of the immersion nozzle is a square having a length of 70 (mm) on each side, and the inner diameter of the immersion nozzle is 70 (mm). The blunt gas blown from the immersion nozzle is argon gas. The ratio A/P of the molten steel throughput P to the argon flow rate A is set to fall within the range of 2.0 to 3.5 (NL/ton). In the range of the AC moving magnetic field strength of 300 to 1000 (Gs), the ratio X/W (Gs/mm) of the AC moving magnetic field strength X to the width W of the cast steel slab is changed, and the immersion nozzle is used. The casting angle was performed by the inclination angle α of the discharge flow.

For the cast steel slabs, the steel slabs are sequentially processed: hot rolling, cold rolling, alloying hot galvanizing, and the surface of the alloyed galvanized steel sheet is continuously measured using an on line surface defect meter. Defects, and from the measured results, by observing the appearance of the defects and performing SEM analysis, ICP analysis, and the like, it is determined that the steel defects (defects caused by the inclusions of the steel slabs), The number of defects per 100 (m) length of the alloyed hot-dip galvanized steel sheet (also referred to as "product defect index") was evaluated. Table 4 shows the results of investigations on the casting conditions and the product defect index of Examples 50 to 71 of the present invention. Similarly in Table 4, the diagonal direction angle θ is calculated by rounding off the second decimal place. Further, the diagonal direction angle θ described in Table 4 The value is the value obtained by rounding off the second decimal place. Further, the value of "α-θ" is a value obtained by rounding off the first decimal place. In Comparative Examples 33 to 37, the inclination angle of the discharge hole toward the downstream side of the swirling flow is also described. Fig. 25 is a view showing the relationship between "α-θ" and "product defect index" of Examples 50 to 71 of the present invention, and the partition is displayed with a ratio of X/W of 0.45.

In addition, although it is not described in Table 4, it is confirmed that the same flow control method is used, but the impregnation nozzle discharge hole is not inclined but is directed to the short side, and the product defect index is increased and reached. 0.45~0.51 (pieces/100m).

In the examples 50 to 60 of the present invention, the ratio of X/W (Gs/mm) is set. It is set at 0.30 or more and does not reach 0.45. As shown in Fig. 25, it can be known that in this case, by setting "α-θ" in the range of -3 to 0 (°), the defect index of the product can be reduced to a particularly low 0.18~ 0.20 (pieces / 100m). In other words, when the ratio (Gs/mm) of X/W is 0.30 or more and less than 0.45, the inclination angle α (°) is set to a range of "θ-3" or more and "θ" or less. The inside is appropriate.

On the other hand, in the inventive examples 61 to 71, the X/W ratio (Gs/mm) was set to 0.45 or more and less than 0.55. It can be known that in this case, by setting "α-θ" in the range of -6~-4 (°), the defect index of the product can be reduced to a particularly low 0.18~0.20 (pieces/100m). . In other words, when the ratio (Gs/mm) of X/W is 0.45 or more and less than 0.55, the inclination angle α (°) is set to be "θ-6" or more and "θ-4" or less. The scope is appropriate. The reason for this is presumed to be that the result of controlling the flow of the molten steel is good by setting the appropriate inclination angle in accordance with the ratio of X/W. Other examples of the present invention can also obtain sufficiently good quality steel embryos.

On the other hand, as shown in Comparative Examples 33 to 37, if the discharge flow was directed to the downstream side of the swirling flow, the product defect index was remarkably increased to 0.65 to 0.68 (pieces/100 m). The reason for this is presumed: it is the result of the conflict and interference between the swirling flow and the reverse flow.

Further, although not described in the present embodiment, it has been confirmed that even in the range of the cast steel slab having a thickness of 220 to 300 (mm), the casting width is 1000 to 2000 (mm), and the molten steel When the throughput is in the range of 3.0 to 8.0, the present embodiment can also be obtained. The example has the same effect. Further, it was confirmed that the same tendency was obtained in the range in which the molten steel discharge angle of the immersion nozzle was 15 to 35 (°). In addition, the shape of the discharge hole of the immersion nozzle and the inner diameter of the immersion nozzle are not limited to the conditions described in the present embodiment, and may be any extent as long as it is within the range that can be considered by those skilled in the art.

[Example 5]

A steel continuous casting machine having a continuous casting mold 1 having a pair of upper magnetic poles 6 and a pair of lower magnetic poles 7 shown in Fig. 12 was used, and aluminum (deoxidized) killed molten steel of about 300 (ton) was cast. Casting test. The cast steel slab has a thickness of 260 (mm), a width of 1000 to 1900 (mm), and a molten steel injection flow rate of 4.0 to 7.5 (ton/min). The discharge angle of the discharge hole of the two-hole type immersion nozzle used (the angle is regarded as a zero degree in the horizontal direction) is 25° below, and the immersion depth of the immersion nozzle (from the molten steel soup surface in the mold to the upper end of the discharge hole) The distance) is 180 (mm) or more and less than 300 (mm). The shape of the discharge hole of the immersion nozzle is a square having a length of 80 (mm) on each side, and the inner diameter of the immersion nozzle is 80 (mm). Argon gas is used as the blunt gas blown from the immersion nozzle. The ratio A/P of the molten steel throughput P to the argon flow rate A is set to fall within the range of 2.0 to 3.5 (NL/ton).

The discharge direction of the discharge flow from the immersion nozzle is divided into: an upstream side of the swirling flow formed by the alternating magnetic field, a downstream side of the swirling flow, and a direction parallel to the long side of the mold (vertical to the short side of the mold) The direction of the three). Even if the spit out direction of the spit out is directed back When the upstream side of the swirling flow and the downstream side of the swirling flow are inclined, the inclination angle α is also changed. Further, casting was also performed by changing the intensity of the alternating current moving magnetic field applied by the upper magnetic pole, the direct current static magnetic field applied by the upper magnetic pole, and the direct current static magnetic field applied by the lower magnetic pole.

For the cast steel slabs, the steel slabs are sequentially processed: hot rolling, cold rolling, alloying hot galvanizing, and the surface of the alloyed galvanized steel sheet is continuously measured using an on line surface defect meter. Defects, and from the measured results, by observing the appearance of the defects and performing SEM analysis, ICP analysis, and the like, it is determined that the steel defects (defects caused by the inclusions of the steel slabs), The number of defects per 100 (m) length of the alloyed hot-dip galvanized steel sheet (also referred to as "product defect index") was evaluated. Table 5 shows the results of investigations on casting conditions and product defect indexes of Inventive Examples 72 to 79 and Comparative Examples 38 to 46. In Table 5, the diagonal direction angle θ and the inclination angle α are values obtained by rounding off the second decimal place.

As shown in Table 5, the intensity of the AC moving magnetic field applied by the upper magnetic pole is controlled within a range of 500 to 900 (Gs); and the intensity of the DC static magnetic field applied by the upper magnetic pole is controlled at 2000 to 3300 (Gs). Within the range; the strength of the DC static magnetic field applied by the lower magnetic pole is controlled within a range of 3000 to 4500 (Gs) for continuous casting. Further, although not described in Table 5, it is also confirmed that when the intensity of the DC static magnetic field applied by the upper magnetic pole and the lower magnetic pole falls outside these ranges, all of them are product defect index deviations. High results. In addition, although it is not described in Table 5, it is also confirmed that when the ratio X/W of the intensity X of the AC moving magnetic field of the upper magnetic pole to the width W of the steel slab is less than 0.30, the product defect index is also High.

In Table 5, the diagonal direction angle θ calculated based on the cast slab thickness D and the slab width W, and the inclination angle α of the discharge flow at the time of casting are described. Further, the diagonal direction angle θ is a value obtained by rounding off the second decimal place.

In the examples 72 to 79 of the present invention, the discharge flow from the immersion nozzle was inclined toward the upstream side of the swirling flow formed by the alternating current moving magnetic field. In this case, the product defect index is reduced to 0.12 to 0.25 (pieces/100 m), and good results are obtained.

On the other hand, in Comparative Examples 38 to 41, the discharge direction was not inclined. The product defect index in this case is 0.35 to 0.42 (pieces/100 m), which is higher than the examples 72 to 79 of the present invention. Further, in Comparative Examples 42 to 43, the discharge direction of the immersion nozzle was inclined toward the downstream side of the swirling flow formed by the AC moving magnetic field. It can be confirmed that the product defect index of this case is 0.55~0.58 (pieces/100m), showing a significant deterioration. The reason for this is presumed: it is because the result of the collision and interference between the swirling flow and the reverse flow on the downstream side of the swirling flow is promoted.

In the examples 80 to 82 of the present invention, the ratio X/W (Gs/mm) of the intensity X of the AC moving magnetic field of the upper magnetic pole to the width W of the steel slab is set to 0.55 or more. The product defect index in this case was 0.30 to 0.32 (pieces/100 m), which was slightly higher than the examples 72 to 79 of the present invention. The reason for this is presumed: it is because the AC moving magnetic field strength X with respect to the width W is too strong, and thus the molten steel flow in the mold is slightly unstable.

Further, although not described in the present embodiment, it has been confirmed that even in the case where the thickness of the cast steel slab is in the range of 220 to 300 (mm), the present embodiment can be obtained. The example has the same effect. Further, the shape of the discharge hole of the immersion nozzle and the inner diameter of the immersion nozzle are not limited to the conditions described in the examples, and may be any extent as long as they are within the range that can be considered by those skilled in the art.

[Embodiment 6]

In the same manner as in the fifth embodiment, a steel continuous casting machine having a casting mold 1 for continuous casting having the upper and lower magnetic poles as shown in Fig. 12 was used, and was cast for about 300 (ton) aluminum (deoxidation). Casting test of Zhenjing molten steel. The cast steel slab has a thickness of 260 (mm), a width of 1600 to 1700 (mm), and a molten steel injection flow rate of 6.0 to 7.0 (ton/min). The discharge angle of the discharge hole of the two-hole type immersion nozzle used is 25 (°) downward, and the immersion depth of the immersion nozzle (from the molten steel in the mold) The distance from the top of the soup to the upper end of the hole is 180 (mm) or more and less than 300 (mm). The shape of the discharge hole of the immersion nozzle is a square having a length of 80 (mm) on each side, and the inner diameter of the immersion nozzle is 80 (mm). The blunt gas blown from the immersion nozzle is argon gas.

In the sixth embodiment, the discharge direction from the immersion nozzle is inclined toward the upstream side of the swirling flow formed by the alternating current moving magnetic field. Further, the intensity of the AC moving magnetic field applied to the upper magnetic pole is controlled within a range of 500 to 900 (Gs), and the intensity of the DC static magnetic field applied to the upper magnetic pole is controlled within a range of 2000 to 3300 (Gs), which is applied. The intensity of the DC static magnetic field at the lower magnetic pole is controlled within the range of 3000 to 4500 (Gs), and the ratio X/W (Gs/mm) of the AC moving magnetic field strength X to the width W of the cast steel slab is changed and Casting was carried out by the inclination angle α of the discharge flow from the immersion nozzle.

For the cast steel slabs, the steel slabs are sequentially processed: hot rolling, cold rolling, alloying hot galvanizing, and the surface of the alloyed galvanized steel sheet is continuously measured using an on line surface defect meter. Defects, and from the measured results, by observing the appearance of the defects and performing SEM analysis, ICP analysis, and the like, it is determined that the steel defects (defects caused by the inclusions of the steel slabs), The number of defects per 100 (m) length of the alloyed hot-dip galvanized steel sheet (also referred to as "product defect index") was evaluated. Table 6 shows the results of investigations on the casting conditions and the defect index of the products of Examples 80 to 103 of the present invention. The value of the diagonal direction angle θ in Table 6 is the value that rounds off the second decimal place; the value of "α-θ" is rounded off the first decimal place. Value. Further, Fig. 26 is a diagram showing the relationship between "α-θ" and "product defect index" of Examples 83 to 106 of the present invention, and the ratio of X/W is 0.45 as a boundary.

In Examples 83 to 94 of the present invention, the X/W ratio (Gs/mm) was set to 0.30 or more and less than 0.45. As shown in Fig. 26, it can be known that in this case, by setting "α-θ" in the range of -2° to 5°, the defect index of the product can be reduced to a particularly low level of 0.13 to 0.15. (one / 100m). In other words, when the ratio (Gs/mm) of X/W is 0.30 or more and less than 0.45, the inclination angle α (°) is set to be "θ-2" or more and "θ+5". The following ranges are appropriate.

On the other hand, it can be understood that the examples 95 to 106 of the present invention have a ratio of X/W (Gs/mm) of 0.45 or more and less than 0.55. When the "α-θ" at this time is in the range of -5 to 2 (°), the product defect index falls to a particularly low level of 0.13 to 0.15 (pieces/100 m). In other words, when the ratio (Gs/mm) of X/W is 0.45 or more and less than 0.55, the inclination angle α (°) is set within a range of “θ-5” or more and “θ+2” or less. It is appropriate.

Further, in Table 6, although only the example in which the thickness and the width of the steel slab are within a certain range is described, it is also confirmed that, for example, the thickness of the steel slab is 220 to 300 (mm). Within the range, the width of the steel slab is in the range of 1000 to 2000 (mm), and has the same degree of effect.

2‧‧‧Molded long side

3‧‧‧Molded short side

4‧‧‧Dip nozzle

5‧‧‧Spit hole

8‧‧‧Fused steel

9‧‧‧ Solidified cast shell

10‧‧‧Molded steel noodle soup in mold

11‧‧‧Spit out

20‧‧‧Continuous casting mold

Claims (11)

A continuous casting method for a steel slab cast piece, wherein the immersion nozzle is disposed in a continuous casting mold, and the molten steel is supplied to the immersion nozzle to cast the molten steel into a continuous casting method, wherein the immersion type The nozzle system has one pair of discharge holes arranged symmetrically with respect to the vertical axis thereof, and the immersion depth of the immersion nozzle (the distance from the molten steel soup surface in the mold to the upper end of the discharge hole) is set to 180 mm or more. Up to 300 mm; the molten steel discharge angle of the discharge hole facing downward from the horizontal direction is set in the range of 15 to 35°; the flow rate of the blunt gas that is blown between the discharge holes from the casting groove and the discharge hole is The ratio A/P of A (NL/min) to the molten steel throughput P (ton/min) is set in the range of 2.0 to 3.5 NL/ton, and the discharge direction of the above-described immersion nozzle is set to pass through the aforementioned immersion nozzle The center of the vertical axis, and the reference plane parallel to the long side surface of the mold, is inclined within the range of the following formula (1), θ-6≦α≦θ+10. . . In the formula (1), when the continuous casting mold is viewed from above in the vertical direction, the angle of inclination of the discharge direction of the immersion nozzle with respect to the reference surface (°); When the continuous casting mold is viewed from a vertically upper side, an angle (an acute angle) formed by a straight line from the center of the vertical axis of the immersion nozzle toward a contact point between the long side of the mold and the short side of the mold and the reference surface is as follows. The angle (°) defined by the equation (2), tan θ = (D / 2) / (W / 2). . . In the formula (2), D is the thickness (mm) of the continuously cast steel slab; and W is the width (mm) of the continuously cast steel slab. The method for continuously casting a steel slab according to claim 1, wherein the α is measured after continuous change in the width of the mold in continuous casting or continuous casting, and if the α does not satisfy the above formula (1) The discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (1). The method for continuously casting a steel slab according to claim 1, which is disposed on the back surface of the long side of the mold, and is disposed opposite to the upper magnetic pole and the pair of lower magnetic poles via the long side of the mold. The position of the discharge hole is set between a position at which a maximum value of a DC static magnetic field applied by the upper magnetic pole and a maximum value of a DC static magnetic field applied by the lower magnetic pole are used, and the upper magnetic pole and the lower magnetic pole are used Applying a DC static magnetic field to brake the molten steel flow. If the intensity of the DC static magnetic field applied by the upper magnetic pole is 1500 Gs or more and less than 2500 Gs (Gauss; 1 Gs = 10 ^-4 T), the immersion nozzle is used. The discharge direction is inclined with respect to the reference plane, and the above formula (1) is replaced by the following formula (3); if the intensity of the DC static magnetic field is 2500 Gs or more and less than 3500 Gs, the impregnation is performed. The discharge direction of the nozzle is inclined with respect to the reference plane, and the above formula (1) is replaced by the following formula (4), θ ≦ α ≦ θ + 5. . . Equation (3) θ+6≦α≦θ+10. . . Equation (4). The method for continuously casting a steel slab according to claim 3, wherein the measurement of the aforementioned α is performed after continuous change of the mold width in continuous casting or continuous casting, and if the strength of the DC static magnetic field is 1500 Gs When the above-mentioned α does not satisfy the above formula (3), the discharge direction of the immersion nozzle is changed so as to match the relationship of the numerical formula (3), and the intensity of the DC static magnetic field is changed. When the amount of 2500 Gs or more is less than 3500 Gs, and the above-mentioned α does not satisfy the above formula (4), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (4). A continuous casting method for a steel slab according to claim 1, wherein the moving direction of the magnetic field is a linear moving magnetic field generating device in the width direction of the mold, in order to The molten steel flow discharged from the nozzle imparts a braking force, and applies a moving magnetic field from the short side of the mold toward the immersion nozzle side; or, in order to impart an acceleration force to the molten steel, is applied from the immersion nozzle side toward the mold The moving magnetic field on the short side is used for flow control, and the discharge direction of the immersion nozzle is inclined with respect to the reference surface, and the above formula (1) is replaced by the following formula (5), θ+ 2≦α≦θ+7. . . Equation (5). The continuous casting method of the steel slab according to claim 5, wherein the α is measured after the change of the width of the mold in continuous casting or continuous casting, and if the α does not satisfy the above formula (5) The discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (5). A continuous casting method for a steel slab according to claim 1, which is disposed on a back surface of a long side of the mold, and is disposed to face a pair of magnetic poles with a long side of the mold, and an alternating magnetic field is applied from the magnetic pole Come to The molten steel is subjected to cyclotron stirring in the horizontal direction, except that the intensity of the aforementioned AC moving magnetic field is set within a range of 300 to 1000 Gs, if the intensity X (Gs) of the aforementioned AC moving magnetic field is the same as that of the continuously cast steel blank. When the ratio X/W (Gs/mm) of the width W (mm) is 0.30 or more and less than 0.45, the discharge direction of the immersion nozzle is set to the upstream side of the swirling flow formed by the alternating magnetic field. And the range which is inclined with respect to the aforementioned reference plane, the above formula (1) is replaced by the following formula (6), and if the ratio X/W (Gs/mm) is 0.45 or more and less than 0.55, The range (1), θ-3≦α≦θ is replaced by the following formula (7) with respect to the range in which the reference plane is inclined. . . Equation (6) θ-6≦α≦θ-4. . . Equation (7). The continuous casting method for a steel slab according to claim 7, wherein the α is measured after the change of the width of the mold in continuous casting or continuous casting, if the ratio X/W (Gs/mm) is When the ratio α is not more than 0.45, and the α does not satisfy the above formula (6), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (6); if the ratio X/W is (Gs/mm) is 0.45 or more and less than 0.55, and if the above-mentioned α does not satisfy the above formula (7), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (7). The method for continuously casting a steel slab according to claim 1, which is disposed on the back surface of the long side of the mold, and is disposed opposite to the upper magnetic pole and the pair of lower magnetic poles via the long side of the mold. The position of the discharge hole is set between a position at which the maximum value of the DC static magnetic field applied by the upper magnetic pole and a maximum value of the DC static magnetic field applied by the lower magnetic pole are applied, and DC is superposed from the upper magnetic pole The static magnetic field and the alternating current moving magnetic field form a swirling flow of the molten steel that rotates in the horizontal direction in the molten steel soup surface in the mold by the alternating magnetic field applied by the upper magnetic pole, and the DC static magnetic field applied by the upper magnetic pole is used. Braking the molten steel stream and braking the molten steel flow by using the DC static magnetic field applied by the lower magnetic pole, except that the intensity of the aforementioned alternating moving magnetic field is set at 500 to 900 Gs (Gauss; 1 Gs = 10 ^-4 T) In the range, the intensity of the DC static magnetic field applied by the upper magnetic pole is set in the range of 2000 to 3300 Gs, and the DC magnetization applied by the lower magnetic pole is The intensity of the field is set in the range of 3,000 to 4,500 Gs, and the ratio of the intensity X (Gs) of the aforementioned AC moving magnetic field to the width W (mm) of the continuously cast steel slab is X/W (Gs/mm). The control is performed at a distance of 0.30 or more and less than 0.55, and the discharge direction of the immersion nozzle is set to be on the upstream side of the swirling flow of the molten steel formed by the alternating-current moving magnetic field, and is inclined with respect to the reference plane . The method for continuously casting a steel slab according to claim 9, wherein if the ratio X/W (Gs/mm) is 0.30 or more and less than 0.45, the discharge direction of the immersion nozzle is relative to The reference plane is inclined, and the above formula (1) is replaced by the following formula (8); if the ratio X/W (Gs/mm) is 0.45 or more and less than 0.55, the impregnating nozzle is used. The range in which the discharge direction is inclined with respect to the reference plane is replaced by the following formula (9), Θ-2≦α≦θ+5. . . Equation (8) θ-5≦α≦θ+2. . . Equation (9). The continuous casting method for a steel slab according to claim 10, wherein the α is measured after continuous change of the mold width in continuous casting or continuous casting, if the ratio X/W (Gs/mm) is When 0.30 or more and less than 0.45, and the above α does not satisfy the above formula (8), the discharge direction of the immersion nozzle is changed to satisfy the relationship of the above formula (8); if the ratio X/W (Gs) In the case where the α is less than 0.45 and not more than 0.55, and the above α does not satisfy the above formula (9), the discharge direction of the immersion nozzle is changed so as to satisfy the relationship of the above formula (9).