JP5014934B2 - Steel continuous casting method - Google Patents

Description

  The present invention relates to a steel continuous casting method in which molten steel in an upper part of a mold is stirred by an electromagnetic stirrer, and the molten steel is cast by applying a DC magnetic field to the molten steel discharged from an immersion nozzle by an electromagnetic brake device.

  In the continuous casting process of steel, for the purpose of improving the quality of cast slabs, for example, a DC magnetic field is applied to molten steel discharged into a mold. It is known that a counter flow opposite to the main flow is generated around the discharge flow of the molten steel in the DC magnetic field (Non-Patent Document 1).

  For example, in normal continuous casting of molten steel, an immersion nozzle 102 that discharges molten steel 100 into a mold 101 is used as shown in FIG. Two downward discharge holes 103 are formed in the vicinity of the lower end of the side surface of the immersion nozzle 102. When a DC magnetic field is applied to the discharge flow 104 of the molten steel 100 discharged from the discharge hole 103 of the immersion nozzle 102, for example, by an electromagnetic brake device, a counter flow 105 in the reverse direction is generated around the discharge flow 104. To do. Then, inert gas bubbles, for example, Ar gas (argon gas) bubbles 106 and alumina or slag-based non-metallic inclusions 107 contained in the discharge flow 104 are transferred to the molten steel 100 in the mold 101 by the counter flow 105. It becomes difficult to penetrate deeply. As a result, the number of Ar gas bubbles 106 and inclusions 107 can be reduced inside the slab where the molten steel 100 is cast. Further, for example, when the strength of the DC magnetic field is increased, the flow velocity of the counter flow 105 is increased, so that the Ar gas bubbles 106 and inclusions 107 are more difficult to enter, and the Ar gas bubbles 106 and inclusions 107 inside the slab are prevented. Can be further reduced.

  The Ar gas bubbles 106 and the inclusions 107 ride on the rising flow 108 in which the counter flow 105 rises along the immersion nozzle 102, concentrate on the periphery of the immersion nozzle 102, and rise to the meniscus 109. In the meniscus 109, the Ar gas bubbles 106 and inclusions 107 that have risen are removed.

  However, the upward flow 108 diffuses horizontally from the immersion nozzle 102 toward the side surface of the mold 101 in the vicinity of the meniscus 109. Due to the diffusion flow 110, the Ar gas bubbles 106 and inclusions 107 that have floated up to the meniscus 109 flow toward the side surface of the mold 101. The Ar gas bubbles 106 and some of the inclusions 107 are not removed by the meniscus 109 and are trapped by the solidified shell formed on the side surface of the mold 101. As a result, the number of Ar gas bubbles 106 and inclusions 107 on the surface of the slab where the molten steel 100 is cast increases. Further, for example, when the strength of the DC magnetic field is increased, the number of Ar gas bubbles 106 and inclusions 107 trapped in the solidified shell further increases.

  Therefore, in order to prevent the Ar gas bubbles 106 and inclusions 107 from being trapped by the solidified shell on the side surface of the mold 101 in this way, for example, by limiting the magnetic flux density of the DC magnetic field, the Ar gas on the slab surface layer A method for minimizing the number of bubbles 106 and inclusions 107 has been proposed (Non-Patent Document 2). Further, by electromagnetically stirring the molten steel 100 in the vicinity of the meniscus 109 in the upper part of the mold 101, a swirl flow 111 is formed in the molten steel 100 in the vicinity of the meniscus 109, as shown in FIG. A method of reducing the trapping in the solidified shell has been proposed (Patent Document 1).

Kensuke Okazawa et al. "Joint behavior of molten steel in a continuous mold using electromagnetic braking technology" Iron and Steel Vol.84 (1998) No.7 H. Yamamura et al. “Optimum magnetic flux density in quality control of casts with level DC magnetic field in continuous casting mold” ISIJ Int. Vol. 41, No. 10 (2001), pp. 1229-1235 JP 2000-271710 A

  However, the method for limiting the magnetic flux density of the DC magnetic field described in Non-Patent Document 2 can reduce the number of Ar gas bubbles 106 and inclusions 107 on the surface of the slab, but the strength of the DC magnetic field is weak. The number of Ar gas bubbles 106 and inclusions 107 inside the slab could not be reduced.

  Moreover, since the method of combining electromagnetic stirring described in Patent Document 1 can increase the strength of the DC magnetic field, the number of Ar gas bubbles 106 and inclusions 107 inside the slab can be reduced. The number of Ar gas bubbles 106 and inclusions 107 on the surface of the slab could not be reduced simply by electromagnetic stirring. The inventors investigated the cause of this, and as shown in FIG. 8, in the vicinity of the meniscus 109, the swirling flow 111 due to electromagnetic stirring interferes with the diffusion flow 110 formed by the rising of the counterflow 105, and the flow is reduced. It has been found that a stagnant area 112 may be formed. Then, it was found that Ar gas bubbles 106 and inclusions 107 were trapped in the flow stagnation region 112.

  As described above, according to the conventional continuous casting method, the Ar gas bubbles 106 and the inclusions 107 remain on the surface layer and inside of the slab, which causes a decrease in strength of the slab and causes surface defects of the slab. There was room for improvement in the quality of the pieces.

  This invention is made | formed in view of this point, and it aims at reducing the Ar gas bubble and inclusion contained in the slab continuously cast, and improving the quality of a slab.

  In order to achieve the above object, the present invention provides an electromagnetic stirrer for stirring the upper molten steel in the mold, and a DC magnetic field having a uniform magnetic flux density distribution in the mold width direction below the mold in the thickness direction of the mold. Immersion in the molten steel in the mold using a continuous casting mold equipped with an electromagnetic brake device that can be applied, and the lower part is provided with a discharge hole for forming an obliquely downward discharge molten steel flow in the mold While blowing Ar gas into the nozzle, the molten steel at the upper part in the mold is stirred by the electromagnetic stirring device to form a swirling flow of the molten steel in the horizontal section of the mold, and the electromagnetic brake device In a continuous casting method of steel in which molten steel is cast by applying a direct current magnetic field having a magnetic flux density of 0.1 Tesla or more to molten steel discharged from a discharge hole formed in a lower portion of the immersion nozzle, the molten steel is discharged from the immersion nozzle. The molten steel is characterized to be discharged so as to satisfy the following formula (2).

However, h: distance from the meniscus to the center of the discharge hole of the immersion nozzle (m), h _B : distance from the meniscus to the center height of the electromagnetic brake device (m), W: mold width (m), D: of the immersion nozzle Outer diameter (m), θ: Geometric molten steel discharge angle (degree) of immersion nozzle, C ₀ : 10 , B _S : Maximum value of magnetic flux density formed in the mold by the magnetic stirrer (T), B _B : Maximum value of magnetic flux density formed in mold by electromagnetic brake device (T), ρ: Molten steel density (kg / m ³ ), A: Sum of cross-sectional areas of discharge holes of immersion nozzle (m ² ), Q: Mass of molten steel Flow rate (kg / sec)

The constant C ₀ in the formula (2) is generally determined by the casting type. The meaning of the constant C ₀ is that the molten steel flow velocity near the upper meniscus in the mold is included in the molten steel. This indicates that the Ar gas bubbles and inclusions are not less than a specified value that suppresses trapping by the solidified shell. That is, the flow velocity difference between the swirling flow and the diffusion flow at the location where the swirling flow of the molten steel near the meniscus in the upper part of the mold formed by the electromagnetic stirring device interferes with the diffusion flow near the meniscus formed by the electromagnetic brake device is The constant C ₀ is determined so as to be equal to or greater than the specified value. For example, when the cast slab is a thin plate having a strict standard for surface defects, a flow velocity of 0.1 m / second or more is generally required. In the present invention, 0.1 m / second is set as a specified value. Yes. The grounds for setting the flow velocity of the molten steel near the meniscus to 0.1 m / sec or more are as follows. For example, referring to the document CAMP-ISIJ Vol.8 (1995) -344 (by Yasuo Sawada et al.), Increasing the flow velocity of the molten steel increases the velocity gradient near the interface between the solidified shell and the molten steel, and is affected by Ar bubbles and inclusions. It has been shown that lift (separation force from the solidified shell) increases. As the flow rate of molten steel increases, the critical particle size of trapped Ar gas bubbles and inclusion particles generally decreases rapidly, and the theoretical trap critical particle size gradually approaches a value of about 50 to 100 μm. . In particular, the decrease in the critical particle size from 0 to 0.1 m / sec is large, and 0.1 m / sec is adopted as the specified value of the critical flow velocity of the molten steel near the meniscus in the present invention.

The specific method for determining the constant C ₀ is that the magnetic flux density formed in the mold by the electromagnetic stirrer is the maximum value B _S and the magnetic flux density formed in the mold by the electromagnetic brake device is the maximum value B _B. The molten steel is cast by changing the molten steel discharge angle θ of the immersion nozzle. Then, the cross section perpendicular to the casting direction of the cast slab (generally referred to as the C cross section) is corroded so as to reveal dendrites which are solidified structures, and the inclination angle is measured. For example, referring to the deflection phenomenon of dendrites growing in a moving magnetic field, iron and steel Vol.86 No.4 (2000), pp45-49 (by Hisao Esaka, Takehiko Fuji, Hiroshi Harada, Eiichi Takeuchi, Keisuke Fujisaki) The dendrite is inclined upstream of the molten steel flow, and it is shown that there is a certain relationship between the angle and the molten steel flow velocity. Using this relational expression, it is confirmed from the measured inclination angle on the slab surface layer that the calculated flow velocity of the portion having the lowest inclination angle is the reference value of 0.1 m / second or more. This constant C ₀ as is determined as a critical value minimum flow rate of the molten steel is 0.1m / sec.

  As a result of investigations by the inventors, when the molten steel discharge angle θ of the immersion nozzle is large, the vertical component of the counterflow opposite to the discharge flow increases, and a fast flow increases to the meniscus along the outer wall of the immersion nozzle. It was found to interfere with the swirling flow of the molten steel at the top of the mold formed by the electromagnetic stirrer. And it turned out that a flow stagnates in this interfering location, Ar gas bubbles and inclusions contained in the discharge flow discharged from the immersion nozzle are trapped on the side surface of the mold and remain in the slab. Therefore, it has been found that it is necessary to control the size of the counterflow opposite to the discharge flow by limiting the molten steel discharge angle θ of the immersion nozzle. Therefore, the inventors further investigated that if the molten steel discharge angle θ of the immersion nozzle satisfies the relational expression between the left side of the equation (2) and sin θ, the vertical component of the counterflow formed by the electromagnetic brake device is sufficient. It was confirmed that Ar gas bubbles and inclusions can be prevented from entering the molten steel. Thereby, Ar gas bubbles and inclusions can be prevented from remaining inside the slab. Further, if the molten steel discharge angle θ of the immersion nozzle satisfies the relational expression between the left side of the equation (2) and sin θ, the flow velocity of the swirling flow formed by the electromagnetic stirring device near the meniscus above the mold is It was found that the swirl flow can be appropriately flowed so as to be equal to or higher than the flow velocity of the diffusion flow formed by, and that Ar gas bubbles and inclusions can be suppressed from being trapped by the solidified shell on the side surface of the mold. Thereby, Ar gas bubbles and inclusions can be suppressed from remaining on the surface layer in the slab. Thus, since the number of Ar gas bubbles and inclusions remaining in both the surface layer and the inside of the slab can be reduced, the quality of the slab can be improved.

  In order for the molten steel discharged from the immersion nozzle to satisfy the formula (2), it is preferable to adjust the molten steel discharge angle θ of the immersion nozzle.

  In order for the molten steel discharged from the immersion nozzle to satisfy the formula (2), a distance h from the meniscus to the center of the discharge hole of the immersion nozzle may be adjusted.

  According to the present invention, Ar gas bubbles and inclusions contained in both the surface layer and the inside of a continuously cast slab can be reduced, so that the quality of the slab can be improved.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is a plan view showing a configuration in the vicinity of a mold of a continuous casting apparatus 1 for carrying out the continuous casting method of steel according to the present embodiment, and FIG. 2 shows a configuration in the vicinity of the mold of the continuous casting apparatus 1. It is a longitudinal cross-sectional view shown.

  As shown in FIG. 1, the continuous casting apparatus 1 has a mold 2 whose horizontal cross section is rectangular, for example. An immersion nozzle 3 is provided in the upper part of the mold 2 as shown in FIG. 2, and the lower part of the immersion nozzle 3 is immersed in the molten steel 4 in the mold 2. Near the lower end of the side surface of the immersion nozzle 3, two discharge holes 5 for discharging the molten steel 4 obliquely downward into the mold 2 are formed. The discharge holes 5 and 5 are formed on the short side 2 a side of the mold 2. The discharge flow 6 discharged from the discharge holes 5 includes Ar gas bubbles 7 blown to clean the inside of the immersion nozzle 3 and alumina or slag inclusions 8.

  In the vicinity of the meniscus 9 on the long side 2b side of the mold 2, as shown in FIGS. 1 and 2, a pair of electromagnetic stirring devices 10, 10 such as electromagnetic stirring coils are provided. Due to the electromagnetic stirring of the electromagnetic stirring device 10, the swirling flow 11 can be formed by swirling the molten steel 4 in the vicinity of the meniscus 9 in the mold 2 in a horizontal plane as shown in FIG.

  An electromagnetic brake device 12 such as an electromagnet is provided below the discharge hole 5 of the immersion nozzle 3 as shown in FIG. The electromagnetic brake device 12 is provided outside the long side 2b of the mold 2 as shown in FIG. 3 and 4, the electromagnetic brake device 12 has a magnetic flux density of 0.1 Tesla or more with respect to the discharge flow 6 of the molten steel 4 immediately after being discharged from the discharge hole 5 in the width direction of the mold 2 ( A DC magnetic field 13 having a substantially uniform magnetic flux density distribution in the long side 2b direction) can be applied in the thickness direction of the mold 2 (short side 2a direction). As shown in FIG. 4, an induction current 14 is generated in the width direction (long side 2 b direction) of the mold 2 by the DC magnetic field 13 and the discharge flow 6 of the molten steel 4 discharged from the discharge hole 5. A counter flow 15 opposite to the discharge flow 6 is formed in the vicinity of the discharge flow 6 by the DC magnetic field 13. The counter flow 15 collides with the immersion nozzle 3 at substantially the same angle as the discharge angle of the discharge flow 6 and branches upstream and downstream. Among the upstream and downstream, the upward flow 16 rises to the meniscus 9 along the immersion nozzle 3. The upward flow 16 diffuses in the horizontal direction in the vicinity of the meniscus 9, and the diffusion flow 17 diffuses in the direction of the short side 2 a of the mold 2.

  As shown in FIG. 2, a solidified shell 18 is formed on the inner surface of the mold 2 by cooling and solidifying the molten steel 4.

  The above immersion nozzle 3, electromagnetic stirring device 10, and electromagnetic brake device 12 need to be installed at a position where the discharge flow 6 of the molten steel 4 discharged from the immersion nozzle 3 is discharged at an angle that satisfies the above equation (2). (See FIG. 5).

  The relational expression between the left side of the equation (2) and sin θ is for ensuring a sufficient vertical component of the counter flow 15 formed by the electromagnetic brake device 12, that is, a discharge flow formed by the electromagnetic brake device 12. 6 shows a conditional expression of a minimum angle of the discharge angle θ of the discharge flow 6 necessary for braking the discharge flow 6. Specifically, the discharge angle θ of the discharge flow 6 is determined so that the position where the discharge flow 6 collides with the short side 2a of the mold 2 is equal to or deeper than the center position of the electromagnetic brake device 12. . Thereby, the vertical component of the counterflow 15 formed by the electromagnetic brake device 12 is sufficiently ensured and the discharge flow 6 is braked, and the Ar gas bubbles 7 and inclusions 8 included in the discharge flow 6 are contained in the molten steel 4. Intrusion can be suppressed.

  The relational expression between the right side of the equation (2) and sin θ is that the flow velocity of the swirl flow 11 of the molten steel 4 near the meniscus 9 formed by the electromagnetic stirring device 10 is the flow velocity of the diffusion flow 17 formed by the electromagnetic brake device 12. The conditional expression of the maximum angle of the discharge angle θ of the discharge flow 6 necessary for the above is shown.

The flow velocity V ₀ of the discharge flow 6 discharged from the discharge hole 5 of the submerged nozzle 3 is expressed by the following equation (3): the mass flow rate Q of the molten steel 4 is the sum A of the cross-sectional areas of the discharge holes 5 of the submerged nozzle 3 It is calculated by dividing the molten steel 4 by the density ρ.

The flow velocity V ₁ of the counter flow 15 of the discharge flow 6 is determined by the magnetic flux density, which is a similar parameter of the electromagnetic force of the electromagnetic brake device 12, and is expressed by the square root of the flow velocity V ₀ of the discharge flow 6 as shown in the following equation (4). This is proportional to the product of the maximum value B _B of the magnetic flux density formed in the mold 2 by the electromagnetic brake device 12.

Flow rate V ₂ of the counter flow upflow 16 15 is branched by colliding with the submerged entry nozzle 3 at a rate approximately the (1 + sinθ) / 2 of the velocity V ₁ of the counterflow 15 as shown in the following formula (5) Distributed.

V ₃ of the diffusion flow 17 in which the upward flow 16 diffuses in the horizontal direction in the vicinity of the meniscus 9 is proportional to the flow velocity V ₂ of the upward flow 16 as shown in the following formula (6).

Integrating the above equation (3) to (6), and a proportional relationship represented by the following formula (7), the following equation: Equation (8) is established by setting the constant C _1.

On the other hand, the flow velocity V ₄ of the swirling flow 11 formed in the molten steel 4 near the meniscus 9 in the mold 2 by electromagnetic stirring of the electromagnetic stirring device 10 shown in FIG. 6 is as shown in the following formula (9). Is proportional to the square root of the electromagnetic force fem, and is proportional to the maximum value B _S of the magnetic flux density formed in the mold 2 by the electromagnetic stirring device 10. By setting the constant C ₂ to the equation (9), equation of the formula (10) is established.

In order to prevent the Ar gas bubbles 7 and inclusions 8 floating on the meniscus 9 in the mold 2 from being trapped on the side surface of the mold 2, the swirling flow 11 needs to flow appropriately. Specifically, as shown in FIG. 6, the flow velocity V ₄ of the swirl flow 11 is the flow velocity of the diffusion flow 17 at a location 19 where the swirl flow 11 and the diffusion flow 17 interfere in the opposite direction so that the swirl flow 11 does not stagnate. it is necessary that the V ₃ or more. Therefore, the following formula (11) is established from the formula (8) and the formula (10), and by setting the constant C ₀ , the following formula (2) identical to the relational expression between the right side of the formula (2) and sin θ ( 12) holds.

The constant C ₀ in the equation (12) is the flow velocity V ₄ of the swirl flow 11 of the molten steel 4 near the meniscus 9 formed by the electromagnetic stirring device 10 and the flow velocity V _{3 of the} diffusion flow 17 formed by the electromagnetic brake device 12. And the flow velocity difference (V ₄ −V ₃ ) is determined to be 0.1 m / second or more. Specifically, first, the magnetic flux density formed in the mold 2 by the electromagnetic stirring device 10 is the maximum value B _S , and the magnetic flux density formed in the mold 2 by the electromagnetic brake device 12 is the maximum value B _B. The molten steel 4 is cast by changing the discharge angle θ of the molten steel 4 of the immersion nozzle 3. The cross section perpendicular to the casting direction of the cast slab is corroded so as to reveal dendrites which are solidified structures, and the inclination angle is measured. Then, using the relational expression between the inclination angle of the dendrite and the flow velocity of the molten steel, the calculated flow velocity of the portion having the lowest inclination angle from the measured inclination angle of the slab surface layer is the above-mentioned reference value of 0.1 m / second or more Make sure that As described above, the constant C ₀ is determined as a critical value at which the flow velocity difference (V ₄ −V ₃ ) of the molten steel becomes 0.1 m / sec.

  The continuous casting apparatus 1 according to the present embodiment is configured as described above. Next, a continuous casting method for the molten steel 4 using the continuous casting apparatus 1 will be described.

  First, the discharge angle θ of the immersion nozzle 3 is adjusted so that the molten steel 4 discharged from the immersion nozzle 3 satisfies the formula (2). Then, the molten steel 4 is discharged into the mold 2 from the discharge hole 5 of the immersion nozzle 3 while blowing Ar gas into the immersion nozzle 3. The molten steel 4 is discharged obliquely downward at a discharge angle θ, and a discharge flow 6 is formed from the discharge hole 5 toward the short side 2 a of the mold 2. The discharge flow 6 includes Ar gas bubbles 7 and inclusions 8, and these Ar gas bubbles 7 and inclusions 8 float in the molten steel 4 in the mold 2.

  At the same time as the molten steel 4 is discharged from the immersion nozzle 3, the electromagnetic brake device 12 is operated. The electromagnetic brake device 12 forms a counter flow 15 opposite to the discharge flow 6, and the counter flow 15 collides with the immersion nozzle 3 to form an upward flow 16 to the meniscus 9. Then, Ar gas bubbles 7 and inclusions 8 floating in the molten steel 4 ride on the upward flow 16 and rise to the vicinity of the meniscus 9.

Simultaneously with the operation of the electromagnetic brake device 12 described above, the electromagnetic stirring device 10 is also operated. By the electromagnetic stirring of the electromagnetic stirring device 10, a swirl flow 11 is formed in the molten steel 4 near the meniscus 9 in the mold 2. Since the flow velocity V ₄ of the swirling flow 11 is equal to or higher than the flow velocity V ₃ of the diffusion flow 17, the swirling flow 11 does not stagnate. Then, the Ar gas bubbles 7 and inclusions 8 that have risen up to the vicinity of the meniscus 9 on the rising flow 16 are swirled by the swirling flow 11 and are not captured by the solidified shell 18 on the side surface of the mold 2, for example, molten oxide. It is taken in and removed by continuous casting powder (not shown).

  Thus, the molten steel 4 from which the Ar gas bubbles 7 and the inclusions 8 have been removed is solidified and cast into a slab.

  According to the above embodiment, since the molten steel 4 discharge angle θ of the immersion nozzle 3 satisfies the relational expression between the left side of the equation (2) and sin θ, the counter flow 15 formed by the electromagnetic brake device 12 The size of the vertical component can be sufficiently secured. Thereby, Ar gas bubbles 7 and inclusions 8 included in the discharge flow 6 of the molten steel 4 discharged from the immersion nozzle 3 can be prevented from entering the molten steel 4. Therefore, Ar gas bubbles 7 and inclusions 8 can be suppressed from remaining inside the slab.

  Further, since the discharge angle θ of the molten steel 4 of the immersion nozzle 3 is set so as to satisfy the relational expression between the right side of the equation (2) and sin θ, the swirling of the molten steel 4 near the meniscus 9 formed by the electromagnetic stirring device 10 is performed. The swirling flow 11 can be appropriately flowed so that the flow velocity of the flow 11 is equal to or higher than the flow velocity of the diffusion flow 17 formed by the electromagnetic brake device 12. As a result, Ar gas bubbles 7 and inclusions 8 contained in the discharge flow 6 of the molten steel 4 discharged from the immersion nozzle 3 can be suppressed from being captured by the solidified shell 18 on the side surface of the mold 2. Ar gas bubbles 7 and inclusions 8 can be removed in the vicinity. Therefore, Ar gas bubbles 7 and inclusions 8 can be suppressed from remaining on the slab surface layer.

  Thus, since the number of Ar gas bubbles 7 and inclusions 8 remaining in both the surface layer and the inside of the slab continuously cast can be reduced, the quality of the slab can be improved.

  In the above embodiment, the discharge angle θ of the immersion nozzle 3 has been adjusted so that the molten steel 4 discharged from the immersion nozzle 3 satisfies the above formula (2), but the discharge hole of the immersion nozzle 3 from the meniscus 9 has been adjusted. The above formula (2) may be satisfied by adjusting the distance h to the center of 5. Thereby, for example, when the width W of the mold 2 is changed, it is not necessary to replace the immersion nozzle 3 itself, and by changing the depth of the immersion nozzle 3, the molten steel 4 is set so as to satisfy the above formula (2). It can be discharged.

  Hereinafter, when the continuous casting method of steel of the present invention is used, the effect of removing Ar bubbles and inclusions contained in the molten steel will be described. In carrying out this example, the continuous casting apparatus 1 previously shown in FIGS. 1 and 2 was used as an apparatus for continuously casting steel.

As the mold 2 of the continuous casting apparatus 1, two types of width W of 1200 mm and 1600 mm, a height of 900 mm, and a thickness of 250 mm were used. Below the mold 2, a vertical portion (not shown) having a length of 2.5 m and a bending portion (not shown) having a bending radius of 7.5 m are provided in this order from the top. The electromagnetic stirrer 10 has a height of 150 mm and is provided at a position where the upper end thereof is the same position as the meniscus 9. The maximum magnetic flux density B _S of the electromagnetic stirring device 10 is 0.06T. Electromagnetic brake device 12 is provided at a position where its center position _{h B} is 500mm depth from the meniscus 9. The maximum magnetic flux density B _S of the electromagnetic brake device 12 is 0.4T. The molten steel 4 using low-carbon aluminum killed steel, as the volumetric flow rate Q / [rho of the molten steel 4, when the width W of the mold 2 is ^{1200mm, 6.5 × 10 -3 m 3} / sec (2.2 × 10 ^{- 2} m / sec) and 9.0 × 10 ⁻³ m ³ / sec (3.0 × 10 ⁻² m / sec), steel is cast, and the width W of the mold 2 is 1600 mm 7.3 × 10 ⁻³ m ³ / sec (1.8 × 10 ⁻² m / sec) and 1.1 × 10 ⁻² m ³ / sec (2.7 × 10 ⁻² m / sec) The steel was cast under the same conditions. As the immersion nozzle 3, a nozzle having an outer diameter D of 150 mm and an inner diameter of 90 mm was used. The immersion nozzle 3 is provided at a position where the center position h of the discharge hole 5 is 300 mm deep from the meniscus 9. In the immersion nozzle 3, circular discharge holes 5 are formed at two locations on the short side 2a side of the mold 2, and the total cross-sectional area A of the discharge holes 5 is 10053 mm ² (diameter 80 mm). As the discharge angle θ of the discharge hole 5, steel was cast under seven conditions of 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, and 45 degrees downward from the horizontal plane. In the case where the width W of the mold 2 is 1200 mm and the volume flow rate Q / ρ is 6.5 × 10 ⁻³ m ³ / sec (2.2 × 10 ⁻² m / sec), the above formula ( In order to be less than the upper limit of the constraint condition of 2), the discharge angle θ is performed up to 50 degrees, 55 degrees and 60 degrees, the width W is 1600 mm, and the volume flow rate Q / ρ is 7.3 × 10 ⁻³ m ³ /. In the case of a second (1.8 × 10 ⁻² m / sec), the discharge angle θ was 50 degrees.

Steel was cast using the continuous casting apparatus 1 described above, and the surface layer of the cast slab and the Ar bubbles 7 and inclusions 8 having a diameter of 100 μm or more contained therein were measured. The inside of the slab was measured from the surface to a depth of 10 mm. In this embodiment, the constant C ₀ is 10.

  Table 1 shows the measurement results of Ar bubbles 7 and inclusions 8 when the width W of the mold 2 is 1200 mm, and Table 2 shows the measurement results of Ar bubbles 7 and inclusions 8 when the width W is 1600 mm. The measurement result of Ar bubbles 7 and inclusions 8 is the reference value (1.0) based on the number of Ar bubbles 7 and inclusions 8 in the slab having the best quality under the conditions of width W and volume flow rate Q / ρ. The ratio of the number of Ar bubbles 7 and inclusions 8 with respect to this reference value is displayed as a quality index. Moreover, in Table 1 and Table 2, it shows about evaluation whether the discharge angle (theta) of the molten steel 4 from the immersion nozzle 3 satisfy | fills the said Formula (2), and if it satisfy | fills Formula (2), it will be "(circle)". If “” does not satisfy the formula (2), “x” is indicated.

  Referring to Tables 1 and 2, when the discharge angle θ of the immersion nozzle 3 satisfies both the lower limit and the upper limit of the above formula (2), the quality index is as low as 1.0 to 1.2, and the casting index It was found that the number of Ar bubbles 7 and inclusions 8 contained in the piece was small, and the quality of the slab was kept constant. On the other hand, when the discharge angle θ does not satisfy either the lower limit or the upper limit of the formula (2), the quality index shows a relatively high value of 1.6 or more, which indicates that the quality is deteriorated. . From the above, it has been found that when molten steel is cast by the casting method of the present invention, Ar bubbles 7 and inclusions 8 can be appropriately removed.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be made within the scope of the ideas described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

  INDUSTRIAL APPLICABILITY The present invention is useful for a continuous casting method of steel in which molten steel at the upper part in a mold is stirred by an electromagnetic stirring device, and the molten steel is cast by applying a DC magnetic field to molten steel discharged from an immersion nozzle by an electromagnetic brake device. is there.

It is a top view which shows the structure of the mold vicinity of the continuous casting apparatus for enforcing the continuous casting method of steel concerning this Embodiment. It is a longitudinal cross-sectional view which shows the structure of the mold vicinity of the continuous casting apparatus for enforcing the continuous casting method of steel concerning this Embodiment. It is explanatory drawing which showed the DC magnetic field at the time of operating an electromagnetic brake device. It is explanatory drawing which showed the flow of the direct current magnetic field at the time of operating an electromagnetic brake device, an induced current, and a counterflow. It is explanatory drawing which showed the flow of the molten steel at the time of implementing the continuous casting method of steel concerning this Embodiment. It is explanatory drawing which showed the flow of the molten steel at the time of implementing the continuous casting method of steel concerning this Embodiment. It is a top view which shows the structure of the mold vicinity of the conventional continuous casting apparatus. It is a longitudinal cross-sectional view which shows the structure of the mold vicinity of the conventional continuous casting apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Continuous casting apparatus 2 Mold 2a Short side of mold 2b Long side of mold 3 Immersion nozzle 4 Molten steel 5 Discharge hole 6 Discharge flow 7 Ar gas bubble 8 Inclusion 9 Meniscus 10 Electromagnetic stirrer 11 Swirling flow 12 Electromagnetic brake device 13 DC magnetic field 14 Inductive current 15 Counterflow 16 Upflow 17 Diffusion flow 18 Solidified shell 19 Where the swirl flow and diffusion flow interfere

Claims (3)

For continuous casting, equipped with an electromagnetic stirrer that stirs the molten steel in the upper part of the mold, and an electromagnetic brake device that can apply a DC magnetic field having a uniform magnetic flux density distribution in the width direction of the mold in the thickness direction below the mold. The mold is immersed in the molten steel in the mold, and while the Ar gas is blown into a submerged nozzle provided with a discharge hole for forming an obliquely downward discharge molten steel flow in the mold, the electromagnetic The upper molten steel in the mold is stirred by the stirring device to form a swirling flow of the molten steel in the horizontal section of the mold, and from the discharge hole formed in the lower portion of the immersion nozzle by the electromagnetic brake device. In a continuous casting method of steel in which molten steel is cast by applying a DC magnetic field having a magnetic flux density of 0.1 Tesla or more to the discharged molten steel,
The molten steel discharged from the immersion nozzle is discharged so as to satisfy the following formula (1).

However, h: distance from the meniscus to the center of the discharge hole of the immersion nozzle (m), h _B : distance from the meniscus to the center height of the electromagnetic brake device (m), W: mold width (m), D: of the immersion nozzle Outer diameter (m), θ: Geometric molten steel discharge angle (degree) of immersion nozzle, C ₀ : 10 , B _S : Maximum value of magnetic flux density formed in the mold by the magnetic stirrer (T), B _B : Maximum value of magnetic flux density formed in mold by electromagnetic brake device (T), ρ: Molten steel density (kg / m ³ ), A: Sum of cross-sectional areas of discharge holes of immersion nozzle (m ² ), Q: Mass of molten steel Flow rate (kg / sec) 2. The continuous steel according to claim 1, wherein the molten steel discharged from the immersion nozzle is discharged so as to satisfy the formula (1) by adjusting the molten steel discharge angle θ of the immersion nozzle. Casting method. The molten steel discharged from the immersion nozzle is discharged so as to satisfy the formula (1) by adjusting the distance h from the meniscus to the center of the discharge hole of the immersion nozzle. The continuous casting method of the described steel.

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