JP5047742B2 - Steel continuous casting method and continuous casting apparatus - Google Patents

Description

  The present invention relates to a continuous casting method and continuous casting apparatus for steel.

  In continuous casting of steel, for example, a stopper or a sliding nozzle (sliding gate) is usually used as a flow rate control device in order to control the mass flow rate of molten steel supplied from a tundish into a mold via an immersion nozzle. The stopper is, for example, a rod made of refractory, and is provided, for example, above the inlet of molten steel formed on the top of the immersion nozzle. Then, the mass flow rate of the molten steel flowing into the immersion nozzle is controlled by moving the stopper up and down relative to the inlet of the immersion nozzle and changing the opening area by changing the distance between the stopper and the inlet. In addition, the sliding nozzle has, for example, three refractory plates in which through holes are formed, and these plates are provided in three layers so as to cover the inlet of the immersion nozzle. The upper and lower two plates are fixed so that the through holes are located above the immersion nozzle, and the intermediate plate can be moved in the horizontal direction. And the mass flow rate of the molten steel flowing into the immersion nozzle is controlled by moving the intermediate plate horizontally and changing the opening area of the through hole of the plate seen from above (non-patent) Reference 1).

  The above-described stopper is used when the mass flow rate of the molten steel is relatively small. The sliding nozzle described above is used when the mass flow rate of the molten steel is relatively large because the controllability of the mass flow rate of the molten steel is higher than that of the stopper.

  When the mass flow rate of the molten steel is controlled using a stopper, the stopper 100 may be eccentric with respect to the inlet 102 of the immersion nozzle 101, for example, as shown in FIG. In this case, as shown in FIGS. 11 (a) and 11 (b), drift occurs in the immersion nozzle 101, and vortices are periodically generated in the vicinity of the discharge holes 103 formed in the lower portion of the immersion nozzle 101. . This vortex moves while twisting in the discharge flow of the molten steel discharged from the immersion nozzle 101. Further, when a sliding nozzle is used, for example, as shown in FIG. 12A, the sliding nozzle 110 is not always fully opened, and is normally used in a state where the intermediate plate 111 is moved horizontally. . In this case, as shown in FIGS. 12A and 12B, since the through hole 114 of the intermediate plate is eccentric with respect to the inlet 113 of the immersion nozzle 112, a drift occurs in the immersion nozzle 112. In the vicinity of the discharge hole 115 formed in the lower part of the immersion nozzle 112, vortices are periodically generated.

  When the vortex is generated in the discharge flow of the molten steel discharged from the immersion nozzles 101 and 112 in this way, the flow of the molten steel in the mold fluctuates periodically. Thereby, the quality of the cast slab was fluctuate | varied in the longitudinal direction of the slab. Moreover, since the inclusions contained in the molten steel are aggregated and enlarged by vortices, the quality of the slab was deteriorated. Therefore, in order to cope with these problems, a method has been proposed in which a throttle or a step is provided in the immersion nozzles 101 and 112 to prevent the drift of molten steel in the immersion nozzles 101 and 112 and to prevent the generation of vortices. (Patent Document 1).

69th and 70th Nishiyama Memorial Technology Lecture Recent advances in bloom and billet continuous casting technology Japan Iron and Steel Institute Japanese Patent Laid-Open No. 11-123509

  However, when the apertures or steps are processed in the immersion nozzles 101 and 112 in this way, there is a problem that the manufacturing cost of the immersion nozzles 101 and 112 increases. In addition, since the inclusions in the molten steel flowing in the immersion nozzles 101 and 112 adhere to and aggregate on the stepped portions in the immersion nozzles 101 and 112, there is an effect of preventing the drift of the molten steel in the immersion nozzles 101 and 112. It fluctuated in series and there was variation in the quality of cast slabs. Furthermore, the inclusions that have agglomerated and enlarged at the steps of the immersion nozzles 101 and 112 flow into the mold, which may deteriorate the quality of the slab.

  The present invention has been made in view of the above points, and in continuous casting of steel, it is possible to suppress the generation of vortex in the molten steel in the immersion nozzle, to suppress the quality fluctuation of the cast slab, and to The purpose is to improve the quality.

In order to achieve the above-described object, the present invention provides a method for continuously casting steel in which molten steel is supplied into a mold by an immersion nozzle. The molten steel in the immersion nozzle is at the same height as the discharge hole of the molten steel in the immersion nozzle. On the other hand, a static magnetic field is applied so as to satisfy the following formula (1).
B _B ² ≧ C ₀ Q / A (1)
However, B _B : Magnetic flux density of static magnetic field (T), C ₀ : 4 × 10 ⁻⁶ , Q: Mass flow rate of molten steel flowing into immersion nozzle (kg / sec), A: Inner cross-sectional area of immersion nozzle (m ² )

Incidentally, the constant _{C 0} of the formula (1) is a 4 × ^{10 -6} fixed value. This constant C ₀ is generally determined by the type of molten metal, but the molten metal in the present invention is molten steel, and is determined so as not to generate vortices in the molten steel in the immersion nozzle. Specifically, for deriving the constant C ₀ , for example, an acrylic model of an actual immersion nozzle is created so that the inside of the immersion nozzle can be directly observed from the outside, and the flow rate for controlling the flow rate of the molten steel flowing into the immersion nozzle A low melting point alloy (tin, lead, bismuth, cadmium alloy having a melting point of 100 ° C. or lower (hereinafter referred to as “low melting point alloy”)) is caused to flow into the immersion nozzle using a control device. Piping is connected to the discharge holes formed at two locations near the lower end of the side surface of the immersion nozzle, and the low melting point alloy flowing through the piping is circulated through the immersion nozzle. And a static magnetic field is applied with respect to the low melting-point alloy in the immersion nozzle of the same height as a discharge hole. In the low melting point alloy, visualization particles (for example, Al ₂ O ₃ particles or SiC particles) are appropriately added to visualize the flow of the low melting point alloy in the immersion nozzle, and the presence or absence of vortices in the immersion nozzle is determined. . In order to determine the presence or absence of vortices in the immersion nozzle, electrodes are placed at two arbitrary points in the immersion nozzle, and the potential difference between the electrodes due to the electromagnetic field generated by the interference between the static magnetic field and the flow of the low melting point alloy is measured. And the magnitude | size may be compared by the upper and lower sides of the discharge hole of an immersion nozzle, and you may determine the presence or absence of a vortex. In other words, if the potential difference measured above and below the discharge hole is opposite in the positive and negative directions, it may be determined that a vortex is generated. In this case, for example, a flow rate sensor used for measuring the flow rate of mercury or a low melting point alloy shown in C.VIVES et al .: Metal. Trans., Vol16B, (1985), p377. Specifically, this flow rate sensor has a cylindrical permanent magnet disposed at the tip of a metal rod, and two copper wire electrodes disposed on the side of the permanent magnet. The permanent magnet is arranged so that the metal rod and the magnetic field are coaxial. When this flow rate sensor is arranged so that the surface containing the two copper wires is perpendicular to the flow of the liquid metal, the interference between the magnetic field formed by the permanent magnet and the flow of the liquid metal causes a gap between the two copper wires. A potential difference occurs. This potential difference is proportional to the flow rate of the liquid metal. Based on this principle, the flow rate of the liquid metal can be measured using a flow rate sensor. If the above flow rate sensor is arranged in the immersion nozzle of this model so that the surface including the two electrodes is perpendicular to the immersion nozzle axis, the flow rate of the low melting point alloy can be directly measured. And in the location where the flow direction of a low melting point alloy changes, if the flow rate sensor is installed in two places in the radial direction of the immersion nozzle and the flow rate of the low melting point alloy is measured, the presence or absence of the vortex flow of the low melting point alloy can be measured. In addition, when a static magnetic field is not applied to the position of the discharge hole of the immersion nozzle, it is necessary to provide a permanent magnet in the flow velocity sensor as described above. However, when a static magnetic field is applied, this static magnetic field is generated by the permanent magnet. There is no need to provide a permanent magnet in the flow sensor because it is an alternative to the magnetic field formed. In addition, when a static magnetic field is applied and a permanent magnet is provided in the flow velocity sensor, the flow of the low melting point alloy is evaluated by measuring the difference between the applied static magnetic field and the magnetic field formed by the permanent magnet. You can also We, by measuring the potential difference between the electrodes before Symbol immersion nozzle, when vortex derived constant C ₀ if it was not generated in the immersion nozzle is a fixed numerical constant C ₀ 4 × 10 ⁻⁶ was derived. The normal operating conditions at this time are, for example, an immersion nozzle having a circular section with a mold thickness of 250 mm, a width of 1 to 2 m, a casting speed of 0.017 to 0.033 m / sec, and an inner diameter of 90 mm. Using.

According to the present invention, since the static magnetic field is applied to the molten steel in the immersion nozzle having the same height as the discharge hole of the immersion nozzle, the induction current is induced by the flow of the static magnetic field and the molten steel flowing in the immersion nozzle. Will occur. Due to the induced current and the static magnetic field, an electromagnetic force opposite to the flow of the molten steel in the immersion nozzle acts. Then, an apparent pressure loss is given to the flow of the molten steel in the immersion nozzle by this reverse electromagnetic force, and the mass flow rate of the molten steel into the mold is controlled using a flow control device such as a stopper or a sliding nozzle. In this case, the generation of vortices in the vicinity of the discharge hole of the immersion nozzle can be suppressed. Further, as a result of investigations by the inventors, it has been found that the minimum value of the magnetic flux density B _B ² of the static magnetic field necessary for suppressing the generation of this vortex is the right side of the equation (1). Since the magnetic flux density B _B ² of the static magnetic field applied in the present invention satisfies the formula (1), vortices are hardly generated in the immersion nozzle. Therefore, the discharge flow of the molten steel discharged from the immersion nozzle into the mold can be rectified, and the quality fluctuation of the cast slab can be suppressed.

  In addition, since the generation of vortices in the immersion nozzle is suppressed by applying a static magnetic field as described above, the diameter of inclusions in molten steel that has been agglomerated and enlarged due to the turbulent flow of the vortices is reduced. be able to. Moreover, since the discharge flow of the molten steel from the immersion nozzle is also rectified as described above, the turbulent flow of the molten steel in the mold can be suppressed, and inclusions can be prevented from aggregating due to the turbulent flow. Therefore, the diameter of inclusions generated in the mold is reduced, and the quality of the slab can be improved.

  It is preferable that the magnetic flux density of the static magnetic field has a maximum value at the position of the discharge hole of the immersion nozzle. Thereby, the static magnetic field applied so that the said Formula (1) may be satisfy | filled can be utilized efficiently.

  The present invention according to another aspect is a continuous casting apparatus for carrying out the steel continuous casting method, a mold for casting molten steel, a flow rate control apparatus for controlling the mass flow rate of molten steel into the mold, An immersion nozzle that discharges molten steel into the mold, and an electromagnetic brake device that applies a static magnetic field that satisfies Equation (1) to the molten steel in the immersion nozzle at the same height as the discharge hole of the immersion nozzle; It is characterized by having.

  You may have the other electromagnetic brake device which applies a static magnetic field further with respect to the molten steel discharged from the discharge hole of the said immersion nozzle.

Wherein provided above the electromagnetic brake device may have a magnetic stirring device for stirring the solvent steel in said mold.

  You may adjust the height of the discharge hole of the said immersion nozzle so that the static magnetic field which the said electromagnetic brake device applies satisfy | fills said Formula (1).

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that a vortex generate | occur | produces in the molten steel in an immersion nozzle, can suppress the quality fluctuation | variation of the cast slab, and can improve the quality of a slab.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is a longitudinal sectional view in the longitudinal direction showing the configuration of the continuous casting apparatus 1 for steel according to the present embodiment, and FIG. 2 is a longitudinal sectional view in the short direction showing the configuration of the continuous casting apparatus 1. .

  As shown in FIGS. 1 and 2, the continuous casting apparatus 1 includes a mold 2 having a rectangular horizontal cross section, for example. An immersion nozzle 3 is provided in the upper part of the mold 2, and the lower part of the immersion nozzle 3 is immersed in the molten steel 4 in the mold 2. The upper end of the immersion nozzle 3 is opened, and an inflow port 5 into which the molten steel 4 flows is formed. Near the lower end of the side surface of the immersion nozzle 3, two discharge holes 6 for discharging the molten steel 4 obliquely downward into the mold 2 are formed. The discharge holes 6, 6 are respectively formed on the short side 2a side of the mold 2. For example, an insulating refractory is used as the material of the immersion nozzle 3.

  Above the immersion nozzle 3, a sliding nozzle 7 is provided as a flow control device. A tundish (not shown) is provided above the sliding nozzle 7, and the mass flow rate of the molten steel 4 flowing from the tundish into the immersion nozzle 3 is controlled by the sliding nozzle 7. The sliding nozzle 7 has two fixed plates 8 and 8 and one sliding plate 9. The fixed plates 8 and 8 and the sliding plate 9 are stacked in three layers so as to cover the inlet 5 of the immersion nozzle 3, and the sliding plate 9 is provided between the fixed plates 8 and 8. The fixed plates 8 and 8 are fixed to the immersion nozzle 3, and the sliding plate 9 can move horizontally in the thickness direction of the mold 2 (short side 2a direction). In the center of the fixed plate 8 and the sliding plate 9, through holes 8 a and 9 a for allowing the molten steel to pass through and flowing into the inlet 5 of the immersion nozzle 3 are formed. The mass flow rate of the molten steel 4 flowing into the immersion nozzle 3 is controlled by moving the sliding plate 9 horizontally and changing the opening area of the through holes 8a, 9a as viewed from above. For example, an insulating refractory is used as the material of the fixing plate 8 and the sliding plate 9.

An electromagnetic brake device 10 such as an electromagnet is provided outside the long side 2b of the mold 2 and at the same height as the discharge hole 6 of the immersion nozzle 3. The electromagnetic brake device 10 has a static magnetic flux density distribution substantially uniform in the width direction (long side 2b direction) of the mold 2 with respect to the molten steel 4 in the immersion nozzle 3 having the same height as the discharge hole 6 of the immersion nozzle 3. The magnetic field 20 can be applied in the thickness direction (short side 2a direction) of the mold 2. The static magnetic field 20 is applied so that the magnetic flux density satisfies the following formula (1).
B _B ² ≧ C ₀ Q / A (1)
However, B _B : Magnetic flux density (T) of static magnetic field 20, C ₀ : Constant (4 × 10 ⁻⁶ ), Q: Mass flow rate of molten steel 4 (kg / sec), A: Inner cross-sectional area of immersion nozzle 3 ( m ² )

The equation (1) indicates that, for example, even when the sliding plate 9 is moved horizontally and the molten steel 4 flowing into the immersion nozzle 3 drifts, the vortex of the molten steel 4 does not occur in the vicinity of the discharge hole 6 in the immersion nozzle 3. ² shows a conditional expression of the minimum magnetic flux density B _B ² of the static magnetic field 20 for achieving the above.

Specifically, as shown in the following formula (2), the electromagnetic force (σvB _B ² ) generated by the electromagnetic brake device 10 is drifted and flows into the immersion nozzle 3 and the inertia force (ρv ²⁾ of the flow of the molten steel 4 flows into the immersion nozzle 3. ) Is necessary. Here, in calculating the mass flow velocity v of the molten steel 4, the mass flow rate Q of the molten steel 4 is divided by the density ρ of the molten steel 4 to obtain a volume flow rate, and divided by the inner cross-sectional area A of the immersion nozzle 3. Calculate the representative flow rate. When the vortex of the molten steel 4 is generated in the immersion nozzle 3, the molten steel 4 flows eccentrically in the immersion nozzle 3, and the flow rate increases compared to the flow rate in the case where there is no uneven flow. , as shown in the following formula (3), it is calculated by multiplying the constant C ₁ representative flow velocity of the molten steel 4. Then, organize the following equation (2) below (3) for the magnetic flux density _B ^{B 2} of the static magnetic field 20 as shown in the following formula (4), when the _{C 1} / sigma constant a constant _{C 0,} the formula (1) is derived.
(ΣvB _B ² ) ≧ C ₁ (ρv ² ) (2)
v = Q / ρA (3)
B _B ² ≧ (C ₁ / σ) (Q / A) (4)
Where σ: electric conductivity of molten steel 4 (S / m) ρ: density of molten steel 4 (kg / m ³ ), v: mass flow rate of molten steel 4 (m / sec), C ₁ : constant

Incidentally, the constant _{C 0} of the formula (1) is a 4 × ^{10 -6} fixed value. This constant C ₀ is determined by the inventors using the actual continuous casting apparatus 1 to control the mass flow rate Q of the molten steel 4 with the sliding nozzle 7 and in the vicinity of the lower discharge hole 6 in the immersion nozzle 3. The constant C ₀ when this vortex does not occur was derived by examining the presence or absence of the occurrence of.

  The continuous casting apparatus 1 according to the present embodiment is configured as described above. Next, a method for rectifying the molten steel 4 in the immersion nozzle 3 using the continuous casting apparatus 1 and continuously casting the molten steel 4 will be described. To do.

  First, the molten steel 4 is caused to flow from the tundish through the sliding nozzle 7 into the immersion nozzle 3. At this time, the sliding plate 9 of the sliding nozzle 7 is moved horizontally in the thickness direction (short side 2a direction) of the mold 2 to control the mass flow rate Q of the molten steel 4 to a predetermined flow rate. If it does so, the drift of the molten steel 4 which goes to the discharge hole 6 formed in the lower part of the immersion nozzle 3 will be formed in the immersion nozzle 3.

  At the same time as the molten steel 4 flows into the immersion nozzle 3, the electromagnetic brake device 10 applies the width direction (long side) of the mold 2 to the molten steel 4 in the immersion nozzle 3 having the same height as the discharge hole 6 of the immersion nozzle 3. The static magnetic field 20 having a substantially uniform magnetic flux density distribution in the 2b direction) is applied in the thickness direction of the mold 2 (short side 2a direction). The static magnetic field 20 is applied so that the magnetic flux density satisfies the formula (1). As shown in FIG. 3, the induced current 22 flows in one direction in the direction of the discharge holes 6 and 6 through the immersion nozzle 3 by the static magnetic field 20 and the drift 21 of the molten steel 4. Due to the induced current 22 and the static magnetic field 20, an electromagnetic brake force 23 opposite to the drift 21 of the molten steel 4 acts. The reverse electromagnetic braking force 23 gives an apparent pressure loss to the drift 21 in the immersion nozzle 3, and the drift 21 of the molten steel 4 near the discharge hole 6 in the immersion nozzle 3 is rectified.

  The molten steel 4 rectified in the vicinity of the discharge hole 6 in the immersion nozzle 3 is discharged into the mold 2 from the discharge hole 6 and cast into a slab in the mold 2.

According to the above embodiment, since the static magnetic field 20 is applied by the electromagnetic brake device 10 to the molten steel 4 in the immersion nozzle 3 having the same height as the discharge hole 6 of the immersion nozzle 3, this static magnetic field. 20 and the drift 21 of the molten steel flowing in the immersion nozzle 3 generate an induced current 22, and the induced current 22 and the static magnetic field 20 cause an electromagnetic brake force 23 opposite to the drift 21 of the molten steel 4 in the immersion nozzle 3. Can act. Then, when the mass flow rate Q of the molten steel 4 into the immersion nozzle 3 is controlled by the reverse electromagnetic brake force 23 using, for example, the sliding nozzle 7, a vortex is generated in the vicinity of the discharge hole 6 of the immersion nozzle 3. Can be suppressed. Further, the minimum value of the electromagnetic density B _B ² of the static magnetic field 20 necessary to suppress the generation of this vortex is the right side of the above equation (1), and the magnetic flux density B _B ² of the static magnetic field applied in the present invention is Since the formula (1) is satisfied, vortices are hardly generated in the immersion nozzle 3. Therefore, the discharge flow of the molten steel 4 discharged from the immersion nozzle 3 can be rectified, and the quality fluctuation of the cast slab can be suppressed.

  Moreover, since the generation of vortices in the immersion nozzle 3 is suppressed by applying the static magnetic field 20 in this way, the intervening included in the molten steel 4 that has conventionally been aggregated and enlarged due to the turbulent flow of the vortices. The diameter of the object can be reduced. Moreover, since the discharge flow of the molten steel 4 discharged from the discharge hole 6 of the immersion nozzle 3 is also rectified, the turbulent flow of the molten steel 4 in the mold 2 is suppressed, and the aggregation of inclusions due to the turbulent flow is also suppressed. Can do. Therefore, the diameter of inclusions generated in the mold 2 is reduced, and the quality of the slab can be improved.

  The static magnetic field 20 applied to the molten steel 4 in the immersion nozzle 3 having the same height as the discharge hole 6 of the immersion nozzle 3 is applied to the immersion nozzle 3 above the discharge hole 6 as shown in FIG. You may apply to. In this case, the induced current 22 circulates in the immersion nozzle 3 because the immersion nozzle 3 is an insulator. As a result, a parallel flow 24 in the same direction as the drift 21 of the molten steel 4 is formed. However, according to the present embodiment, simultaneously with the formation of the parallel flow 24, the electromagnetic brake force 23 opposite to the drift 21 of the molten steel 4 in the immersion nozzle 3 acts, so that the drift 21 can be rectified. .

In the above embodiment, the electromagnetic brake device 10 is preferably installed such that the maximum value at the position of the discharge hole 6 of the magnetic flux density B _B immersion nozzle 3 of the static magnetic field 20. Thereby, the static magnetic field 20 applied so that the said Formula (1) may be satisfy | filled can be utilized efficiently, and the operating efficiency of the electromagnetic brake device 10 can be improved.

  In the above embodiment, the sliding nozzle 7 is used as the flow rate control device, but a stopper 30 may be used as shown in FIG. The stopper 30 has a spherical tip, and is provided above the inlet 32 of the molten steel 4 above the immersion nozzle 31. The inlet 32 of the immersion nozzle 31 has a shape that fits the tip of the stopper 30. Then, the stopper 30 is moved up and down with respect to the inlet 32 of the immersion nozzle 31, and the opening area is changed by changing the distance between the stopper 30 and the inlet 32, whereby the molten steel 4 flowing into the immersion nozzle 31 is changed. Control mass flow. Other configurations are the same as those of the continuous casting apparatus 1 of the above embodiment. In such a case, for example, even when the stopper 30 is eccentric with respect to the immersion nozzle 31 and the drift of the molten steel 4 occurs in the immersion nozzle 31, the electromagnetic brake device 10 can immerse the same height as the discharge hole 33 of the immersion nozzle 31. By applying the static magnetic field 20 to the molten steel 4 in the nozzle 31, the drift of the molten steel 4 can be rectified.

  In the above embodiment, the electromagnetic brake device 10 applied the static magnetic field 20 having a substantially uniform magnetic flux density distribution in the width direction (long side 2b direction) of the mold 2, but as shown in FIG. You may use the electromagnetic brake 41 which applies the static magnetic field 40 locally only to the molten steel 4 in the immersion nozzle 3 of the same height as the discharge hole 6 of the immersion nozzle 3. As a result, the electromagnetic force necessary for applying the static magnetic field 20 to the molten steel 4 outside the immersion nozzle 3 becomes unnecessary, so that the molten steel 4 near the discharge hole 6 in the immersion nozzle 3 can be efficiently rectified. .

  In the continuous casting apparatus 1 of the above embodiment, as shown in FIGS. 7 and 8, the molten steel 4 immediately after being discharged into the mold 2 from the discharge hole 6 of the immersion nozzle 3 is provided below the electromagnetic brake apparatus 10. Another electromagnetic brake device 51 that applies the static magnetic field 50 may be provided. In such a case, the width direction of the mold 2 (long side 2b direction) with respect to the discharge flow 52 of the molten steel 4 discharged in the direction of the short side 2a of the mold 2 from the discharge hole 6 of the immersion nozzle 3 by another electromagnetic brake device 51. ) Is applied in the thickness direction (short side 2a direction) of the mold 2 with a substantially uniform magnetic flux density distribution. Due to the static magnetic field 50 and the discharge flow 52, an induced current 53 flows in the width direction of the mold 2 (long side 2b direction). Due to the induced current 53 and the discharge flow 52, a counter flow 54 in the opposite direction to the discharge flow 52 is formed in the mold 2. The counter flow 54 flows toward the immersion nozzle 3, collides with the immersion nozzle 3, and branches upstream and downstream. Among the upstream and downstream, the upward flow 55 rises to the meniscus 56 along the immersion nozzle 3. The upward flow 55 diffuses in the horizontal direction in the vicinity of the meniscus 56, and the diffusion flow 57 diffuses in the width direction of the mold 2 (long side 2b direction). According to the present embodiment, a counter magnetic field 50 is applied by another electromagnetic brake device 51 to generate a counter flow 54 in the mold 2, so that inclusions contained in the molten steel 4 penetrate deeply into the mold 2. Can be suppressed. Further, inclusions that have floated up to the meniscus 56 by the counterflow 54 can be removed in the vicinity of the meniscus 56. Therefore, the inclusions contained in the slab can be reduced and the quality can be improved. The electromagnetic brake device 10 and the other electromagnetic brake device 51 may have an integrated structure.

  In the continuous casting apparatus 1 of the above embodiment, as shown in FIG. 9, an electromagnetic stirring device 60 such as an electromagnetic stirring coil is provided on the long side 2 b side of the mold 2 above the electromagnetic brake device 10. May be. As shown in FIG. 10, the molten steel 4 in the vicinity of the upper meniscus 56 in the mold 2 can be swirled in a horizontal plane by the electromagnetic stirring of the electromagnetic stirring device 60 to form a swirling flow 61. Thereby, it is possible to suppress the inclusions contained in the molten steel 4 near the meniscus 56 from adhering to the side surface of the mold 2. Therefore, the inclusions contained in the slab can be reduced and the quality can be improved.

  In the above embodiment, the electromagnetic brake device 10 is installed so as to apply the static magnetic field 20 to the molten steel 4 in the immersion nozzle 3 having the same height as the discharge hole 6 of the immersion nozzle 3. When the brake device 10 is fixed to the mold 2, the immersion depth of the immersion nozzle 3 may be adjusted so that the discharge hole 6 of the immersion nozzle 3 has the same height as the electromagnetic brake 10.

  Hereinafter, when the steel continuous casting method of the present invention was used, the number of bubbles and inclusions contained in the cast slab was measured for the effect of suppressing the generation of vortices in the molten steel in the immersion nozzle. It demonstrates based on a result. In carrying out the present embodiment, the continuous casting apparatus 1 previously shown in FIGS. 1 and 2 is used as an apparatus for continuous casting of steel, and the electromagnetic brake apparatus is used in the width direction of the mold 2 (long side 2b direction). The static magnetic field 40 is locally applied only to the electromagnetic brake device 10 for applying the static magnetic field 20 having a substantially uniform magnetic flux density distribution and the molten steel 4 in the immersion nozzle 3 having the same height as the discharge hole 6 of the immersion nozzle 3. Two types of electromagnetic brake devices, ie, the electromagnetic brake 41 for applying the pressure, were used.

As the mold 2 of the continuous casting apparatus 1, a mold having a width of 1200 mm, a height of 900 mm, and a thickness of 250 mm was 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. As the immersion nozzle 3, a nozzle having an outer diameter 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 of the discharge hole 6 is 300 mm deep from the meniscus. The immersion nozzle 3 is formed with two circular discharge holes 6 on the short side 2a side of the mold 2, the inner cross-sectional area A of the immersion nozzle 3 is 6362 mm ² (inner diameter 90 mm), and the discharge angle of the discharge hole 6 is 30 degrees. Uniform static magnetic field 20 electromagnetic brake device 10 of the uniform type of applying a is a 0.5T maximum magnetic flux density B _B at a position where a 500mm depth from the meniscus, the half at the position of the discharge port 6 of the immersion nozzle 3 of capable of generating a magnetic flux density _{B B} of 0.25T. A local electromagnetic brake device 41 that locally applies a static magnetic field 40 has a discharge hole 6 at the center of the immersion nozzle 3 in the width direction (long side 2b direction) of the mold 2 and in the depth direction of the mold 2. It is installed in the center. Electromagnetic brake device 41 can generate a magnetic flux density _{B B} of 0.3T in the range of 200mm from the center position in the width direction and the height direction. The molten steel 4 was made of low-carbon aluminum killed steel, and the casting speed of the molten steel 4 was cast under two conditions of 0.025 m / sec and 0.033 m / sec.

Steel was cast using the above continuous casting apparatus 1, and 10 samples of a slab having a full width of a cast slab, a length of 100 mm in the casting direction, and a depth of 50 mm from the surface were collected. Then, the number of bubbles and inclusions having a diameter of 100 μm or more contained in these slab samples was measured, and the average value and standard deviation were calculated. In this embodiment, the constant C ₀ is 4 × 10 ⁻⁶ .

Table 1 shows the measurement results of bubbles and inclusions when the casting speed of the molten steel 4 is 0.025 m / sec, and Table 2 shows the measurement results of bubbles and inclusions when the casting speed is 0.033 m / sec. As the measurement results of the bubbles and inclusions, the number of bubbles and inclusions in the slab cast without applying the static magnetic fields 20 and 40 by the electromagnetic brake devices 10 and 41, and the number of bubbles and inclusions relative to the particle size With the standard deviation of each as a reference value (1.0), an average value index and a standard deviation index of the number of bubbles and inclusions with respect to the reference value are shown. Tables 1 and 2 also show the evaluation of whether or not the magnetic flux density B _B ² of the static magnetic fields 20 and 40 satisfies the formula (1). If the formula (1) is satisfied, “◯ "Is shown, and if the formula (1) is not satisfied," x "is shown.

Referring to Tables 1 and 2, when the magnetic flux density B _B ² of the static magnetic fields 20 and 40 satisfies the formula (1), either the uniform electromagnetic brake device 10 or the local electromagnetic brake device 41 is used. Even if it used, the average value index | exponent was 0.3-0.4. From this, it was found that the number of bubbles and inclusions contained in the slab was reduced as compared with the case where the static magnetic fields 20 and 40 were not applied. In addition, since the standard deviation index is 0.2 to 0.3, it is found that there is little variation in the particle size of the bubbles and inclusions, and the bubbles and inclusions having a large particle size are hardly present in the slab. . Therefore, it was found that when the steel continuous casting method of the present invention is used, the generation of vortices of the molten steel 4 in the immersion nozzle 3 can be appropriately suppressed, and the quality of the slab can be improved.

  The present invention is useful for a continuous casting method and continuous casting apparatus for steel.

It is a longitudinal cross-sectional view of the longitudinal direction which shows the structure of the continuous casting apparatus concerning this Embodiment. It is a longitudinal cross-sectional view of the transversal direction which shows the structure of the continuous casting apparatus concerning this Embodiment. It is a longitudinal cross-sectional view of the immersion nozzle which shows the static magnetic field near the discharge hole of an immersion nozzle, an induced current, the drift of molten steel, and an electromagnetic brake force. It is a longitudinal cross-sectional view of the immersion nozzle which shows the static magnetic field above the discharge hole of an immersion nozzle, an induced current, the drift of molten steel, and an electromagnetic brake force. It is a longitudinal cross-sectional view which shows the structure of the continuous casting apparatus concerning other embodiment. It is a longitudinal cross-sectional view which shows the structure of the continuous casting apparatus concerning other embodiment. It is a longitudinal cross-sectional view of the transversal direction which shows the structure of the continuous casting apparatus concerning other embodiment. It is a longitudinal cross-sectional view which shows the structure of the continuous casting apparatus concerning other embodiment. It is a longitudinal cross-sectional view of the transversal direction which shows the structure of the continuous casting apparatus concerning other embodiment. It is a top view which shows the structure of the continuous casting apparatus concerning other embodiment. It is the longitudinal cross-sectional view of the immersion nozzle which showed a mode that the molten steel which flows in the conventional immersion nozzle was drifting. It is the longitudinal cross-sectional view of the immersion nozzle which showed a mode that the molten steel which flows in the conventional immersion nozzle was drifting.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Continuous casting apparatus 2 Mold 3 Immersion nozzle 4 Molten steel 5 Inlet 6 Discharge hole 7 Sliding nozzle 8 Fixed plate 8a Through hole 9 Sliding plate 9a Through hole 10 Electromagnetic brake device 20 Static magnetic field 21 Diffusion 22 Induction current 23 Electromagnetic brake force

Claims (6)

In a continuous casting method of steel in which molten steel is supplied into a mold by an immersion nozzle,
A continuous casting method of steel, wherein a static magnetic field is applied to the molten steel in the immersion nozzle at the same height as the discharge hole of the molten steel in the immersion nozzle so as to satisfy the following formula (1).
B _B ² ≧ C ₀ Q / A (1)
However, B _B : Magnetic flux density of static magnetic field (T), C ₀ : 4 × 10 ⁻⁶ , Q: Mass flow rate of molten steel flowing into immersion nozzle (kg / sec), A: Inner cross-sectional area of immersion nozzle (m ² ) 2. The continuous casting method for steel according to claim 1, wherein a magnetic flux density of the static magnetic field becomes a maximum value at a position of a discharge hole of the immersion nozzle. A continuous casting apparatus for carrying out the steel continuous casting method according to claim 1 or 2,
A mold for casting molten steel;
A flow rate control device for controlling the mass flow rate of molten steel into the mold,
An immersion nozzle for discharging molten steel into the mold,
An electromagnetic brake device that applies a static magnetic field that satisfies the formula (1) to the molten steel in the immersion nozzle at the same height as the discharge hole of the immersion nozzle;
A continuous casting apparatus characterized by comprising: The continuous casting apparatus according to claim 3, further comprising another electromagnetic brake device that applies a static magnetic field to the molten steel discharged from the discharge hole of the immersion nozzle. Wherein provided above the electromagnetic brake device, and having an electromagnetic stirring apparatus for stirring the solvent steel in said mold, the continuous casting apparatus according to claim 3 or 4. The continuous casting according to any one of claims 3 to 5, wherein the height of the discharge hole of the immersion nozzle can be adjusted so that the static magnetic field applied by the electromagnetic brake device satisfies the formula (1). apparatus.

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