JP7200722B2 - In-mold flow control method in curved continuous casting equipment - Google Patents

Description

The present invention relates to an in-mold flow control method and an in-mold flow control device in a curved continuous casting apparatus.

In recent slab continuous casting apparatuses, vertical bending type continuous casting apparatuses having a vertical portion of 2 to 3 m directly below the mold are often used. This is to solve the problem of bubbles and non-metallic inclusions under the skin of the cast slab by floating and separating the bubbles and non-metallic inclusions in the vertical portion directly below the mold (see, for example, page 434 of Non-Patent Document 1). At the lower end of the vertical portion directly below the mold, the slab is bent into a curved shape. In this type, the slab is bent back at the position where the curved portion transitions to the horizontal portion, and then pulled out horizontally.

In the vertical bending type continuous casting apparatus, since the slab is bent at the lower end of the vertical portion, the surface of the slab is subjected to bending deformation. The amount of bending deformation increases as the slab thickness increases. Therefore, when casting a steel grade with high crack susceptibility or when manufacturing a slab with a thickness exceeding 300 mm, a curved continuous casting apparatus is used instead of a vertical bending type. This is because, in the curved continuous casting apparatus, the cast slab is not subjected to bending deformation immediately below the mold because the shape is curved from the mold portion, and no slab surface flaws caused by vertical bending are generated.

Molten steel for continuous casting is fed from a ladle through a tundish into a mold from a submerged nozzle provided at the bottom of the tundish. A discharge hole for discharging molten steel is provided on a side surface near the bottom of the submerged nozzle. The discharge direction of the discharge hole is parallel to the long side of the mold, and the discharge flow is discharged toward the short side of the mold. The discharge flow that collides with the short side of the mold forms an upward flow that rises along the short side and a downward flow that descends. Since the downward flow reaches deep into the unsolidified molten steel, bubbles and non-metallic inclusions carried along with the downward flow also reach deep into the unsolidified molten steel. Especially in curved continuous casting equipment, since there is no vertical part directly below the mold, bubbles and non-metallic inclusions that have reached a deep position in the unsolidified molten steel rise and are captured by the solidified shell on the upper surface side. It is not preferable because it remains in the slab and causes quality defects in the slab.

In order to improve the surface quality of the cast slab, a method of providing an electromagnetic stirrer in the mold section and placing the electromagnetic stirrer facing the back of the long side of the cast slab is often used (see, for example, Patent Documents 1 and 2). By imparting propulsive forces in opposite directions to the unsolidified molten steel near the long sides in the mold, a swirl flow can be imparted in the horizontal section to the unsolidified molten steel at the molten steel surface position.

In order to improve the quality of the cast slab, there is known a method of disposing an electromagnetic brake (direct current magnetic field generator) in the mold for the purpose of reducing the flow velocity of the discharge flow that flows out from the discharge hole of the submerged nozzle. In particular, it is common to apply an electromagnetic brake in the thickness direction in which the magnetic flux density is uniform over the entire width of the mold. It is well known that it is necessary to place As one aspect of the electromagnetic brake, two electromagnets are arranged so as to sandwich the discharge hole of the submerged nozzle above and below. A technique of braking the molten steel flow velocity at the surface position with a brake is known (see page 463 of Non-Patent Document 1).

JP 2006-043763 A JP 2016-168603 A

Iron and Steel Handbook, 5th Edition, Vol. 1, Ironmaking and Steelmaking, pp. 434, 463

When using an electromagnetic stirrer and an electromagnetic brake (a DC magnetic field generator that applies a DC magnetic field with a uniform magnetic flux density distribution in the width direction to the thickness direction of the mold) in the mold, an electromagnetic brake should be placed below the electromagnetic stirrer. to place. As for the position to install the discharge hole of the submerged nozzle, the discharge hole is arranged at the electromagnetic brake arrangement position below the electromagnetic stirrer so that the discharge flow from the discharge hole of the submerged nozzle crosses the magnetic field belt formed by the electromagnetic brake. It is necessary to As a result, the discharge hole arrangement position of the submerged nozzle becomes a position deep from the melt surface position. On the other hand, in a curved continuous casting apparatus, the slab curves as it becomes deeper from the surface of the molten steel, so the distance between the immersion nozzle and the solidified shell on the long side becomes narrower. There is a limit.

As described above, as one aspect of the electromagnetic brake, two stages of electromagnets are arranged so as to sandwich the discharge hole of the submerged nozzle above and below. There is known a technique of braking the molten steel flow velocity at the surface position with an electromagnetic brake in the upper stage. However, when continuous casting was performed with the arrangement of the discharge holes of the submerged nozzle and the electromagnetic brake as described above, the electromagnetic brake at the lower stage could not sufficiently brake the downward flow after the nozzle discharge flow collided with the short side. It was found that the internal quality of the slab was not sufficiently improved due to the downward flow caused by the discharge flow from the submerged nozzle, even though the electromagnetic brake was installed. Therefore, it has been considered difficult to achieve both surface quality and internal quality in curved continuous casting equipment.

SUMMARY OF THE INVENTION An object of the present invention is to provide an in-mold flow control method and an in-mold flow control device that can achieve both surface quality and internal quality in a curved continuous casting apparatus.

That is, the gist of the present invention is as follows.
[1] A mold flow control method in a curved continuous casting apparatus, comprising:
An electromagnetic stirrer that forms a swirling flow in a horizontal cross section is installed at the mold surface position, and a DC magnetic field generator that applies a DC magnetic field with a uniform magnetic flux density distribution in the width direction to the mold thickness direction below it. (hereinafter also referred to as "electromagnetic brake").
An immersion nozzle having a discharge hole for discharging molten metal toward the short side of the mold is provided, and the lower end of the discharge hole of the immersion nozzle is positioned above the upper end of the core of the DC magnetic field generator,
The relationship between the injection flow rate Q (kg/s), the immersion depth L (m) of the immersion nozzle discharge hole, the core thickness D (m) of the electromagnetic stirrer and the thrust F (Pa/m) satisfies the following formula (1) and
Curved continuous casting characterized in that the relationship between the magnetic flux density B (T) of the electromagnetic brake, the nozzle discharge hole average flow velocity V (m/s), and the nozzle discharge hole inner diameter X (m) satisfies the following formula (2): In-mold flow control method in equipment. Here, σ: Electric conductivity of molten steel (S/m), ρ: Density of molten steel (kg/m ³ ).
F/(Q×D/L)≧80 (Pa·s/kg/m) (1)
(σB ² X)/(ρV) ≧ 0.4 (-) (2)
[2] The curved type according to claim 1, wherein the thrust force F (Pa/m) of the electromagnetic stirrer and the magnetic flux density B of the electromagnetic brake satisfy the following equations (3) and (4). In-mold flow control method in continuous casting equipment.
5000≦F≦15000 (Pa/m) (3)
B ≤ 1.0 (T) (4)

INDUSTRIAL APPLICABILITY The present invention can provide a slab with good internal quality by applying an electromagnetic brake while achieving good surface quality by applying electromagnetic stirring to the molten metal surface position in the mold in a curved continuous casting apparatus. . It can be applied not only to materials for thin plates, but also to slab casting for thick plates and steel pipes.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the in-mold flow control apparatus of this invention, (A) is a top view, (B) is front sectional drawing. FIG. 4 is a diagram showing the relationship between a flow discharged from a submerged nozzle and an electromagnetic brake, where (A) is a front cross-sectional view and (B) is a cross-sectional view taken along line BB. FIG. 4 is a diagram showing the relationship between a flow discharged from a submerged nozzle and an electromagnetic brake, where (A) is a front cross-sectional view and (B) is a cross-sectional view taken along line BB. FIG. 2 is a diagram showing the relationship between the left side of equation (1) relating to the electromagnetic stirring thrust and the portion where the discharge flow collides with the short side of the mold, (A) is a plan view showing the relationship between the discharge flow and the short side of the mold, ) is the graph. It is a cast slab cross-sectional view showing the downward flow position at the position of the electromagnetic brake, (A) shows the case where only the electromagnetic brake is used, and (B) shows the case where the electromagnetic stirring and the electromagnetic brake are used together. FIG. 4 is a diagram showing the relationship between the left side of the equation (1) relating to the electromagnetic stirring thrust and the maximum current density in the core center height cross section of the electromagnetic brake. FIG. 4 is a diagram showing the relationship between the left side of the equation (1) and the flow rate ratio regarding the electromagnetic stirring thrust. It is a figure which shows the relationship between the (2) Formula left side regarding electromagnetic brake braking force, and flow rate.

This is the case where an electromagnetic stirrer is placed at the mold surface position, and an electromagnetic brake (a DC magnetic field generator that applies a DC magnetic field having a uniform magnetic flux density distribution in the width direction in the mold thickness direction) is placed below it. If an attempt is made to arrange the discharge hole of the immersion nozzle within the static magnetic field range (core range) of the electromagnetic brake, the immersion depth of the immersion nozzle in the mold becomes extremely deep as described above. In a curved continuous casting apparatus, since the solidified shell on the long side is curved in the mold, if the immersion depth of the immersion nozzle is too deep, the distance between the immersion nozzle and the solidified shell on the long side becomes narrow. There is a limit to increasing the immersion depth of the nozzle.

On the other hand, in order to make the immersion depth of the immersion nozzle shallower, continuous casting was performed with the position of the immersion nozzle discharge hole positioned above the arrangement position of the electromagnetic brake. In spite of installing an electromagnetic brake, the downward flow caused by the discharge flow from the submerged nozzle did not sufficiently improve the quality of the cast slab. found.

Therefore, first, when the position of the discharge hole of the submerged nozzle is arranged above the arrangement position of the electromagnetic brake, the cause of the insufficient operation of the electromagnetic brake against the downward flow was investigated.

In normal continuous casting using an electromagnetic brake, as shown in FIG. The entire discharge flow 11 directed to the short side 3 is located within the static magnetic field range 8 . In the discharge stream 11, an induced electromotive force 22 is generated by movement of the conductive molten metal across the static magnetic field 21 within the static magnetic field range 8, and an induced current 23 flows due to the induced electromotive force 22. A braking force acts on the flow 11, and the electromagnetic brake operates. In order for the induced current 23 to flow due to the induced electromotive force 22, the current must be able to form a closed loop. In the cross section of FIG. 2(B), the molten metal filled around the discharge flow 11 forms a closed loop of the induced current, so that the induced current 23 is formed and the electromagnetic brake can operate.

On the other hand, as shown in FIG. 3A, when the position of the discharge hole 5 of the submerged nozzle 4 is arranged above the core upper end 9 of the electromagnetic brake 7, the discharge flow 11 discharged from the discharge hole 5 is short. It collides with the side shell 16 to form a descending flow 12 which enters the static magnetic field range 8 of the electromagnetic brake 7 for the first time. As the downward flow 12 within the static magnetic field region 8 moves the conductive molten metal across the static magnetic field 21, an induced electromotive force 22 is generated. Downstream 12 descends along short shell 16 . The thickness of the solidified short side shell 16 is still thin at the electromagnetic brake arrangement position in the mold. Therefore, even if an attempt is made to form an induced current closed loop by the induced electromotive force 22 in the downward flow, a sufficient current cannot flow through the short-side shell 16 in contact with the downward flow 12, so that a sufficient induced current 23 cannot be generated. I came up with the idea. Therefore, based on this idea, a magnetohydrodynamic analysis was performed.

Electromagnetic fluid analysis was carried out for the case where the positional relationship between the electromagnetic brake 7 and the discharge hole 5 of the submerged nozzle 4 is as shown in FIG. It could be confirmed.

Next, as shown in FIG. 1, an electromagnetic stirrer 6 is placed at a molten metal surface position 17 in the mold 1, and when a swirling flow 14 of the molten metal is formed in the horizontal cross section of the mold by electromagnetic stirring, the immersion A study was made on how the swirl flow 14 affects the discharge flow 11 from the discharge hole 5 of the nozzle 4 . If the discharge hole 5 of the submerged nozzle 4 is arranged within the core height range of the electromagnetic stirrer, the swirling flow 14 generated by electromagnetic stirring and the discharge flow 11 from the submerged nozzle 4 directly interfere with each other. The discharge hole 5 of the nozzle 4 is installed. Under these conditions, we first performed a magnetohydrodynamic analysis. As schematically shown in FIG. 1A, the discharge flow 11 from the discharge hole 5 toward the short side 3 is affected by the swirl flow 14 formed in the horizontal section by the electromagnetic stirrer 6, and the thickness of the slab is increased. It has been found that the impact position of the discharge flow 11 at the 3 positions of the short side is not the center of the thickness of the short side, but the nozzle discharge flow is discharged toward the corner on the diagonal line.

Regarding the conditions that affect the relationship between the stirring flow and the injection flow, the description in Patent Document 1 is known. According to the same document, the thrust F (Pa/m) of the electromagnetic stirrer, the immersion depth L (m) of the immersion nozzle, the core thickness D (m) of the electromagnetic stirring coil (height direction), the injection flow rate Q (kg/ s) is related to
Z=F/(Q×D/L) (1)'
is affected by the value of Specifically, regarding the thrust F of the electromagnetic stirrer 6, a brass plate is placed at a position 15 mm from the inner wall surface of the mold, the electromagnetic stirrer 6 is driven, and the force acting on the brass plate is measured using a strain gauge or the like. The unit is Pa/m. The core thickness D is the core thickness (height direction) of the electromagnetic stirring coil, and the immersion depth L is the height from the upper end of the core of the electromagnetic stirring device 6 to the upper end of the discharge hole 5, both of which are shown in FIG. Street. Normally, the upper end of the core of the electromagnetic stirrer 6 is aligned with the melt surface position 17 . The unit of the injection flow rate Q is kg/s.

Therefore, electromagnetic fluid analysis was performed under various conditions, and the position at which the discharge flow 11 collided with the short side 3 was evaluated. Regarding the short-side collision position, the end portion of the short side 3 on the long side 2 side is set to "0", and the thickness central portion of the short side 3 is set to "0.5". As shown in FIG. 4A, when the discharge flow collides with the center of the thickness of the short side like the discharge flow 11A, the short side collision position is 0.5, and when it collides like the discharge flow 11B, the short side collision position is 0.5. The position is 0.2, and the short-side collision position is 0 in both cases of collision, such as discharge flow 11C and discharge flow 11D. Next, the results were plotted with the above equation (1)′ on the horizontal axis and the short side collision position at which the discharge flow 11 collided with the short side 3 on the vertical axis. As shown in FIG. 4B, when the value (F/(Q×D/L)) on the horizontal axis is 0, the discharge flow collides with the thickness center of the short side, and as the value on the horizontal axis increases, The discharge flow moves from the center of the short side to the long side. When the value of the horizontal axis is 80, the short side collision position is 0, and the discharge flow 11 reaches the corner position where the short side 3 and the long side 2 meet. From the above, by satisfying the following formula (1), the discharge flow 11 from the submerged nozzle 4 can be deflected to the long side regardless of the injection flow rate, and the collision position of the main stream can be shifted from the corner to the long side. I know I can shift.
F/(Q×D/L)≧80 (Pa·s/kg/m) (1)

The numerator on the left side of the above equation (1) is an index indicating the inertial force of the stirring flow. On the other hand, the denominator indicates the degree of flow caused by the discharge flow 11 at the lower end of the core of the electromagnetic stirring coil. When D/L=1, the upper end of the nozzle discharge hole and the lower end of the core coincide with each other, and when D/L≧1, the agitation flow and the discharge flow directly interfere with each other. Conversely, the smaller the D/L, that is, the farther the ejection hole is from the lower end of the core, the smaller the effect of the ejection flow at the lower end of the core of the electromagnetic stirring coil. In the present invention, preferably, the upper end of the discharge hole 5 is arranged below the lower end of the core of the electromagnetic stirring coil, so that D/L<1. The left-hand side of equation (1) indicates the ratio of the flow strengths of the nozzle discharge flow and the agitation flow. This indicates that the impact is large. Specifically, the relationship between the immersion depth and the core thickness is adjusted according to the thrust and the injection flow rate, and the numerical value on the left side is set to 80 Pa s/kg/m or more, so that the discharge flow from the immersion nozzle is increased regardless of the injection flow rate. It can be deflected to the long side, and the collision position of the mainstream can be shifted from the corner to the long side (FIG. 4(B)).

When the electromagnetic stirrer 6 is not provided, the discharge flow 11 collides with the center of the thickness of the short side 3, so as shown in FIG. Even if the induced electromotive force 22 is generated by being pressed against the short side shell 16, it is difficult to form a closed loop of the induced current, and a sufficient induced current does not flow. On the other hand, when the electromagnetic stirrer 6 is provided and the swirling flow 14 by electromagnetic stirring is applied above the discharge hole 5, the position of the descending flow 12 moves from the center of the thickness of the short side to the long side as shown in FIG. (B) shows. In the example of FIG. 5(B), the side opposite to the side where the downward flow 12 contacts the long-side shell 18 in the thickness direction of the slab contacts the molten metal 19 . As a result, it is expected that a closed loop of induced current 23 due to the induced electromotive force 22 generated in the downward flow 12 can form in the molten metal 19 around the downward flow 12 .

Therefore, when the value of the left side of the above equation (1) is changed variously, the behavior of the induced current 23 generated in the downward flow 12 passing through the electromagnetic brake arranged below the discharge hole, and the resulting downward flow. We examined how the braking behavior changes.

In addition to the specifications used for the electromagnetic fluid analysis, the same electromagnetic fluid analysis was performed for the case where the electromagnetic brake 7 was arranged below the discharge hole 5 . The magnetic flux density B of the electromagnetic brake 7 is 0.4 T, and the core thickness (height direction) of the electromagnetic brake 7 is 200 mm. Generally used electromagnetic brakes have a core thickness of 200 to 300 mm. In the present invention, the core thickness of the electromagnetic brake is not particularly limited. FIG. 6 shows a diagram in which the left side of the above equation (1) is plotted on the horizontal axis as in FIG. 4B and the maximum current density is plotted on the vertical axis. The maximum current density means the maximum current density within the horizontal cross section at the core thickness center of the electromagnetic brake. As is clear from FIG. 6, the maximum current density is minimal when the value on the horizontal axis (left side of formula (1)) is zero when electromagnetic stirring is not activated, and the value on the horizontal axis (left side of formula (1)) is It was found that the maximum current density increases as the value increases, and the left side of the equation (1) saturates at 80. That is, as assumed above, the discharge flow 11 from the discharge hole 5 is deflected from the thickness center of the short side 3 to the long side 2 side due to the swirl flow 14 formed above the discharge hole 5 by electromagnetic stirring. As a result, it was found that when the downward flow 12 passes through the electromagnetic brake 7 arranged below the discharge hole 5, braking by the induced current 23 can be sufficiently expected.

As an index indicating that a uniform plug flow is formed below the electromagnetic brake 7, the ratio of the maximum descending flow velocity 13 to the casting velocity 15 in a horizontal section 50 mm below the magnetic field zone (hereinafter referred to as "flow velocity ratio") ) was defined (see FIG. 3(A)). As the flow velocity ratio becomes smaller and closer to 1, a uniform flow close to a plug flow is formed.

Similarly, based on the results of the magnetohydrodynamic analysis, the relationship was investigated with the horizontal axis representing the left side of equation (1) and the vertical axis representing the flow velocity ratio. The results are shown in FIG. As a result, it was found that the flow velocity ratio was 1 regardless of the injection flow rate, that is, a uniform downward flow was obtained. As described above, when the flow velocity distribution was analyzed in detail, it was found that the discharge flow 11 from the discharge hole 5 of the submerged nozzle 4 can be deflected to the long side by satisfying the expression (1). is shifted from the corner to the long side. In addition, as described above, it can be confirmed that the maximum current density seen in the core height center cross section at that time also increases as the numerical value on the left side of equation (1) increases. It is known that about 5 times the current density can be obtained by doing the above, and due to this action, the electromagnetic brake fully operates on the downward flow that descends inside the electromagnetic brake, and a uniform downward flow is generated below the electromagnetic brake. It is considered to have been realized.

Next, conditions for the electromagnetic brake for carrying out the present invention will be described.

Under a DC magnetic field generator (electromagnetic brake) (also referred to as a "uniform electromagnetic brake") that applies a DC magnetic field with a uniform magnetic flux density distribution in the width direction in the mold thickness direction, the downward flow is uniformly distributed in the cross section. We investigated the conditions for the conversion by magnetohydrodynamic analysis. Assume that the magnetic flux density B (T) of the uniform electromagnetic brake, the nozzle discharge hole average flow velocity V (m/s), the nozzle discharge hole inner diameter X (m), and the horizontal axis is the left side of the following equation (2) ((σB ² X)/( ρV)), and the vertical axis is the same flow velocity ratio as above, and the results are shown in FIG. As a result, it was found that the cross-sectional distribution of the downward flow can be made uniform by satisfying the following equation (2). Here, σ: Electric conductivity of molten steel (S/m), ρ: Density of molten steel (kg/m ³ ). Also, the evaluation is performed under the condition that the value of the left side of the equation (1) is 100.
(σB ² X)/(ρV) ≧ 0.4 (-) (2)
Based on the above results, we decided to adopt the above formula (2).
In the evaluation of FIG. 7 described above, the evaluation is performed under the condition that the value of the left side of the above equation (2) is 0.7.

Further, preferred conditions of the present invention will be explained.

The electromagnetic stirrer 6 is arranged at a melt surface position 17 in the mold 1 . The electromagnetic stirrer 6 being "located at the melt surface position 17" means that the melt surface position 17 is positioned between the upper end and the lower end of the core of the electromagnetic stirring coil of the electromagnetic stirrer.
Regarding the stirring thrust F of the electromagnetic stirrer 6, when the stirring thrust F is 5000 Pa/m or more, a stirring flow velocity of 20 cm/s or more can be imparted. Therefore, preferably, a stirring thrust of 5000 Pa/m or more is applied. Regarding the upper limit of the stirring thrust, the power supply and coil cooling equipment will be enormous, and the loss due to the current induced in the copper plate and the stainless steel plate installed on the back of the copper plate due to deformation of the copper plate will also increase. For normal use, a stirring thrust of 15000 Pa/m or less is used. That is, the following formula (3) was used as a preferable condition.
5000≦F (Pa/m)≦15000 (3)

As for the magnetic flux density B of the uniform electromagnetic brake, the higher the better, but when applying the uniform electromagnetic brake to a curved continuous casting machine, the distance between the magnetic poles is about 300 mm. , and the following formula (4) are preferable conditions.
B ≤ 1.0T (4)

The in-mold flow control device for realizing the in-mold flow control method in the curved continuous casting apparatus of the present invention includes an electromagnetic stirrer that forms a swirling flow in a horizontal cross section, and is installed near the molten metal surface in the mold. An immersion nozzle having a discharge hole for discharging molten metal toward the short side of the mold. is provided, the lower end of the discharge hole of the submerged nozzle is located above the upper end of the core of the DC magnetic field generator, and the thrust F (Pa/m) of the electromagnetic stirrer and the magnetic flux density B of the DC magnetic field generator are the above (3 ) is characterized by satisfying the expression (4).

Ultra-low carbon steel was produced by refining in a converter, treatment in a reflux type vacuum degasser, and addition of alloys. This molten steel was cast into a slab having a thickness of 360 mm and a width of 1800 mm using a curved continuous casting apparatus with a radius of curvature of 10.5 m. An electromagnetic stirring device 6 is provided in the mold 1, and several electromagnetic stirring coils with different core thicknesses D (m) (height direction) and thrust F (Pa/m) are prepared, and the upper end of the core is aligned with the molten metal surface position in the mold. It was set up so that The DC magnetic field generator (electromagnetic brake 7) that applies a DC magnetic field having a uniform magnetic flux density distribution in the width direction in the thickness direction of the mold has a core thickness (height direction) of 0.2 m, and the center of the core height is 0.2 m. It was set at a position 0.5 m below the hot water level. A maximum magnetic field of 0.6 T can be applied to the magnetic flux density B at the center of the thickness.

The casting speed was 0.8 to 1.2 m/min, and 3 Nl/min of Ar gas was flowed into the nozzle. The ejection hole 5 of the submerged nozzle 4 was fixed downward at 25°, and the immersion depth L (m) of the ejection hole 5, the nozzle ejection hole inner diameter X, and the ejection hole average flow velocity V were changed for casting. Here, the discharge hole inner diameter X is the diameter of a circle having the same area as the discharge hole area, and the injection flow rate Q is twice the nozzle discharge hole area on the left and right of the nozzle (discharged diagonally downward) for the nozzle discharge hole average flow velocity. Therefore, the value obtained by dividing by the vertical cross-sectional area was taken as the average flow velocity V. The thrust force F of the electromagnetic stirrer is a value obtained by setting a brass plate at a position 15 mm from the inner wall of the mold, driving the electromagnetic stirrer, and measuring the force acting on the brass plate using a strain gauge or the like. Pa/m.

The number of air bubbles/inclusions in the slab was evaluated by cutting out a sample of 200 mm in overall width×length in the casting direction from the slab.
Regarding the surface quality of the slab, the upper surface and the lower surface were each ground for bubbles/inclusions in the surface of 200 mm in total width x length to a depth of 10 mm from the surface at intervals of 1 mm, and the number of bubbles/inclusions of 100 μm or more was investigated.
As for the inner layer of the slab, the number of bubbles and inclusions was investigated in the same manner as the surface at 40 mm to 80 mm (accumulated zone) on the upper surface side.
By dividing the number of defects in each example by the number of defects in Comparative Example 3 for both the surface layer and the inner layer, the surface layer defect number index and the inner layer defect number index were obtained.
In addition, as casting conditions, the relationship with the parameters shown in the formulas (1) to (3) was investigated, and the results are summarized in Table 1. Note that since the maximum magnetic flux density B of the electromagnetic brake is 0.6 T, it is not listed in Table 1 because it satisfies the equation (4) under any conditions. Numerical values outside the scope of the present invention are underlined.

As is clear from the results in Table 1, it was found that the apparatus and method described in the present invention can produce good cast slabs free of surface layer defects and inner layer defects.
On the other hand, in Comparative Example 1, the electromagnetic brake was not operated, the magnetic flux density B of the electromagnetic brake was 0, the expression (2) was not satisfied, and the inner layer defect number index was unsatisfactory. In Comparative Example 2, the electromagnetic stirring was not operated and the thrust force F was 0, so the equation (1) was not satisfied, and both the surface defect number index and the inner layer defect number index were unsatisfactory. In Comparative Example 3, neither the electromagnetic brake nor the electromagnetic stirring was operated, so both the surface defect number index and the inner layer defect number index were unsatisfactory.

REFERENCE SIGNS LIST 1 mold 2 long side 3 short side 4 immersion nozzle 5 discharge hole 6 electromagnetic stirrer 7 electromagnetic brake 8 static magnetic field range 9 core upper end 11 discharge flow 12 downward flow 13 maximum downward flow velocity 14 swirling flow 15 casting speed 16 short side shell 17 Molten surface position 18 Long side shell 19 Molten metal 21 Static magnetic field 22 Induced electromotive force 23 Induced current

Claims (2)

A mold flow control method in a curved continuous casting apparatus, comprising:
An electromagnetic stirrer that forms a swirling flow in a horizontal cross section is installed at the mold surface position, and a DC magnetic field generator that applies a DC magnetic field with a uniform magnetic flux density distribution in the width direction to the mold thickness direction below it. (hereinafter also referred to as "electromagnetic brake").
An immersion nozzle having a discharge hole for discharging molten metal toward the short side of the mold is provided, and the lower end of the discharge hole of the immersion nozzle is positioned above the upper end of the core of the DC magnetic field generator,
The relationship between the injection flow rate Q (kg/s), the immersion depth L (m) of the immersion nozzle discharge hole, the core thickness D (m) of the electromagnetic stirrer and the thrust F (Pa/m) satisfies the following formula (1) and
Curved continuous casting characterized in that the relationship between the magnetic flux density B (T) of the electromagnetic brake, the nozzle discharge hole average flow velocity V (m/s), and the nozzle discharge hole inner diameter X (m) satisfies the following formula (2): In-mold flow control method in equipment. Here, σ: Electric conductivity of molten steel (S/m), ρ: Density of molten steel (kg/m ³ ).
F/(Q×D/L)≧80 (Pa·s/kg/m) (1)
(σB ² X)/(ρV) ≧ 0.4 (-) (2) The curved continuous casting apparatus according to claim 1, wherein the thrust force F (Pa/m) of the electromagnetic stirrer and the magnetic flux density B of the electromagnetic brake satisfy the following equations (3) and (4). in-mold flow control method.
5000≦F≦15000 (Pa/m) (3)
B ≤ 1.0 (T) (4)

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