JP2000288699A - Continuous casting method of steel using static magnetic field - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an ingot having no internal defect controlling a flow of submerging efficiently without installing an excessive electric magnet or consuming useless electric power by applying in parallel in the longitudinal direction within the cross section of the ingot the magnetic field of a suitable magnetic flux density according to the maximum casting speed of a continuous casting machine and a casting speed in operation. SOLUTION: Molten steel is jetted nearly horizontally or diagonally downward toward both side short sides of a casting mold from a dipping nozzle installed in the central part within the casting mold of a continuous casting machine which manufactures a cast slab or cast bloom whose cross section is an oblong, a static magnetic field is applied in the direction of the long side of the casting mold to a flow of descending generated by a collision between a part of the jet flow and both side short sides of the casting mold, whereby the flow of the molten steel within the ingot is controlled and also the operation is performed so that a magnetic flux density B (gauss) of the applied static magnetic field satisfies the formula: 600×(Vc)1/2<=B<=1700×(Vc)1/2. (Here, Vc expresses the casting speed (m/min), and the measuring position of the magnetic flux density is the position equivalent to the center between magnetic poles.).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved continuous casting method for producing a slab having no internal defects by controlling the flow of molten steel in a mold by the action of a static magnetic field.

[0002]

2. Description of the Related Art FIG. 1 is a schematic explanatory view showing a state of molten steel flow in a slab in a conventional continuous casting method, in which 1 is a short side mold, 2 is a long side mold, and 3 is an immersion mold. Nozzle, 4 is molten steel, 5 is a solidified shell, 6 is nonmetallic inclusions, and 15 is a guide roll. Note that FIG. 1A is a cross-sectional view as viewed from the long side, and FIG. 1B is a cross-sectional view as viewed from the short side.

In such continuous casting, the molten steel 4 is ejected from the immersion nozzle 3 substantially horizontally or obliquely downward toward the short sides (short-side mold) on both sides. When the gas (shown by A in FIG. 1) sunk deeply, air bubbles and alumina, etc., which are lighter than the molten steel, also entered the slab deeply along the flow of the molten steel, and did not float and separate on the surface of the molten steel. The object 6 is captured. This then becomes an internal defect in the steel product. Such internal defects in steel products have become a particularly significant problem in casting deep drawing steel, casting extremely low carbon steel by a curved continuous caster, continuous casting of thin slabs, and the like. These will be described.

[0004] First, a thin steel sheet whose product is subjected to deep drawing (in the above case) is liable to crack if a defect is present inside the steel sheet, so that particularly strict internal quality is required. In order to meet such strict internal quality requirements, deep drawing steel sheets are usually cast at a low casting speed of about 0.8 to 1.5 m / min, so that bubbles, alumina, etc., flow into the molten steel flow. To prevent it from getting deeply into the slab.
However, even if the casting is performed at a low speed while sacrificing productivity as described above, the occurrence of internal defects cannot be completely prevented, and a more reliable internal defect prevention technique has been required.

Further, in ultra-low carbon steel sheets having excellent press formability and a carbon concentration of 0.01% by mass or less, defects such as air bubbles and the like are liable to exist inside the slab due to the softness of the material. In particular, when casting ultra-low carbon steel using a curved continuous caster having no vertical portion (in the above case), there is a problem that air bubbles that have entered are trapped inside the curve, and blister defects are likely to occur. For this reason, when casting ultra-low carbon steel, a continuous casting method using a vertical bending type continuous caster having a vertical portion having a length of several meters from the mold to the upper roll stand is widely adopted. That is, in such a vertical bending type continuous casting machine, even if the air bubbles enter the inside of the mold, the air bubbles are hardly captured by the solidified shell in the vertical portion.

In order to cast an ultra-low carbon steel sheet with a curved continuous caster, it is necessary to cast at a low casting speed of about 1.3 m / min or less in order to prevent occurrence of blister defects. In addition, the productivity is reduced as compared with the case where a vertical bending type continuous casting machine is used. However, in order to convert the existing curved continuous caster to a vertical bending continuous caster, the remodeling range is too wide, and in addition to the mold and the roll stand for the entire curved part,
It is necessary to remodel the base of the continuous caster, resulting in a large remodeling cost and a long-term shutdown. For this reason, even if the casting speed is equal to or higher than 1.3 m / min, the occurrence of blisters can be prevented and the remodeling cost can be reduced, as in the vertical bending type continuous casting machine while maintaining the curved shape. It has been desired to develop an internal defect reduction technology that can shorten the operation stoppage required for the remodeling.

Furthermore, the length (thickness) in the short side direction is 200 to
Instead of the conventional process of casting a slab having a thickness of about 300 mm and reducing the thickness by hot rolling, a thin slab having a thickness of 150 mm or less is cast from the beginning to reduce the hot rolling cost. Slab continuous casting (the above case) has been widely adopted in recent years. In such continuous casting of thin slabs, in order to ensure the same productivity as conventional continuous casting, it is necessary to increase the casting speed by an amount corresponding to the reduced thickness.

When the slabs have the same width (length in the long side direction), for example, a slab having a thickness of 240 mm is applied to 1.6 m / mi.
In order to secure the same productivity as that of the conventional continuous casting at a casting speed of n, at least about 2.5 m / min for a 150 mm thick slab and at least 3.8 m / min for a continuous thin slab 100 mm thick. Casting speed is required. However, the necessity of changing the operating conditions in this way is a factor of deteriorating the internal quality of steel manufactured by continuous thin slab casting. For this reason, in thin slab continuous casting that requires high-speed casting at a casting speed of about 2.5 m / min or more, casting is usually performed at a casting speed of 2.5 m / min or less even in the case of a vertical continuous casting machine. There is a need for more advanced techniques for preventing internal defects than conventional continuous casting.

There have been proposed various techniques for responding to the demand for such techniques for preventing internal defects, which reduce the flow of molten steel by applying a static magnetic field to a region where the flow velocity of molten steel is high. For example, as shown in FIG. 2 [FIG. 2 (a) is a cross-sectional view as viewed from the long side, and FIG. 2 (b) is a cross-sectional view as viewed from the short side] in JP-A-57-17356. There is disclosed a technique in which an electromagnet 9 including an electric coil 7 and an iron core 8 is arranged around a mold, and a static magnetic field generated by the electromagnet 9 is applied to a region where the flow speed of the molten steel is high to reduce the flow of the molten steel.

However, when a static magnetic field is applied locally, the molten steel flow A bypasses the region where the magnetic field is weak, as shown in FIG. The effect of simply arranging the electromagnet is not exhibited.

For this reason, for example, Japanese Patent Application Laid-Open No. 2-28
No. 4750 discloses a mold of a continuous casting machine for producing a slab slab or a bloom slab having a rectangular cross section (hereinafter, these may be simply referred to as "slab" collectively). A technique has been proposed in which a static magnetic field is applied to the entire region (hereinafter, sometimes referred to as the “width direction”) to cut off the bypass route of the molten steel flow. Further, for example, Japanese Patent Application Laid-Open No. 5-55220 proposes a technique in which a magnetic field action region is formed in two steps above and below a mold, and a certain degree of quality improvement is exhibited.

However, all of these techniques have insufficient effect of suppressing the downward flow in the region near the short side of the mold (near both ends in the width direction) and reduce defects of nonmetallic inclusions in the slab. There was a problem not to do. The cause of such a problem is considered as follows. All of the above-mentioned technologies apply a magnetic field in the direction of the short side of the mold (hereinafter, sometimes referred to as the “thickness direction”) to the molten steel flow flowing down the mold having a rectangular cross section. As shown in FIG. 3, a current is induced in the mold width direction at the center of the mold width, and the magnetic field and the current are orthogonal in the horizontal plane, so that an upward electromagnetic force is generated according to Fleming's law, The flow will be braked. On the other hand, in the vicinity of the short side of the mold, even when a magnetic field is applied in the thickness direction of the mold, current is hardly induced in the width direction of the mold. Weak electromagnetic force. Therefore, the infiltration of molten steel along the short side surface cannot be sufficiently suppressed, and many nonmetallic inclusions remain inside at both ends in the width direction.

In a method of casting while applying a static magnetic field to a molten steel flow injected into a mold from a continuous casting tundish through an immersion nozzle, a technique which refers to a necessary magnetic flux density is as follows. ) Japanese Patent No. 275
No. 0320 and (2) JP-A-10-180427 are also known. These are all technologies that apply a magnetic field in the thickness direction.However, even in these technologies, there is still an essential problem that even if a static magnetic field having a higher magnetic flux density is applied, the penetration of molten steel cannot be sufficiently suppressed. It remains unsolved.

That is, in the technique (1), the maximum discharge speed v (m / sec) from the discharge port of the straight immersion nozzle is used.
c), magnetic flux density B (Tesla: 1 Tesla = 10000 gauss), magnetic field application range L (mm), etc.
Although B × L is specified, basically, a high magnetic flux density is applied (see FIG. 9 described later). In the technique (2), the Stuart number N = σB2 / ρV calculated from the electric conductivity σ, the magnetic flux density B, the slab thickness L, the flow velocity V of the molten steel at the upper end of the magnetic field application range, the density ρ, and the like, N = 3
It discloses a casting method in which the casting method is set to × 10 ^{−3 to} 7 × 10 ⁻³ . However, even in this technique, a larger magnetic flux density is applied (see FIG. 10 described later).

[0015]

SUMMARY OF THE INVENTION The present inventors have been studying from the viewpoint of solving the above-mentioned problems for a long time. A plurality of sets of electric coils are arranged so that the axial direction of these coils is substantially parallel to the long side direction of the cross section of the slab to form an electromagnet, and the magnetic field in the long side direction of the mold penetrates the molten steel. (Japanese Patent Application No. Hei 10-87665) has been proposed. The configuration of such a control device will be described with reference to the drawings.

FIG. 4 is a longitudinal sectional view showing an example of the configuration of the control device proposed by the present inventors, in which 7b and 7c are electric coils, 8b is an iron core, and 12 is a mold frame. ,
13 is a foot roll, 14 is a top cover, 15, 15
a indicates a guide roll, and 16 and 16a indicate roll stand frames, respectively (3 is the immersion nozzle described above). FIG. 5 is a plan view for explaining the configuration near the mold in FIG. 4. In FIG. 5, reference numeral 20 denotes a long-side copper plate back plate;
Is a long side copper plate, 22 is a short side copper plate back plate, and 23 is a short side copper plate, and these constitute a mold. 25a indicates a magnetic pole N, and 25b indicates a magnetic pole S.

In the control device shown in FIGS. 4 and 5, a pair of electric coils 7b and 7c whose axial directions are substantially parallel to the width direction of the mold are wound around the iron core 8b and arranged beside the long sides of both sides of the mold section. By doing so, an electromagnet is formed, and a direct current E in the same direction is applied to both coils. By adopting such a configuration, a magnetic field in the width direction of the cast slab (the left-right direction in FIG. 5) (the direction thereof is indicated by reference numeral B) can be effectively applied.

According to this technique, the infiltration of molten steel along the short side can be sufficiently suppressed, so that nonmetallic inclusions remaining in the slab can be greatly reduced. Was. However, this technique also has some problems as described below, and there is still room for improvement.

As mentioned above, in continuous casting, the casting speed has a significant effect on the internal quality of the product.
Then, in a continuous casting machine having a large maximum casting speed determined by the machine length and the thickness of the slab, such as a thin slab continuous casting machine, it is considered that the flow-in speed is high and the internal quality improvement effect appears up to a larger magnetic flux density. On the other hand, in a continuous casting machine having a small maximum casting speed, since the flow speed is inherently low, the internal quality improvement effect may be saturated even if the magnetic flux density is increased beyond a certain limit. Also, in the same continuous casting machine, when casting deep-drawing steel with strict internal quality at a low speed, and when casting general-purpose steel whose internal quality is not as strict as deep-drawing steel at a high speed, it is optimal. It is considered that the casting speed is naturally different.

However, in the prior art, since the optimum magnetic flux density according to the casting speed was unknown, it was necessary to apply a magnetic flux density more than necessary in order to surely reduce the sinking flow. There is a problem in that it is not possible to recover the capital investment by installing the device, or to waste power that does not contribute to the improvement of the internal quality.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a static magnetic field having an appropriate magnetic flux density according to the maximum casting speed of a continuous casting machine and the casting speed during operation. By applying in parallel to the longitudinal direction of the inside, it is possible to efficiently control the sinking flow without installing an excessive electromagnet or consuming unnecessary electric power, and to produce a cast piece without internal defects. It is to provide a continuous casting method of steel.

[0022]

The continuous casting method according to the present invention, which has solved the above-mentioned problems, comprises an immersion method installed in the center of a continuous casting machine for producing a slab cast or a bloom cast having a rectangular cross section. Molten steel is ejected from the nozzle toward the short sides on both sides of the mold substantially horizontally or diagonally downward, and a static magnetic field is applied in the direction of the long side of the mold against the downward flow generated when a part of the jet collides with the short sides on both sides of the mold. Is applied to control the molten steel flow inside the slab and to operate so that the applied magnetic flux density B (Gauss) of the static magnetic field satisfies the following equation (1). .

600 × (Vc) ^1/2 ≦ B ≦ 1700 × (Vc) ^1/2 (1) where Vc is the casting speed (m / min), and the measurement position of the magnetic flux density is the center of the mold. Position.

The object of the present invention is to provide a continuous casting machine for producing a slab slab or bloom slab having a rectangular cross section from an immersion nozzle installed in the center of the mold in a substantially horizontal direction toward both short sides of the mold. Molten steel is ejected obliquely downward, and a downward magnetic field generated when a part of the jet collides with the short sides on both sides of the mold is applied with a static magnetic field in the direction of the long side of the mold to cause the molten steel flow inside the slab to flow. In addition to the control, the magnetic flux density B (Gauss) of the applied static magnetic field is also achieved by operating so as to satisfy the following equation (2).

25 × (Vc × W) ^1/2 ≦ B ≦ 40 × (Vc × W) ^1/2 (2) where Vc is the casting speed (m / min), and W is the length in the long side direction. (Mm), and the measurement position of the magnetic flux density is a position corresponding to the center between the magnetic poles.

In each of the above continuous casting methods, more specific operating conditions include the following configurations (1) to (3).

(1) A thin steel facing slab to be deep drawn is cast at a casting speed of 1.5 m / min or less.

(2) The mold is a curved continuous caster having no vertical portion, and casts ultra-low carbon steel having a carbon concentration of 0.01 mass% or less at a casting speed of 1.3 m / min or more. .

(3) A thin slab whose length in the short side direction is 150 mm or less is cast at a casting speed of 2.5 m / min or more.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have considered the above conventional problems and studied an appropriate magnetic flux density according to the casting speed. In this study, since it is difficult to measure the squeeze flow rate in actual continuous casting of steel, we conducted a model experiment using a low-melting metal and measured the squeeze flow rate, and based on the similarity rule, determined the effect of the actual machine. evaluated. FIG. 6 (schematic illustration) shows the configuration of the model experimental machine used at this time. In the figure, 30 is a molten metal surface, 31 is a container (made of SUS304) corresponding to a mold, 32 is an electromagnet, 33 is a current meter, 34 Indicates a heater, and P indicates a pump.

The model experiment basically has a width of 9
00 mm, thickness: 240 mm, casting speed: 1.67 m /
Although this is a model experiment of 1/6 size related to continuous slab casting of min, the effect at an arbitrary casting speed can be converted based on the number of Stewart. In this model experiment, regarding the application of the conventional magnetic field in the thickness direction, the depth from the molten steel surface was 0 to 120 mm and 480 mm.
A magnetic field in the thickness direction was applied to two regions of 〜600 mm over the entire width. Regarding the application of the width direction magnetic field of the present invention, the width direction magnetic field was applied over the entire width to a position at a depth of 660 to 1530 mm from the molten steel surface.

As a result, the following has been found. First, FIG.
Is a graph showing the relationship between the distance from the surface of the molten metal and the flow velocity of the dive, in correspondence between the model machine and the actual machine. From this result, it can be seen that when the magnetic field is applied in the width direction, the effect of suppressing the dive is obtained with a lower magnetic flux density than when the magnetic field is applied in the thickness direction. In particular, in continuous casting of a slab having a width of about 900 mm, when a magnetic field is applied in the thickness direction, there is a problem that the flow rate of the dive increases rather than when no magnetic field is applied. When a magnetic field is applied to the, the flow rate of the squeeze is reduced.

FIG. 8 is a graph showing the relationship between the magnetic flux density B and the flow velocity (1 m depth from the molten metal surface) in the actual machine when the casting speed Vc is 1 m / min. As is clear from this result, until the magnetic flux density reaches about 750 Gauss,
As the magnetic flux density increases, the squeezing velocity decreases rapidly. However, if the magnetic flux density B is further increased, the squeezing velocity hardly decreases, or rather increases slightly, and the magnetic flux density B exceeds 1700 gauss. It can be seen that applying the static magnetic field is useless.

Based on the above results, FIG.
In the shown apparatus configuration, the relationship between the casting speed Vc and the magnetic flux density is shown.
When the relationship was examined, the result shown in FIG. 9 was obtained. Immediately
FIG. 9 shows an appropriate magnetic flux density according to the casting speed Vc.
The lower line L1 is B = 600 × (V
c)^1/2, The upper line L2 is B = 1700 × (Vc)^{1
/ 2}It satisfies the relationship.

As is apparent from FIG. 9, the casting speed Vc
Increases, the appropriate magnetic flux density B increases in proportion to the square root of the casting speed Vc. In other words, the area between these lines L1 and L2 is a region satisfying the relationship of the above-described formula (1). In this region, the slab of molten steel can be efficiently suppressed to produce a slab without internal defects. It was.

FIG. 9 also shows the operating conditions of the embodiment described in the aforementioned Japanese Patent No. 2750320 with a circle. However, a magnetic flux density higher than the upper limit of the magnetic flux density considered to be appropriate in the present invention is applied. You can see that there is.

FIG. 10 is a graph comparing the range of the appropriate magnetic flux density B in the method of the present invention with the operating conditions disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 10-180427 (prior art). In FIG. 10, those of the prior art described above as examples are marked with a circle, and those considered as comparative examples are marked with a cross. As is apparent from FIG. 10, since the magnetic field is applied in the thickness direction also in the conventional technique, the optimum range of the magnetic flux density B is different, and the magnetic flux density B is larger than the range of the magnetic flux density B of the present invention. It can be seen that That is, according to the method of the present invention, it is possible to sufficiently suppress the infiltration of molten steel even at a low magnetic flux density B corresponding to the comparative example in the prior art.

In the above description, the influence of the slab size (length in the long side direction) on the optimum magnetic flux density range is not clear. In order to cast slabs of various sizes by continuous casting, it is desirable to further reduce the power consumption by more strictly defining the magnetic flux density according to the slab size. Therefore, the present inventors further set the length in the mold long side direction when converted to the actual machine from the above 900 mm to 1500 mm.
The effect of the slab length direction on the optimum magnetic flux density range was investigated by conducting a model experiment in which the number was increased.

As a result, under the condition that the casting speed Vc (m / min) is constant, the optimum magnetic flux density for suppressing the infiltration of the molten steel flow increases as the width W increases.
It has been found that if the product of c and the width W (length in the length direction: mm) of the slab is kept constant, the optimum magnetic flux density will be almost constant. From these facts, by setting the magnetic flux density B in the range of the following expression (2), it is possible to further reduce unnecessary power consumption.

25 × (Vc × W) ^1/2 ≦ B ≦ 40 × (Vc × W) ^1/2 (2) FIG. 11 shows an example in which the casting speed Vc is 1.5 m / m.
In the case of in, the length W of the slab in the long side direction is set to 600
FIG. 9 shows an optimum magnetic flux density range defined by the above equations (1) and (2) when changed to 〜1800 mm. In FIG. 11, lines L1 and L2 denote the lower and upper magnetic flux densities of the equation (1), respectively, by lines L3 and L2.
Reference numerals 4 denote the lower and upper limits of the expression (2), respectively.

As is clear from FIG. 11, the lines L3 and L3
4 is narrower than the magnetic flux density range of expression (1) sandwiched between lines L1 and L2, and the optimum magnetic flux density range is more strictly determined according to the length of the slab. It can be seen that by defining the above, wasteful power consumption can be further reduced.

The purpose of the present invention is to operate the system so as to satisfy the relationship of the above formula (1) or (2). Specific application examples of the present invention will be described. For example, when casting a slab for a thin plate subjected to deep drawing such as a two-piece beverage can at a casting speed of about 1.0 m / min so that cracks caused by internal inclusion defects do not occur during processing. By applying a magnetic field in the width direction having a magnetic flux density of about 1000 gauss, the penetration is further reduced, and the occurrence of internal defects can be more reliably prevented. Compared to the conventional case where a magnetic field of about 2000 Gauss is applied in the width direction, a smaller electromagnet may be provided, and there is no unnecessary power consumption. In particular, when casting a slab for a deep drawing steel sheet having a width of 1000 mm or less, the quality improvement effect becomes remarkable by applying a magnetic field in the width direction as compared with the application of a magnetic field in the thickness direction that deteriorates the internal quality.

An ultra-low carbon steel having a carbon concentration of about 0.005% and a slab width of about 1000 to 1800 mm is
When casting at a casting speed of about 1.8 m / min using a curved continuous caster, applying a width direction magnetic field of about 1500 gauss is effective without excessive capital investment and unnecessary power consumption. The generation of blisters can be prevented. When remodeling work to add a means for applying a magnetic field in the width direction to an existing curved caster, the improvement range of the caster body is limited to the mold and the roll just below the mold, except for the newly installed electrical equipment. Limited to the stand. Therefore, in addition to the remodeling of the roll stand for the entire curved part, and in some cases, the remodeling cost and operation required to suppress the generation of blisters are compared with the remodeling of the vertical bending caster, which requires improvement to the base of the caster. The suspension period can be greatly reduced.

Further, a thin slab continuous caster was used to obtain a 100 m thick
When casting a slab having a width of about 1500 mm and a width of about 1500 mm at a casting speed of 5 m / min, applying a width direction magnetic field of about 2500 gauss efficiently without excessive capital investment and wasteful power consumption. Generation of internal defects can be reduced. Thin slab casters often use long molds with a length of about 1.2 m, and it is easy to secure a space in the lower part of the mold where an electromagnet for applying a magnetic field in the width direction can be secured. It is advantageous to prevent the electromagnet from being damaged by the molten steel leaking down.

Incidentally, also in the thin slab continuous casting machine, it is of course possible to install an electromagnet on the roll stand below the mold. Also, in the thin slab continuous caster, at the top of the mold,
By using a mold with a thicker central part in the width direction, a continuous casting method that secures a space for immersing a large cross-sectional area immersion nozzle in the molten steel in the mold and reduces the flow rate of molten steel discharged from the immersion nozzle is widely used. Although it is used, it is also a desirable embodiment to use such a method in combination with a method of applying a magnetic field in the width direction to improve the effect of reducing the sneak flow.

[0046]

According to the present invention, the static magnetic field having an appropriate magnetic flux density according to the maximum casting speed of the continuous casting machine and the casting speed during operation is parallel to the longitudinal direction in the cross section of the slab. A continuous casting method of steel that can efficiently control sunk flow and produce slabs without internal defects without installing excessive electromagnets or wasting power by applying I realized it.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a state of molten steel flow in a slab in a conventional continuous casting method.

FIG. 2 is a schematic explanatory view of a technique for reducing the flow of molten steel by applying a static magnetic field to a region where the flow velocity of molten steel is fast.

FIG. 3 is a view for explaining a state of a molten steel flow when a magnetic field in a short side direction of a mold is applied.

FIG. 4 is a longitudinal sectional view showing an example of a configuration of a control device proposed by the present inventors previously.

FIG. 5 is a plan view for explaining a configuration near a mold in FIG. 4;

FIG. 6 is a schematic explanatory view showing a configuration of a model experimental machine.

FIG. 7 is a graph showing the relationship between the distance from the surface of the molten metal and the flow velocity of the sunk in the model machine and the actual machine in association with each other.

FIG. 8 is a graph showing the relationship between the magnetic flux density and the sinking flow velocity in an actual machine when the casting speed is 1 m / min.

FIG. 9 is a graph showing an appropriate magnetic flux density according to a casting speed.

FIG. 10 is a graph showing a comparison between a range of an appropriate magnetic flux density in the method of the present invention and operating conditions shown in the prior art.

[Fig. 11] The length of the slab in the long side direction is 600 to 1800m.
7 is a graph showing an optimum magnetic flux density range defined by the expressions (1) and (2) when the value is changed to m.

[Explanation of symbols]

 Reference Signs List 1 mold (short side) 2 mold (long side) 3 immersion nozzle 4 molten steel 5 solidified shell 6 nonmetallic inclusions 7, 7a to 7l electric coil 8, 8a, 8b iron core 9, 9a electromagnet 15, 15a to 15c Guide rolls 16, 16a Roll stand frame 30 Hot surface 31 Container corresponding to mold 32 Electromagnet 33 Current meter 34 Heater

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takehiro Nakaoka 1-5-5 Takatsukadai, Nishi-ku, Kobe F-term in Kobe Steel Research Institute Kobe Research Institute 4E004 AA09 MB11 NC01

Claims (5)

[Claims] 1. A molten steel is poured substantially horizontally or obliquely downward from an immersion nozzle installed at the center of a mold of a continuous casting machine for producing a slab slab or a bloom slab having a rectangular cross section toward both short sides of the mold. A part of the jet collides with the short sides on both sides of the mold to apply a static magnetic field in the direction of the long side of the mold to control the molten steel flow inside the slab, A continuous magnetic flux density B (Gauss) satisfying the following expression (1). 600 × (Vc) ^1/2 ≦ B ≦ 1700 × (Vc) ^1/2 (1) where Vc is the casting speed (m / min), and the measurement position of the magnetic flux density is the position corresponding to the center between the magnetic poles. And 2. A molten steel is poured substantially horizontally or obliquely downward from the immersion nozzle installed in the center of the mold of a continuous casting machine for producing a slab slab or a bloom slab having a rectangular cross section toward both short sides of the mold. A part of the jet collides with the short sides on both sides of the mold to apply a static magnetic field in the direction of the long side of the mold to control the molten steel flow inside the slab, A continuous magnetic flux density B (Gauss) that satisfies the following equation (2). 25 × (Vc × W) ^1/2 ≦ B ≦ 40 × (Vc × W) ^1/2 (2) where Vc is the casting speed (m / min) and W is the length in the long side direction (mm). Where the magnetic flux density is measured at a position corresponding to the center between the magnetic poles. 3. A slab for a thin steel sheet to be deep drawn,
3. The continuous casting method according to claim 1, wherein the casting is performed at a casting speed of 1.5 m / min or less. 4. A curved continuous caster in which a mold does not have a vertical portion, and casts ultra-low carbon steel having a carbon concentration of 0.01% by mass or less at a casting speed of 1.3 m / min or more. The continuous casting method according to claim 1, wherein 5. The continuous casting method according to claim 1, wherein a thin slab having a length in a short side direction of 150 mm or less is cast at a casting speed of 2.5 m / min or more.