JP2002248551A - Continuous casting method for steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the single flow or the pulsation of the discharge flow of molten metal to be supplied into a mold through an immersion nozzle to make operation stable and to reduce the occurrence of surface flaws on a plate stock after rolled. SOLUTION: In supplying the molten metal into the mold by means of an immersion nozzle having two or more discharge holes and continuous-casting a cast steel piece having a rectangular or roughly rectangular section 600 mm or more in width, the molten metal to be supplied into the mold from a tundish is given a whirl within the range of an angular velocity between 6π and 15π (rad/sec) inside the immersion nozzle. This reduces the single flow or the pulsation of the discharge flow of the molten metal to be supplied into the mold from the tundish, in the continuous casting of a bloom or slab, thereby enabling stable casting with decreased meniscus variation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for discharging molten steel discharged from a molten steel supplied into a mold through a submerged nozzle during continuous casting using a submerged nozzle having two or more discharge holes. Stabilize operations by reducing one-sided flow and pulsation,
The present invention relates to a continuous casting method for steel capable of reducing the occurrence of surface flaws on a sheet material after rolling.

[0002]

2. Description of the Related Art In continuous casting of steel, in many cases,
An immersion nozzle is used to supply molten steel to the mold, but during continuous casting of aluminum killed steel or the like, deposits such as alumina deposit on the inner surface of the nozzle. When deposits accumulate on the inner surface of the nozzle, the discharge flow from the immersion nozzle becomes uneven left and right, and there is a problem that surface defects occur during rolling. In steel plates and the like used for automobile exteriors, the required level of surface properties is high, and generation of these flaws is a serious problem.

[0003] In order to solve these problems, it has often been practiced to control the flow of molten steel in a mold. For example, various methods have been proposed for controlling the flow in a mold by accelerating or decelerating the molten steel flow by applying an electromagnetic force to the molten steel flow discharged from an immersion nozzle. In addition, various methods have been implemented in which a new hole is added to the discharge holes, which are usually two on the left and right sides, or a method of modifying the shape of the immersion nozzle, such as processing the hole shape. Further, many studies have been made on a method of preventing the adhesion of alumina or the like by changing the material of the immersion nozzle itself or introducing an inert gas and maintaining the initial flow state.

In addition, recently, it has been proposed to impart a swirl to a molten steel flow passing through an immersion nozzle.
This proposal is to reduce the penetration depth of inclusions by generating a swirling flow in the mold during continuous casting of cast pieces originally having a round cross section or a regular polygon, and even a rectangular cross section close to a square, In order to improve the cleanliness of the steel, to maintain the temperature of the meniscus portion in the mold, and to prevent skinning at this portion, it was studied to generate a swirl in the molten steel flow in the immersion nozzle. Things.

There has been reported an example in which these findings are applied to continuous casting of a slab or a bloom having a rectangular cross section generally called a bloom, which is generally cast using an immersion nozzle having two discharge holes. According to these findings, by imparting swirl to the molten steel flow in the immersion nozzle, the maximum discharge flow velocity from the two discharge holes can be reduced, drift in the mold can be prevented, and inclusions in the molten steel can be aggregated. It is reported that various effects can be expected such as enlargement.

[0006] However, most of the findings investigating the effects on the flow are based on the results measured with a water model, and most of the investigations on molten steel are based on the results of flow analysis. The knowledge from the water model cannot be directly applied to molten steel because the physical properties such as specific gravity, interfacial tension, and viscosity are greatly different from actual ones. In addition, there is a problem in that it is impossible to determine the effect of improving the flaw generation rate which is effective during actual manufacturing with a water model or flow analysis.
Under such circumstances, although there have been reports on the change of the molten steel discharge flow due to the application of swirl, the conditions for imparting swirl that have the effect of improving the quality of the continuous cast slab of actual steel have not been clarified.

For example, Japanese Patent Application Laid-Open No. H11-47896 proposes a method of using a nozzle provided with a spiral projection on the inner wall as means for imparting swirling. Although it has been shown that this method can provide a certain effect, the molten steel flowing through the shaft portion without the spiral flows down almost without turning, so that a sufficient effect cannot be obtained. In addition, as the alumina deposition in the immersion nozzle progresses, the effect further decreases.

In Japanese Patent Publication No. 6-47691, an electromagnetic force is applied to molten steel in a pipe by a magnetic field generator installed outside the pipe to impart a swirling flow in a direction perpendicular to the flow to increase the coagulation and enlargement of inclusions. A method has been proposed. However,
A long rotating magnetic field generator is required to provide a high rotational velocity that can improve the discharge flow and the flow in the mold, and it is not only difficult to incorporate it into the actual continuous casting process, but also equipment cost Is also not realistic because it will increase.

Further, JP-A-7-303949, JP-A-11-239852, and JP-A-11-9059
No. 3 proposes a method of imparting a swirling flow by devising a supply structure of molten steel to an immersion nozzle, and JP-A-10-263765 proposes a method of devising a gas blowing structure.

[0010]

However, any of the above proposals for imparting swirl to the molten steel flow to the casting mold requires the necessary swirling conditions and casting conditions in a molten steel system for performing actual continuous casting. Details were not disclosed. In addition, there is a problem that a rotation at a sufficient rotation speed cannot be provided due to an inappropriate rotation applying method, and a desired effect cannot be sufficiently obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. The present invention clarifies the details of the necessary swirling conditions and casting conditions in a molten steel system for actual continuous casting, and discharges them from a submerged nozzle. It is an object of the present invention to provide a continuous casting method of steel capable of imparting a swirl at a sufficient rotation speed to a flow and sufficiently obtaining an intended effect.

[0012]

In order to achieve the above-mentioned object, a method for continuously casting steel according to the present invention is provided in a mold using a dip nozzle having two or more discharge holes. In supplying molten steel and continuously casting a steel slab having a rectangular or substantially rectangular cross section having a width of 600 (mm) or more, an angular velocity of 6π to 15π (rad) is applied to molten steel supplied to a mold from a tundish in a nozzle. / Sec). By doing so, it is possible to reduce one-sided flow and pulsation of the discharge flow from the immersion nozzle supplied from the tundish into the mold when continuously casting slabs of a shape called bloom or slab Thus, stable casting with little variation in meniscus in the mold can be performed. Further, by rolling such a slab, it is possible to reduce the occurrence of surface flaws on the sheet material.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied various conditions for imparting turning in actual continuous casting of steel, and as a result, have found suitable conditions for preventing product flaws. Was established.

That is, in the first continuous casting method for steel according to the present invention, molten steel is supplied into a mold using a dip nozzle having two or more discharge holes, and a width of 60 mm or more.
When continuously casting steel slabs having a rectangular or approximately rectangular cross section of 0 (mm) or more, the angular velocity in a nozzle immersed in molten steel supplied from a tundish to a mold is 6π to 15π.
(Rad / sec).

First, the reason why the appropriate turning angular velocity is determined as described above in the first continuous casting method for steel according to the present invention will be described. 1 (a) and 1 (b), or a swiveling mechanism 1 shown in FIG. 2 in which the diameter in the immersion nozzle tube is sequentially shifted in the rotational direction and twisted. Was inserted into the immersion nozzle, and continuous casting was performed.

The turning angular velocity at this time was calculated as follows, and was compared with the state of occurrence of product defects at this time. The swirling angular velocity is calculated as follows: the required time T = A × (H / Q) for passing through the swiveling mechanism, which can be calculated from the molten steel discharge flow rate Q per unit time, the flow path cross-sectional area A, and the length H of the swirling mechanism. It is a value θ / T that can be calculated from a turning angle θ that can be geometrically calculated assuming that turning is ideally applied along the flow path during passage by the structure of the applying mechanism.

In the immersion nozzle, the above-mentioned swiveling mechanism 1 is provided.
Are installed, casting is performed under conditions with different turning speeds, and the results of investigating the occurrence of flaws on the coil surface are shown in FIG. The investigation was performed by visually observing the coil surface and examining the ratio of the number of failed coils.

The turning angular velocity in FIG. 3 is 0 (rad / s).
ec) is the result when using a conventionally used immersion nozzle having no swirling mechanism, but in this case, about 2.5 to 3% of defects occurred. Also,
When the swirling angular velocity is smaller than 6π (rad / sec), the effect of imparting swirling is small, and the flow in the mold causes one-sided flow and pulsation as in the case where ordinary swirling is not applied. Scratches occurred.

On the other hand, in order to increase the turning angular velocity, a more precise structure of the turning mechanism is required. In particular, when the turning angular velocity is higher than 15π (rad / sec), clogging occurs in this portion, and the flow rate increases. It has been found that not only the resistance is increased but also a problem such as melting of a specific location in the immersion nozzle is not preferable.

Therefore, in the present invention, an appropriate turning angular velocity is not less than 6π (rad / sec) and not less than 15π (rad / s).
ec) It was specified as follows. The range of the swirling angular velocity is not limited to the structure of the swirling applying mechanism 1 for applying the swirling flow as shown in FIGS. A similar concept holds for general.

In addition to the above-described method of providing the swirling mechanism in the immersion nozzle, a method of applying the electromagnetic force and a method of devising the structure of the entrance to the immersion nozzle can be considered as a method of imparting the swirl. Can be Although there is a problem that it is impossible to calculate the angular velocity geometrically by these methods, in this case as well, the angular velocity is 6
It goes without saying that the same effect can be obtained as long as a turn of π to 15π (rad / sec) can be provided. However, even with these methods, it is technically difficult to obtain a high turning speed exceeding 6π as in the method of providing the turning imparting mechanism in the immersion nozzle.

As described above, the first method for continuously casting steel according to the present invention does not specify the structure for imparting the turning, and may be selected in view of the effect of imparting the turning, the production cost, the durability, and the like. A structure is preferable in which the flow velocity distribution in the cross section in the nozzle hole of the nozzle becomes a distribution close to point symmetry.

However, for example, Japanese Patent Application Laid-Open No. 11-478
In a method of installing a spiral projection on the inner wall as proposed in Japanese Patent No. 96, the height of the spiral cross section is at most 25% of the inner diameter of the nozzle as a more preferable embodiment. As described above, the molten steel flowing through the pipe flows down almost without turning.

Incidentally, the swirling flow imparted in the immersion nozzle is attenuated as it flows down due to flow resistance between the inner wall of the nozzle hole and the like. In particular, between the molten steel and the refractory, as time elapses after the start of casting, erosion and formation of deposits occur on the inner surface of the nozzle hole, and the attenuation becomes remarkable as compared with the result obtained with a water model or the like.

Therefore, the inventors of the present invention provide a swivel of 6π to 15π (rad / sec) by the swivel applying mechanism, and variously change the distance from the lower end of the swivel applying mechanism to the upper end of the discharge hole. And the flaw occurrence rate was investigated. The result is shown in FIG.
As shown in the experiment of the present inventors, in the experiment of the present invention, the swirling mechanism was installed immediately below the tundish, and when the distance from the outlet of the swirling mechanism to the discharge hole exceeded 600 mm, the flaw generation rate was swirled. It was found that there was almost no difference from the case where no was given. That is, an appropriate angular velocity of 6π to 1
It has been clarified that even if a turn of 5π (rad / sec) is given, the expected effect cannot be obtained if the length after the turn is given becomes long.

Thus, according to the experiments of the present inventors,
The distance from the lower end of the rotation applying mechanism to the upper end of the discharge hole is 6
It has been found that it is desirable to be within 00 mm. This distance increases when the turning angular velocity is set to a high value. However, when the turning angular velocity exceeds 600 mm, the total length of the immersion nozzle becomes longer, which is not preferable in terms of operation stability and cost.

On the other hand, according to an experiment conducted by the present inventors, the installation position of the swiveling mechanism was lowered to 100 mm above the discharge hole.
It was also found that the effect of reducing flaws was small even when the turning imparting mechanism was installed at a position less than. Further, when the structure of the cast slab after solidification was examined, it was found that there was a solidification delay portion near the immersion nozzle. When such a solidification delay portion occurs, there is a concern that a vertical crack or breakout may occur.
This is considered to be because the turbulence of the flow is large near the exit of the turning imparting mechanism. Based on the above findings, in the second continuous casting method of steel according to the present invention, in order to prevent the occurrence of flaws after rolling, the lower part of the swirling mechanism is 100 mm or more from the upper end of the discharge hole of the immersion nozzle, The turning imparting mechanism is set to be at a position of 600 mm or less.

The swiveling mechanism has a flow resistance due to its structure. If the flow resistance increases, the pressure required to flow the required flow rate increases, and there is a problem in that it becomes difficult to control the flow rate by a flow rate control mechanism installed above the swirling mechanism. The magnitude of the flow resistance increases when the cross-sectional area of the flow path of the swirling mechanism is small or when the swirling angle is increased with a short swiveling length.

Assuming that the height of the molten steel head required for flowing a fluid having a flow rate of Q (ton / min) through a path having a flow path cross-sectional area of S (cm ² ) is h, the flow rate Q is represented by the following equation (1). Can be expressed as

[0030]

## EQU1 ## Q = ρcS (2gh) ^1/2

In the above formula 1, ρ is the density of the fluid, c is the resistance coefficient of the flow path, and is a value that changes depending on the flow path resistance.
As a result of continuous casting under various conditions, the present inventors set the resistance coefficient c of the flow path to 0.85 in the swirling mechanism and set the required flow rate to the height h from the flow control position to the upper end of the swirling mechanism.
1 (m) and the minimum flow path cross-sectional area S1 (c
From m ² ), it was found that the flow rate control would be difficult unless the value was smaller than the value that could be calculated by the above-described formula 1. The equation obtained by rearranging both sides is Equation 2 below.

[0032]

[Equation 2] Q / S1 ≦ 0.186 × (h1) ^1/2

Here, the flow control position required to determine the height h1 refers to a portion where the cross-sectional area of the flow control section such as a sliding gate or a stopper is minimized.

Further, the length of the turning applying mechanism is shortened,
If the structure is such that a large angle of rotation is provided in a short time, the flow resistance of the rotation applying mechanism becomes large, and flow control becomes difficult. As a result of casting performed by the present inventors using various turning imparting structures, the length from the inlet side to the outlet side of the turning imparting mechanism is L (m), and the diameter of the turning imparting mechanism is d. (M), the turning angle given at that portion is nπ (r
In the case of ad), it has been found that a casting problem does not occur if the mechanism for imparting swirl to the molten steel flow in the nozzle satisfies the relationship of the following equation 3 between L, d, and n.

[0035]

## EQU3 ## L ≧ 1.1 × n × d

Based on these findings, the present inventors set the molten steel supply amount to Q (ton / min), the minimum flow path cross-sectional area of the swirling mechanism provided in the immersion nozzle to Sl (cm ² ), and the flow rate When the height from the control position to the upper end of the turning applying mechanism is defined as hl (m), the relationship of Expression 2 is satisfied, and the length from the entrance side to the exit side of the turning applying mechanism is L ( m), when the diameter of the swiveling mechanism is d (m), and the swiveling angle given at that portion is nπ (rad), the nozzle satisfying the relationship of Equation 3 between L, d and n The third continuous casting method for steel according to the present invention using a mechanism for imparting swirl to the inner molten steel flow has been completed.

The present inventors further studied the flow path structure below the turning imparting mechanism. We have Q (to
n / min), the shape of the immersion nozzle was variously changed and the continuous casting was actually performed. The cast slab was rolled, and the surface properties of the cold-rolled steel sheet were investigated.
/ Min), assuming that the minimum flow path cross-sectional area of the immersion nozzle below the swirl imparting mechanism is S0 (cm ² ), a steel sheet with less surface flaws can be obtained by casting so as to satisfy the following equation (4). It was found that it can be manufactured. This is the fourth steel continuous casting method according to the present invention.

[0038]

[Equation 3] 0.07 ≦ Q / S0 ≦ 0.1

In the fourth continuous casting method for steel according to the present invention, when Q / S0 is larger than 0.1, that is, the minimum flow path cross-sectional area below the swirling mechanism is excessive with respect to the amount of molten steel passed. If it is small, the flow resistance in the swiveling mechanism increases, and the sensitivity of flow adjustment by a sliding gate, a stopper, or the like arranged above the immersion nozzle decreases.

On the other hand, when Q / S0 is smaller than 0.07, that is, when the minimum flow path cross-sectional area in the lower part of the swirling mechanism is relatively large with respect to the amount of molten steel passing, the upper part of the swirling flow applying mechanism is used. , The molten steel pressure in the immersion nozzle does not flow evenly into the upper part of the swirling mechanism, and the flow stabilizing effect in the mold is reduced.
Based on this finding, in the fourth continuous casting method for steel according to the present invention, Q / S0 is specified in the range of 0.07 or more and 0.1 or less. As described above, when imparting a swirl to the molten steel flow, more suitable casting conditions can be obtained by adjusting the flow path cross-sectional area of each part to an appropriate range according to the flow rate of the molten steel.

Incidentally, in order to prevent clogging of the immersion nozzle, an inert gas such as Ar is often blown into the immersion nozzle. In the method of the present invention, the blowing of the inert gas is effective for preventing the clogging of the immersion nozzle.
If a large amount is blown in, the molten steel flowing down the immersion nozzle may not flow evenly into the swirling mechanism. Therefore, in the present invention, A
When an inert gas such as r is blown, it is desirable that the flow rate of the blown gas be 10 N l / min or less.

It is of course possible to apply a swirl to the molten steel flow in the immersion nozzle at the time of continuous casting of round cast pieces having a small sectional area called billets or cast pieces having a rectangular cross section close to a square. In the continuous casting of such a slab, a straight type nozzle is often used, but in this case also, the effect of reducing the immersion depth of the molten steel can be obtained by imparting swirling.

However, an object of the present invention is to reduce the one-sided flow of molten steel discharged from a tundish into a mold during continuous casting of a slab having a shape called bloom or slab, which occurs after rolling. The purpose is to reduce the surface flaws of the plate material, and the conditions for this are specified.

Accordingly, a steel slab having a rectangular or substantially rectangular cross section having a width of 600 mm or more, which is a condition for casting a slab for such an application, is provided with a immersion nozzle having two or more discharge holes in a mold. The present invention is effective in continuous casting using

Further, when the molten steel flow swirled in the immersion nozzle is discharged from a normal two-hole nozzle to cast a wide cast slab, the molten steel discharge flow collides with the long side surface of the cast slab. Breakout may occur if a severe coagulation delay is noticeable. Therefore, in actual continuous casting, the installation direction of the discharge holes should not be parallel to the slab width, but should be a certain angle, or should be asymmetric with respect to the slab thickness center plane. Is desirable. However, since these appropriate conditions change depending on the discharge flow rate and the turning speed, it is necessary to appropriately set the conditions according to the casting conditions.

[0046]

Embodiments of the present invention will be described below. In order to confirm the effect of the present invention, casting was performed using a vertical bending type continuous casting machine. An extremely low carbon steel slab having a thickness of 210 mm and a width of 1800 mm was cast at a casting speed of 1.1 to 1.6 m / min. The casting was carried out by changing the internal structure of the immersion nozzle, the swirling condition of the molten steel, the supply amount of the molten steel, and the like. These are shown in Table 1 below together with the results.

A refractory having the structure shown in FIG. 1 or FIG. 2 was used for the swiveling mechanism provided in the immersion nozzle.
The presence or absence of flaws was determined by visually observing the coil surface after cold rolling, and the proportion of failed coils was investigated.

[0048]

[Table 1]

In Comparative Example 1 in which no rotation was given, 2.8 was obtained.
%. On the other hand, in Examples 1 to 7 in which the turning of the angular velocity was from 6π to 15π, all the flaws were 1.5% or less, and the improvement effect was obvious. In addition, in Examples 1 to 7, the fluctuation of the molten metal surface in the mold and the difference between the left and right molten metal surface heights of the immersion nozzle were also reduced. This is considered to be the effect of suppressing the one-sided flow and the pulsation and stabilizing the flow in the mold.

On the other hand, even in the case where the turning was given, the flaw generation rate was almost the same as that in the case where the turning was not given in Comparative Example 2 where the angular velocity was 5.4π. Under the condition where the flaw was generated at a high rate, a phenomenon was observed in which a large temperature difference occurred between the left and right of the immersion nozzle in the temperature of the mold copper plate. This is a phenomenon caused by one-sided flow in the molten steel flow supplied into the mold.

However, even in the embodiment having the remarkable improvement effect described above, the flaw occurrence rate was slightly deteriorated in the embodiment 3 in which the installation height of the swirl imparting mechanism was set near the discharge hole. In addition, a solidification delay portion occurred in the solidified shell. on the other hand,
In the fourth embodiment in which the turning imparting mechanism is installed immediately below the sliding gate, although not as large as the conventional method, 1.5%
High flaw generation rate. This is considered to be because the imparted rotation was attenuated in the immersion nozzle, and the effect was reduced. In the fourth embodiment, the distance between the flow control unit and the turning mechanism is small, the responsiveness due to the opening and closing of the flow control unit is slightly reduced, and the casting speed must be reduced when the amount of molten steel in the tundish decreases. And the quality of this part deteriorated.

Also, in the fifth embodiment in which the length of the swiveling mechanism is shortened, the responsiveness due to the opening and closing of the flow control unit is slightly reduced. It is considered that this occurred because the resistance of the turning applying mechanism increased.

Further, in Example 6 in which the inner diameter of the nozzle below the turning imparting mechanism was enlarged, one-sided flow occurred, and the flaw occurrence rate slightly increased. Conversely, in Example 7 in which the inner diameter of the nozzle below the swirl applying mechanism was smaller, the responsiveness due to the opening and closing of the flow control unit was slightly reduced, although the flaw occurrence state did not change significantly.

[0054]

As described above, by applying the method of the present invention, the discharge flow of molten steel supplied from the tundish into the mold during continuous casting of a slab having a shape called bloom or slab. Pulsation and pulsation can be reduced, and stable casting with little variation in meniscus in the mold can be achieved. Further, by rolling such a slab, it is possible to reduce the occurrence of surface flaws on the sheet material.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a first example of a mechanism for imparting a swirl to a molten steel flow in a nozzle.

FIG. 2 shows a second mechanism for imparting a swirl to the molten steel flow in the nozzle.
FIG. 3 is a diagram showing an example of the above.

FIG. 3 is a diagram showing a change in a flaw occurrence rate when the turning angular velocity is variously changed.

FIG. 4 is a third view of a mechanism for imparting a swirl to the molten steel flow in the nozzle.
FIG. 3 is a diagram showing an example of the above.

FIG. 5 is a diagram showing a change in the flaw occurrence rate when the distance between the lower end of the swirl applying mechanism in the nozzle and the discharge hole is variously changed.

[Explanation of symbols]

 1 Turning mechanism

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yujo Marukawa 4-33, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries, Ltd. (72) Inventor Yuichi Tsukaguchi 1850 Minato, Wakayama-shi, Wakayama Sumitomo Inside the Wakayama Works, Metal Industry Co., Ltd. (72) Masayuki Kawamoto 4-33, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries Co., Ltd. (72) Shigeta Hara 2- Yamadaoka, Suita City, Osaka Prefecture 1 Osaka University Faculty of Engineering (72) Inventor Shinichiro Yokotani 4-1 Miyashiromachi Gakuendai, Minamisaitama-gun, Saitama 4-1 Within Japan Institute of Technology (72) Inventor Kazuo Nonobe 1175 Urayaibe, Bizen-shi, Okayama Prefecture Reference) 4E004 FB10 MB20 NB01 NB02 NC01

Claims (4)

[Claims] 1. A molten steel is supplied into a mold using an immersion nozzle having two or more discharge holes, and a steel slab having a rectangular or roughly rectangular cross section having a width of 600 (mm) or more is obtained. During continuous casting, the angular velocity in the molten steel supplied from the tundish to the mold is 6π to 1 in the immersion nozzle.
A method for continuously casting steel, wherein a turning is provided within a range of 5π (rad / sec). 2. An immersion nozzle having an angular velocity of 6π to 1
2. The steel continuity according to claim 1, wherein the turning within a range of 5π (rad / sec) is given by a turning imparting mechanism installed at a position of 100 to 600 (mm) from the upper end of the discharge hole in the immersion nozzle. Casting method. 3. The supply amount of molten steel is Q (ton / min), and the minimum flow path cross-sectional area of the swirling mechanism provided in the immersion nozzle is Sl.
(Cm ² ), when the height from the flow control position to the upper end of the swirling mechanism is hl (m), the relationship of the following formula is satisfied, and between the inlet side and the outlet side of the swirling mechanism. Is the length of L (m), the diameter of the turning applying mechanism is d (m), and the turning angle given at that portion is nπ (rad). The continuous casting method according to claim 1 or 2, wherein a mechanism for imparting a swirl to the molten steel flow in the nozzle that satisfies the relationship is used. Q / S1≤0.186 * (h1) ^1/2 ... L≥1.1 * nxd ... 4. When the molten steel supply amount is Q (ton / min) and the minimum flow path cross-sectional area of the immersion nozzle below the swirl applying mechanism is S0 (cm ² ), the relation of the following equation is satisfied. The method for continuously casting steel according to claim 1, wherein the steel is cast. 0.07 ≦ Q / S0 ≦ 0.1 ...