JPH11320053A - Method for controlling fluid of molten steel in continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method of the fluid of molten steel, with which the impurity at the loose side of a slab with a bending type continuous caster can be reduced. SOLUTION: An electromagnetic induction stirring device is disposed at the interval between (L0 +H/2) to (2m-H/2), (wherein, L0 is the distance from a meniscus of the molten steel to a position, at where the solidified interface in the loose side becomes in the perpendicular state, and H is the height of the electromagnetic induction stirring device). Non-circular flow flowing to the same direction at both long wall sides is formed to the molten steel with the electromagnetic induction device, and the intensity of the non-circular flow is changed changed over into strong flow and weak flow in the following frequency (f). 1 sec <= f <=(10<3> W/F<1/2> ) sec, (wherein, L is the distance from the meniscus of the molten steel to the center of the height of the electromagnetic induction stirring device and F is the thrust of the electromagnetic induction stirring device). Further, instead of change-over into the strong flow and the weak flow, the non-circular flow can be changed over from the one direction to the reverse direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In the continuous casting of a curved mold or a bending type, after casting molten steel in a vertical direction, a slab is moved laterally. Hereinafter, these are collectively referred to as curved continuous casting. The present invention relates to a continuous casting method for producing a slab by such curved continuous casting.

[0002]

2. Description of the Related Art FIG. 3 is a schematic view of a conventional curved continuous casting, in which (A) is a longitudinal sectional view, and (B) and (C) are II sectional views. In the figure, 1 is a mold, 2 is molten steel, 3 is a solidified shell,
4 is an immersion nozzle, 5-1 and 5-2 are electromagnetic induction stirrers,
6 is a flux.

[0003] In the molten steel 2 supplied from the immersion nozzle 4, inclusions in the molten steel in a pre-process such as a tundish are liable to be mixed, and the flux 6 covering the molten steel during the injection.
Is easy to get involved. In addition, since an inert gas is often blown into the immersion nozzle 4 during casting, the molten steel 2 may contain gas bubbles. These inclusions, flux and gas bubbles (abbreviated as impurities in this specification) are involved in the molten steel injection flow 2 ′ supplied from the immersion nozzle and infiltrate into the molten steel.

The impurities infiltrated into the molten steel float in the molten steel 2 because they are lighter than the molten steel, reach the flux 6 and are absorbed by the flux and removed from the molten steel. 7A and 8 in FIG. 3A are examples of impurities. The impurities 8 existing at the solidified shell interface on the fixed side in FIG. 3A are removed by floating in the molten steel 2 because there is nothing that hinders the floating. On the other hand, impurities 7 present at the solidified shell interface on the loose side side
As a result, the solidified shell 3 protruding from the upper part prevents the ascent. As a result, there is a problem in that the impurities 7 are not removed and are caught by the solidified shell, resulting in defects of the slab after the solidification is completed.

[0005] Although not limited to curved continuous casting, a linear motor type electromagnetic induction stirrer for generating a moving magnetic field of a linear motor is provided so as to sandwich the long side surface of the slab being cast, and the inside of the solidified shell is provided. A technique for forming a swirling flow in molten steel is known. 5-1 and 5-2 in FIG. 3 are examples of the electromagnetic induction stirrer. The electromagnetic induction stirrer 5-1 moves the molten steel on the 5-1 side in the direction of arrow 9-1 by forming a moving magnetic field, and the electromagnetic induction stirrer 5-2 moves with the moving magnetic field formed by the 5-1. By forming a moving magnetic field in the opposite direction, 5-
The molten steel on the second side is moved in the direction of arrow 9-2. As a result,
As shown in the figure, a steady swirling flow with a constant swirling speed is formed in the molten steel 2 as shown in the figure.

The present inventors have proposed an electromagnetic induction stirrer 5-1.
A steady swirling flow of arrows 9-1 and 9-2 is formed in the unsolidified molten steel 2 by 5-2, and the impurities 7 on the loose side in FIG. 3 are transferred to the fixed side by this swirling flow and floated and removed. An attempt was made. However, according to the knowledge of the present inventors, in the method using a steady swirling flow in which the swirling speed is always constant, the impurities 7 are locally accumulated without turning to the fixed side, and a portion where the impurities 7 are accumulated is generated in the slab. The problem occurs. The reason for this is not clear, but the steady swirling flow has a large flow velocity, as shown in FIG.
(C) There is a stagnant place indicated by 7 ', and it is considered that the impurity 7 does not move to the fixed side, but accumulates in the stagnant place 7'.

Although different from slab continuous casting, Japanese Patent Application Laid-Open
No. 44858 discloses a method for improving a final solidified portion accompanied by porosity at the center of a slab when a cylindrical or prismatic billet is manufactured by continuous casting.
It describes that an electromagnetic induction stirrer is arranged near the final solidification part of 7 m, and a swirling flow whose direction is reversed is used. However, since this method is a method for improving the final solidified portion, the place where the electromagnetic induction stirrer is provided is located below the mold near the final solidified portion.
From the meniscus of the molten steel in the mold.
m above the continuous casting device.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce impurities in the slab on the loose side and prevent the accumulation of such defects when manufacturing a slab with a curved continuous casting machine. An object is to provide a continuous casting method for molten steel that can be produced.

[0009]

Means for Solving the Problems and Embodiments of the Invention
FIG. 1 is a schematic explanatory view of an example of the present invention, and FIG.
(B), (C), and (D) are cross-sectional views. The present invention relates to continuous slab casting by a curved continuous casting machine. In the present invention, a pair of electromagnetic induction stirrers arranged so as to sandwich the long side surface of the slab at a height where the distance to the meniscus 10 of the molten steel is L in the following formula (1) is used. That is, the electromagnetic induction stirrer is disposed at a position where the distance L between the meniscus of the molten steel and the center of the height of the electromagnetic induction stirrer is within the range of the following expression (1).

L ₀ + (H / 2) <L <2m− (H / 2) (1) Above point P in FIG. 1 (A), the interface 11 between the loose-side solidified shell and the molten steel Is inclined upward and downward below the point P, and downward at the point P.
In the equation (1), L ₀ is the distance from the meniscus 10 to the point P. The point P is grasped in association with the casting conditions by calculation or by observing the top of the broken-out slab. In the equation (1), H is the height of the electromagnetic induction stirrer 5-1 or 5-2.

Above the point P, even if impurities are present in the vicinity of the interface 11 of the solidified shell, the interface of the solidified shell is widened, so that the rising and floating is not hindered, and the solidified shell is removed by the solidified shell. There is no. For this reason, the electromagnetic induction stirrer is disposed below L ₀ + (H / 2). In addition, impurities of a size that causes a problem in quality, which are involved in the molten steel injection flow 2 ′, penetrate into the molten steel up to 2 m below the meniscus, but do not penetrate deeper. For this reason, the electromagnetic induction stirrer is arranged above 2 m- (H / 2).

According to the present invention, the non-swirling flow 9 flowing in the same direction on any long side of the unsolidified molten steel 2 inside the solidified shell 3.
-1 ', 9-2' are formed. This non-rotating flow is energized so that the moving direction of the moving magnetic field formed by the electromagnetic induction stirrer 5-2 and the moving direction of the moving magnetic field formed by the electromagnetic induction stirrer 5-1 are the same. Obtained by

According to the present invention, the strength of the non-swirling flow is
The strong currents 9-1 'and 9-2' in FIG. 1B and the weak currents 9-1 "and 9-2" in FIG. 1C are periodically switched. This switching is performed by changing the current value flowing through the electromagnetic induction stirrers 5-1 and 5-2,
This can be performed by periodically switching between a high current value (ampere) and a low current value (ampere).

Further, in the present invention, the period f (second) for switching between the strong flow and the weak flow is set within the range of the following equation (2).

1 second ≦ f ≦ (10 ³ · L / ΔF) seconds (2) If the period f of stirring is less than 1 second, the molten steel 2 cannot follow the change in the strength of the moving magnetic field. The flow of molten steel is less effective because it cannot be changed as desired. The present inventors have carried out an electromagnetic induction stirring by changing the period f, but examines the slab produced was investigated whether the occurrence of accumulation of impurities, cycle (10 ³
It has been found that accumulation of impurities occurs when the time is longer than L / ΔF) seconds. The reason for this is not clear, but the period is (1
0 ³ · L / √F), it becomes 9-1 ', 9
It is considered that -2 'is due to the fact that 9-1 "and 9-2" flow like a steady flow, and a place where stagnation occurs in the molten steel flow, and impurities accumulate in this part.

According to the findings of the present inventors, for example, the non-swirl flows 9-1 'and 9-2' in FIG.
1 ', 9-2' in FIG. 1D, which is opposite to 1 ', 9-2'.
A remarkable effect is obtained in the reduction of impurities that are periodically switched to the direction of 2 ″ ′ and the prevention of accumulation of impurities. That is, the present invention also provides an electromagnetic induction stirrer using the same (3)
In this method, the direction of the non-swirling flow is switched between the direction toward one short side and the direction toward the other short side at the same cycle as the following equation (4) same as the above equation (2). . In addition, the reason for specifying as in Expressions (3) and (4) is the same as the reason for specifying in Expressions (1) and (2).

L ₀ + H / 2 <L <2 m−H / 2 (3) where L: distance between the meniscus of the molten steel and the center of the height of the electromagnetic induction stirrer L ₀ : loose from the meniscus of the molten steel Distance to the position where the interface between the solidified shell on the side and the molten steel is vertical H: Height of the electromagnetic induction stirrer 1 second ≤ f ≤ (10 ³ · L / √F) seconds ………………………………………………………………………………………………………………………………………… (4) ： Period (second) of non-whirl flow toward one short side and non-whirl flow toward another short side L: Distance between meniscus of molten steel and center of height of electromagnetic induction stirrer F: Electromagnetic induction stirrer Thrust (N / m ² )

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors used a curved continuous casting machine having a bending radius of 10.5 m to cast a low carbon steel slab having a width of 1000 mm and a thickness of 250 mm at a casting speed of 1.3 m / min. The invention was tested during continuous casting. Note that the immersion nozzle was an immersion nozzle having a discharge hole having a discharge angle of 25 degrees downward, into which Ar gas for preventing nozzle blockage was blown at a rate of 5 L / min. The electromagnetic induction stirrer is 1500m wide
m and a height of 250 mm, and a half of the device height is arranged at a position 1500 mm below the molten steel meniscus.

The inventors of the present invention assumed that the first casting period corresponding to about 1/4 of the total casting amount from the start of casting to the conventional method in which electromagnetic induction stirring was not performed at all, and about 1/4 to about 1 / In the second casting period of No. 2 at 10 kN / m ² , a steady swirling flow of FIG. 3 (B) is formed and agitated, and in the third casting period of about 1/2 to about 3/4, (B) of FIG. ) And (C) are switched at a cycle of 3 seconds. The thrust of (B) in the third casting period is 10 kN /
In m ² , the thrust of (C) is 5 kN / m ² . In the fourth casting period after the third casting period until the end of the casting, the present invention in which (B) and (D) of FIG. 1 are switched at a cycle of 3 seconds was performed. The thrusts of (B) and (D) in the fourth casting period were both 10 kN / m.
²

After the casting is completed, a sample is taken from the slab in each casting period, and is 20 mm to 40 m below the long side surface on the loose side.
The abundance of impurities in the portion m was evaluated. FIG. 2 shows the result. The width end in the figure is 20 to 40 mm below the surface of the slab 40 mm from the short side, and the center of the width is the center of the slab width.

As shown in FIG. 2, during the first casting period in which electromagnetic induction stirring is not performed, the evaluation of impurities is generally high and the amount of impurities is large. The second casting stage, which forms a conventional steady swirl flow,
The impurity score at the center and one of the width ends is low, but the impurity score at the width end downstream of the swirling flow is extremely high, and impurities are accumulated in this portion. In the third casting period and the fourth casting period of the present invention, the scores of impurities are significantly lower than those in the first casting period,
And there is no accumulation of impurities.

In the third casting period and the fourth casting period of the present invention, the reason why the amount of impurities is small and there is no accumulation of impurities is not clear, but the flow of the molten steel formed by the present invention is in a direction parallel to the long side. This oscillation is thought to be due to the fact that the molten steel was stirred evenly and did not generate stagnation. It is considered that the impurity 7 in FIG. 3 was floated and removed away from the interface 11 between the solidified shell and the molten steel due to the swing.

[0023]

According to the present invention, when a slab is manufactured by a curved continuous casting machine, impurities on the loose side of the slab can be reduced. In addition, it is possible to effectively prevent generation of an impurity accumulation portion.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method for controlling molten steel flow according to the present invention.

FIG. 2 is a schematic explanatory view of a conventional curved continuous casting.

FIG. 3 is an explanatory diagram of an effect of the present invention.

[Explanation of symbols]

1: Mold, 2: Molten steel, 2 ': Injection flow of molten steel, 3:
Solidified shell, 4: immersion nozzle, 5 (5-1, 5-
2): electromagnetic induction stirrer, 6: flux, 7: impurity, 8: impurity, 9: (9-1, 9-2, 9-)
1 ', 9-2', 9-1 ", 9-2", 9-1 "', 9-
2 "'): Moving direction and flow strength of molten steel, 10: Meniscus of molten steel, 11: Interface between solidified shell and molten steel.

Continuation of the front page (72) Inventor Takahiro Isono 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works

Claims (2)

[Claims] In a slab continuous casting by a curved continuous casting machine, a pair of electromagnetic inductions arranged so as to sandwich a long side surface of a slab at a height up to a meniscus of molten steel as L in the following formula (1). Using a stirrer, a non-swirl flow is formed in the molten steel inside the solidified shell on both long sides in the same direction, and the strength of the non-swirl flow is determined by the following equation (2): A method for controlling molten steel flow in continuous casting, characterized by switching to flow. L ₀ + H / 2 <L <2 m−H / 2 (1) where L: distance from the meniscus of the molten steel to the center of the height of the electromagnetic induction stirrer L ₀ : solidification of the molten steel from the meniscus to the loose side Distance to the position where the interface between the shell and molten steel is vertical H: height of electromagnetic induction stirrer 1 second ≤ f ≤ (10 ³ · L / √F) seconds ... (2) where f: strong non- Cycle of swirling flow and weak non-swirling flow (seconds) L: Distance between meniscus of molten steel and center of height of electromagnetic induction stirrer F: Thrust of electromagnetic induction stirrer (N / m ² ) 2. A pair of electromagnetic inductions arranged so as to sandwich a long side of a slab at a height where the meniscus of molten steel reaches L in the following formula (3) in continuous slab casting by a curved continuous casting machine. Using a stirrer, a non-swirl flow is formed in the molten steel inside the solidified shell on both long sides in the same direction, and the direction of the non-swirl flow is set to a short side of 1 with a period f of the following formula (4). A method for controlling molten steel flow in continuous casting, characterized by switching between a heading direction and a direction toward another short side. L ₀ + H / 2 <L <2 m−H / 2 (3) where L: distance between the meniscus of the molten steel and the center of the height of the electromagnetic induction stirrer L ₀ : from the meniscus of the molten steel to the solidified shell Distance to the position where the molten steel interface becomes vertical H: Height of electromagnetic induction stirrer 1 second ≤ f ≤ (10 ³ · L / √F) seconds ... (4) However, the short side of f: 1 Period (seconds) of the non-swirl flow toward the other and the non-swirl flow toward the other short side L: distance between the meniscus of molten steel and the center of the height of the electromagnetic induction stirrer F: thrust of the electromagnetic induction stirrer (N / m) ² )