JP3125661B2 - Steel continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting steel for producing a high quality slab by controlling the flow of molten steel in a mold by electromagnetic force.

[0002]

2. Description of the Related Art In continuous casting of steel, the flow velocity of molten steel in a mold, particularly the flow velocity of molten steel immediately below the surface of molten steel in a mold, is generally generated by inclusion of mold powder and inclusions mainly composed of alumina which is a deoxidation product. It is known that there is a strong relationship with slab defects. For this reason, many attempts to control the flow velocity of the molten steel just below the surface of the molten steel have been proposed. These attempts can be roughly classified into those that improve the shape of the discharge port of the immersion nozzle and those that attempt to control the flow of molten steel by using electromagnetic force.

[0003] The present invention belongs to the latter. Japanese Patent Application Laid-Open No. 62-252650 discloses a method using electromagnetic force.
In the official gazette (hereinafter referred to as prior art 1), the level difference of molten steel on the left and right of the immersion nozzle is detected, and the direction of electromagnetic stirring and the driving force for moving the molten steel are adjusted so as to eliminate the level difference by electromagnetic stirring. Thus, a method for stably producing high quality cast slabs has been disclosed.

In Japanese Patent Application Laid-Open No. Hei 4-9255 (hereinafter referred to as prior art 2), a plurality of eddy current level meters are provided in the width direction of a slab, and an electromagnetic force applying device is provided outside the mold. ,
A method is disclosed in which when a level difference of a molten metal level exceeds an allowable range, an electromagnetic force for suppressing swelling of the molten metal level is applied to reduce entrapment of powder and inclusions.

[0005]

However, usually, when a level difference occurs on the surface of molten steel in a mold, at the time when the level difference is detected, the phenomenon of entrainment of the mold powder due to generation of a vortex or the like on the surface of the molten steel. Has occurred. In both the prior art 1 and the prior art 2, the direction of the electromagnetic stirring and the propulsive force of the molten steel are adjusted after detecting the level difference on the surface of the molten steel, that is, measures must be taken after the entrainment of the mold powder occurs. Therefore, the occurrence of entrapment of the mold powder cannot be fundamentally prevented. Therefore, these techniques cannot completely prevent the entrapment of the mold powder.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is intended to prevent the occurrence of swelling of the surface of molten steel in a mold and the entrainment of mold powder caused by a sudden change in flow velocity, thereby achieving high quality. The purpose is to produce slabs.

[0007]

According to the first aspect of the present invention, the same poles of the magnetic poles are opposed to each other on both sides of the immersion nozzle by sandwiching the mold on the outer wall of the mold parallel to the discharge port of the immersion nozzle. Using a moving magnetic field application device that moves in the width direction of the immersion nozzle, and a molten steel flow velocity measurement device that is arranged on both sides of the immersion nozzle and measures the flow velocity near the surface of the molten steel in the mold in a non-contact manner, the molten steel flow velocity measurement device on both sides of the immersion nozzle The magnetic field strength of the moving magnetic field applying device and the moving magnetic field direction are set such that the flow velocity direction measured in the step becomes symmetric with respect to the immersion nozzle, and the absolute value of the measured flow velocity value is 0.3 m / sec or less. And a continuous casting method for steel.

According to a second aspect of the present invention, in the first aspect of the present invention, the moving magnetic field is set so that the difference between the flow velocity values of the molten steel flow velocity measuring devices disposed on both sides of the immersion nozzle is 0.05 m / sec or less. A continuous casting method for steel, comprising controlling a magnetic field strength of an application device and a moving magnetic field direction.

According to a third aspect of the present invention, in the method of the first or second aspect, the moving magnetic field applying device can be independently controlled on the left and right sides independently. It is.

The present inventors conducted a water model experiment on a continuous casting mold and found the following. The molten steel discharge flow from the immersion nozzle flowing toward the short side of the mold does not flow linearly, but reaches the short side of the mold while meandering between the long sides of the mold, and branches into an upward flow and a downward flow. . This meandering flow is
This is a so-called adhesion jet, and the jet adheres to the long side surface of one of the molds due to the negative pressure generated by the flow of the molten steel, but the jet flows due to the resistance with the long side surface of the mold. It separates from the surface and becomes an attached jet on the opposite long side of the mold. This occurs repeatedly. Therefore, even if the molten steel flow flows out equally from the two molten steel discharge ports of the immersion nozzle,
There is a slight time difference between the left and right to reach the molten steel surface.
This time difference is one of the causes of the mold powder being caught in the molten steel. As a countermeasure, it is necessary to control and eliminate the time difference or to form a molten steel discharge flow that does not meander in advance.

In order to prevent the molten steel discharge flow from meandering between the long sides of the mold, in a moving magnetic field applying device for moving the magnetic field distribution in the width direction of the slab, as shown in FIG. When the opposite poles of the magnetic field are opposed to each other, the flow of the molten steel abuts against the magnetic flux and flows, so that meandering occurs and the powder or the like is involved in the molten steel. Therefore, in the present invention, as shown in FIG. 1, the same polarity of the magnetic field is opposed to increase the magnetic flux in the traveling direction of the molten steel flow. By doing so, no magnetic flux crossing the molten steel flow is generated, and meandering is prevented because the molten steel flow flows along the magnetic flux. In the drawing, solid arrows indicate the direction of magnetic flux, and broken arrows indicate the direction of movement of the magnetic field. The dashed line indicates the direction of the molten steel flow.

The molten steel flow discharged from the immersion nozzle collides with the solidified shell near the inner wall on the opposite short side of the mold and separates into an ascending flow and a descending flow. On the surface of molten steel, it flows toward the center of the mold.
On the other hand, on the molten steel surface around the immersion nozzle, the flow from the short sides of the left and right molds toward the center of the mold collides, and the molten steel follows the floating of the inert gas such as Ar blown into the immersion nozzle to prevent the adhesion of alumina. Since it flows, the flow direction is not constant on the surface of the molten steel around the immersion nozzle, and the flow is complicated.

In FIG. 1, the flow direction of the molten steel surface in the mold is such that the direction from the short sides of the left and right molds toward the center of the mold is defined as the positive direction of the flow, and the opposite direction is defined as the negative direction. Is shown in FIG. As is clear from FIG.
If the absolute value of the flow velocity exceeds 0.3 m / sec, the quality deteriorates. Therefore, in the present invention, the flow velocity values of the molten steel flow velocity measuring devices on both sides of the immersion nozzle are in directions symmetric with respect to the immersion nozzle,
By controlling the magnetic field strength and the moving magnetic field direction of the moving magnetic field applying device so that the absolute value range of the flow velocity value is 0.3 m / sec or less, the flow velocity of the molten steel on the surface of the molten steel in the mold is controlled on both sides of the immersion nozzle. , The vortex and swelling do not occur on the surface of the molten steel in the mold, the flow of the molten steel in the mold is stable, and the entrainment of mold powder can be prevented.
High quality slabs can be obtained.

FIG. 6 shows a conventional casting condition in which a moving magnetic field applying device is not controlled by a rectangular mold. When the surface flow velocity of molten steel is measured on the left and right sides of the immersion nozzle, the difference between the surface flow velocity of the left and right molten steels and the rolling to a thin steel plate are performed. It shows the relationship of the quality defects confirmed by the above. The surface velocity of the molten steel is 1/4 of the casting width of the slab.
Was measured at a symmetrical left and right position separated from the immersion nozzle by the distance of 浸漬 to the short side of the mold. As is apparent from this, if the difference between the absolute values exceeds 0.05 m / sec, the quality deteriorates.

As shown in FIG. 8, the difference between the surface velocities of the molten steel and the surface velocities of the molten steel are controlled by a moving magnetic field applying device so that the absolute value of the surface velocities of the molten steel is within a range of 0.3 m / sec or less. It was found that the quality was further stabilized by making the surface flow velocity difference of 0.05 m / sec or less.

However, this optimum value varies depending on the type of steel.
Some steel types are wider than this range, but at least within this range, all steel types are satisfied.

If the surface velocity of the molten steel in the mold is close to the immersion nozzle, the surface velocity of the molten steel is irregular and cannot be constant, and cannot be a representative value of the surface velocity of the molten steel. The discharge flow from the immersion nozzle fluctuates greatly under the influence of the upward flow colliding with the short side mold, and cannot be a representative value of the surface velocity of the molten steel. Therefore, the position of the molten steel anemometer should be set at a distance of 1/6 to 1/3 of the casting width from the immersion nozzle, and preferably measured near the distance of 1/4 of the casting width where the fluctuation of the molten steel surface flow rate is small. Is preferred.

In order to control the flow of molten steel as described above, it is desirable that the moving magnetic field applying device can be independently controlled on the left and right sides of the immersion nozzle.

[0019]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view showing the vicinity of a continuous casting machine mold according to an embodiment of the present invention. 1 is the long side of the mold, 2 is the short side of the mold,
3 and 5 are moving magnetic field applying devices on the left, 4 and 6 are moving magnetic field applying devices on the right, 7 is a surface velocimeter for molten steel on the left, 8 is a surface velocimeter for molten steel on the right, 9 is an immersion nozzle, and 10 is molten steel. The flow of molten steel just below the surface is shown. The moving magnetic field applying devices 3 and 5 on the left and the moving magnetic field applying devices 4 and 6 on the right can independently control the moving magnetic field direction and the magnetic field strength. N and S of the moving magnetic field applying devices 3, 5, and 4 and 6 indicate magnetic poles, and the moving magnetic field applying devices face the same pole in the thickness direction of the mold.

The magnetic flux generated from the magnetic pole moves at a constant speed from the short side of the mold toward the immersion nozzle. Since the magnetic flux is not a direct current but an alternating current, the maximum magnetic flux density moves from the short side of the mold toward the immersion nozzle, and then the maximum magnetic flux in the opposite direction moves from the short side of the mold toward the immersion nozzle. The moving magnetic field moving from the short side of the mold toward the immersion nozzle is
An induced current is generated in the molten steel and serves as a driving force for moving the molten steel in the moving magnetic field direction. The magnetic field strength is controlled by increasing or decreasing the current supplied to the moving magnetic field applying device, thereby increasing or decreasing the magnetic flux density.

The discharge flow of the molten steel cast from the tundish (not shown) into the mold through the immersion nozzle 9 collides with the short side 2 of the mold and separates into a downward flow and an upward flow. It rises along the short side 2 and flows toward the direction of the immersion nozzle from the short side of the mold on the surface of the molten steel in the mold. Further, an inert gas such as Ar blown into the immersion nozzle 9 to prevent the adhesion of alumina starts floating in the molten steel toward the short side 2 of the mold as soon as passing through the discharge port of the immersion nozzle 9. With the floating of the inert gas, the molten steel also forms a flow toward the mold short side 2.

As described above, on the surface of the molten steel in the mold, the flow from the short side 2 of the mold toward the immersion nozzle 9 and the immersion nozzle 9
And the flow toward the mold short side 2 cancels out, and at the measurement position of the surface flow velocity, the difference is measured as the flow velocity in the direction of the flow with the larger flow velocity.

This flow is measured by the molten steel flow velocity measuring devices 7 and 8, and the flow direction is symmetrical with respect to the immersion nozzle, and the absolute value of the measured flow velocity value is 0.3 m / sec or less. More preferably, the difference between the left and right flow rates is 0.0
In the control flow shown in FIG.
The magnetic field strength of the moving magnetic field applying device and the moving magnetic field direction are controlled.

[0025]

This embodiment is an example in which a slab of low carbon aluminum killed steel is cast. The cast slab is 1200mm wide,
At a thickness of 220 mm, the casting speed is 1.0 m / min to 2.0 m / min, and the frequency of the moving magnetic field applying device is 0.5 Hz at a casting speed of 1.0 m / min and 1 at a casting speed of 1.5 m / min. 2.0Hz, casting speed 2.0m /
There are three conditions of 2.0 Hz in min. That is, the magnetic flux density is 0.036T at the maximum at a casting speed of 1.0 m / min.
The test was performed under the conditions of a maximum of 0.042 T at 5 m / min and a maximum of 0.046 T at 2.0 m / min. The frequency of the moving magnetic field applying device is a moving magnetic field applying device that can be varied from 0.5 Hz to 10.0 Hz. The position of the molten steel flow meter was symmetrical at a distance of 300 mm from the immersion nozzle.

The comparative example was carried out by casting slabs of the same size at the following levels. The frequency of the moving magnetic field applying device is 0.5 Hz at a casting speed of 1.0 m / min, the magnetic flux density is constant at 0.036 T, and the casting speed is 1.5 m / m.
Three conditions of 1.0 Hz in, constant magnetic flux density of 0.042 T, casting speed of 2.0 Hz at 2.0 m / min, and constant magnetic flux density of 0.048 T were performed.

The molten steel surface anemometer used in the present invention generates a magnetic field perpendicular to the moving conductive object to be measured, and generates at least two magnetic field components perpendicular to the object to be measured. An AC magnetic field type flow velocity indicated by an apparatus for measuring the flow velocity of an object to be measured based on a differential signal of at least two magnetic fields detected at different positions in the moving direction of the object and at a position where the magnetic field is symmetric. It is a sensor.

FIG. 4 shows the measured values of the flow velocity on the molten steel surface measured simultaneously on the left and right sides in this embodiment. As shown in FIG. 4, it can be seen that the absolute values of the left and right molten steel surface flow velocities are controlled to 0.3 m / sec or less and the flow velocity difference is controlled to 0.05 m / sec or less.

As shown in FIG. 5, in the embodiment of the present invention, the index of the quality defect in the cold rolled coil as the final product is reduced by 70% as compared with the comparative example. Further, the width of the index of the quality defect was narrowed, and a slab having good surface properties was obtained.

[0030]

According to the present invention, the same poles of the magnetic poles are opposed to the outer wall of the mold parallel to the discharge port of the immersion nozzle on both sides of the immersion nozzle, and the magnetic field is moved in the width direction of the mold. Controlling the magnetic field strength and moving magnetic field direction of the moving magnetic field applying device by arranging the moving magnetic field applying device and the molten steel flow velocity measuring device arranged on both sides of the immersion nozzle and measuring the flow velocity near the surface of the molten steel in the mold in a non-contact manner And the molten steel flow on the molten steel surface in the mold
In the direction symmetrical with respect to the immersion nozzle, the range of the flow velocity value is set to 0.
By setting the speed to 3 m / sec or less and the speed difference between the left and right to 0.05 m / sec or less, meandering of the molten steel flow can be prevented, and a high-quality slab can be stably manufactured.

[Brief description of the drawings]

FIG. 1 is a plan view showing a relationship between a moving direction of a magnetic field near a molten steel surface, a magnetic flux density, and a flow of molten steel according to an embodiment of the present invention.

FIG. 2 is a plan view showing a relationship between a moving direction of a magnetic field near a molten steel surface, a magnetic flux density, and a flow of molten steel in a conventional example.

FIG. 3 is a control flowchart of the embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a flow velocity value on the left molten steel surface and a flow velocity value on the right molten steel surface in the example of the present invention.

FIG. 5 is a diagram showing a relationship between an example and a conventional example and a quality defect index.

FIG. 6 is a diagram showing a conventional relationship between a flow velocity difference between left and right molten steel surfaces and a quality defect index.

FIG. 7 is a diagram showing the relationship between the flow velocity value on the right molten steel surface, the flow velocity value on the left molten steel surface and quality defects according to the present invention.

FIG. 8 is a diagram showing the relationship between the flow velocity value on the right molten steel surface, the flow velocity value on the left molten steel surface, and quality defects when the flow is controlled according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 Mold long side 2 Mold short side 3, 5 Left moving magnetic field applying device 4, 6 Right moving magnetic field applying device 7 Left molten steel surface velocimeter 8 Right molten steel surface velocimeter 9 Immersion nozzle 10 Flow of molten steel

────────────────────────────────────────────────── ─── Continued on the front page (72) Noriko Kubo, Inventor Nippon Kokan Co., Ltd. 1-2-1, Marunouchi, Chiyoda-ku, Tokyo (56) References JP-A-7-241649 (JP, A) JP-A-6 -604 (JP, A) JP-A-5-329595 (JP, A) JP-A-63-60056 (JP, A) JP-A-4-319905 (JP, A) JP-A-7-24559 (JP, A) JP-A-7-112252 (JP, A) JP-A-9-168847 (JP, A) JP-A-8-187557 (JP, A) JP-A-4-9255 (JP, A) 155515 (JP, A) JP-A-9-47853 (JP, A) JP-A 8-327648 (JP, A) JP-A 8-197196 (JP, A) JP-A 8-141711 (JP, A) JP-A-8-108257 (JP, A) JP-A-7-290214 (JP, A) JP-A-5-38559 (JP , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/115 B22D 11/04 311 B22D 11/16 104

Claims (3)

(57) [Claims] In a continuous casting method of steel for controlling the flow of molten steel in an electroforming mold by an electromagnetic force, the same polarity of a magnetic pole is sandwiched between outer sides of the casting mold on both sides of an immersion nozzle and parallel to a discharge port of the immersion nozzle. Using a moving magnetic field applying device that opposes and moves the magnetic field in the width direction of the mold, and a molten steel flow velocity measuring device that is arranged on both sides of the immersion nozzle and measures the flow velocity near the molten steel surface in the mold in a non-contact manner, the immersion nozzle The flow velocity direction measured by the molten steel flow velocity measurement device on both sides is symmetric with respect to the immersion nozzle, and the absolute value of the measured flow velocity value is 0.3 m.
A continuous casting method for steel, characterized in that the magnetic field strength and the moving magnetic field direction of the moving magnetic field applying device are controlled so as to be not more than / sec. 2. A method for controlling a magnetic field intensity and a moving magnetic field direction of a moving magnetic field applying device such that a difference between flow speed values of molten steel flow speed measuring devices disposed on both sides of an immersion nozzle is 0.05 m / sec or less. The continuous casting method for steel according to claim 1, wherein: 3. The continuous casting method for steel according to claim 1, wherein the moving magnetic field applying devices can be independently controlled on the left and right sides.