JPH10263763A - Method for controlling fluidity in continuously casting strand and device for controlling fluidity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shift fine inclusion upward to the upper part of a braking zone, to reduce the development of product defect caused by the fine inclusion and to improve the quality degradation by making small of magnetic flux density near the short sides of a mold in comparison with that near the center in the width direction and giving the braking force to molten metal flowed down from a nozzle. SOLUTION: A pouring nozzle 2 is arranged at the upper part of the mold 1 having the rectangular cross section. The lower end part of the pouring nozzle 2 is arranged in the condition of dipping into the molten metal 3 in the mold 1. An electromagnetic coil 4 constituting a main part of the electromagnetic brake is arranged to the outer periphery of the mold 1 approaching the lower end part of the pouring nozzle 2. The DC magnetic field is generated in the thickness direction of the mold 1 by impressing DC power to the electromagnetic coil 4 and the upward brake force is generated to the poured stream 8 from the pouring nozzle 2 to foam the stream as the straightening. The magnetic flux density near the short sides of the mold 1 is made to lower that near the center in the width direction to form the rising streams 9a, 9b near the short sides to float up again the fine inclusion flowed in a strand through this passage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling a flow in a continuous casting strand for controlling a molten steel flow in the strand in a continuous casting apparatus by using an electromagnetic coil.

[0002]

2. Description of the Related Art In a continuous casting process, when a molten metal in a tundish is poured into a mold, the flow of the molten metal fluctuates due to the opening degree and the casting speed of a sliding nozzle installed between the immersion nozzle and the tundish. In the case of occurrence of oxidized inclusions on the inner wall of the immersion nozzle, the symmetry of the velocity distribution of the molten metal flowing inside the immersion nozzle deteriorates, and the velocity distribution of the molten metal discharged from the immersion nozzle Even worse symmetry. As a result, a drift phenomenon in which symmetry of the molten metal in the long and short sides of the mold is lost in the mold occurs.

When the drift occurs, the non-metallic inclusions in the molten metal also reach deep inside the mold as the molten metal discharged from the immersion nozzle reaches deep inside the mold as compared with the case where there is no drift. I do. Most of the nonmetallic inclusions float on the surface of the molten metal, but some do not float and are trapped inside the slab, which induces product defects.

As a means for controlling the drift of molten metal in a mold, a method has been proposed in which an electromagnetic brake is provided in the mold to control the molten metal. That is, a magnetic field is applied to the molten metal discharged from the nozzle by energizing the electromagnetic coil, and the discharge flow is decelerated to reduce the penetration depth. Specific examples thereof include PCT International Publication No. WO95 / 26243 and Japanese Patent Application No. 6-50873.

[0005] PCT International Publication No. WO 95/26243
In the method described in the above, an electromagnetic coil is placed in a mold, and an electric field (or magnetic flux) is applied by the electromagnetic coil so that the meniscus flow rate on the surface of the molten steel is in the range of 0.20 to 0.40 m / sec. Is controlling. This allows
Uniform injection amount control in the width direction becomes possible.

In the method disclosed in Japanese Patent Application No. 6-50873, a DC magnetic field having a uniform magnetic flux density in the width direction of a rectangular cross-section mold is applied in the thickness direction of the mold, and a braking force is applied to the injection flow to continuously apply the braking force. In performing casting, the molten metal injection flow from the injection nozzle is discharged flat and downward, and the flow below the coil installed below the discharge port of the injection nozzle is rectified. By this rectification, intrusion of inclusions into the interior can be reduced, and generation of defects due to inclusions can be prevented.

[0007]

However, in the above-mentioned PCT International Publication No. WO95 / 26243, a rapid flow occurs due to the electromagnetic brake near the short side of the rectangular cross-section mold, and a braking leak occurs. That is, as shown in the mold plan view of FIG. 4A and the front sectional view of FIG.
From the relationship between the injection flow discharged at an angle to the short side from the discharge port of No. 1 and the DC magnetic field from the electromagnetic coil 12, the induced current wraps around the short side of the mold, and the acceleration force 13
Acts downward, so that the braking effect is reduced as shown in FIG. As a result, non-metallic inclusions (alumina-based inclusions) riding on the nozzle injection flow near the short side penetrate deep into the strand pool, causing product defects.

In Japanese Patent Application No. 6-50873,
Although the problem of poor braking is eliminated because the flow is made uniform, there is no place (path) for re-emerging micro-inclusions that have flowed into the strand, and they remain trapped below the electromagnetic coil. Cause product defects.

The present invention has been made in view of the above problems, and has as its object to provide a flow control method in a continuous casting strand that can reduce the amount of inclusions below an electromagnetic brake portion. I have.

[0010]

According to a first aspect of the present invention, there is provided a method for injecting molten metal downward from an injection nozzle into a mold having a rectangular cross section. The molten metal flow control method and apparatus for applying a predetermined braking force to an injection flow of molten metal from the injection nozzle by a magnetic force of an electromagnetic coil disposed on the outer periphery of the mold or in a mold wall, And the magnetic flux density in the vicinity of the short side is smaller than that in the vicinity of the center in the width direction.

According to the method and the apparatus, the electromagnetic coil exhibits a braking effect when operating as an electromagnetic brake, and also forms a passage near the short side of the mold to re-emerge minute inclusions flowing into the strand. The fine inclusions rise with the rising flow of the molten metal and move to the upper part of the braking region. As a result, product defects caused by minute inclusions trapped in the strand are reduced, and the quality of the product can be improved.

A specific method and apparatus for realizing the object of the present invention according to the present invention is such that when the strand width is W ₁ and the formation width of the magnetic flux density is W _2. , 0.05 (m) ≦ W ₂ ≦ 0.25W ₁ (m) is satisfied and the magnetic flux density other than near the short side is B ₁ , and the magnetic flux density near the short side is B ₂ , 0.3 ≦ (B ₂
/ B ₁ ) ≦ 0.7.

According to this method, in addition to the electromagnetic brake functioning effectively, a passage for re-emerging minute inclusions flowing into the strand is reliably formed, so that the quality of the product can be improved. .

[0014]

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

FIG. 1 is an explanatory diagram showing the principle of the flow control method according to the present invention. FIG. 2 is a schematic configuration diagram of a continuous casting facility to which the flow control method of the present invention is applied.

As shown in FIG. 2, an injection nozzle 2 connected to a tundish (not shown) is provided above a mold 1 having a rectangular cross section. The lower end of the injection nozzle 2 is disposed so as to be immersed in the molten metal 3 in the mold 1. On the outer periphery of the mold 1 (or in the inner wall of the mold) close to the lower end of the injection nozzle 2, an electromagnetic coil 4 constituting a main part of the electromagnetic brake is installed.

When a DC current is applied to the electromagnetic coil 4, as shown in FIG. 1A, when a DC magnetic field 5 is generated in the mold thickness direction over the entire mold width direction, Fleming's left-hand rule is used. An induced current 6 is generated in the width direction of the mold. Then, an upward braking force 7 is generated by Fleming's right hand rule, and the injection nozzle 2 is generated by the braking action.
Is rectified.

As described above, in this state, Japanese Patent Application No.
As described in Japanese Patent No. 50873, there is no place (path) for re-emerging minute inclusions flowing into the strand, and the fine inclusions remain captured below the electromagnetic coil. Therefore, in the present invention, as shown in FIG. 1B, the magnetic flux density in the vicinity of the short side is lower than that in the vicinity of the center in the width direction in order to form an upward flow near the short side. The specific values are as follows.

When the strand width is W ₁ (m), the width of the low magnetic flux density portion is W ₂ (m), the magnetic flux density other than the short side is B ₁ , and the magnetic flux density of the short side is B ₂ , 0.3 ≦ (B ₂ / B ₁ ) ≦ 0.7 0.05 ≦ W ₂ ≦ 0.25W ₁ Here, when B ₂ / B ₁ is 0.3 or less, the injection flow 8 (discharge flow) bypasses the magnetic field zone, and the braking effect is not formed. If the ratio is 0.7 or more, it is difficult to obtain the effects of the present invention. Further, W _{2 is set} to 0.05
If it is shorter than m, the length of the nonmetallic inclusions excluding the solidified shell becomes shorter. If W ₂ is longer than 0.25 × W ₁ (m), it is difficult to obtain the effects of the present invention.

As described above, by reducing the magnetic flux density applied to the short side of the mold 1, as shown in FIG.
a, 9b are formed, and the fine inclusions flowing into the strand through this path re-emerge. Therefore, it is possible to reduce product defects caused by the capture of the minute inclusions.

The present inventors have tried to control the flow of molten metal under the following conditions.

[Target metal] Low-carbon aluminum killed steel [Specifications of casting equipment] Casting strand width (W ₁ ): 1,500 mm Cast slab thickness: 250 mm Casting speed: 2 m / min Injection nozzle: Downward straight nozzle Magnetic field (electromagnetic brake) (Center position): 500 mm from the meniscus. As a comparative example, when the electromagnetic brake was not provided (test I), the electromagnetic brake was provided, but the magnetic flux density was uniform over the entire area (test J), and FIG. In the three cases where the magnetic flux density near the short side was reduced as described above (test K), the internal non-metallic inclusion index (the part solidified below the electromagnetic brake area) was measured.
Was obtained.

As is apparent from FIG. 3, in the test J according to the prior art, the internal nonmetallic inclusion index is reduced to about １ ／ of the test I without the electromagnetic brake. However, Test K according to the present invention has a further lower internal non-metallic inclusion index than Test J.

As described above, according to the present invention, the minute inclusions that have flowed into the strand do not remain trapped below the electromagnetic coil, so that re-emerging is facilitated. Therefore, it is possible to reduce product defects caused by capturing minute inclusions.

[0025]

As described above, according to the present invention as set forth in claims 1 and 2, when a magnetic braking force is applied to the molten metal from the injection nozzle using an electromagnetic coil, the vicinity of the short side of the mold is reduced. Since the magnetic flux density is made smaller than near the center in the width direction, product defects due to minute inclusions trapped in the strand are reduced, and the quality of the product can be improved.

The present invention described in claims 3 and 4 provides:
The magnetic flux density given by the electromagnetic coil is expressed by the relationship between the strand width W ₁ and the formation width W ₂ of the magnetic flux density near the short side, and the relationship between the magnetic flux density B ₁ other than near the short side and the magnetic flux density B ₂ near the short side. Since the predetermined value is set, a passage for re-emerging the minute inclusion flowing into the strand is reliably formed, and the quality of the product can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the principle of a flow control method according to the present invention.

FIG. 2 is a schematic configuration diagram of a continuous casting facility to which the flow control method of the present invention is applied.

FIG. 3 is a comparative explanatory diagram for comparing the effects of the present invention with those of the conventional art.

FIG. 4 is an explanatory view showing the reason why the electromagnetic braking effect is reduced near the short side of the rectangular cross-section mold.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Injection nozzle 3 Molten metal 4 Electromagnetic coil 5 DC magnetic field 6 Induction current 7 Braking force 8 Injection flow 9a, 9b Ascending flow

Claims (4)

[Claims] 1. A molten metal is injected downward from an injection nozzle into a mold having a rectangular cross section, and the molten metal is injected from the injection nozzle by the magnetic force of an electromagnetic coil disposed on the outer periphery of the mold or in the mold wall. In the method for controlling the flow of molten metal for applying a predetermined braking force to the continuous casting strand, wherein the magnetic flux density near the short side of the mold is made smaller than near the center in the width direction. Flow control method. 2. An injection nozzle for injecting molten metal downward into a mold having a rectangular cross section, an electromagnetic coil disposed on the outer periphery of the mold or in the mold wall, and In a molten metal flow control device that applies a predetermined braking force to an injection flow of molten metal, the magnetic flux density near a short side of the mold is controlled to be smaller than that near a center in a width direction. Flow control device in the continuous casting strand. 3. When the strand width is W ₁ and the width of the magnetic flux density is W ₂ , 0.05 (m) ≦ W ₂ ≦ 0.25
When the relationship of W ₁ (m) is satisfied and the magnetic flux density near the short side is B ₁ and the magnetic flux density near the short side is B ₂ , 0.3 ≦ (B ₂ / B ₁ ) ≦ 2. The method according to claim 1, wherein the relationship of 0.7 is satisfied. 4. When the strand width is W ₁ and the width of the magnetic flux density is W ₂ , 0.05 (m) ≦ W ₂ ≦ 0.25
When the relationship of W ₁ (m) is satisfied and the magnetic flux density near the short side is B ₁ and the magnetic flux density near the short side is B ₂ , 0.3 ≦ (B ₂ / B ₁ ) ≦ 3. The flow control device in a continuous casting strand according to claim 2, wherein the relationship is set so as to satisfy a relationship of 0.7.