JPH08224642A - Continuous casting method for steel - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a method for easily shortening the component mixing region in continuous casting of different steel types. [Structure] By using a pair or a plurality of pairs of pressure rolls arranged below the mold and above the solidification completion position of the molten steel, the joint portion of the molten steel of the previous charge and the molten steel of the subsequent charge is Until the pressure roll is reached, a reduction at a speed commensurate with the solidification shrinkage speed of the previously charged unsolidified molten steel contained in the solidification shell is locally applied to the solidified slab. Alternatively, or additionally, when the molten steel seam passes through the pressure roll, a reduction of less than or equal to the solidification shrinkage amount of the molten steel of the previous charge contained in the solidification shell is applied to the solidified slab. To do. It is more effective to use an electromagnetic brake together or a shield plate together. .

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 different types of steel in which molten steel having a previous charge is cast, and subsequently, molten steel having a different charge from the molten steel of the previous charge is subsequently cast.

[0002]

2. Description of the Related Art Continuous casting in which molten steels of a plurality of ladles are sequentially poured into a mold of the same continuous casting machine is widely practiced.
However, in the continuous casting of different steel types, in which the molten steel of the previous charge is poured and then the molten steel of the subsequent charge is cast, the composition is different from that of the molten steel of the previous charge. A component mixing zone is generated at. There is a problem that the slab of the portion corresponding to this component mixing region is scrapped or its use is limited because the components are uncertain.

When the injection speed is lowered or the injection is temporarily interrupted at the seam, the depth of penetration of the molten steel in the subsequent charge becomes shallow, and therefore the component mixing region becomes short. However, when the injection speed is extremely reduced or temporarily suspended, for example, the traveling speed of the slab in the water injection cooling zone of the continuous casting device also decreases or stops, so that the residence time in the water injection cooling zone is long. Therefore, it will receive an excessive amount of water cooling than other parts. This impairs the uniformity of the quality of the cast slab. In addition, the extreme decrease or suspension of the injection speed hinders smooth operation of the bending device and the slab drawing device.

Therefore, in order to shorten the component mixing area, a steel shielding plate for preventing the molten steel in the mold from moving in the vertical direction is charged into the joint portion at the end of the injection of the molten steel of the previous charge,
The method of injecting molten steel of the later charge on it is widely performed. However, as will be described in detail later, the uncharged molten steel of the previous charge contained in the solidification shell at the start of the injection of the molten steel of the subsequent charge continues to solidify and shrink even after the shield plate is charged. . Therefore, only by inserting the shield plate, a large number of contraction holes are generated below the shield plate. Further, there is a problem that the molten steel of the later charge is sucked below the shielding plate due to the solidification shrinkage of the unsolidified molten steel of the previous charge, and a component mixing region is generated under the shielding plate.

In Japanese Patent Application No. 5-96526, after the start of injection of molten steel of the later charge, a support roll group in the secondary cooling zone is used to roll down the strand formed of the molten steel of the previous charge in the thickness direction. A device for doing so is described. FIG. 3 is an explanatory view thereof, 1 is a seam, 2 is a mold, 3 is unsolidified molten steel of the previous charge contained in the solidified shell, 4 is solidified shell produced from the molten steel of the previous charge, and 5 is 10
It is a pair of reduction rolls.

The idea of this process is that, in order to keep the shape of the seam portion 1 constant, a reduction commensurate with the solidification shrinkage at each roll position is successively given by each roll. By doing so, the component mixing range is shortened. However, according to this idea, from the time when the seam portion 1 is generated until the solidification of this portion is completed, it is necessary to control the reduction to compensate for the solidification contraction of each portion by each roll, and the operation is It becomes extremely complicated. Further, as shown in FIG. 3, when the reduction rolls could not be arranged in all the parts from the lower part of the mold to the solidification completion position, the intended effect was often not obtained.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of easily shortening the component mixing area in continuous casting of different steel types.

[0008]

The continuous casting method for steel according to the present invention comprises: (1) casting a molten steel having a previous charge, and subsequently casting a molten steel having a different charge from the molten steel of the previous charge. In a continuous casting method of steel by continuous casting of different steel types, by using a pair of or a plurality of pairs of pressure rolls arranged below the mold and above the completion position of the molten steel, the molten steel of the previous charge is used. And until the joint portion of the molten steel of the later charge reaches the pressure roll, it is commensurate with the solidification shrinkage rate of the unsolidified molten steel of the previous charge contained in the solidification shell at the start of injection of the later molten steel. With a reduced speed,
It is characterized in that it is locally applied to the slab that is solidifying.

Alternatively, (2) in a continuous casting method of steel by continuous casting of different steel types, in which after casting the molten steel of the previous charge, subsequently casting molten steel of the subsequent charge having a different composition from the molten steel of the previous charge, By using a pair or a plurality of pairs of pressure rolls arranged below the mold and above the solidification completion position of the molten steel, the joint portion of the molten steel of the previous charge and the molten steel of the subsequent charge is pressed. In addition to the reduction of the speed corresponding to the solidification shrinkage rate of the previously charged unsolidified molten steel contained in the solidified shell at the time of starting the injection of the molten steel later until reaching the roll, the seam portion When passing through a pressure roll, a reduction of less than or equal to the solidification shrinkage amount of the uncharged molten steel of the previous charge contained in the solidification shell below the seam is locally applied to the solidified slab. Characterized by giving .

At this time, (3) using a continuous casting apparatus in which an electromagnetic brake for forming a direct-current magnetic field in a direction traversing the molten steel in the mold is arranged in the mold, the subsequent start of casting of the molten steel is performed under the formation of the direct-current magnetic field. Should be done in.

[0011]

FIG. 1 is an explanatory view of the present invention, in which 1 is a seam portion, 2 is a mold, and 3 (satin finish) is a previous charge contained in the solidification shell when the injection of molten steel for the later charge is started. Unsolidified molten steel, 4 is solidified shell, 6 is a pair of pressure rolls, 7
Is the molten steel of the later charge. In the present invention, a pair of pressure rolls 6 are arranged below the mold 2 and above the solidification completion position e of the molten steel. The molten steels 3, 7, the solidified shell 4, and the solidified slab are pulled out in the direction of arrow 9.

First, the first invention of the present application will be described with reference to FIG.

The unsolidified molten steel 3 within the range connecting a, b and e in FIG. 1 is drawn a and b after the time t ₁ has elapsed.
Moves to a ', b', solidifies and contracts, and the volume contracts from the range connecting a, b, e to the range connecting c, d, e. That unsolidified molten steel 3 is a during the time t ₁ ',
The volume decreases by the volume V ₁ shown by the range connecting b ′, d, and c.

In the first invention of the present application, the solidification shrinkage rate of the unsolidified molten steel 3 during the time t ₂ until the joint portion 1 of the molten steel of the preceding charge and the molten steel of the subsequent charge reaches the pressure roll 6. A reduction at a speed commensurate with (ΔV / Δt) is applied to the solidified slab by using a pair of pressure rolls 6 or a plurality of pairs of rolls adjacent thereto.

As described above, in the present invention, the unsolidified molten steel 3
Since the reduction is performed at a speed commensurate with the solidification contraction speed of the molten steel, the shapes of the molten metal surfaces a and b of the seam portion 1 are unsolidified molten steel 3
Is not dented even when it solidifies and contracts, and is maintained in a smooth a ", b" shape when it reaches the pressure roll 6. Therefore, as shown in FIG. 4 (a), the solute concentration distribution in the seam in the cast piece is linear, and as shown in FIG. 4 (b), insertion in the casting direction, which is observed when no reduction is performed, is prevented. To be done. Therefore, the component mixing area can be shortened.

In the present application, the reduction is a speed commensurate with the solidification shrinkage speed of unsolidified molten steel, but the commensurate range is from 0.5 × (ΔV / Δt) to 1.5 × (ΔV in operation. / Δt)
It is the range of, and by controlling the reduction in this range,
The effect of significantly shortening the component mixing range can be obtained.

In the present invention, V, t and (ΔV / Δt) can also be calculated using the solidification rate formula of molten steel, for example, D = K ₁ t ^1/2 + K ₂ . However, since K ₁ and K ₂ vary greatly depending on operating conditions such as the temperature of molten steel and the strength of water cooling, it is preferable to set these values based on the operating record.

Next, the second invention of the present application will be described with reference to FIG. As described above, when the time t ₂ elapses, the joint portion 1 (a, b) reaches the pressure roll 6 and a,
b, reaches a ", b". Then, during this time t ₂ , the molten steel in the hatched portion completes solidification. On the other hand, the previously charged unsolidified molten steel in the solidified shell below the joints a and b is not completely solidified, and f,
It remains in a built-in state within the range connecting e and g.

The unsolidified molten steel of the preceding charge is f, due to solidification contraction until the joint portion is completely solidified.
The volume decreases by the volume V ₂ shown by the range connecting g, i, and h. Therefore, there is no means for adjusting the volume change of V ₂ after the joint portions a ″ and b ″ have passed the portion of the pressure roll 6. The second invention of the present application uses the pressure roll 6 when the joint portions a ″ and b ″ pass through the portion of the pressure roll 6.
It is intended to apply a reduction of not more than an amount commensurate with ₂ to the solidified slab. By applying this reduction, the straight lines f and g become the dotted lines f and j. Although it becomes convex like g, it approaches f and g by the time solidification is completed.

In the present invention, the reduction amount at this time is V ₂ or less, but it is preferable to select it in the range of 0.5 × V _{2 to} V _{2 in} operation. As described above, according to the second invention of the present application, since the solidification shrinkage amount of the uncharged molten steel of the previous charge after the joint portions a ″, b ″ have passed through the portion of the pressure roll 6 can be adjusted, The length of the component mixing zone becomes even shorter.

The third invention of the present application will be described. Here, the electromagnetic brake 8 is also used. FIG. 2 is an explanatory view of this electromagnetic brake, 2 is a mold, 10 is a molten steel injection nozzle, 11 is a magnet of the electromagnetic brake, and 12 is a static magnetic field generated by the magnet 11. First, a static magnetic field is formed in a direction across the molten steel in the mold to inject the molten steel. When molten steel is injected into this static magnetic field, a Lorentz force that impedes penetration into the molten steel beyond the static magnetic field acts on the injection flow of the molten steel that attempts to penetrate below the static magnetic field beyond the static magnetic field.

As a result, the depth of penetration of the injection flow into the molten steel is significantly reduced. Therefore, in carrying out the present invention as described above, when a static magnetic field is formed and molten steel of the later charge is injected, the molten steel of the later charge penetrates into the molten steel of the earlier charge, resulting in a shallow depth. The mixing of the molten steel of the second charge and the molten steel of the later charge is suppressed, and the component mixing region becomes further shorter.

In the invention of the present application, a known shield plate may be used in combination. Here, the solidification shrinkage amounts V ₁ and V ₂ of the molten steel of the previous charge below the shield plate are reduced by the pressure roll 6. Adjusted by Therefore, in the present invention, the conventional problem that a large number of contraction holes are generated in the slab generated from the molten steel below the shielding plate, and the conventional method that the molten steel of the later charge is sucked below the shielding plate It is possible to effectively prevent the occurrence of problems.

[0024]

【Example】

(Example 1) When continuously casting dissimilar steel types using the continuous casting apparatus as shown in FIG. 1, low carbon steel (carbon concentration 0.04%) was first, and then medium carbon steel. (Carbon concentration 0.15%) was cast. The casting speed is 1.3 m / min. The mold size is 200 cm (width) × 25 cm (thickness).
The solidification constant under these conditions is 23 mm / min ^1/2 .

Subsequent to finishing the injection of the low carbon steel into the mold, the injection of the medium carbon steel was started. An electromagnetic brake as shown in FIG. 2 was provided in the mold to suppress the mixing of both molten steels in the mold. As shown in FIG. 1, the slab was rolled down by a roll which was placed 18 to 24 m below the meniscus and whose interval could be controlled by hydraulic pressure. The rolling was performed in the pattern shown in FIG. 5 in order to compensate the solidification shrinkage amount of the molten steel pool below the seam position. As a result, if no reduction is performed, 1.
After 53 meters, it became possible to reduce the amount of molten steel drawn in to 0.32 meters.

(Embodiment 2) When continuously casting different steel grades using the continuous casting apparatus as shown in FIG. 1, low carbon steel (carbon concentration: 0.05%) was first tested, Medium carbon steel (carbon concentration 0.17%) was cast. Casting speed is 1.3
m / min. Mold size is 200 cm (width) x 25 cm
(Thickness). The coagulation constant under these conditions is 23 mm /
It is ^1/2 a minute.

Subsequent to finishing the injection of the low carbon steel into the mold, the injection of the medium carbon steel was started. An electromagnetic brake as shown in FIG. 2 was provided in the mold to suppress the mixing of both molten steels in the mold. As shown in FIG. 1, the slab was rolled down by a roll which was placed 18 to 24 m below the meniscus and whose interval could be controlled by hydraulic pressure. The rolling was performed in the pattern shown in FIG. 6 in order to compensate the solidification shrinkage amount of the molten steel pool below the seam position. As a result, it was possible to reduce the drawing amount of molten steel after lapping to 1.5 m after the reduction of 1.53 m without the reduction.

[0028]

According to the present invention, since the solidification shrinkage of molten steel is locally adjusted by using a pressure roll, as described in the prior art, when the reduction is performed by all the support rolls in the secondary cooling zone. Compared with, the rolling operation is extremely easy. Therefore, according to the present invention, the component mixing region can be shortened by a simple method in continuous casting of different steel types.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the present invention.

FIG. 2 is an explanatory diagram of an electromagnetic brake used in the present invention.

FIG. 3 is an explanatory view of a known pressing roll.

FIG. 4 is a diagram showing a solute concentration distribution in a seam portion of a cast slab, and FIG. 4 (a) shows a case where a reduction as in the present invention is performed,
Is the case where no reduction is performed.

FIG. 5 is a diagram showing a pattern of reduction in Example 1.

FIG. 6 is a diagram showing a pattern of reduction in Example 2.

[Explanation of symbols]

1: seam part, 2: mold, 3: unsolidified molten steel of previous charge, 4: solidified shell of molten steel of previous charge,
5: Known pressing roll, 6: Pressure roll of the present application,
7: Molten steel of later charge, 8: Electromagnetic brake, 9:
Drawing direction of cast slab, 10: Molten steel injection nozzle, 1
1: magnet, 12: static magnetic field.

Claims (3)

[Claims] 1. In a continuous casting method of steel by continuous casting of different steel types, in which a molten steel of a previous charge is cast, a molten steel of a subsequent charge having a different composition from that of the molten steel of a previous charge is subsequently cast, And using a pair or a plurality of pairs of pressure rolls arranged above the solidification completion position of the molten steel until the joint between the molten steel of the first charge and the molten steel of the second charge reaches the pressure roll. In the meantime, at the time of starting the injection of the later molten steel, the reduction of the speed corresponding to the solidification shrinkage rate of the unsolidified molten steel of the previous charge built in the solidification shell,
A continuous casting method for steel, which is locally applied to a solidified slab. 2. In a continuous casting method of steel by continuous casting of different steel types, in which the molten steel of the previous charge is cast and subsequently the molten steel of the subsequent charge having a different composition from that of the molten steel of the previous charge is continuously cast. And using a pair or a plurality of pairs of pressure rolls arranged above the solidification completion position of the molten steel until the joint between the molten steel of the first charge and the molten steel of the second charge reaches the pressure roll. During this period, when the subsequent injection of molten steel is started, the seam passes through the pressure roll in addition to the reduction of the speed corresponding to the solidification contraction speed of the uncharged molten steel of the previous charge contained in the solidification shell. In this case, a reduction of not more than an amount corresponding to the solidification shrinkage amount of the uncharged solidified molten steel of the previous charge contained in the solidified shell below the seam portion is locally applied to the solidified slab. The continuous casting method for steel. 3. A continuous casting apparatus in which an electromagnetic brake that forms a direct current magnetic field in a direction that traverses molten steel in the mold is arranged in the mold, and the subsequent start of casting of molten steel is performed under the formation of the direct current magnetic field. A continuous casting method for steel according to claim 1 or 2, characterized in that