JPH11347700A - Continuous casting method and continuous casting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a continuous casting method, with which the rolling reduction can be executed at thinner thickness than that with the conventional unsolidified rolling reduction method and a cast slab having good quality is obtd. SOLUTION: Just below a mold 1 having 120-50 mm thickness of the case slab at the outlet side, non-rolling reduction zone, which does non undergo the rolling reduction of 400-1000 mm, is provided. In the downstream side thereof, three groups of unsolidified rolling reduction rolls are provided. Further, on the downstream side thereof, there are provided four groups of semi-solidified rolling reduction rolls for executing the rolling reduction to the cast slab, in which the fluidity of molten steel at the center part thereof is eliminated before perfectly solidifying. After making the solidified shell grow to some degree in the cast slab having 120-50 mm thickness at the outlet side of the mold, the rolling reduction is executed in the unsolidified state, in which the molten steel is fluidized at the center part of the cast slab. Further successively, the rolling reduction is executed in the semi-solidified state, in which the fluidity of molten steel at the central part of the cast slab is eliminated but the perfect solidification is not yet developed, so as to make the thin cast slab having thickness <=40 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a continuous casting method and a continuous casting apparatus. The thin slab cast by the continuous casting machine is further thinly rolled by a group of rolling mills in the subsequent process and formed into a thin plate. The number of processes can be reduced, and equipment costs such as rolling equipment can be reduced. The present invention relates to a continuous casting method and a continuous casting apparatus for casting such a thin slab.

[0002]

2. Description of the Related Art When casting a thin cast piece with a continuous casting apparatus, it seems that the thickness of the mold should be reduced. However, the thickness of the mold is limited by the thickness of a nozzle for injecting molten steel.
It cannot be thinned without limit. In the type in which the casting mold has a thickness substantially parallel to the casting direction, if the thickness is less than 90 mm, stable casting becomes difficult. Therefore, there is a type in which the entrance side of the mold is kept thick and is drawn toward the exit side, and the exit side thickness is set to 120 to 50 mm.
Regardless of which mold is used, in order to make the slab thinner than the mold exit side thickness, conventionally, the unsolidified rolling method in which the molten steel is reduced while the molten steel is flowing in the slab drawn from the mold is used. (Conventional Example I).

[0003] However, under unsolidified pressure, each of the long sides is 2
Since the reduction must be completed before the two solidified shells are joined, the thickness of the slab that can be reduced under unsolidified pressure is limited by the growth amount of the solidified shell at the reduced position. In order to reduce the thickness of the slab, the rolling start position should be set immediately below the mold to complete the reduction while the solidified shell is thin. It affects the condition and causes breakage or surface cracking due to uneven solidification. In addition, if the amount of reduction per roll is increased so that the rolling completion point is on the upstream side, internal cracks occur, so the reduction amount is 10 mm per roll.
Below, the rolling completion point must be 1900 mm or more from the surface of the molten steel. Therefore, it is practically impossible to complete the reduction while the solidified shell is thin, and it is still impossible to continuously produce a sufficiently thin cast piece.

On the other hand, in a non-solidified region of a slab, a method in which the slab is guided only by a guide roll and no reduction is applied, and after the solidification is completed, the slab is largely reduced by using a large reduction roll is disclosed in Japanese Unexamined Patent Publication (Kokai) No. H8-08380.
No. 164460 (conventional example II). However, after the solidification is completed, even when a small amount of reduction is applied, a large reduction force is required, and the equipment cost increases, such as a large reduction mechanism or a large roll. In addition, problems such as cracks occurring in the slab during rolling due to a decrease in the corner temperature of the slab tend to occur, and the slab quality is reduced.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a continuous casting method and a continuous casting apparatus which can reduce the thickness even more than the conventional unsolidified rolling reduction method and have good slab quality. And

[0006]

According to the continuous casting method of the present invention, in order to produce a slab having a thickness of 40 mm or less in a continuous casting apparatus, a slab having a thickness of 120 to 50 mm on the mold exit side is formed into a solidified shell. After growing to some extent, it is lowered in the unsolidified state where the molten steel is flowing at the center of the slab, and subsequently, even in the semi-solid state where the flow of the molten steel at the center of the slab disappears but is not completely solidified. It is characterized by rolling down. In the continuous casting apparatus according to the second aspect of the present invention, 40
A non-rolling area of 0 to 1000 mm not reduced is provided, and a non-solidification rolling roll group for rolling down a non-solidified slab is provided downstream thereof, and further downstream there is no flow of molten steel at the center of the slab. A semi-solidification reduction roll group for reducing a slab before completely solidifying is provided.

[0007]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a continuous casting apparatus according to an embodiment of the present invention, and FIG. 2 is a graph showing a correlation between slab temperature and deformation resistance. In FIG. 1, reference numeral 1 denotes a mold, 2 denotes a support roll in a non-press-down region 2A, 3 denotes a press roll in an unsolidified press-down region 3A, and 4 denotes a press roll in a semi-solid-press region 4A.

The casting mold 1 may be one having parallel long sides facing each other, or one having a narrow interval between the long sides from the entrance side to the exit side, but having an exit side thickness of 120 to 50 mm. . The non-rolling area 2A is located immediately below the mold 1, and is 400 to 1000 mm.
Has a length of The slab A during this time is guided by the support roll 2, but is not reduced. The molten steel cast in the mold 1 is cooled by primary cooling in the mold 1, a solidified shell s is formed on the surface of the slab A, and solidification is further solidified by secondary cooling with spray water or the like in the group of support rolls 2 subsequently. Will be promoted.

In the unsolidified rolling region 3A following the non-rolling region 2A, the unsolidified slab A is reduced by the rolling rolls 3. In this unsolidified state, the molten steel is flowing at the center of the slab A, and can be lowered by a small force. Also, since the rolling force can be small, the roll pitch can be reduced by using a small-diameter roll, so that bulging due to the molten steel static pressure is less likely to occur. During this unsolidification reduction, the slab A naturally cools, and the thickness of the solidified shell s increases. Then, the thickness of the slab is reduced by the reduction by the reduction roll 3. The point at which the solidified shell s generated from both surfaces of the slab A comes into contact is the solidification completion point 6 and the end point of the unsolidified rolling reduction region 3A.

Subsequent to the solidification completion point 6, a semi-solidification reduction region 4A is provided further downstream. This semi-solidified rolling region 4A is in a state where the molten steel does not flow at the center of the slab A, but the slab is not completely solidified.
In other words, in this semi-solid state, the average temperature of the slab section is 1200 ° C.
Alternatively, it is a region where the slab center temperature does not become 1350 ° C. to 1400 ° C. or lower, and a region where the average temperature of the solidified shell is 1250 ° C. to 1300 ° C. The present inventor has found that in the semi-solidified rolling region 4A, the rolling can be reduced with a rolling force much smaller than the reaction force in the solidified state conventionally considered.

That is, as shown in FIG. 2, in the solidification reduction region where the solidified slab was reduced in Conventional Example II, the average temperature of the solidified shell was about 1100 ° C., and the deformation resistance was 4 kg / mm 2. However, since the average temperature of the solidified shell is 1250 to 1300 ° C. in the semi-solidification reduction region 4A in the present invention, the deformation resistance is 1%.
kg / mm2 or less, which means that a rolling force of about 1/4 or less of the conventional one is sufficient. Therefore, the rolling roll 4 having the same small diameter as the rolling roll 3 used for the unsolidified rolling can be used also in the semi-solidified region 4A, so that the roll pitch can be reduced. Therefore, the newly formed solidified shell does not bulge, and rolls down in a high temperature region where the rolling temperature (1100 ° C or higher) can be secured outside the brittle zone of the slab, causing internal cracks in the slab. do not do.

The rolling in the unsolidified rolling region 3A and the semi-solid rolling region 4A is performed by raising and lowering and tilting a rolling segment in which small-diameter rolling rolls are arranged at a small pitch. The thickness of the slab obtained by the unsolidification reduction and the semi-solidification reduction can be freely set by changing the amount of vertical movement and the amount of tilt of the reduction segment.

Further, the solidification completion point 6 moves upstream or downstream due to the fluctuation of the casting speed.
Although the length of the uncoagulated rolling region 3A and the length of the semi-solidified rolling region 4A also vary, the deformation resistance in the semi-solidified region does not increase at a stretch, and even when the solidification completion point moves, the deformation resistance is reduced to a predetermined thickness. can do.

Although the continuous casting apparatus shown in FIG. 1 is of a vertical type, the same configuration can be applied to a curved type.

[0015]

According to the present invention, it is possible to continuously cast a slab having a lower slab quality and a better slab quality than the conventional unsolidified rolling method.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a continuous casting apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a correlation between a slab temperature and a deformation resistance.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 support roll in non-rolling area 2A 3 roll in unsolidified rolling area 3A 4 roll in semi-solidifying rolling area 4A

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[Procedure amendment]

[Submission date] May 19, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

That is, as shown in FIG. 2, in the solidification reduction region where the solidified slab was reduced in Conventional Example II, the average solidification shell temperature was about 1100 ° C., and the deformation resistance was 4 kg / mm ^2. However, since the average temperature of the solidified shell is 1250 to 1300 ° C. in the semi-solidification reduction region 4A in the present invention, the deformation resistance is 1 kg.
/ Mm ² or less, so that a rolling force of about 1/4 or less of the conventional one can be used. Therefore, a reduction roll 4 having a small diameter similar to the reduction roll 3 used for unsolidification reduction is formed in the semi-solidified region 4A.
, The roll pitch can be made small. Therefore, the solidified shell that has just been formed does not bulge, and it is rolled down in a high-temperature region where the rolling temperature (1100 ° C or higher) outside the brittle zone of the slab can be secured.
No internal cracks occur in the slab.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Tetsuji Shiozaki 5-2 Sokai-cho, Niihama-shi, Ehime Pref. Sumitomo Heavy Industries, Ltd.

Claims (2)

[Claims] In order to produce a slab having a thickness of 40 mm or less in a continuous casting apparatus, after a solidified shell is grown to a certain degree on a casting slab having a thickness of 120 to 50 mm on the mold exit side, molten steel flows in the center of the slab. A continuous casting method characterized in that the rolling is performed in a non-solidified state, and further reduced in a semi-solid state in which the flow of molten steel in the central portion of the slab has disappeared but is not completely solidified. 2. A 400-mm mold directly under a mold having an outlet thickness of 120 to 50 mm.
Provide a non-rolling area that does not reduce to 1000 mm, and provide a group of unsolidified rolling rolls that rolls down the unsolidified slab in the downstream, and further downstream, the flow of molten steel in the center of the slab disappeared, but completely A continuous casting apparatus comprising a group of semi-solid reduction rolls for reducing a slab before solidification.