JPH03198964A - Method and apparatus for executing rolling reduction to strand in continuous casting - Google Patents

Abstract

PURPOSE:To reduce segregation and to prevent the development of cavity in continuous casting for metal, particularly steel by changing direction of the rolling reduction to the right angle according to progressing of a strand and executing at least two times of rolling reductions. CONSTITUTION:The casting strand 5A continuously cast and drawn out from a water cooled mold has molten metal 6 in inner part thereof and the rolling reduction is applied with the first step rolls 21 at just before this solidification is completed. Successively, by applying the rolling reduction in the direction perpendicular to the direction of the first step with the second step rolls 22, this is deformed and further, the direction of rolling reduction is changed to the right angle according to progressing of the strand 5A, and by executing at least two times of rolling reductions, the unsolidified part is almost eliminated to make a cast billet 7. By executing the rolling reduction with the rolls in the direction different at each time, as difficulty to the rolling reduction caused by work hardening is relieved and also compressive action to the unsolidified part 6 is favorably executed, the rolling reduction is more effectively executed and the reduction of center segregation and the prevention to the development of cavity can be obtd.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to improvements in rolling techniques for reducing segregation and preventing the formation of cavities in continuous casting of metals, particularly steel. [Prior Art] In continuous casting of steel, a slight reduction is performed immediately before solidification of the molten metal inside the cast strand exiting the water-cooled mold to reduce center segregation and prevent the formation of cavities. is being carried out. If only to compensate for the volumetric shrinkage due to solidification, the reduction rate is 3.
% is sufficient, and such a reduction is called a light reduction, and a high reduction exceeding this is called a large reduction. In either case, pinch rolls and reduction roll segments are often used as rolling means, but a hydraulic press may be used for large reductions. Conventional rolling involves applying force to the cast strand in only one direction. For example, in the case of curved strands, which is the most common continuous casting method,
The strand is cast in a water-cooled mold with a constant radius of curvature, then curves until it becomes horizontal, where it is rolled down while passing through a row of pinch rolls, and finally straightened into a straight line and cut into a cutter. heading to The pinch rolls have their shafts arranged horizontally in each stage, with the rolls on the lower side of the strand being fixed in position, and the rolls on the upper side of the strand being variable. When attempting to perform a relatively high rolling reduction using pinch rolls, it is sufficient to carry out rolling reduction in multiple stages, but this is not always easy due to the problem of work hardening. If the steel to be continuously cast is to be processed into thin pieces, such as wire rods, it is possible in principle to continuously cast strands with a small cross section so that the amount of rolling from the strand to the product can be minimized. should be a good idea. However, for continuous casting, casting into a strand with a large cross section is more advantageous in terms of workability and quality. A large cross section makes it easier to stabilize the molten metal level in the water-cooled mold, and there are fewer slag entanglements, inclusions just below the surface layer, or blowholes. Therefore, it is desirable to carry out continuous casting with a large cross-section and to perform a high reduction rate so as to be able to provide the desired small-section slab. Also,
Continuous casting is mostly carried out to cast strands with rectangular cross-sections, including squares, and casting strands with circular cross-sections (including hexagonal or larger polygons) is less common. The main reasons for this are problems with the handling of the resulting slabs, such as the fact that slabs with a circular cross section tend to roll, and that they are often rolled into a square cross section during subsequent rolling. However, from the standpoint of casting itself, a circular cross section is preferred.
The effect of electromagnetic stirring of the molten metal (both in the water-cooled mold and in the secondary cooling zone) is higher in circular molds, said to be three times as effective as in rectangular cross-section molds for the same power consumption, reducing segregation. This is because it can be easily done.
6 (Problems to be Solved by the Invention) In view of the above-mentioned current state of the technology in continuous casting, the purpose of the present invention is to more effectively reduce the reduction of the cast strand, and to form a desired material from a strand with a large cross section that is advantageous for operation. We have developed a continuous casting strand reduction method and the equipment used to carry out the process, which enables the production of slabs with small cross sections and the production of slabs with a square cross section from strands with a circular cross section, which are advantageous in terms of quality. It is about providing.

[Means to solve the problem]

The continuous casting strand reduction method of the present invention shows typical aspects of the cast strands (5A, 5
B>, in a continuous casting method in which rolling is performed immediately before the solidification of the molten metal (6) inside the metal is completed, the direction of rolling is changed at right angles as the strand progresses, and rolling is performed at least twice. It is characterized by The continuous casting strand reduction device of the present invention, which implements the above method, reduces the cast strand (5A, 5B) coming out of the water-cooled mold (1) immediately before the molten metal (6) inside the strand finishes solidifying. A continuous casting apparatus equipped with means (2) is characterized in that there are at least two sets of rolling means (2), and the rolling directions are arranged at right angles to each other.The example shown in FIG. The casting strand (5A) has a curved shape, and involves an operation of rolling it down at a position approaching horizontality and then straightening it into a straight line. .3>, the first stage (21) has a horizontal roll axis and performs vertical rolling, the second stage (22) has a vertical roll axis and performs horizontal rolling. The third stage (23) is again set horizontally and is configured to perform longitudinal reduction respectively to form a slab (7A).The following roll (3) is also set horizontally with its roll axis, This is a straightening roll for straightening the strands. Each roll with a horizontal axis has a fixed position on the lower side of the strand, and a variable position on the upper side. Fig. 2 In the example shown in, the cast strand (5B)
has a circular cross section, and while descending vertically, it is lightly rolled down by upper pinch rolls (21, 22, 23, 24), and further rolled down by pinch rolls (4) consisting of lower rolls (41° 42). , it becomes a slab (7B) with a small diameter rectangular cross section. In this device, the back half of the four-stage pinch roll has two stages (21, 22) and two stages (23, 24).
>The rolling direction is changed by 90 degrees. The present invention is not limited to the mode in which the rolling direction is changed for each stage as shown in FIG. 1, but also the mode shown in FIG. 2. Obtaining small diameter slabs from large cross-section casting strands is
As shown in FIG. 2, it is preferable to carry out the light reduction using another reduction roll following the light reduction, but it is also possible to carry out the reduction by increasing the reduction ratio of each reduction roll shown in FIG. [Function] In the embodiment shown in Fig. 1, the cast strand (5A)
At point A, there is molten metal (6) inside as shown in the cross section in Figure 3A, and at point B just before the solidification of the metal is completed,
At this point, it is rolled down by the first stage roll (21), and becomes as shown in FIG. 3B. Then, at point C, the second
When it is rolled down in a direction perpendicular to the above direction by the corrugated rolls (22), it is deformed as shown in FIG. At this stage, most of the unsolidified portion disappears. Rolling down the rolls in different directions each time not only alleviates the difficulty of rolling down due to work hardening mentioned above, but also makes it more advantageous to apply compressive force to the unsolidified area, making it possible to roll the rolls more effectively. This serves the purpose of reducing segregation and preventing the formation of cavities. By adjusting the roll spacing in the vertical and horizontal directions, slabs with desired sizes on both long and short sides can be produced. In the embodiment shown in FIG.
, 24) and secondary rolling by the lower rolls (41, 42>), a slab with a small diameter rectangular cross section (
7B). The situation is as shown in Figure 4, with a,
The shapes of the strand (5B) at points b, c and d are as shown in Figure 4 a, b, c and d, respectively, with rolls if any, and the shape of the strand (5B) is as shown in Figure 4 a, b, c and d, respectively,
7B) is as shown in FIG. 4e. It goes without saying that the effect obtained in the case of FIG. 1 is also realized in the embodiment of FIG.

【Effect of the invention】

According to the present invention, strand reduction in continuous casting can be performed more effectively than before, and can be useful for reducing center segregation and preventing the formation of cavities. If the degree of reduction is adjusted to achieve a high overall yield, the casting itself can be carried out with a large cross-section strand, while a slab of the desired small diameter can be obtained depending on the application. Similarly, a strand of excellent quality can be obtained by forming a strand with a circular cross section, which is advantageous in terms of continuous casting technology, and making it into a square shape by rolling.

[Brief explanation of drawings]

1 and 2 are side views of the main parts of the apparatus for explaining the aspect of strand reduction in continuous casting of the present invention, and FIG.
The figures show the case of vertical strands. 3A-3D show the cross-sectional shape of a cast strand subjected to rolling according to the present invention and the arrangement of pinch rolls, with A, B, C and D corresponding to A, B of FIG.
, C and D are cross-sectional views. Figures 4a-e also show the cross-sectional shape and pinch roll arrangement of a cast strand subjected to rolling according to the invention; Figures a, b, c, d and e also show the second Corresponding a, b in the figure. Corresponding to points c, d and e. 1... Water-cooled mold 2... Reduction roll 21. 22. 23... Light reduction roll 3... Straightening roll 4 (41, 42>... Reduction roll 5A... Casting strand (dog-convex type) ) 5B... Cast strand (vertical type) 6... Unsolidified portion 7A, 7B... Cast piece

Claims (6)

[Claims] (1) In a continuous casting method in which a cast strand that has been continuously cast and exits a water-cooled mold is rolled down just before the molten metal inside the strand finishes solidifying, the direction of rolling is changed perpendicularly as the strand progresses; A continuous casting strand rolling method characterized by performing rolling at least twice. (2) In continuous casting, where the casting strand is curved and the strand is rolled down at a position approaching horizontality and then straightened into a straight line, at least four stages of pinch rolls are used, and the first stage is 2. The rolling method according to claim 1, wherein the rolling is performed in the longitudinal direction, the second stage is the horizontal direction, and the third stage is the vertical direction again, and the final stage is where the straightening is performed. (3) The cast strand has a circular cross section,
3. The rolling method according to claim 1 or 2, wherein said rolling is transformed into a substantially rectangular cross section by repeated rolling. (4) The rolling method according to any one of claims 1 to 3, wherein the rolling is carried out by adjusting the degree of rolling so as to give a slab of a desired small cross-sectional size by repeated rolling. (5) In a continuous casting device equipped with a means for rolling down the cast strand coming out of the water-cooled mold just before the molten metal inside the strand finishes solidifying, there are at least two sets of rolling means, and the rolling directions are perpendicular to each other. A continuous casting strand rolling device characterized by being installed so that. (6) Equipped with at least four stages of pinch rolls for rolling down and straightening the curved cast strand coming out of the water-cooled mold, the first stage and third stage of the pinch rolls have their roll axes horizontally, and the second stage and the fourth stage is provided vertically, and among the horizontally provided rolls, the lower part of the strand is fixed in position, and the upper part is variable.
Reduction device.