JPH08257714A - Continuous casting apparatus - Google Patents

Abstract

PURPOSE: To restrain the segregation and to shorten the time of heat treatment by dividing rolls in the width direction of a cast slab, forming the roll diameter to large in the width corresponding to a prescribed solid phase ratio, compensating the shrinkage of vol. at the time of solidifying and executing the rolling reduction. CONSTITUTION: The solidifying shrinkage rate in unsolidified part at the center part of the cast slab 1 at the inlet of a rolling reduction part, is obtd. and the necessary rolling reduction rate is obtd. from the material balance in the cross section so as not to develop the fluid of molten steel. The rolling reduction can be executed preferentially to the center part of the cast slab 1 by using the divided rolling reduction rolls 6 fixed to a segment frame 4 with a bearing 5. Since the rolling reduction is not directly executed to the bearing 5 part but the displacement having the same degree as the rolling reduction with the rolls 6 is executed, the rolling reduction can be executed only in the unsolidified width at the center part of the cast slab 1. The roll diameter in the width corresponding to the part having <=0.7 solid phase ratio in the cast slab 1 is formed to large to compensate the shrinkage of vol. and then, the segregation is restrained, and the shortening of the heat treatment time and the improvement of the productivity can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting apparatus for suppressing the occurrence of slab center segregation in a steel continuous casting process.

[0002]

2. Description of the Related Art As a technique for preventing center segregation of a slab in a continuous casting process, there is a method by light reduction of a slab, which is disclosed in Japanese Patent Publication No. 3-6855. It is known that the center segregation of the slab is caused by the flow and accumulation of molten steel in which the solute is concentrated at the final stage of solidification. The flow of the molten steel is generated by sucking the unsolidified molten steel from the upstream to compensate the volume reduction due to the solidification shrinkage. As a measure for preventing center segregation, there is a light reduction method for preventing molten steel flow by reducing the volume corresponding to the solidification contraction in the final stage of solidification by applying a light reduction to the slab. Specifically, in a continuous casting machine, a roll located at the final solidification stage where the central solid fraction of the slab is 0.3 to 0.7 is used as a slab reduction roll, and a light reduction method for deforming the slab Was developed.

In slab continuous casting, the width of the slab may exceed 2 m, and in a single roll, the distance between the bearings becomes large, so the roll bends. When the roll bends, a sufficient force is not applied to the width center portion of the slab, and a predetermined slab deformation cannot be obtained at the slab center portion, which originally requires reduction. As a countermeasure against this, improvement of the roll strength is effective, but there is a restriction on the roll interval from the viewpoint of preventing bulging between the rolls, and it has been impossible to increase the roll diameter in order to increase the strength. In order to solve this, a technique for dividing rolls into at least two pieces in the width direction and providing a bearing to prevent roll deflection is developed.

[0004]

By the method of controlling the center segregation by the light reduction of the split rolls, it becomes possible to evenly reduce the wide surface even for a slab such as a slab having a large flatness ratio, and it is possible to improve the center segregation. It was However, when the thickness of the cast piece is increased to improve the productivity, the deformation resistance of the solidified portion on the short side is large, and a predetermined reduction amount cannot be obtained.

An object of the present invention is to provide a continuous casting apparatus capable of suppressing the occurrence of center segregation of continuously cast slabs.

[0006]

SUMMARY OF THE INVENTION The present invention is a continuous casting apparatus having a mold and one or a plurality of light reduction segments along a direction in which a cast piece is drawn from the mold, wherein at least the light reduction segment is provided. Some have rolls divided into at least two or more in the width direction of the cast slab, and the roll diameter is changed to other widths corresponding to the region where the solid fraction of the slab is 0.7 or less. The continuous casting apparatus is characterized in that it has a rolling reduction larger than the portion, and the increment of the diameter is configured to correspond to the rolling reduction capable of compensating for the volume contraction in the final stage of solidification.

[0007]

The operation will be described below with reference to the drawings. Figure 1 (A)
[FIG. 3] is a cross-sectional view of the cast slab 7 at the inlet of the draft zone, which has an unsolidified portion 2 in the center of the cast slab. When the amount of solidification shrinkage that occurs when this part solidifies is determined and the material balance in the cross section is considered so that there is no molten steel flow, the solidification shrinkage equivalent area 3 which is the required reduction amount by the roll shown in FIG. Is required.

FIG. 2 shows a schematic view of a roll under light pressure according to the present invention. The division reduction roll 6 is fixed to the segment frame 4 by a bearing 5. By using this reduction roll 6, it is possible to preferentially reduce the central portion of the cast slab 7. Although the bearing 5 portion provided on the split roll does not directly perform the rolling reduction, the bearing 5 is displaced by the strength of the solidified portion 1 on the long side, which is equivalent to the rolling reduction. That is, it is not necessary to deform the entire width of the cast slab 7, and only the portion having the width corresponding to the required area may be volume-compensated with the required reduction amount. For that purpose, it has been found that the solidification profile of the slab 7 is obtained in the casting direction, and the unsolidified width of the central portion may be reduced by a roll.

Further, the boundary between the non-solidified portion 2 of the slab and the solidified portion 1 is the solid fraction at the central portion of the thickness of the slab, and is optimally set to 0.7 which is the solid fraction at the limit of the flow of molten steel. It was discovered. When the rolling width of the roll is made narrower than this, in addition to the molten steel flow from the upstream, molten steel flow from the center to the end occurs,
Segregation becomes worse. Further, when the roll reduction width is set to have a solid phase ratio of 0.7 or more, the reduction efficiency is reduced by the deformation resistance of the solid phase portion at the end, but compared with the case where the reduction width is narrow. If so, the deterioration of segregation is not so remarkable.

[0010]

[Example] Regarding a slab having a width of 2200 mm and a thickness of 300 mm,
The width of the unsolidified region in the region where the solid fraction at the center of the thickness of the cast strip at the inlet of the rolling zone is 0.7 or less is 1800 mm. This width changes depending on the casting speed and the secondary cooling conditions,
By keeping the operating conditions constant, the required roll reduction width can be determined in terms of equipment. The central solid fraction is 0.3 to 0.7 by the split roll with the reduction width of 1800 mm.
Fig. 3 shows the segregation scores for the case of rolling under the same conditions and the case of rolling under the same conditions with a conventional split roll. Here, the segregation score is an index of the sum of products of the size of segregation and the number of each size, and the larger the value, the worse the segregation.

[0011]

According to the present invention, segregation can be suppressed to half that of the conventional one, so that the heat treatment time for diffusing the solute elements in the segregation can be shortened to about 1/4, the productivity is improved, and the heating The required fuel was saved.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section of a slab and deformation of the slab due to light reduction of the present invention.

FIG. 2 is a schematic view of a light reduction roll according to the present invention.

FIG. 3 is a diagram showing the effect of improving the segregation score according to the present invention.

[Explanation of symbols]

 1 Cross-section of cast piece (solidified portion) 2 Cross-section of cast piece (non-solidified portion) 3 Area equivalent to solidification shrinkage 4 Segment frame 5 Bearing 6 Rolling roll 7 Cast piece

Claims (1)

[Claims] 1. A continuous casting apparatus having a mold and one or more light reduction segments along a direction of withdrawing a cast piece from the mold, wherein at least a part of the light reduction segment is cast. It has a roll divided into at least two or more in the width direction of the slab, and the solid fraction of the slab is 0.7.
It has a rolling part having a roll diameter larger than the other parts with respect to the width corresponding to the following region, and is configured such that the increment of the diameter corresponds to a rolling amount capable of compensating for the volume contraction in the final stage of coagulation. Continuous casting equipment.