JPS63215353A - Production of continuously cast billet - Google Patents

Abstract

PURPOSE:To facilitate the treatment of a cast billet and to improve the quality by executing the casting by a water cooling mold having round shape or polygonal shape in the cross section and also cutting the continuously cast material after executing rollingreduction. CONSTITUTION:The mold having round shape or polygonal shape in the cross section is used as the water cooling mold 6 for continuous casting machine and roll groups I, II, III for rolling-reduction are arranged one after another. Then, the roll groups I, II alternately arrange vertical mill and horizontal mill one after another and apply the prescribed quantity of the rolling-reduction to the continuously cast material 2. In this way, the continuously cast material 2 having round shape or polygonal shape is reduced by rolling before completion of solidification in the center part, and the development of center segregation and cavity are prevented. The continuously cast material 2, reduced by rolling and straightened by the roll group III, is cut at the prescribed length, to obtain the cast billet 4. As the cast billet 4 is formed into the square shape, the treatment is facilitated and the development of cavity and center segregation are prevented, and the quality is improved.

Description

[Detailed description of the invention]

Ability to excel in ordinary dishes

[Industrial application field]

The present invention relates to a method for manufacturing slabs by continuous casting of metal, particularly steel.

[Conventional technology]

Since the advent of the continuous casting method as a steel casting technology, its high productivity has been praised and it has come to be widely used in place of the conventional steel ingot casting method. Continuous casting has problems in that segregation and cavities tend to occur in the center, but these problems are being alleviated with advances in technology. That is, as a method for improving the above-mentioned segregation and cavities, techniques such as in-mold N magnetic stirring, strand electromagnetic stirring, or a combination thereof are employed. When performing in-mold electromagnetic stirring, in order to avoid entrainment of lubricating powder and maximize the stirring effect, it is desirable that the cross-sectional shape of the water-cooled mold be polygonal, such as circular or hexagonal. However, slabs with a circular or hexagonal cross-sectional shape tend to roll, making it difficult to maintain the slabs during the continuous casting process and handle them during rolling. The inventors tried making a continuous cast slab with a circular cross section, but during heating prior to rolling,
We experienced a problem with slabs rolling in the heating furnace. Not only will the slabs be too close to the furnace wall, or the slabs may come into contact with each other, making it impossible to achieve the desired uniform heating, but also making it impossible to extract the slabs from the furnace. Another problem is that even with the continuous casting method using electric w1 stirring, it is extremely difficult to completely eliminate the formation of cavities in the center. If a slab with cavities is heated as it is, internal oxidation along the axial direction will proceed due to the infiltration of air, and the oxidized portion will be cut off after rolling, resulting in many negative effects such as a decrease in yield. Attempts have been made to weld the end faces before heating to prevent oxidation, so to speak, but the work is still done in harsh environments with hot slabs, and the efficiency of the work is low. not good.

[Problems to be solved by the invention]

In view of the above-mentioned circumstances, an object of the present invention is to solve the problem of the central cavity of the slab without any problem in handling during the slab preparation process or heating process even if a circular or polygonal water-cooled mold is used. The objective is to provide a manufacturing technology for cast slabs. It is also an object of the present invention to provide a method for producing a continuous cast slab in which segregation is significantly reduced in response to the increasingly stringent demands for improving the quality of steel materials. [Means for solving the problem] As shown in Fig. 1, the method for producing continuous cast slabs of the present invention is to place molten metal into a water-cooled mold having a circular or polygonal cross section. The continuously cast material 2 having a circular or polygonal cross section is cast onto a roll 7.8.
Alternatively, the rolled material 3 is rolled in step 9, and then cut into a predetermined length to obtain the slab 4. The continuous casting material is a continuous casting material 2A with a circular cross section as shown in Fig. 2.
T: If the rolled material 3A is rectangular in cross section, it is best to roll it down by roll rolling to make a rolled material 3A with a rectangular cross section. Continuously cast material 2B, which has a polygonal cross section as shown in FIG. As shown in the figure, it is appropriate to use rolled material 3B whose cross section is substantially square.In any case, it is suitable to use rolled material 3B, which is convenient for taking in and out of the heating furnace and handling in the furnace, and does not easily roll. , the cross-sectional shape has a low center of gravity. 4. Polygon here means, of course, a pentagon or more that exceeds a quadrilateral, but due to the convenience of manufacturing water-cooled molds, it is actually a hexagon or more, such as A hexagonal shape as shown in Figure 3 would be preferred. A decagon or larger polygon is substantially circular. Depending on its purpose, the roll roll may be shaped like the one shown in Figure 2. Select flat roll 7A (8A, 9A>) and caliber roll 7B (88°9B> as shown in Figure 3. Caliber rolls may be a combination of calibers of different shapes, such as hexagonal → rectangular. The position of the flat rolls may be horizontal (H mill), vertical (■ mill), or even diagonally, and a combination of these is also possible.The timing of rolling down the continuous cast material 2 is as follows. After exiting the guide roll under the water-cooled mold, the curvature is corrected by the straightening roll and it can be selected arbitrarily until it is cut into slabs.While the center of the continuous cast material is still unsolidified. If you press down,
Not only can the formation of a cavity in the center be prevented, but also center segregation can be virtually eliminated. This is clear from the graph of FIG. 4, which shows data of Examples described later. On the other hand, if the core is rolled down after it has solidified, it will have little effect on center segregation, but it will prevent the formation of a center cavity. The first group of roll positions indicated by the symbol ■ in FIG. 1 are intended for the former case, and the second group of rolls indicated by the symbol ■ are at positions for executing the winner. The roll group indicated by the symbol ■ is a straightening roll, which corrects the bending of the slab, but may also play the role of rolling down to solidify and restore the center part. It is better to roll down the rolls in two or three stages rather than in one stage (especially when changing the cross section from round to square), so add the rolling blades to some rolls while the center is still unsolidified, and roll down the rolls in two or three stages. It is conceivable that a reduction blade may be added after the solidification. Of course, not only does this pose no problem, but it also makes it possible to first eliminate center segregation with the first half of the rolls, and then use the second half of the rolls to shape the product into a shape that is convenient for handling, including charging into a heating furnace. The location for rolling may be determined depending on the properties, cross-sectional size and shape of the target steel, and considering the difficulty of configuring the equipment.
If the cross section is small, for example, 150 m in diameter, the center segregation will be small, so only the second group of rolls will be sufficient. A total reduction amount of several to 10% is sufficient. [Function] The continuous casting slab manufacturing method of the present invention overcomes the drawback of circular or polygonal materials, such as easy rolling, by changing the cross section to a square or something close to it by roll reduction. Roll reduction can prevent the formation of cavities at the center of the slab, and can also eliminate center segregation to a high degree. Since rolling is carried out when the continuously cast material is still at a high temperature and has low deformation resistance, the required power is relatively small. The reason why the center cavity can be eliminated with a relatively small amount of reduction is that when reduction is directly connected to continuous casting, the inside of the continuous cast material is hotter than the outside, and the reduction blade has a large effect on the inside. This is thought to be because the cavity is easily compressed and disappears. On the other hand, in the conventional method of heating and rolling the material once it is made into a slab, there is almost no temperature difference between the inside and outside of the material, and when rolling is applied, the rolling reduction is large on the surface layer and small on the inside, so A larger reduction is required to eliminate the cavity. This fact is clear from the data in FIG. 5, and the graph in the figure shows that defects due to internal non-bonding are eliminated according to the present invention at a lower forging ratio than in the past. [Example 1] A steel having a composition of 0.45% C-0.25% 5i-0.75% Mn-balance Fe was continuously cast in a water-cooled mold with a circular cross section of 370M in diameter. The following caliber rolls were installed at the positions marked with and () in Fig. 1 to sequentially deform the continuously cast material, and it was finished into a slab with a square cross section of -side 300 m. Group Lo - /L' JLEμk
D-) I Ototan Shikee 1st stage (V Mill) 1%
45 in 2nd stage (H mill) 1% 45 in 3rd stage
Stage (V mill) 1.5% 45t ■ 4th stage (H mill) 1°5% 50 to 5th stage (■ mill) 2
% 55 to 6th stage (H mill) 2% 55
No cracks on the surface due to rolling were observed. Of course, there is no problem of the slab rolling around in the heating furnace. On the cut surface of the obtained slab, as shown in Fig. 4,
Samples were taken at various points on a line extending from the center to both left and right sides, and the C content was measured. For comparison, continuous casting was carried out in a water-cooled mold with a rectangular cross section having approximately the same finished dimensions, and C segregation on the cut surface was also examined for continuous cast slabs that were not subjected to the reduction according to the present invention. The results are also shown in FIG. The vertical axis of the graph in the figure is the ratio of the C content C in the slab to the C content layer C8 in the ladle, that is, in the molten steel. [Example 2] Using the same steel as in Example 1, a continuous casting material was made using a mold with a circular cross section of 160 # in diameter. Apply roll pressure as shown below at the position ■ in Figure 1, and -
Side 134! rI! It was made into a square slab of r1. Roll pressure reduction amount 1: Goro L force 1st stage Calibur roll 2% 15 to 2nd stage
Calibur roll 2% 15 was placed in the third stage Calibur roll 2% 15t In this case as well, no cracks on the surface or inside due to rolling were observed. Since the rolling reduction was carried out after the solidification of the center of the continuously cast material had been completed, the center segregation was not significantly improved, but the center cavity was significantly improved. By manufacturing slabs by continuous casting according to the present invention, the slabs finally obtained do not have a cavity in the center, and are free from the problem of oxidation caused by the presence of cavities. In addition, center segregation is greatly improved especially when rolling is performed before the solidification of the center is completed, making it easier to pass strict quality standards. For example, by reducing C segregation, which has the greatest effect on hardenability, the distortion caused by variations in hardenability can be significantly reduced. Needless to say, by making the final shape of the slab into a shape that does not easily roll, such as a rectangular cross section, it becomes convenient to handle, including taking it in and out of the heating furnace, so that the desired uniform heating is achieved and the quality requirements are met. It becomes easier to respond to In general, according to the manufacturing method of the present invention, the size of the slab obtained using a water-cooled mold with the same cross-sectional area can be made larger than when using the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a conceptual cross-sectional view for explaining the method for manufacturing a continuously cast slab of the present invention. FIG. 2 and FIG. 3 are both explanatory diagrams showing that the continuously cast material in the slab manufacturing method of the present invention becomes a slab whose cross-sectional shape has been changed by rolling reduction. FIG. 4 is a graph showing the state of C segregation on the cut surface of the slab obtained in the example of the present invention in comparison with that according to the prior art. FIG. 5 is a graph showing the relationship between the forging ratio and the internal defect index of the slab produced by the method of the present invention in comparison with the conventional method. 1... Molten steel 2 (2A, 2B>... Continuously cast material 3 (3A, 3B)... Reduced material 4 (4A, 4B>... Slab 6... Water-cooled mold 7 (7A, 7B>, 8 (8A, 8B>, 9 (9A
. 9B＞・・・Roll Patent Applicant Daido Steel Co., Ltd. Agent Patent Attorney Souo Suga Figure 1 Figure 211 Figure 3 ◇ Figure 4

Claims (5)

[Claims] (1) Continuous casting is performed by pouring molten metal into a water-cooled mold with a circular or polygonal cross section, and the resulting continuous cast material with a circular or polygonal cross section is rolled and then cut into predetermined lengths. A method for producing continuously cast slabs, which comprises obtaining slabs by continuous casting. (2) The method for manufacturing a slab according to claim 1, in which a continuously cast material having a circular cross section is rolled down to have a rectangular cross section. (3) The method for manufacturing a cast slab according to claim 1, wherein the continuous casting material having a polygonal cross section is rolled down to reduce the number of squares in the cross section. (4) The method for producing a slab according to claim 1, wherein roll reduction is performed before the continuous casting material completes solidification. (5) The method for producing a slab according to claim 1, wherein roll reduction is performed after the continuous cast material has solidified.