JPH0818116B2 - Continuous casting slab manufacturing method - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

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

[Prior art]

Since the continuous casting method was introduced as a steel casting technology, its high productivity has been evaluated, and it has become widely used in place of the conventional steel ingot casting method. The continuous casting has a problem that segregation and cavities are likely to occur in the central portion, but it is being alleviated by technological progress. That is, as a method of improving the segregation and the cavity, a technique of electromagnetic stirring in a mold, a technique of strand electromagnetic stirring, or a combination thereof is adopted. When performing electromagnetic stirring in the mold, it is desirable to make the cross-sectional shape of the water-cooled mold circular in order to avoid the inclusion of lubricating powder and maximize the stirring effect. However, since a slab having a circular cross-sectional shape tends to roll, it is difficult to maintain the slab after the continuous casting process and to handle it during rolling. The inventors tried a continuous cast piece having a circular cross section, but experienced a problem that the cast piece rolled in a heating furnace during heating prior to rolling. The slabs may be too close to the furnace wall side, or the slabs may come into contact with each other so that desired burning cannot be performed and the slabs cannot be extracted from the furnace. As another problem, it is extremely difficult to eliminate the generation of the central cavity even by the continuous casting method in which electromagnetic stirring is performed. When a cast slab with cavities is heated as it is, internal air proceeds along the axial direction due to the invading air, and the oxidized portion has to be cut off after rolling, and there are many negative points such as a decrease in yield. In order to prevent oxidation, it has been attempted to weld the end faces before heating, so to speak, so to speak, but this is a work in a bad environment targeting slabs that are still hot, Is not very efficient.

[Problems to be Solved by the Invention]

In view of the above circumstances, the object of the present invention is to solve the problem that even if a circular water-cooled mold is used, there is no hindrance to the handling in the slab maintenance step and the heating step, and the presence of the central cavity of the slab is caused. It is to provide a technology for manufacturing the cast slab. It is also included in the object of the present invention to provide a method for producing a continuous cast piece in which segregation is further reduced in response to a demand for improving the quality of steel materials which are becoming increasingly severe in recent years.

[Means for Solving the Problems]

As shown in FIG. 1, the continuous casting slab manufacturing method of the present invention is carried out by continuously injecting a molten metal 1 into a water-cooled mold having a circular cross section, particularly molten steel, to obtain a circular cross section. Before the solidification of the continuous cast material 2 is completed, the material is rolled by a roll group I or a roll group I and a roll group II to obtain a rolled material 3 having a quadrangular cross section, and then cut into a predetermined length to obtain a slab 4.
Consists of getting. The continuous cast material 2 having a circular cross section as shown in FIG. 2 is first rolled into a rolled material 3A having a substantially square cross section by roll rolling. The rolled material 3A can be used as it is in the subsequent steps, but if desired, the rolled material 3A can be further rolled to form a rolled material 3B having a substantially rectangular cross section. In any case, the roll has a cross-sectional shape which is convenient for rolling in and out of the heating furnace and handling in the furnace, and which does not easily roll. Depending on the purpose, the flat roll 7A (8A, 9A) shown in FIG. 2 and the caliber roll 7B (8B, 9B) as shown in FIG. 3 are selected as the reduction rolls. The caliber roll may be a combination of calibers having different shapes, and the position of the flat roll may be horizontal (H mil), vertical (V mil), or even in an oblique direction, and there are combinations of two or more thereof. obtain. As for the timing of rolling down the continuous cast material 2, if the central portion of the continuous cast material is not solidified, not only the generation of a cavity in the central portion can be prevented but also the central segregation can be substantially eliminated. This is clear from the graph of FIG. 4 showing the data of the examples described later. The first group of rolls indicated by reference numeral I in FIG. 1 is intended to be rolled down while the central portion is not solidified,
The second group of rolls indicated by II are positions for rolling down after solidification. The roll group indicated by reference numeral III is a straightening roll, which corrects the bending of the slab, but also plays a role in the reduction after the center solidification. It is better to carry out the roll reduction over 2 to 3 steps rather than 1 step. Therefore, some rolls apply a reduction force while the center part is not solidified, and the other rolls apply a reduction force after solidified. There may be cases. Of course, this does not cause any problems, but it is possible to eliminate the central segregation by the first half roll and form it by a latter half roll into a shape convenient for handling such as charging into the heating furnace. The position of reduction may be determined according to the properties of the target steel, the cross-sectional size and shape, and considering the difficulty of the equipment configuration. The total reduction amount is about several to 10%.

[Action]

The method for producing a continuously cast slab of the present invention eliminates the drawback of a circular material that is easily rolled by changing the cross section into a substantially quadrangle or a substantially quadrangle by rolling down. Cavity at the center of the slab can be prevented by rolling down the roll, and center segregation can be highly resolved. Since the reduction is performed at the stage where the continuous cast material is still at high temperature and the deformation resistance is small, the required power is comparatively small. The reason why the central cavity can be eliminated with a relatively small amount of reduction is that when performing reduction directly linked to continuous casting,
It is considered that the inside of the continuous cast material has a higher temperature than that of the outside, the rolling force largely acts on the inside, and the cavity is easily pressed and disappears. On the other hand, in the conventional method in which the slab is once cast and then heated and rolled down, there is almost no temperature difference between the inside and outside of the material, and when the rolling is applied, the rolling reduction is large in the surface layer part and small in the inside. A larger amount of 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 the defects due to the internal non-compression bonding are eliminated by the present invention at a lower training ratio than the conventional one.

【Example】

Steel having a composition of 0.45% C-0.25% Si-0.75% Mn-the balance Fe was continuously cast in a water-cooled mold having a circular cross section with a diameter of 370 mm. The following caliber rolls are provided at the positions of roll group I or roll groups I and II in FIG. 1, and the continuous cast material is sequentially deformed as shown in FIG.
00A Roller 3A with a nearly square cross section, or 300m on a side
Finished material 3B having a substantially square cross section of m. No crack due to rolling was observed on the surface of these rolled materials, that is, the cast pieces. Of course, there was no trouble such as slab rolling in the heating furnace. On the cut surface of the obtained slab having substantially a square cross section (rolled material 3B), as shown in FIG. 4, samples were taken at various points on the line extending from the center to both the left and right sides, and the C content was measured. For comparison, continuous segregation was also performed in a water-cooled mold having a rectangular cross section with almost the same finished size, and C segregation of the cut surface was also examined for continuous cast pieces that were not subjected to reduction according to the present invention. The results are shown together in FIG. The vertical axis of the graph in the figure is the ratio of the C content C of the slab to the C content Co of the molten steel, that is, the molten steel.

【The invention's effect】

By performing the continuous casting slab production according to the present invention, the finally obtained slab has no cavity at the center, and there is no inherent problem of oxidation caused by the presence of the cavity. Also, since the center segregation is greatly improved,
Easy to pass stringent quality standards. For example, by reducing the C segregation that has the greatest effect on the hardenability, the strain caused by the variation in the hardenability is significantly reduced. Needless to say, by making the final shape of the slab into a shape with a square cross-section that is difficult to roll, it becomes convenient for handling, including in and out of the heating furnace, and therefore the desired burning is performed and the quality requirements can be met. Will be easier. Further, according to the manufacturing method of the present invention, the size of the cast piece obtained by using the water-cooled mold having the same cross-sectional area can be made larger than that in the case of the conventional method.

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view for explaining the method for producing a continuously cast slab of the present invention. 2 and 3 are explanatory views showing that the continuous cast material in the cast product manufacturing method of the present invention is a cast product whose cross-sectional shape is changed by roll rolling. FIG. 4 is a graph showing the state of C segregation in the cut surface of the cast piece obtained in the example of the present invention, compared with that in 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, compared with the case of the prior art. 1 …… Molten steel 2 (2A, 2B) …… Continuous cast material 3 (3A, 3B) …… Rolling material 4 (4A, 4B) …… Cast piece 6 …… Water-cooled mold 7 (7A, 7B), 8 (8A , 8B), 9 (9A, 9B) …… Roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-175065 (JP, A) JP-A-50-85523 (JP, A)

Claims (1)

[Claims] 1. A molten metal is poured into a water-cooled mold having a circular cross section for continuous casting, and the obtained continuous cast material having a circular cross section is subjected to roll pressure reduction before completion of solidification to obtain a cross section. A method for producing a continuously cast slab, which comprises forming a slab by making a quadrangle and then cutting it into a predetermined length.