JPS60148651A - Continuous casting machine - Google Patents

Abstract

PURPOSE:To obtain a defectless slab without forming a negative segregation zone by providing an electromagnetic stirrer or ultrasonic wave impressing device before the point where the solidification of a billet is completed and disposing a forging device of a reciprocating type near the point where the solidification is completed. CONSTITUTION:A molten metal supported by supporting rolls 3 descends from a casting mold 11 and is electromagnetically stirred by an electromagnetic stirrer 9 before the billet completes solidification. The billet is forged by a forging device 7 of a reciprocating type near the point where the solidification is completed. The dendrite cut by the flow of the molten steel by the stirrer 9 settles and an equi-axed crystal region is formed near the crater end. The billet is subjected to continuous forging of the plane by the device 7 in the state of having the equi-axed crystal zone in the central part, by which central segregation is considerably improved. The defectless continuous casting slab is obtd. without forming the negative segregation zone by the above-mentioned method.

Description

Detailed Description of the Invention (Technical Field) The technical content described in this specification related to reducing center segregation that occurs at the center of plate thickness in a continuous casting machine is to reduce the center segregation that occurs at the center of the thickness of a continuous casting machine. Although rolling reduction, application of ultrasonic waves, addition of steel wire, and low-temperature casting are some of the methods we are aiming for, we have aimed to reduce central segregation, which is particularly advantageous, by combining some of these with forging. 〇 (Background technology) The central segregation of continuously cast slabs is as shown in Fig. 1.
The molten steel components such as O, S, and P become concentrated at the center of the thickness of the final solidification zone (a) and appear as positive segregation 2. This center segregation causes deterioration of mechanical properties in the thickness direction of thick plates and cracks caused by concentrated hydrogen, but it is one of the quality defects that cannot be avoided in conventional casting methods. Figure 2 shows the generation mechanism of @center segregation.

The pores generated by the solidification shrinkage of the solidified tip 10 and the bulging of the solidified shell la act as a suction force, sucking in the concentrated molten steel 1b at the solidified tip and remaining in the center as positive segregation. If the solidification completion point is uneven in the direction, the problem will be even worse.

(Prior art and its problems) Some attempts have been made to prevent center segregation, such as electromagnetic stirring in the secondary cooling zone, but they have not been able to reduce micro segregation and cannot be said to be sufficiently effective. On the other hand, as shown in Figure 2, there is also a method in which the vicinity of the solidification tip lO is lightly compressed by rolls 8 and 8, and the solidification shrinkage of the 10 portions of the solidification tip is compensated for under the full pressure. In the case of rolling down, since it can only be rolled down in points in the casting direction 5, it is not possible to sufficiently prevent solidification shrinkage and bulging that occur between the upper and lower rolls in the figure, and valley rolling acts as a concentrated load. Therefore, internal cracks as shown in 6 in Fig. 2 tend to occur at the solidification interface, and a large reduction cannot be achieved. For this reason, it is not possible to sufficiently eliminate uneven solidification in the width direction of the slab, and the actual situation is that micro-porous segregation may be promoted.

(Start of the idea) From this point of view, we tried a method of continuously forging the area near the solidification completion point of the slab using a flat forging die. 0 2) The pressure surface of the forging die can be set so that the strain at the solidification interface of the slab can be reduced, and the amount of reduction can be larger than that with roll reduction, which can prevent uneven solidification completion points in the width direction. However, under strong pressure, it is difficult for concentrated molten steel to enter the crater end, and conversely, the center segregation can be prevented due to the surface support. (Objective of the Invention) This invention advantageously avoids the formation of negative segregation bands without impairing the advantages in forging process, and improves soundness. An object of the present invention is to propose a continuous casting machine that can easily obtain continuous cast material. This continuous casting machine is characterized by being equipped with a stirring device 9 or an ultrasonic application device, and at least a pair of reciprocating pressing devices 7 near the solidification stage of the slab.

(Specific Description) According to the above-described structure of the present invention, even microscopic segregation can be improved without generating a negative segregation zone in the center of the continuous casting machine. The following will explain based on one example.

In Fig. 8, 11 is a mold, la is a slab solidification section, 1b is a slab end solidification section, 8 is a support roll, 7 is a forging device, 8 is its driving device, 9 is an electromagnetic stirring device, and IO is a casting machine. A single drawing roll is shown.

When a slab is rolled down using only the continuous pressing device 9, the solidified interface has columnar crystals, so the concentrated molten steel between the trees is easily squeezed out, which tends to form a negative segregation zone in the center. be.

However, if the electromagnetic stirring device 9 is installed above and operated as shown in the figure, the cut dendrites will settle due to the flow of the molten steel, and an equiaxed crystal region will be formed near the crater end to be forge-bonded. An ultrasonic wave applying device has the same effect.

It has been experimentally revealed that if the forging process is performed with the equiaxed crystal band sandwiched in the center in this way, the center segregation in the center can be improved without forming a negative segregation band in the center. It is.

As explained above, the basic knowledge of this invention is that the forging process can be performed with the equiaxed crystal region formed in the center, and therefore, the method of generating equiaxed crystals does not necessarily have to be based on electromagnetic stirring. For example, a method may be used in which ultrasonic waves are applied to the slab through rolls, or other consideration in terms of operation may be low-temperature casting, addition of steel wire into the mold, etc.

(Example) Casting was carried out under the conditions shown in Table 1 using a combination of the electromagnetic stirring device 9 shown in FIG. 8 and a continuous forging device, and the mounting position of the electromagnetic stirring device 9 was LOn from the mold meniscus. This mounting position was selected so that the crystal nuclei generated by stirring the molten steel would not be remelted and an unsolidified region could be formed, and the mounting position of the forging press was selected so that it would not remelt the crystal nuclei generated by stirring the molten steel.
Installed near the end. The obtained slab was cut in a cross section perpendicular to the casting direction, and the segregation degree of phosphorus (P) was examined using a 50 μφ macro analyzer as a representative.

As a result, it was confirmed that the maximum segregation degree of P in the conventional casting method was 13, but in the case of this invention, which combines electromagnetic stirring and continuous forging, the maximum segregation degree was improved to 6. Even in the case of sulfur print, very good slabs were obtained with almost no negative segregation zones observed.

Table 1 (Effects of the Invention) According to the present invention, a sound continuously cast slab can be obtained without impairing the advantages of forging and without the formation of negative segregation zones.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing center segregation occurring in a slab. Fig. 2 is an explanatory diagram of behavior under light roll reduction. Fig. 8 is a cross-sectional view along the casting direction showing an embodiment of the present invention.・Solidified shell part lb of the slab...Flow area lO of the unsolidified area of the slab...Non-flow area 2 of the unsolidified area of the slab...Center segregation 8...Reduction and support roll 4・
... Reduction blade 6 ... Casting direction 6 ... Internal crack 7 ... Forging device 8 ... Forging reciprocating device 9 ... Electromagnetic stirring device 10.
... Driving roll for drawing slabs 11 ... Mold 〇 Procedural amendment July 3, 1980 1. Indication of the case 1982 Patent Application No. 8571 2. Title of invention Continuous casting machine 3. Amendments to be made Relationship with the Patent Applicant (125) 1 person other than Kawasaki Steel Co., Ltd. 5゜6, Subject of amendment: ``Brief explanation of the aspect of the invention ≦&-'' in the specification 1, Page 2 of the specification, No. 15 Correct "microsegregation" in the row to "semimic p-segregation." 2. On page 8, line 9, ``1 microscopic segregation'' is corrected to ``1 semi-microscopic segregation''. 8. On page 4, line 20, ``Micro-4 segregation'' is corrected to ``Semi-micro segregation.'' 4. On page 5, line 8, ``18 is a support roll'' is corrected to ``18 is a support roll.'' 5. The section between page 6, line 8 and page 7, bugyo is corrected as follows. [Casting was carried out under the 8 conditions shown in Table 1 using the combination of the electromagnetic stirring device 9 shown in FIG. 8 and the continuous forging device. That is, casting was carried out in the case where neither electromagnetic stirring nor continuous forging was performed, the case where only continuous forging was performed, and the case of the present invention where both electromagnetic stirring and continuous forging were performed. Here, the mounting position of the electromagnetic stirring device 9 was set to be 10 m from the meniscus in the mold. This mounting position was selected so that the crystal nuclei generated by stirring the molten steel do not remelt and there is a considerable amount of unsolidified area.The mounting position of the forging press is located at the crater end of the slab. It was installed nearby. The obtained slab was cut in a cross section perpendicular to the casting direction, and
The degree of segregation of phosphorus (P) was investigated as a representative using a macro analyzer in μ, and the segregation of P was also investigated in the plate thickness direction and over 50 m in the casting direction using 8 drill samples. Figure 4 shows the semi-micro segregation investigated with a macro analyzer, and shows that the maximum segregation degree of P in the conventional casting method (+-s A) is 18 & compared to that in the case of this invention, which combines electromagnetic 1° stirring and continuous forging (case In C), it was confirmed that the maximum segregation degree was improved to 6. When only continuous forging was performed without electromagnetic stirring (Case B), the semi-micro segregation of phosphorus was 6, which is also affected by the negative macroscopic segregation in the center of the coke. Figure 5 shows the macro segregation in the thickness direction of the slab for case B, and clear negative segregation is observed in the center, and the component segregation in the pouring direction shown in Figure 6 also shows a phenomenon in which the molten steel gradually becomes thicker. This is known to be unfavorable in terms of product quality.In other words, if only continuous forging is performed, a macroscopic negative segregation zone will occur in the center, and as a result, the components will gradually become concentrated in the pouring direction. However, it has become clear that if this technology is applied in combination with electromagnetic stirring, etc. to achieve equiaxed crystallization in the center, these drawbacks can be eliminated and both semi-micro and macro segregation can be significantly improved. . Table 1 (8) (Effects of the Invention) According to the present invention, it is possible to obtain a sound continuously cast slab without impairing the advantages of forging and without the formation of negative segregation zones. ” 6, page 8, 6.1, add the following between lines. [Figure 4 shows the difference between the conventional method of semi-micro segregation and the present invention, Figure 5 shows macro segregation in the plate thickness direction when only large roll reduction is used, and Figure 6 shows changes in macro segregation in the casting direction. . 7. Hand out new drawings, Figures 4 to 6. Figure 4 Figure 5 Electromagnetic [#a Pressure: 4L Group: LL Tomorrow: Yes Yes

Claims (1)

[Claims] t. In a continuous steel casting machine, an electromagnetic stirring device 9 or an ultrasonic application device is installed before the solidification completion point of the slab, and at least one pair of reciprocating forging devices 7 is installed near the solidification completion point of the slab. A continuous casting machine characterized by: