JPH0628785B2 - Large reduction method of slab in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to unsolidification from the top portion, which is feared to occur when large reduction is performed in the vicinity of the solidification tip of a cast piece drawn from a continuous casting mold. The present invention relates to a reduction method capable of effectively preventing leakage of molten steel and ensuring sound quality.

(Prior Art) There are various methods for improving the internal quality of continuous cast slabs. Among them, it is effective to greatly reduce the vicinity of the solidification tip of the slab, and specifically A method of using and a method of using a forging die are known. In this regard, as literatures, for example, JP-A-61-14058, JP-A-61-4246,
JP-A 61-132247, JP-A 60-82257, JP-A 60-1
No. 21054 or JP-A No. 61-37356 is referred to.

(Problems to be solved by the invention) By the way, when performing the large reduction by applying the above-mentioned technology to the slab drawn from the continuous casting mold, if the large reduction is continued even after the pouring is finished, the inside of the slab remains unsatisfactory. While the solidified molten steel may spurt from the top of the slab and damage the continuous casting machine, if the reduction is stopped at the end of casting to prevent such molten steel blast, the slab located upstream of that It was not possible to improve the internal quality of the product, forcing a significant decrease in yield.

Therefore, although a reduction is performed after the solidification of the slab is completed or under a condition close to the completion of the solidification, or at the end of the casting, a cold material is introduced to solidify the topmost portion of the slab, and then a trial is performed to perform the reduction. In the former case, since it is far from the proper rolling condition, the effect of improving center segregation etc. cannot be obtained, and in the latter case, the internal molten steel pushed up by the rolling breaks through the weak part of the solidified shell and leaks steel, or Since the solidified shell is deformed and the slab size becomes larger than the specifications of the continuous casting machine, there is a disadvantage that drawing cannot be performed.

We propose a rolling-down method that can improve internal quality such as center segregation without causing the molten steel to scatter from the topmost portion caused by large reduction after the completion of supplying molten steel to the continuous casting mold. That is the object of the present invention.

(Means for Solving Problems) The present invention is a method of largely reducing the vicinity of the solidification tip of a cast piece drawn from a continuous casting mold with a roll or a forging die, in which casting into the continuous casting mold is performed. After finishing,
After stopping the withdrawal of the slab, insert a metal frame that surrounds the cross-sectional contour of the unsolidified molten steel and stores the leaked molten steel due to rolling at the top of the slab in the continuous casting mold, and then withdraw the slab. It is a large reduction method of a slab in continuous casting, which is characterized by performing large reduction while restarting.

(Operation) In order to continue large reduction while maintaining the quality of the slab obtained by continuous casting, the unsolidified thickness of the slab in the rolling reduction must be kept within an appropriate range, but usually within this range If the reduction is continued, unsolidified molten steel will flow out from the topmost portion of the cast piece as described above. Therefore, in the present invention, this molten steel outflow amount is estimated in advance from the rolling reduction condition,
Then, after finishing casting into the continuous casting mold, a metal frame for preventing leakage of molten steel having a volume larger than this outflow amount,
By fixing to the solidified shell at the top of the cast piece in the continuous casting mold, the molten steel was prevented from being ejected by large reduction by the metal frame so that the steel could be pressed down to the top at the optimum reduction condition.

Incidentally, in inserting the metal frame into the top of the slab in the continuous casting mold, it is necessary to evacuate the immersion nozzle and the tundish car. Since it has to be stopped, solidification proceeds during that time, and the unsolidified thickness of the slab in the lower part of the slab changes to deviate from the proper rolling condition.

In such a case, it is desirable to set the withdrawal speed of the slab after resuming reduction to be higher than the optimum speed before stopping the withdrawal, and to return to the predetermined speed when the unsolidified thickness has recovered to the optimum value. By adding the above, it is possible to reduce the entire length of the slab under optimal conditions, and thus it is possible to advantageously reduce center segregation inside the slab.

Further, the metal frame used in the practice of the present invention is not limited in its shape as long as leakage of molten steel due to rolling can be prevented, but it is necessary to have an internal volume larger than the amount of leakage molten steel calculated by the following formula.

However, the long side length of the metal frame l ₁ <W The short side length of the metal frame l ₂ <T t: Sum of the time required for the slab drawn from the continuous casting mold to reach the rolling position and the time required for the top treatment (the time required from the insertion of the metal frame to the restart of the slab withdrawal during the top treatment time) ( Min) k: constant (20 ≦ k ≦ 30) L: distance from the meniscus to the rolling down device (mm) α: solidification shrinkage coefficient W: slab width (mm) T: slab thickness (mm) Now, FIG. 1 is a schematic diagram of a metal frame suitable for carrying out the present invention, in which the metal frame 1 is constituted by a partition wall 1a surrounding the cross-sectional contour of the unsolidified molten steel of the cast slab 2 and the lower part thereof is This is an example of a slightly squeezed structure, and such a structure has an advantage that it is easy to fix the slab in the mold to the solidified shell 2a. In addition, if the handle 3 is provided above the partition wall 1a, the metal frame 1
It is very convenient when inserting into the top of the slab 2.
Further, in the case of application to a curved continuous casting machine, if the height of the partition wall corresponding to the outer peripheral side of the curved surface of the slab is made different, as shown in FIG. In the above, since the upper surface of the metal frame 1 is substantially parallel to the molten metal surface, it is possible to prevent steel leakage while moving from the vertical direction to the horizontal direction, and it is possible to maintain the slab rear end in a good shape.

The metal frame 1 has an open upper part and also has an open upper end as shown in FIGS. 3 (a), (b) and (c) in order to completely prevent leakage of molten steel. It is more preferable to cover it with the expanded metal 6 for preventing the molten steel from scattering, or to dispose a lid of the steel plate 7 or the like on a part or all of it.

If there is a problem of internal pressure in the form of FIG. 3 (c), it can be dealt with by providing an opening in a part thereof.

(Example) By applying a curved continuous casting machine, the thickness 27
A slab with a width of 0 mm and a width of 340 mm (steel type SUJ2) was cast near the solidification tip while forging (70 mm reduction), and there was no leakage of molten steel during casting, and the internal quality of the slab obtained. I investigated. In the above casting, when the casting into the continuous casting mold is completed, the size b ₁ : 220 mm, a ₁ : 280 mm, h ₂ : 500 mm, at the top of the slab,
A metal frame (see FIG. 3 (a)) having a h ₁ : 300 mm was inserted.

The results are shown in Table 1 together with the survey results when the conventional method was applied.

From Table-1, when applying the reduction according to the present invention, during casting,
In particular, it was confirmed that there was no leakage of molten steel even after a large reduction after the continuous casting mold had been cast, and that the effect of improving center segregation was significantly higher than that of the conventional method.

(Effect of the Invention) According to the present invention, it is possible to completely prevent the leakage of molten steel that has occurred during the reduction work after the end of casting, and it is possible to always perform the reduction at the optimum position. The yield of one piece is greatly improved. Further, since the present invention can be carried out only by installing a metal frame having a simple structure and controlling the drawing speed of the slab, it costs little and can be easily applied to a conventional continuous casting machine.

[Brief description of drawings]

FIG. 1 is a schematic view of a metal frame suitable for carrying out the present invention, FIG. 2 is a cross-sectional view at the time of drawing a cast piece, and FIGS. 3 (a), (b) and (c) are It is a schematic diagram which shows the other example of the metal frame suitable for implementing this invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koichi Kushida, Koichi Kushida 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (no address), Kawashima Steel Works Ltd., Mizushima Works (72) Inventor Hisao Yamazaki, 1 Kawasaki-cho, Chiba City Kawasaki Steel Co., Ltd. Technical Research Division

Claims (2)

[Claims] 1. A method of greatly reducing the vicinity of a solidified tip of a cast piece drawn from a continuous casting mold with a roll or a forging die, after the casting into the continuous casting mold is finished, Once stopped, insert a metal frame that surrounds the cross-sectional contour of unsolidified molten steel and stores leaked molten steel due to rolling in the topmost part of the cast in the continuous casting mold, and restart the withdrawal of the cast piece while continuing to A method for large reduction of a slab in continuous casting, characterized by performing reduction. 2. A drawing resuming speed of a cast piece after inserting a metal frame is increased more than a drawing speed before that, and a predetermined value is reached when an unsolidified thickness of the cast piece reaches a range of an appropriate rolling reduction condition. The method according to claim 1, wherein the drawing speed is restored.