JPH10128501A - Method for reducing oscillation mark of continuous cast slab and continuous casting mold therefor - Google Patents

Abstract

(57) [Problem] To provide a method for reducing the occurrence of oscillation marks in continuous casting and a mold therefor. SOLUTION: The taper amount of the inner surface of the mold for continuous casting is set to 1.5% / m or more and 3.0% / m or less above the reference position with the meniscus level in the mold as a reference position and below the reference position. 0.7% / m or more and less than 1.5% / m.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving the surface properties of a slab produced by a continuous casting method, and more particularly to a method for reducing oscillation marks and a mold therefor.

[0002]

2. Description of the Related Art The surface quality of a continuous cast slab is governed by the initial solidification state from just below the mold surface to approximately 2 mm. Therefore, studies have been made from the viewpoint of uniform generation of shells in the mold and reduction of oscillation marks, and many improvement means have been embodied. For the former, improvement of powder, optimization of mold taper, slow cooling technology in mold, stirring of molten steel in mold, electromagnetic mold, ultrasonic application, etc.
For the latter, improvements in oscillation conditions have been made and considerable results have been achieved. However, among the above techniques, the slow cooling technique is often liable to induce operational troubles such as seizure between the mold and molten steel, breakout, etc.
In addition, the electromagnetic field mold has just started research and has not yet been realized. On the other hand, regarding the optimization of the oscillation conditions, it is necessary to simultaneously respond to changes in powder properties and other various casting conditions, and to optimize the whole as a whole, which is complicated and lacks universality. Was.

[0003] As for the optimization of the mold taper, Japanese Patent Application Laid-Open No. Hei 2-207945 discloses a "mold for continuous casting of a round casting edge", which describes the shape of the mold (mold) and the meniscus (the level of the molten metal surface at the time of casting). A technique is disclosed in which the upper part is expanded in an S shape along a specific curvature, and the middle part and the lower part are contracted by a specific curvature and a taper to prevent breakout and increase the casting speed. Further, Japanese Utility Model Application Laid-Open No. 59-165748 discloses a technique in which the inner surface of a cylindrical mold has a structure in which the inner surface is narrowed in two steps in a casting direction, and a gap generated between a mold tube surface and a solidified shell is minimized. Have been. However, in these techniques, there is no mention of improvement of the mold surface properties, much less mention of the reduction of oscillation marks,
There is no disclosure of a technology that is effective in reducing oscillation marks.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to effectively prevent the occurrence of an oscillation mark which has not been sufficiently solved by the above technology. In particular, the present invention provides means for reducing the occurrence of oscillation marks without causing defects in the techniques employed for improving the surface properties of continuous cast slabs. Further, the present invention is intended to cope with the synchronization between continuous casting and rolling, whose practical use has been promoted in recent years, by reducing the number of oscillation marks.

[0005]

Means for Solving the Problems The present inventors have considered the generation mechanism of the oscillation mark, and have found that the tip of the solidified shell falls down to the inner surface of the mold in the early stage of solidification, and the molten mold powder in that portion. Was found to be the cause of the generation of oscillation marks, and the problem was that the generated oscillation marks were brought to a continuous cast slab after solidification as it was, leading to the completion of the present invention. . Therefore, first, in reducing the oscillation mark of the continuous cast slab, the present invention sets the taper amount of the inner surface of the mold for continuous casting to 1.5 times above the reference position with the meniscus level in the mold as a reference position.
% / M or more and 3.0% / m or less to reduce the tip of the initially solidified shell from falling into the inner surface of the mold, and 0.7% / m or more and 1.5% / m or less below the reference position.
When the continuous casting slab is drawn out, the oscillation mark is stretched and smoothed when the continuous casting slab is drawn.

Further, the present invention provides a continuous casting mold for realizing the above-described method, wherein the inner surface of the mold is tapered.
With the meniscus level in the mold as a reference position, it is 1.5% / m or more and 3.0% / m or less above the reference position, and 0.7% / m or more below the reference position.
It is to be less than 5% / m. Furthermore, by providing a means for applying a high-frequency electromagnetic field to a position corresponding to the meniscus level in the mold, the tip of the solidified shell at the initial stage of solidification is more reliably prevented from falling into the inner side of the mold, and the object of the present invention is more reliably achieved. To achieve that.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the taper amount of the inner surface of a mold for continuous casting is increased above the meniscus level in the mold as a reference position. Specifically, it is 1.5% / m or more and 3.0% / m or less. As a result, the tip of the tip portion of the initially solidified shell is prevented from falling into the mold inner surface. This is derived from the following considerations on the behavior of the tip of the solidified shell in the early stage of solidification of the continuous cast slab by the present inventors.

As shown in FIGS. 1 and 3, in the process of the continuous casting group casting, a solidified shell 2 starts to be formed in the vicinity of the molten steel level of the molten steel 3 in the mold 1. in this case,
The solidified shell 2 exhibits a behavior 2 'in which the shell tip falls down inward of the mold due to solidification shrinkage. This behavior is promoted by the formation of the slag rim 6 in the casting process and the repeated collision of the shell tip against the rim 6 by the oscillation of the mold. On the other hand, in order to stabilize the stable operation of continuous casting and maintain the surface quality of the cast slab, a so-called unmelted continuous cast powder 5 and a molten powder 4 are stably held on the molten steel 3, and the cast slab is drawn out. When
Although the powder 5 and the molten powder 4 function as a lubricant between the mold 1 and the solidified shell 2, when the above-mentioned initial solidified shell 2 has fallen, the falling part 2 ′ and the slag rim 6 Flows into the gap 7 between This inflow occurs when the speed of the downward movement of the mold due to the oscillation becomes higher than the speed of drawing out the slab, whereby the generation of the oscillation mark becomes remarkable as shown in FIG.

[0009] Increasing the taper amount θ ₁ in the mold reduces this falling 2 ′. The range of the effect varies depending on other casting conditions and cannot be unconditionally determined. However, the range is approximately 1.5% / m or more and 3.0% or more.
/ M or less. Therefore, in the present invention, the taper amount of the inner surface of the mold for continuous casting is 1.5% / m or more above the meniscus level in the mold as a reference position.
0% / m or less.

On the other hand, below the meniscus level, the mold taper is set to an amount commensurate with the solidification shrinkage of the slab. In this manner, the initial solidified shell generated in the meniscus portion is forcibly elongated by the mold having a reduced taper. As a result, the oscillation mark generated by the fall of the initially solidified shell is corrected, and as a result, the oscillation mark is reduced and the surface properties of the slab are improved. The amount of taper below the meniscus is an amount commensurate with the amount of slab solidification shrinkage, that is, 0.7% / m or more and 1.5% / m or less, as in a normal mold.

FIG. 4 is a schematic diagram showing a steady state of casting by a mold according to the present invention. As shown here, the inner surface taper θ ₁ of the mold above the meniscus portion is larger than that of the lower portion θ ₂ , and has a wide mold shape. The specific value of the taper of the mold is, for the above-mentioned reason, θ ₂ is an amount commensurate with the shrinkage amount of the solidified shell 2 in the mold, that is, 0.7% / m or more and less than 1.5% / m. , theta ₁ is above or more values is 1.5% / m or more. This way,
The solidified shell 2 generated in the strong taper portion θ ₁ is weakly tapered portion θ ₂
Because it is elongated at the time of passing, even if the oscillation mark generated by the collision between the slag rim and the solidified shell occurs when the meniscus part initial solidification shell falls or the powder flows in, it is extended at the lower part of the mold,
It is possible to smooth. Also, as described above, increasing the inner surface taper of the mold at the upper part of the meniscus has led to less collapse of the solidified shell,
Due to these synergistic effects, the number of oscillation marks is greatly reduced as compared with the prior art.

As means for further improving the effects of the present invention,
It is also effective to add the electromagnetic field generator 9 at a position corresponding to the meniscus portion. As a result, uniform cooling of the solidified shell becomes possible, the contact of the initial solidified shell at the meniscus level with the mold becomes soft, the fall of the shell is reduced, and the oscillation mark nozzle is generated in combination with the above-described effect. Is further reduced.

FIG. 4 shows the result of comparing the depth of the oscillation mark generated on the slab surface by continuously casting the same material under the same other casting conditions. As shown here, according to the present invention, the depth of the oscillation mark can be reduced to about 1
/ 2 to 1/3, which contributes to the improvement of the slab surface quality.

[0014]

According to the present invention, the generation depth of the oscillation mark can be significantly reduced. This makes it possible to improve the surface characteristics of a steel plate or the like manufactured through the continuous casting process, and to significantly reduce the number of man-hours for maintenance of the continuous cast slab. It can also contribute to synchronization between the continuous casting process and the rolling process.

[Brief description of the drawings]

FIG. 1 is a partial sectional view schematically showing a steady casting state in a continuous mold.

FIG. 2 is an explanatory diagram of oscillation mark generation.

FIG. 3 is a partial cross-sectional view schematically showing an oscillation mark generation mechanism.

FIG. 4 is a partial cross-sectional view schematically showing a steady casting state in a mold according to the present invention.

FIG. 5 is a comparative diagram showing the effect of reducing slab surface oscillation marks according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 continuous casting mold 2 solidified shell 3 molten metal 4 molten powder 5 unmelted powder 6 slag rim 7 oscillation mark 8 dendrite 9 electromagnetic field generator

Claims (3)

[Claims] 1. A taper amount of an inner surface of a mold for continuous casting,
With the meniscus level in the mold as a reference position, 1.5% / m or more and 3.0% / m or less above the reference position are set to reduce the tip of the initially solidified shell toward the inner surface of the mold and reduce the reference. 0.7% below the position
/ M or more and less than 1.5% / m, wherein the oscillation mark is extended and smoothed during drawing of the continuous cast slab, thereby reducing the oscillation mark of the continuous cast slab. 2. A taper amount of an inner surface of a continuous casting mold.
With the meniscus level in the mold as a reference position, it is 1.5% / m or more and 3.0% / m or less above the reference position, and 0.7% / m or more below the reference position.
Continuous casting mold for reducing oscillation mark of continuous cast slab characterized by being less than 5% / m 3. The continuous casting mold according to claim 2, further comprising means for applying a high-frequency electromagnetic field to a position corresponding to the meniscus level in the mold.