JPH04178247A - Continuous casting method of steel by casting mold having electromagnetic field - Google Patents

Abstract

PURPOSE:To obtain an ingot excellent in inner and outer quality by providing vertical slits at a specified interval on one hand, giving a frequency of a specified range to an electromagnetic coil and performing a continuous casting as molten metal and a solidified shell near the meniscus in a casting mold are held independently by electromagnetic force. CONSTITUTION:Vertical slits 4 are provided at intervals of 10-140mm on the casting mold wall above a position 50-150mm below the meniscus and a frequency of 5-20kHz is given to an electromagnetic coil of the outer periphery for a continuous casting. In this way, steel can be cast continuously by the casting mold having an electromagnetic field wherein troubles of entrainment and breakout of casting mold lubricant are constrained. When the interval between the vertical slits is <=10mm, water cooling structure in the casting mold wall is hardly constituted, therefore, the interval between the vertical slits should be formed in the range of 30-75mm. In this way, the variation of the molten metal surface is constrained, the casting mold lubricant is prevented from being entrained, the solidified shell near the meniscus is held independently by electromagnetic force, consequently, the ingot excellent in inner and outer quality can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for continuous casting of steel using a mold having an electromagnetic field.

[Prior art and the problem to be solved by the invention] A mold is constructed using the electromagnetic force of a high-frequency magnetic field, molten metal is poured into the mold, and the outer peripheral surface of the molten metal is held independently by the electromagnetic force, and Continuous casting is performed while cooling in the lower part.

[Special Publication No. 1-60337, Tetsu to Hagane 71st Year (1
985) No. 16, pp. 19-20] Continuous casting using the mold described above is applied to metals such as aluminum, which are light and have good thermal conductivity, or is applied to metals such as steel, which are relatively heavy and have poor thermal conductivity. In the case of metal, continuous casting while holding the molten steel independently using the above-mentioned mold requires an extremely slow casting speed, which has not yet been put to practical use.

On the other hand, for steel, an electromagnetic coil is installed on the outer periphery near the position where the meniscus is formed in the conventionally used water-cooled mold, and the electromagnetic force of the electromagnetic field from this electromagnetic coil is used to cool the molten steel near the meniscus in the mold. Continuous casting is also being carried out while holding the solidified shell on its own.
8)! A study has been published on the relationship between oscillation marks and initial solidification in continuous casting when using electromagnetic force from an electromagnetic coil installed around the outer periphery of a water-cooled mold. The present applicant has also repeatedly researched this type of technology, and has formed an upwardly widening tapered portion having longitudinal slits at predetermined intervals on the mold wall above the meniscus 150 mm to 150 mm. Proposed a continuous casting mold with an electromagnetic coil on the outer periphery [Patent application 1986-30]
No. 3721 (Japanese Unexamined Patent Publication No. 2-147150). In this proposed continuous casting mold, powder that has become a slag easily enters between the mold and the solidified shell. lubrication is sufficiently distributed, restrictive breakout is less likely to occur, and high-speed casting is possible.

By the way, the present applicant has continued to conduct research after that, and the casting of the area above the meniscus 150 mm to 150 mm.

Continuous casting of steel has been attempted using a mold with an electromagnetic field, which has longitudinal slits formed at predetermined intervals in the mold wall and an electromagnetic coil provided around its outer periphery. During the research process, some slabs with inclusion defects involving mold lubricant were found in the cast slabs, and when the cause was investigated, it was discovered that the molten steel flow caused by electromagnetic force in the mold during casting. It was discovered that this caused the melt level to fluctuate, which caused the meniscus to become unstable and involve the mold lubricant, resulting in inclusion defects.

Therefore, with the aim of solving the above problem, we conducted further research and developed a method for continuous casting of steel using a mold with an electromagnetic field that suppresses fluctuations in the level of molten metal in the mold during casting.

[Means to solve the problem]

The gist of the present invention, which was developed under the above circumstances, is to use a mold having an electromagnetic field formed by forming vertical slits at predetermined intervals in the mold wall above the meniscus 150 mm to 150 mm and providing an electromagnetic coil around the outer periphery of the vertical slits. In the continuous steel casting method, the longitudinal slit is 10-140 mm.
The electromagnetic coil is provided with a spacing of 5 to 20 mm.
This is a continuous casting method of steel using a mold having an electromagnetic field that applies a frequency of Hz and continuously casts the molten steel and solidified steel near the meniscus in the mold while self-sustaining by electromagnetic force.

[For production]

The present invention will be explained in detail below.

FIG. 1 is an explanatory diagram of a mold having an electromagnetic field applied to the method of the present invention, in which fil is a water-cooled mold;
2) is an electromagnetic coil, (5) is an immersion nozzle, and vertical slits (4) are formed at 35 mm intervals in the mold wall (3) above the meniscus 150 mm to 150 mm of the water-cooled mold (1). , an electromagnetic coil (2) on its outer circumference
Or is provided.

The present applicant has conventionally used a mold having the above electromagnetic field and set the frequency of the current flowing through the electromagnetic coil (2) to 3kHz.
has been used to investigate the lubrication performance between the mold and the solidified shell. During this process, slabs with inclusion defects involving mold lubricant were occasionally found in the cast slabs, and the cause of this was investigated.

As a result, we believe that the cause is fluctuations in the molten metal level due to the flow of molten steel generated by electromagnetic force in the mold during casting, which makes the meniscus unstable and involves the mold lubricant, and the electromagnetic coil (2) As a result of conducting an experiment by changing the frequency of the current flowing through the tube, it was found that as the frequency increases, the amount of variation in the meniscus decreases, as shown in FIG. In particular, when the frequency is increased to 5 kHz or more, the amount of fluctuation becomes less dexterous, which makes it possible to suppress mold lubricant entrainment. On the other hand, when the frequency is increased in this way, the amount of variation in the meniscus is reduced, but the lines of magnetic force tend to concentrate near the inner surface of the mold, which heats the solidification shell formed within the mold and delays solidification. The limit for the solidified shell to withstand pulling out from the mold is that it must be below the surface temperature of the slab or the zero ductility temperature, which is just below the solidus temperature of the steel, but the current flowing through the electromagnetic coil (2) frequency is 2
If it exceeds 0 kHz, the surface temperature of the slab will exceed this and breakage of the solidified shell will occur, increasing the incidence of breakouts as shown in FIG. 2. Therefore, in the present invention, the frequency of the current flowing through the electromagnetic coil is specified in the range of 5 to 20 kHz, thereby suppressing the problems of mold lubricant entrainment and breakout, and making it possible to produce steel using a mold that has an electromagnetic field. This made continuous casting possible.

On the other hand, as mentioned above, even if the frequency of the current flowing through the electromagnetic coil is 5 to 20 kHz, the mold wall (
3) is influenced by the spacing of the vertical slits (4), and as shown in FIG. Density attenuation is reduced, spacing is 140mm
If it is less than 50%, the attenuation rate will be 50% or less, and the above-mentioned frequency can be effectively applied to small scale equipment such as a power supply. However, when the distance is less than 10mm,
The water-cooling structure inside the mold wall becomes difficult to construct, making it difficult to manufacture a water-cooled mold. Therefore, the interval between the vertical slits (4) is
Preferably, it is good to form within the range of 30 to 75 cities.

In addition, the width of the vertical slit should be wide enough to prevent the molten steel in the mold from flowing out of the slit, and there is no particular specification. This is preferable in terms of preventing the outflow of the magnetic flux and suppressing the attenuation of the magnetic flux density.

〔Example〕

A slit of about 0.3 mm wide is made at 46 mm intervals above the part 100 mm below the meniscus on the short side mold wall, and a slit of about 0.3 mm wide is made at 46 mm intervals above the part 100 mm below the meniscus on the long side mold wall.
An electromagnetic coil is provided on the outer periphery of a slab continuous casting mold for slab size 230 x 1250 mm in which slits of about 0.3 mm width are formed at mm intervals so as to cover the range from 50n++n above the meniscus to 100mm below the meniscus. Using a mold with an electromagnetic field (see Figure 1), steel types:
Low carbon (C: 0.08 wt%) aluminum quilt steel was continuously cast at a casting speed of 1.6 m/min while maintaining the molten steel temperature in the tundish at 1550 to 1560°C.

The frequency of the current flowing through the electromagnetic coil at this time is 10kHz
Therefore, the maximum magnetic flux density on the inner surface of the mold is 600 to 100.
It was 0 Gauss.

During this casting process, visual observation revealed that the casting could be carried out with almost no fluctuation of the molten metal level in the mold, and no inclusion defects involving the mold lubricant were found in the internal quality of the resulting slab. .

〔Effect of the invention〕

As described above, according to the continuous casting method of steel using a mold having an electromagnetic field according to the present invention, it is possible to perform casting in which fluctuations in the melt level in the mold are suppressed during casting by the electromagnetic coil provided on the outer periphery of the water-cooled mold. Therefore, it is possible to prevent the mold lubricant from being drawn into the slab, and the molten steel and solidified shell near the meniscus in the mold are independently held by electromagnetic force.
A slab with excellent internal and external quality can be obtained.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a mold having an electromagnetic field applied to the method of the present invention, Fig. 2 is a graph showing the relationship between frequency, meniscus fluctuation amount, and breakout rate, and Fig. 3 is a slit diagram. FIG. 3 is a graph diagram showing the relationship between spacing and magnetic flux density attenuation rate. (1) Water-cooled mold (2)! Magnetic coil (3) Mold wall (4) Vertical slit (5) Immersion nozzle Patent applicant: Kobe Steel, Ltd. Representative Patent attorney: Akira Kanemaru - Figure 1

Claims (1)

[Claims] In a continuous casting method for steel using a mold having an electromagnetic field, in which vertical slits are formed at predetermined intervals in the mold wall above a portion 50 mm to 150 mm below the meniscus, and an electromagnetic coil is provided on the outer periphery of the mold, the vertical slits are 10
~140 mm apart, while the electromagnetic coil has 5
A continuous casting method for steel using a mold having an electromagnetic field, characterized in that a frequency of ~20 kHz is applied and continuous casting is carried out while molten steel and solidified shell near the meniscus in the mold are self-supported by electromagnetic force.