JPH05200513A - Method for continuously casting metal - Google Patents

Abstract

PURPOSE:To prevent sticking to promote slow cooling and to produce a cast slab having good surface characteristic at high speed by preventing the surface defect caused by a triple point and supplying molten lubricant. CONSTITUTION:A tundish 1 for storing molten metal, a nozzle 2 integrated with the tundish, a metal-made cooling mold 3 having plural slits 4 in the casting direction and directly connected with the nozzle and a coil 5 for conducting high frequency current while surrounding this mold are provided. Then, in this continuous casting method, the molten lubricant is supplied to a gap part P near the triple point generated by electromagnetic field of the coil from plural supplying pipes 6 embedded in the slit parts. Metal powder is mixed in the lubricant and further, the metal-made supplying pipe can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface defects of a slab generated during continuous casting of metal, particularly casting using a casting device in which a tundish and a mold are directly connected (hereinafter referred to as a direct-connection type continuous casting device). At this time, the present invention relates to a continuous metal casting method for preventing surface defects generated from a molten metal supply nozzle (hereinafter referred to as a hot water supply nozzle) and a portion where a mold and molten metal are simultaneously in contact with each other (hereinafter referred to as a triple point).

[0002]

2. Description of the Related Art Conventionally, in continuous casting, a method of supplying molten metal from a tundish through a long dipping nozzle has been often used. However, this method does not sufficiently block the atmosphere and the molten metal. For example, there is a problem that inclusion of inclusions due to excessive flow of molten steel, nozzle clogging, or difficulty in manufacturing thin slabs. In order to solve these problems, a casting method using a direct-connection type continuous casting apparatus is used. To improve the quality of the slab and increase the casting speed by this method, for example, Japanese Patent Laid-Open No. 51-65023.
Japanese Patent Laid-Open Publication No. 58-356 and Japanese Patent Laid-Open Publication No. 58-356 disclose methods of utilizing electromagnetic force.

In the method described in Japanese Patent Laid-Open No. 51-65023, an energizing coil is provided on the upstream side of the mold, and an alternating current is supplied to the energizing coil to generate an electromagnetic pinch force, which melts the molten metal. This is a method of confining it in a specific space or suppressing the inflow to holes or joints for stable continuous casting, but it is still the idea of sealing gaps, and this method is also used for actual operation. In order to improve the shape and arrangement of the coil and the mold, it is necessary to locally densify the induced current on the molten metal surface near the triple point. However, if this densification is carried out, the heat value of Joule increases at the same time, and therefore a method for effectively cooling the coil and the molten metal must be added, which causes a problem to be solved.

The method described in Japanese Patent Laid-Open No. 58-356 is intended for horizontal continuous casting, in which an energizing coil for magnetic field generation is arranged near the surface of the mold facing the tundish, and the joining surface of the mold and the tundish is joined. It aims to speed up casting by eliminating molten metal from the. However, even when this equipment is used, it has the same problems as the method described in the above-mentioned JP-A-51-65023.

In particular, when a refractory nozzle, a metal mold, and a triple point by molten metal are formed as in the apparatus described in JP-A-51-65023, it is adjacent to the refractory mold for cooling by the mold. The solidified shell grows and adheres to the part to be covered. Since the solidified shell is pulled out along with casting, the refractory is damaged, and this often causes defects on the surface of the slab. In order to prevent surface defects at the triple points, it is better to remove molten metal from here, but for this purpose it is necessary to suppress the generation of so-called invalid induced current inside the mold and to bring the coil as close to the mold as possible. There is.

However, if the energizing coil is brought too close to the mold from the upstream side of the mold, short-circuiting may occur, or Joule heat may be generated at the corners of the mold. Therefore, in the above method in which the pinch force generated in the coil is applied to the surface of the molten metal from the upstream side of the mold, it is difficult to reliably remove the molten metal from the triple point, and therefore, the lubricant can be smoothly supplied. If you can't do it, you could break out in extreme cases.

On the other hand, in order to increase the speed of casting, it is necessary to lubricate between the mold and the slab, but it is difficult to convey the powdery lubricant as it is in a thin supply pipe.
Instead, a method of using a liquid lubricant such as repseed oil can be considered. However, this method also has problems such as occurrence of a bubbling phenomenon due to gasification in the high temperature mold, and breakage of the solidified shell due to this phenomenon.

[0008]

In the direct connection type continuous casting apparatus, surface defects are likely to occur from the triple point. The object of the present invention is to eliminate molten metal from this triple point and to supply molten lubricant to the cavity formed therein, thereby preventing the occurrence of surface defects and casting high quality slabs at high speed. An object of the present invention is to provide a continuous casting method.

[0009]

The present inventors have various means for effectively eliminating molten metal from the triple point during continuous casting (see cavity P in FIG. 1) to prevent the generation of surface defects. As a result of repeated studies, the following findings were obtained. That is, a. The method of directly excluding the molten metal at the triple point by using the pinch force generated between the energizing coil and the molten metal is not effective because the induced current is generated more in the mold than in the molten metal.

B. The induced current is positively generated in the mold using the energizing coil, and the secondary pinch force generated between the mold and the molten metal is utilized, whereby the molten metal at the triple point can be reliably eliminated.

C. In order to increase the pinch force at the triple points particularly, a slit portion may be formed in the portion of the mold that is in contact with the refractory hot water supply nozzle, and the energizing coil may be arranged so as to surround the slit portion.

D. With the above structure c, it is not necessary to dispose the mold and the current-carrying coil close to each other, so that the risk of short-circuiting between the mold and the coil is small.

E. If a lubricant is supplied to the cavity formed by removing the molten metal through the slit portion of the mold, more stable casting can be performed.

F. If the molten lubricant is supplied from the supply pipe embedded in the slit portion, more stable casting can be performed.

The present invention has been made on the basis of these findings, and its gist resides in the following continuous casting method.

A tundish for storing molten metal, a nozzle integral with the tundish, a metal cooling mold having a plurality of slits in the casting direction directly connected to the nozzle, and a high-frequency current circulating around the mold. By a continuous casting device equipped with a coil that energizes, from a plurality of supply pipes embedded in the slit part, the preheated and melted lubricant is supplied to the cavity inside the mold near the triple point generated by the electromagnetic field of the coil. A method of direct-coupling continuous casting, characterized by:

In the above continuous casting method, the lubricant supply pipe is made of metal, and / or metal powder is mixed with the lubricant to melt the lubricant with an induction current generated by the electromagnetic field of the coil. Is desirable.

[0018]

First, an apparatus for carrying out the method of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a vertical direct-connection type continuous casting device. FIG. 2 is a perspective view of a part of the mold showing an installation example of the lubricant supply pipe embedded in the slit portion of the mold.

As shown in the figure, a refractory tundish 1 of this casting apparatus has a hot water supply nozzle 2 which is integral with the tundish 1, and a metal cooling mold 3 is fitted and directly connected to the nozzle 2. .. A plurality of slits 4 extending in the longitudinal direction of the mold are formed in the upper portion of the mold 3 in contact with the molten metal 13, more specifically, in the lower end portion of the nozzle 2 including at least the cavity P, and the slits 4 are provided. The energizing coil 5 is arranged so as to circulate around the outer periphery of the mold part. In the vicinity of the cavity P formed at the triple point of the mold 3, a plurality of metal lubricant supply pipes 6 insulated from the mold by a refractory material are embedded. This is connected to a storage container 8 for powder lubricant (mold powder) 7 installed outside. A vibration exciter 9 that gives a slight vibration is attached to the storage container 8. 1 and 2, 11 is a refractory for insulation,
12 indicates solidified shells respectively.

When the coil 5 is energized and an electromagnetic field is applied by a high-frequency current using the above-mentioned device, the pinch force removes the molten metal at the triple point to form the cavity P.

On the other hand, when a slight vibration is applied to the storage container 8 using the vibrator 9, the mold powder 7 is conveyed into the supply pipe 6. Due to the electromagnetic field, an induced current is generated in the supply pipe 6, and the Joule heat melts the mold powder 7. Mold powder, which was difficult to convey as a powder, can be supplied in a molten state in this way, and gasification that occurs when using a liquid lubricant,
The bubbling problem can be avoided.

As the material of the lubricant supply pipe 6, a high melting point metal material such as Ti is desirable. Further, if the effective value or frequency of the high-frequency current flowing through the energizing coil is increased, the Joule heat generated also increases, so that the amount of melted lubricant can be controlled. If the mold powder is not sufficiently melted by the Joule heat alone, or if the mold powder is clogged in the carrier supply pipe, it is possible to auxiliary heat the mold powder beforehand by using the heater 10. On the other hand, since the amount of the mold powder to be conveyed can be controlled by changing the frequency of the microvibration applied to the storage container 8 by the vibrator 9, it is possible to control the supply amount of the molten powder. it can.

Further, it is desirable to previously mix the mold powder with a metal powder that is harmless to the quality of the slab. Even if the supply pipe 6 is made of a metal such as Ti or a non-metal such as a refractory, the induced current also causes the powder itself to generate heat, which facilitates melting and supply to the cavity P, resulting in a current value. Energy saving effects such as reduction of

As described above, according to the method of the present invention, the molten metal is eliminated from the triple point by utilizing the electromagnetic force in the direct-connection type continuous casting apparatus, and the pre-melted mold powder is supplied to the cavity formed by this. It is possible to prevent the generation of surface defects in combination with the promotion of the slow cooling effect on the mold surface, and it is possible to manufacture a slab having good surface properties.

Further, the method of the present invention does not require another new heat source or apparatus for preliminarily melting the lubricant, and an additional equipment such as a heater for heating is sufficient, and thus is an economical method. ..

[0026]

Example 1 Using the apparatus shown in FIGS. 1 and 2, continuous casting of round-section cast slab was carried out for molten steel by the method of the present invention. The equipment and casting conditions are as follows.

Mold: Inner diameter 150 mm, wall thickness 35 mm, length 1000 mm Slit: Width 0.2 mm, length 150 mm, 32 energizing coil: Outer diameter 30 mm, wall thickness 2 mm, winding number 4 Current effective value 20000 A, frequency 20 KHz steel Composition: C = 0.2%, Mn = 0.4%, Si = 0.3%, P
= 0.02%, S = 0.02% _{Powder: SiO 2 = 33.6%, CaO} = 35.0%, Al 2 O 3 =
2.7%, MgO = 4.9% Na ₂ O = 9.7%, K ₂ O = 0.5%, F = 3.9%, Fe ₂ O ₃ =
3.9% MnO = 0.1%, FreeC = 4.1% Melting point 1130 ℃ Molten steel head: 60 to 90mm Molten metal nozzle inner diameter: 130mm Molten steel temperature: 1540 ℃ Casting speed: 2.5m / min Lubricant supply pipe: Inner diameter 1mm, outer diameter 3.5mm, (Made of Ti) 32
Setting temperature of this heater: 1000 ℃ Casting is supplying cooling water at room temperature to the mold and energizing coil.
Molten steel was supplied from the tundish into the mold, and drawn for 60 seconds at a speed of 2.5 m / min. As shown in FIG. 2, the metal lubricant supply pipe was embedded in the pores provided in the slit while being insulated with a refractory material. At this time, the vibration exciter was adjusted to supply the molten lubricant at a rate of 4.2 g / sec from the lubricant supply pipe.
From the temperature measurement result of the thermocouple buried in the mold, the temperature of the lubricant supply pipe at this time was about 1150 at a position 10 mm from the mold inner wall.
At ~ 1250 ° C, the lubricant was fully molten. As a result of casting,
No surface defects due to breakout or cold shut, which were observed when no electromagnetic force was applied, were not seen, and a slab of good quality was obtained. On the other hand, for comparison, the heater was set to 1200 ° C. to melt the lubricant in advance, electromagnetic waves were not applied, and casting was also performed under the same conditions as above, but the lubricant melts, Since no cavity is formed in the mold near the triple point, the lubricant is not supplied,
A normal cast state was not obtained. As a result, defects such as cracks were also found on the surface of the slab.

[0028]

Example 2 Using the same apparatus as in Example 1, the lubricant supply pipe was changed to a quartz pipe, and the lubricant was changed to a powder in which 5% by weight of Fe powder having an average particle diameter of 150 μm was mixed. Other conditions were the same, and continuous casting was carried out. As a result, no difference was found in the performance of the lubricant and the supply pipe, and sufficient supply of the lubricant was obtained. Therefore, a good cast piece was obtained as in the case of applying the electromagnetic force of Example 1. We also implemented a method that uses a Ti tube and the above-mentioned powder mixed with Fe powder, but
It was confirmed that the lubricant was sufficiently melted and supplied even if the coil frequency or effective current value was further reduced by about 20% due to the heat generation improving effect of the powder itself, which is recognized as about 20%.

[0029]

By the method of the present invention, surface defects caused by triple points are prevented, and by supplying a molten lubricant, seizure is prevented and gentle cooling is promoted, and good surface properties are obtained. It enables the production of the slab to be performed at high speed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a direct connection type continuous casting apparatus for carrying out the method of the present invention.

FIG. 2 is a perspective view of a part of a mold showing one example of installation of a lubricant supply pipe embedded in a slit part of the mold for carrying out the method of the present invention.

[Explanation of symbols]

1: Tundish 2: Hot water nozzle 3: Mold
4: Slit 5: Energizing coil 6: Lubricant supply pipe 7: Lubricant (mold powder) 8: Lubricant storage container 9: Vibrator 10: Heater 11: Insulation refractory 12: Solidified shell 13: Molten metal P : Cavity at triple point

Claims (2)

[Claims] 1. A tundish for storing molten metal, a nozzle integral with the tundish, a metal cooling mold having a plurality of slits in the casting direction which are directly connected to the nozzle, and a high-frequency wave circulated around the mold. In a continuous casting device equipped with a coil for passing an electric current, through a plurality of supply pipes embedded inside the slit, in the mold cavity near the triple point generated by the electromagnetic field of the coil, preheated and melted A continuous casting method for molten metal, which comprises supplying a lubricant. 2. A lubricant supply pipe is made of metal, and / or a metal powder is mixed with the lubricant, whereby the lubricant is melted by an induction current generated by an electromagnetic field of the coil. The continuous casting method according to claim 1.