JPH0780614A - Continuous casting method preventing pick-up of oxygen in steel - Google Patents

Abstract

PURPOSE:To prevent the pick-up of oxygen in molten metal at the time of flowing from a ladle to a tundish by blowing the inert gas into a space surrounding a joint part and isolating the molten metal between the ladle and a refractory nozzle from air. CONSTITUTION:The space B in the inside of a compressible material 8 is formed with the inside of a fastening tool 6, the outside of a ladle nozzle 2 and the upper surface of a long nozzle 4 so as to be thin as annular-state around the lower end part 2b of the ladle nozzle 2 and keep this space to almost airtight. The ladle nozzle 2 and the long nozzle 4 having such a constitution are used and the lower end of the long nozzle 4 is dipped into a tundish, and the molten metal A is poured into the tundish from the ladle while blowing inert gas such as argon gas, from a pipe 7 through a gas flowing hole 6a so as to increase the pressure in the space B. Then, inclusion is floated up and separated in the tundish and the clean molten metal is poured into a mold to form a cast slab.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a continuous casting method,
Specifically, an oxygen pick-up in steel when injecting molten metal through a ladle nozzle provided at the bottom of a ladle that stores molten metal and a refractory cylinder such as a long nozzle joined to the ladle nozzle. The present invention relates to a continuous casting method for preventing the above.

[0002]

2. Description of the Related Art Conventionally, in a continuous casting process, molten metal (hereinafter referred to as molten metal) after refining is poured from a ladle into a tundish, and non-metallic inclusions such as slag and tundish flux are included in the tundish. The slab is formed by injecting the purified molten metal that has been floated and separated into the mold.

For the injection of the molten metal into the tundish, as disclosed in Japanese Patent Laid-Open No. 2-235555, a long nozzle (refractory tube) made of refractory is joined to a ladle nozzle, and the long nozzle There is a continuous casting method in which the tip is immersed in the molten metal in the tundish and then the molten metal injection is started. According to this continuous casting method, it is possible to prevent the non-metallic inclusions floating on the upper surface of the molten metal in the tundish from being knocked into the molten metal due to the falling energy of the molten metal flow at the start of pouring.

By the way, in the case of steel, the cleanliness of the molten metal after the refining has remarkably advanced due to the development of secondary refining technology in recent years.
As an evaluation, it appears as a reduction of oxygen in steel. Therefore, in the process of continuously casting such a low-oxygen molten metal, a frequent problem is how to maintain the cleanliness of the molten metal. Specifically, oxygen pickup of the melt in the ladle, when moving from the ladle to the tundish, or also in the tundish, and in the mold has been viewed as a problem.
Oxygen pickup can be prevented in the ladle, tundish, and mold by degassing due to flux etc. and proper selection of refractories.

[0005]

However, at present, the oxygen pick-up of the molten metal when moving from the ladle to the tundish is degassed at the joint between the ladle nozzle and the long nozzle joined to the ladle nozzle. Is difficult,
Those that can be completely prevented have not been put to practical use.

For example, a method of sealing the joint between the ladle nozzle and the long nozzle by using a sealing material made of silicone and resin as disclosed in JP-A-63-152687 is often adopted. There is. However, in such a method, the joint between the ladle nozzle and the long nozzle is
There is a disadvantage that negative pressure is generated as the molten metal flows, and air is blown in through a small gap.

Therefore, as shown in FIG. 4, around the lower end of the ladle nozzle 2 below the nozzle fastener 1 for fastening and fixing the ladle nozzle 2, that is, the joining of the ladle nozzle 2 and the long nozzle 4 together. A sealing ring 3 made of an annular pipe is attached in the vicinity of the portion 4a, and a plurality of outlets formed on the ladle nozzle 2 side of the ring 3 are connected to the joint portion 4a.
A method of moving the molten metal A while spraying an inert gas toward it is also generally performed. However, even with this method, it is not possible to completely block the entrainment of air around the joint 4a.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a continuous casting method for preventing oxygen pick-up in steel for preventing oxygen pick-up of molten metal when moving from a ladle to a tundish. Especially.

[0009]

In order to achieve the above object, a continuous casting method for preventing oxygen pickup in steel according to the present invention is a ladle nozzle provided at the bottom of a ladle for storing molten metal and the ladle. When pouring the molten metal into a tundish through a refractory cylinder joined to the lower end of the nozzle, at the joint between the ladle nozzle and the refractory cylinder, it is arranged near the lower end of the ladle nozzle. A compressible substance is disposed between the lower end surface of the tightening tool and the upper end surface of the refractory tube so as to surround the outer circumference of the ladle nozzle, and the outer peripheral surface of the ladle nozzle, the tightening tool, A space surrounding the joint is formed by the compressible substance and the refractory tube, and an inert gas is blown into the space through a flow path provided in the fastening tool, so that the refractory is removed from the ladle. The feature is that the molten metal between the barrels is cut off from the air. There.

[0010]

According to the continuous casting method for preventing oxygen pick-up in steel according to the present invention, a space is formed around the joint between the ladle nozzle and the refractory tube, and the space is increased so as to increase the pressure. Since the molten metal is moved while blowing the active gas, only the inert gas enters the molten metal inside the nozzle and the air does not enter, and it becomes possible to prevent oxygen pickup in steel.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The continuous casting method for preventing oxygen pickup in steel according to the present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings.

According to the present invention, the molten metal stored in the ladle is tanned through a ladle nozzle attached to the bottom of the ladle and a long nozzle (refractory tube) joined to the lower end of the ladle nozzle. This is a continuous casting method for preventing oxygen pick-up in steel when it is poured into a dish, and is characterized in that the connection structure between the ladle nozzle and the long nozzle is different from the conventional one.

FIG. 1 is a sectional view showing an embodiment of a connecting structure of a ladle nozzle and a long nozzle used in the present invention.

The long nozzle (refractory cylinder) 4 is formed such that the upper end 4b thereof is spread in a funnel shape, and the inner surface of the upper end 4b is joined to the lower end 2b of the ladle nozzle 2. Is.

The ladle nozzle 2 is attached to the bottom of a ladle (not shown), its inner diameter is substantially the same as that of the long nozzle 4, and a step 2a is formed horizontally on the outer surface thereof. The lower end portion 2b below the step 2a is formed thinner than the other portions. The upper surface of the fastener 6 is in close contact with the step 2 a of the ladle nozzle 2.

The fastener 6 is for fixing the ladle nozzle 2 by pushing up the step 2a of the ladle nozzle 2 and is an annular body having an inner diameter slightly larger than the outer diameter of the ladle nozzle 2. It is attached around the lower end 2b of the ladle nozzle 2. A vent hole (flow passage) 6a for blowing gas is horizontally formed in the fastener 6, and one end of a pipe 7 for sending gas is fitted into the vent hole 6a. On the lower surface of the fastening tool 6, a groove 6b for improving the sealing property is formed in an annular shape. The groove 6b is provided for the compressed compressible substance 8 to enter.

A compressible substance 8 is in close contact with the lower surface of the fastener 6 and the upper surface of the long nozzle 4. This compressible material 8
Are arranged all around the ladle nozzle 2.
The compressible substance 8 used here is not particularly limited as long as it has compressibility and heat resistance, but for example, a ceramic such as kao wool (manufactured by Isolite), FIBERMAX felt (manufactured by Toshiba Monoflux), etc. Fibers can be used.

When the compressible substance 8 is arranged, it is attached to the ladle nozzle 2 side in advance when the ladle nozzle 2 and the long nozzle 4 are joined. For example, a compressible substance 8 that is slightly longer than the length of the upper surface of the long nozzle 4 and the lower surface of the fastener 6 after joining, for example, 20% longer, is wrapped around the ladle nozzle 2 and tied with a wire (van wire). The end of this wire is wrapped around the fastener 6. When the long nozzle 4 is joined, it is compressed by the upper surface of the long nozzle 4, and the upper surface of the compressible substance 8 and the lower surface of the fastener 6 and the lower surface of the compressible substance 8 and the upper surface of the long nozzle 4 are arranged in close contact with each other. To do.

A space B is formed by the inside of the compressible substance 8, the inside of the fastener 6, the outside of the ladle nozzle 2 and the upper surface of the long nozzle 4. In other words, this space B is thinly formed in an annular shape around the lower end portion 2b of the ladle nozzle 2 and is kept in a substantially airtight state.

Here, the joint 4a between the ladle nozzle 2 and the long nozzle 4 in the space B is formed by the compressible substance 8.
In order to prevent the ventilation holes 6a from being separated from each other, the plate material 10 is previously attached to the outside of the lower end portion 2b of the ladle nozzle 2 by the plate material 1
It is preferable that the upper end and the lower end of 0 be arranged near the vent hole 6a and the joint portion 4a of the fastener 6, respectively.

The plate member 10 is made of an iron plate or the like, and as shown in FIG. 2, a bent portion 10a is formed in the central vertical direction.
Its cross section is substantially L-shaped. The plate member 10 has a space B so as to guide the gas from the ventilation hole 6a to the joint portion 4a.
It is arranged inside. It is sufficient to dispose the plate member 10 at one place in the vicinity of the ventilation hole 6a, but it may be arranged at two or more places.

The ladle nozzle 2 and the long nozzle 4 having the above-mentioned connection structure are used, and the lower end of the long nozzle 4 is immersed in the molten metal in the tundish to increase the pressure in the space B. As described above, the molten metal A is injected from the ladle into the tundish while blowing an inert gas such as argon gas from the pipe 7 through the ventilation hole 6a. And
Inclusions are floated and separated in a tundish, and the purified molten metal is poured into a mold to form a slab.

According to the continuous casting method for preventing oxygen pick-up in steel according to the present invention, air does not enter the molten metal A from the joint portion 4a because the space B is in the pressurized state of the inert gas. Further, since the plate member 10 is arranged, the joint portion 4a and the vent hole 6a are not separated from each other, and the joint portion 4a can be maintained in the inert gas pressure increasing state. Further, when the ladle nozzle 2 and the long nozzle 4 are joined, the compressible substance 8 is mounted on the ladle nozzle 2 side in advance, so that the compressible substance 8 can be easily arranged. The compressible substance 8 does not hinder the centering of the joining work. Further, since the compressible substance 8 is mounted on the ladle nozzle 2 side, it is easy to replace the ladle every time the ladle is replaced, and the above-mentioned effect can be maintained even during multiple casting. Further, according to such a continuous casting method for preventing oxygen pickup in steel, good sealability can be maintained by replacing the inexpensive compressible substance 8.
Further, the amount of the inert gas can be reduced as compared with the conventional continuous casting method in which the inert gas is blown by the sealing ring 3.

Regarding the fastener 6, the ladle nozzle 2
Can be attached to, and if the flow path of the inert gas can be formed,
Any type may be used, a flow path may be formed in a conventional nozzle fastening tool (bionette), or it may be separately provided for fixing a compressible substance. Further, the structure of the ladle nozzle 2 and the long nozzle 4 is not limited to the illustrated example, and the fastener 6 can be attached to the ladle nozzle 2,
A compressible substance 8 is arranged between the refractory cylinder such as the long nozzle 4 joined to the ladle nozzle 2 and the fastener 6, and the closed space B is provided.
Any material can be used as long as it can be formed, and conventionally known materials can be used.

(Example) The continuous casting method of the present invention and the conventional continuous casting method were applied to RH-treated SUS304Al-less material under the casting conditions of heat size of 100 ton and tundish capacity of 15 ton. The steel types are Si and Mn deoxidized without deoxidizing with Al,
The oxygen value in the steel of this steel type is lower than the oxygen equilibrium value of Si and Mn, and the oxygen value in the steel is close to the CO equilibrium under high vacuum during RH treatment. It is a highly sensitive condition.

As a comparative example, a conventional continuous casting method was performed. In this method, as shown in FIG. 4, a sealing ring 3 is attached in the vicinity of a joint 4a between a ladle nozzle 2 having an inner diameter of 70 mm and a long nozzle 4, and the ring 3 is bored on the ladle nozzle 2 side. The molten metal A was moved at 1.4 ton / min while spraying argon gas at 5 l / sec.

The example of the present invention uses the same ladle nozzle 2 and long nozzle 4 as in the above comparative example, and as shown in FIG. 1, a plate material 10, a fastener 6 having a vent hole 6a and a compressible material. 8 is arranged, the ladle nozzle 2 and the long nozzle 4 are joined to form a sealed space B, and the air is shut off while blowing the argon gas into the sealed space B at a rate of 3 l / sec. The amount of melt A was moved. As the compressible substance 8, a kaolin wool manufactured by Isolite Co. having a thickness of 15 mm and having a length obtained by extending the length from the lower surface of the fastening tool 6 to the upper surface of the long nozzle 4 by 20% is used. Kao wool was wrapped around the ladle nozzle 2 in double layers.

FIG. 3 shows the oxygen concentration in steel of the molten metal in the tundish by these continuous casting methods. In this figure,
From the end of degassing, the tundish representative (45% of casting
The oxygen concentration in the steel by the oxygen pickup in the steel up to the molten metal in the tundish at that time is shown. As can be seen from this figure, the molten metal of the conventional continuous casting method has an oxygen concentration in the steel of 8 to
The average was 18 ppm at 25 ppm. On the other hand, the molten metal of the continuous casting method of the present invention has an oxygen concentration in steel of −2 to 5 pp.
m, an average of 2 ppm, and taking into consideration the oxygen concentration brought close to the high vacuum equilibrium after degassing of this steel type, the degassing (air cutoff) of the joint 4a between the ladle nozzle and the long nozzle is almost complete. it is conceivable that.

[0029]

As described in detail above, according to the continuous casting method for preventing oxygen pickup in steel according to the present invention,
Since an inert gas is blown into the space surrounding the joint between the ladle nozzle and the refractory tube, air does not enter the molten metal from the joint between the ladle nozzle and the refractory tube, and the tundish is removed from the ladle. It is possible to prevent oxygen pickup of the molten metal when moving to. Therefore, the molten metal having reduced oxygen in the steel by refining can be continuously cast without being oxidized, and a high quality slab can be formed.

Further, if the compressible substance is attached to the ladle nozzle side in advance, it does not hinder the refractory barrel joining work at all, and it is easy to replace the compressible substance each time the ladle is replaced.
The effect described above can be maintained even during continuous casting.
Further, according to the continuous casting method for preventing such oxygen pickup in steel, good sealability can be maintained by exchanging an inexpensive compressible substance, and a relatively small amount of inert gas is sufficient. It is possible to obtain a good sealing effect, and it is possible to improve the sealing property without increasing the running cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a connection structure between a ladle nozzle and a refractory tube used in a continuous casting method according to the present invention.

FIG. 2 is a perspective view showing a plate member used in the connection structure shown in FIG.

FIG. 3 is a graph showing the oxygen concentration in steel of the molten metal in the tundish by the continuous casting method according to the present invention and the conventional continuous casting method.

FIG. 4 is a cross-sectional view showing a connection structure between a ladle nozzle and a refractory tube used in a conventional continuous casting method.

[Explanation of symbols]

 2 Ladle nozzle 2a Stage 2b Lower end 4 Refractory tube (long nozzle) 4a Joint 4b Upper end 6 Tightening tool 6a Flow path (vent) 8 Compressible substance A Molten metal (molten metal) B Space

Claims (1)

[Claims] 1. When pouring the molten metal into a tundish through a ladle nozzle provided at the bottom of a ladle for storing molten metal and a refractory cylinder joined to the lower end of the ladle nozzle. , At the joint between the ladle nozzle and the refractory tube, between the lower end surface of the fastener arranged near the lower end of the ladle nozzle and the upper end surface of the refractory tube A compressible substance is arranged so as to surround the outer periphery, and a space surrounding the joint is formed by the outer peripheral surface of the ladle nozzle, the fastening tool, the compressible substance and the refractory tube. Continuous casting for preventing oxygen pickup in steel, characterized in that an inert gas is blown into a space through a flow path provided in the fastener to block molten metal between the refractory cylinder from the ladle and air. Method.