JPH0839205A - Continuous casting method - Google Patents

Abstract

(57) [Abstract] [Purpose] In continuous casting, it is aimed to improve productivity and slab quality by preventing clogging of the immersion nozzle. [Structure] (1) When supplying molten steel from a ladle into a tundish via a refractory pipe that can be removed from the ladle,
The cross-sectional area of the pipe is more than 1 time the total cross-sectional area of the dipping nozzle.
It is a continuous casting method that is less than doubled. (2) The continuous casting method according to (1) above, which uses a refractory pipe in which a refractory mass is arranged in the middle of the molten steel flow path. [Effect] Since it is possible to reliably prevent the alumina from adhering to the immersion nozzle, it is possible to perform continuous casting, not only stabilize the continuous casting operation, but also improve the quality of the cast piece.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous steel casting method.

[0002]

Immersion nozzles are currently used in continuous casting processes to feed molten steel from a tundish into a mold without oxidizing it. The mainstream of the material of the immersion nozzle is mainly alumina and carbon. In such a submerged nozzle, alumina precipitated in the steel adheres to the inner wall of the nozzle with the elapse of casting time, and in severe cases, nozzle clogging may occur and casting may be stopped, which deteriorates the productivity of continuous casting. There was a problem. In addition, the clogging of the immersion nozzle also disturbs the flow of molten steel in the mold, thus increasing inclusion defects due to powder entrainment.

As one of means for solving this problem, for example, as shown in Japanese Patent Publication No. 58-3467,
It is known that a porous cylindrical refractory (inner hole body) that is concentric with the inner hole of the immersion nozzle is provided in the main body of the immersion nozzle, and Ar and other inert gas are blown from the inner wall of the porous refractory material. . This gas blowing reduces the contact area between the inner wall of the immersion nozzle and the molten steel, and further stirs the molten steel, or forcibly separates the deposits with gas bubbles to grow alumina inclusions on the inner wall of the immersion nozzle. It has the effect of preventing.

Further, as another means, for example, JP-A-64
As disclosed in Japanese Patent Publication No.-40154, ZrO ₂
-By using a CaO-C material for the inner wall of the immersion nozzle,
CaO in a refractory and Al ₂ O _{3 in} molten steel are reacted with each other to form a low melting material of calcium aluminate. This low melt is washed away with a molten steel flow to give a minute melting loss to prevent the deposit.

[0005]

However, in the former case, it is necessary to blow a large amount of Ar gas into the molten steel in order to reliably prevent the adhesion of alumina to the inner wall of the immersion nozzle. In this case, the blown Ar gas must be blown. The bubbles do not completely float, and are trapped at the solidification interface in the mold, and become bubble-type defects that occur after hot rolling and cold rolling.

On the other hand, like the latter, a nozzle is used to prevent the immersion nozzle from being clogged without performing Ar gas blowing, but when the casting time is long or the cleanliness of molten steel deteriorates, It becomes impossible to supply enough CaO for lowering the melting point of alumina adhered to the inner wall of the immersion nozzle, and the immersion nozzle is clogged in the latter half of casting. Therefore, ZrO
_The current situation is that the _2- CaO-C material immersion nozzle also does not provide a reliable blocking prevention measure.

[0007]

SUMMARY OF THE INVENTION (1) In continuous casting of steel, refractory material is used when molten steel in a ladle is supplied into a tundish through a pipe made of a refractory material removable from the ladle. This is a continuous casting method characterized in that the cross-sectional area of the inner hole of the pipe made is at least 1 time and less than 4 times the total cross-sectional area of the inner hole of the immersion nozzle, and (2) fireproof in the middle of the molten steel flow path. In the continuous casting method according to (1) above, a refractory pipe in which a lump of material is arranged is used.

[0008]

In order to prevent nozzle clogging, the present inventors first conducted various experiments and studies on the immersion nozzle clogging mechanism. As a result, the molten steel is oxidized by oxygen supplied from the atmosphere, refractory, or slag to form an oxide, which serves as a binder to bond the alumina in the molten steel with the inner wall of the immersion nozzle, resulting in clogging of the immersion nozzle. I found out that It was also found that the lower the molten steel stagnation area and the molten steel temperature, the easier the clogging of the immersion nozzle.

Therefore, various preventive measures are conceivable from the mechanism of clogging of the immersion nozzle, but since the main cause of the clogging of the immersion nozzle is adhesion of alumina, it is industrially possible to reduce the alumina itself in the molten steel. The inventors have devised a method for removing alumina using a refractory pipe, which is believed to enable stable continuous casting.

The degree of removal of alumina does not need to be extremely enhanced in cleanliness, and it is sufficient that alumina in the molten steel can be reduced to the extent that the immersion nozzle is not clogged. As the method, by keeping the molten steel in the same state as passing through the immersion nozzle, if the molten steel after removing alumina in the molten steel is passed through the immersion nozzle, it is considered that clogging in the immersion nozzle does not occur. To be

Therefore, as shown in FIG. 3, a refractory pipe 2a having the same inner diameter and material as the immersion nozzle 5 is installed in the tundish 1, and the molten steel in the ladle 3 is inserted through the refractory pipe 2a. No. 4 is fed into the dipping nozzle 5 to obtain a slab 6
I tried casting one after another. After casting, the state of adhesion of alumina to the immersion nozzle 5 and the refractory pipe 2a was observed.

As a result, it has been confirmed that the adhesion of alumina to the inner wall of the immersion nozzle 5 can be reliably prevented. However, the refractory pipe itself installed in the tundish was clogged due to adhesion of alumina, and as a result, casting was stopped at the sixth charge. In other words, the better the alumina removal efficiency of the refractory pipe, the more the immersion nozzle can be blocked, but there is a problem that the productivity of continuous casting deteriorates, and the refractory pipe can be replaced during casting. First, the refractory pipe 2a needs to be removable from the ladle 3 and the tundish 1.

At present, when the molten steel 4 is supplied from the ladle 3 to the tundish 1, it is prevented from being oxidized by air through the long nozzle 9. Therefore, as shown in FIG. 1, instead of the long nozzle 9, the immersion nozzle 5
Using the refractory pipe 2b made of the same material as the above, the molten steel 4 is supplied from the ladle 3 to the tundish 1, and the molten steel 4 is supplied into the immersion nozzle 5 to cast a slab 6 by continuous 9-charge casting. did. The refractory pipe 2b was replaced every two charges when the ladle was replaced.

After casting, the immersion nozzle 5 and the refractory pipe 2
The state of adhesion of alumina to b was observed. As a result, when the cross-sectional area of the inner hole of the refractory pipe 2b is smaller than the total cross-sectional area of the inner hole of the immersion nozzle 5, the supply of the molten steel 4 from the ladle 3 to the tundish 1 cannot follow the casting speed, Since the casting is interrupted, the cross-sectional area of the inner hole of the refractory pipe 2b needs to be at least 1 time the total cross-sectional area of the inner hole of the immersion nozzle 5.

If the cross-sectional area of the refractory pipe 2b is more than four times the cross-sectional area of the dipping nozzle 5, the molten steel 4 and the refractory pipe 2b will be in poor contact with each other, and the refractory pipe 2b will be damaged.
Since the inclusions of alumina are not sufficiently removed in the interior and the immersion nozzle 5 is clogged, the refractory pipe 2b is formed.
The cross-sectional area of the dipping nozzle must be less than 4 times the total cross-sectional area of the dipping nozzle 5.

As a result of optimizing the cross-sectional area of the refractory pipe 2b, the adhesion of alumina to the inner wall of the immersion nozzle 5 is the same as when the refractory pipe 2b is installed in the tundish 1. It was confirmed that it can be surely prevented.

Further, since the refractory pipe 2b was exchanged every two charges, the amount of alumina adhered to the refractory pipe 2b did not reach such a level that the casting was stopped within the casting time of two charges. The material of the refractory pipe 2b does not necessarily have to be the same as the material of the dipping nozzle 5, but it is a fired refractory material or amorphous refractory material such as magnesia, alumina, chamotte, etc., which is used in ordinary steelmaking processes. But good.

Further, as shown in FIG. 2, when the refractory mass 10 is arranged in the molten steel flow path of the refractory pipe 2b, the alumina can be further removed and the adhesion of the alumina to the inner wall of the immersion nozzle 5 can be surely prevented. . The material of the refractory mass may be the same as that of the immersion nozzle, or may be magnesia, alumina, chamotte, or the like. The size of the lump is not particularly limited, but a diameter of about 30 to 70 mm is preferable.

[0019]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples. Components C: 0.003%, Si: 0.01%, Mn: 0.45 held in a 270 ton ladle
%, P: 0.016%, S: 0.015%, Al: 0.
Molten steel containing 045% and Ti: 0.045% was supplied into the tundish, and further cast into a continuous casting mold using a reverse Y-type alumina graphite immersion nozzle.

The casting time is 400 minutes and the number of strands is 2. The flow rate of Ar gas blown from the immersion nozzle was constant at 10 Nl / min, and the amount of molten steel passing through the immersion nozzle was 4 t / min. The slab size is 245 mm thick
A coil having a width of 1500 mm and a length of 8700 mm was cut into one coil. The slab was hot-rolled and cold-rolled by a conventional method to finally obtain a cold-rolled steel sheet having a thickness of 0.7 mm and a width of 1500 mm.

Regarding the slab quality, the number of occurrence of inclusion defects per coil was evaluated by visual observation on an inspection line after cold rolling. The clogging condition of the immersion nozzle was evaluated by collecting the nozzle after casting and dividing the deposit thickness of alumina deposited on the inner wall immediately above the discharge hole by the casting time to determine the deposition rate.

[0022]

[Table 1] Casting conditions and results of Examples and Comparative Examples

As shown in the casting results of Table 1, in the embodiment, the cross-sectional area of the refractory pipe is set to be 1 time or more and less than 4 times the cross-sectional area of the dipping nozzle, and the pipe can be removed from the ladle and the tundish. As a result of replacing the refractory pipe every two charges when replacing the ladle, alumina deposits on the dipping nozzle could be reliably prevented industrially, and as a result, the number of coil defects was eliminated.

In Comparative Examples 1 and 2, alumina adhesion to the dipping nozzle could be reliably prevented industrially, and as a result, the number of coil defects was eliminated, but in Comparative Example 1, refractory pipes were used. Since it was installed in the tundish and had a structure that could not be replaced during casting, the refractory pipe itself was blocked, and casting was stopped after 6 charges.

Further, in Comparative Example 2, since the cross-sectional area of the refractory pipe was smaller than 1 time the cross-sectional area of the dipping nozzle, the molten steel supply from the ladle to the tundish followed the supply speed from the tundish to the mold. I couldn't do it and stopped casting after 3 charges. In Comparative Example 3, since the cross-sectional area of the refractory pipe was larger than 4 times the cross-sectional area of the immersion nozzle, alumina in molten steel could not be sufficiently removed by the refractory pipe, and as a result, the immersion nozzle was blocked and casting was stopped. .

[0026]

As described above, according to the present invention, it is possible to reliably prevent the alumina from adhering to the immersion nozzle, so that it is possible to perform continuous casting, not only the continuous casting operation is stabilized, but also the quality and the stabilization of the slab are improved. This is a continuous casting method that is industrially effective in that it can realize the above and that the yield is significantly improved.

[Brief description of drawings]

FIG. 1 is a view showing a refractory pipe installed between a ladle and a tundish.

FIG. 2 is a cross-sectional view of a mode in which a refractory mass is arranged in a molten steel flow path of a refractory pipe.

FIG. 3 is a view showing a refractory pipe installed in a tundish.

[Explanation of symbols]

1: Tundish, 2 (2a, 2b): Refractory pipe, 3: Ladle, 4: Molten steel, 5: Immersion nozzle,
6: cast slab, 7: mold, 8: powder, 9: long nozzle, 10: refractory lump, 11: refractory-based mesh support member.

Claims (2)

[Claims] 1. In continuous casting of steel, when supplying molten steel of a ladle into a tundish through a removable refractory pipe from the ladle, the cross-sectional area of the inner hole of the refractory pipe is immersed in the nozzle. The continuous casting method is characterized in that the total cross-sectional area of the inner hole is set to 1 time or more and less than 4 times. 2. The continuous casting method according to claim 1, wherein the refractory pipe is a refractory pipe in which a refractory mass is arranged in the molten steel flow path.