JPH09276998A - Method for reusing immersion nozzle for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the reuse of a nozzle and to reduce the cost of a steelmaking by using the used immersion nozzle, in which the inclusion stuck layer exists on the inner tube of the nozzle body by using to continuous casting of Al deoxidized steel, etc., as the immersion nozzle for continuously casting a high oxygen-containing steel. SOLUTION: On the inner tube surface of the immersion nozzle used to the continuous casting of the Al deoxidized steel or Al-complex deoxidized steel, an inclusion stuck layer composed of the oxide of Al2 O3 , etc., over the whole body and a little quantity of granular iron exists. At the time of reusing this immersion nozzle to the continuous casting of the high oxygen-containing steel, the inclusion stuck layer over on the whole inner tube surface serves as the protecting layer to restrain the reaction between the immersion nozzle body and the molten steel (high oxygen-containing steel). Further, since the inclusion, particularly Al2 O3 inclusion, is very little in the high oxygen-containing steel, it is no fear that the clogging of the nozzle is developed caused by further sticking of the inclusion on the inclusion stuck layer at the time of passing the molten steel through the immersion nozzle.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for reusing an immersion nozzle for continuous casting of steel.

[0002]

2. Description of the Related Art At the present time, an Al ₂ O ₃ --SiO ₂ --C type material is most widely used as a dipping nozzle used for injecting molten steel from a tundish into a mold in a steelmaking process. However, these immersion nozzles may be treated with Al deoxidizing or Al composite deoxidizing (eg Al-S
i, Al-Ti) steel, a phenomenon occurs in which Al ₂ O ₃ inclusions in the molten steel or inclusions containing Al ₂ O ₃ adhere to the working surface of the immersion nozzle. Considering the case of Al deoxidized steel as an example, the mechanism is as follows.

Since Al deoxidized steel is deoxidized with metallic Al, many Al ₂ O ₃ inclusions are present in the molten steel. At the time of continuous casting of Al deoxidized steel, first, Al ₂ O ₃ -S
Inside the iO ₂ -C-based material, the reaction of the formula (1) occurs between SiO ₂ and carbon in the material:

Embedded image SiO ₂ (solid) + C (solid) = SiO (gas) + CO (gas) (1)

Next, the generated SiO and CO gas diffuses at the interface between the immersion nozzle and the molten steel, causes Al in the molten steel to react with the following equations (2) and (3), and Reticulated alumina forms on the tube surface (working surface):

Embedded image ₃ SiO (gas) +2 Al = Al ₂ O ₃ (solid) +3 Si (2)

Embedded image 3CO (gas) +2 Al = Al ₂ O ₃ (solid) +3 C (3) Here, Al , Si, and C represent Al , Si, and C dissolved in molten steel, respectively.

[0005]

As shown in FIG. 1, Al ₂ O ₃ inclusions in molten steel adhere to the reticulated alumina formed on the surface of the inner tube of the immersion nozzle by the mechanism as described above. An inclusion deposit layer composed of Al ₂ O ₃ and a small amount of granular iron is formed in the inner tube of the immersion nozzle. Since this inclusion adhering layer sinters with the surface of the inner tube of the immersion nozzle, it is difficult to peel it off, and when it becomes thick to a certain extent, the inner tube of the nozzle is blocked and it becomes impossible to use it continuously.

The immersion nozzle in such a state has been conventionally discarded, and as a result, the cost of steelmaking increases, and there is also a possibility of causing a problem of environmental pollution.

Accordingly, it is an object of the present invention to provide a method for reusing a spent immersion nozzle used in continuous casting of steel in which there is a layer of inclusion deposits on the inner tube of the body.

[0008]

That is, the method of reusing the immersion nozzle for continuous casting of steel according to the present invention is directed to Al deoxidation or Al deoxidation.
It is characterized in that it is used for continuous casting of composite deoxidized steel, and that a used immersion nozzle having an inclusion deposit layer over the entire inner tube surface of the immersion nozzle body is used as an immersion nozzle for continuous casting of high oxygen content steel. To do.

[0009]

DETAILED DESCRIPTION OF THE INVENTION High oxygen content steel is widely used as a base metal material for enamel and the like. This steel type has A
l Compared with deoxidized steel or Al composite deoxidized steel, it has the following two characteristics: The oxygen content of Al deoxidized steel or Al composite deoxidized steel is about 2
0 ppm, but that of high oxygen content steel is 200-60
Oxygen in Al deoxidized steel or Al composite deoxidized steel is mostly Al.
_Although it exists in the form of inclusions such as ₂ O _3, most of oxygen in the high oxygen content steel exists in a dissolved state, and there are few inclusions.

Even in continuous casting of high oxygen content steel, the Al ₂ O ₃ --SiO ₂ --C type immersion nozzle is generally used at present. This dipping nozzle is usually Al ₂ O ₃ : 40
˜50% by weight, SiO ₂ : 15 to 25% by weight, C: 20
When used for continuous casting of high oxygen content steel, the damage occurs due to the following two reasons: (a) Carbon (C) in the immersion nozzle is oxygen in the molten steel. The structure of the surface of the immersion nozzle becomes brittle and is washed away by the molten steel flow; (b) Fe or Mn in the molten steel is an oxide Fe ₂ O ₃ , M
Dissolution in the form of nO in the immersion nozzle and formation of a low melting point compound results in tissue embrittlement and outflow.

As described above, the inner tube surface (operating surface) of the immersion nozzle used for continuous casting of Al deoxidized steel or Al composite deoxidized steel is entirely covered with oxides such as Al ₂ O ₃ and a small amount. There is an inclusion adhering layer consisting of granular iron. If this submerged nozzle can be reused for continuous casting of high oxygen content steel, the inclusion adhering layer adhering over the entire surface of the inner pipe functions as a protective layer, and the submerged nozzle body and molten steel
It will suppress the reaction with (high oxygen content steel).

Further, since inclusions, especially Al ₂ O ₃ inclusions are very small in the high oxygen content steel, when the molten steel passes through the immersion nozzle, the inclusions are further deposited on the inclusion adhesion layer. There is no risk of adhesion and blockage of the nozzle.

Further, Al ₂ O ₃ --SiO ₂ which is currently widely used for continuous casting of Al deoxidized steel or Al composite deoxidized steel.
In the -C type immersion nozzle, the inclusion adhering layer adhering to the nozzle inner tube is difficult to separate from the nozzle inner tube. Therefore, considering the following two points, in the present invention, inclusions are spread over the entire surface of the nozzle inner tube. Al ₂ O ₃ —SiO _{2 with} an adhesion layer
-It is preferable to use a C-based used dipping nozzle: (1) The steelmaking cost reduction effect according to the present invention is great; (2) Large inclusions may occur in molten steel due to the separation of the inclusion adhesion layer. There is no.

The thickness of the inclusion adhering layer on the inner tube of the immersion nozzle body is preferably in the range of 2 to 15 mm. If the thickness of the inclusion adhering layer is less than 2 mm, it is not preferable because the effect of protecting the inclusion adhering layer on the immersion nozzle body is small, and if the thickness exceeds 15 mm, the nozzle inner pipe diameter becomes small and molten steel Is not preferable because it may affect the passage of In addition, according to the experimental results of the present inventors, when the inclusion adhesion layer contains SiO ₂ and TiO ₂ in a total amount of more than 15% by weight, Fe and Mn in the high oxygen content steel are in an oxide form. May dissolve in the adhesion layer to form a compound having a low melting point and accelerate the outflow of the inclusion adhesion layer. Therefore, it is desirable that the inclusion adhering layer in the inner tube of the used immersion nozzle main body is substantially composed of Al ₂ O ₃ and granular iron which is an unavoidable impurity, but from the group consisting of SiO ₂ and TiO _2. 1 selected
One or two components may be contained in a total amount of 15% by weight or less.

[0015]

The present invention will be further described with reference to the following examples. Example 1 As the reusing dipping nozzle, the one shown in FIG. 2 was used. This submerged nozzle body is made of Al ₂ O ₃ —SiO ₂ —C based material, and before being subjected to continuous casting of high oxygen content steel,
Used for Al deoxidized steel. The immersion nozzle had a total height of 800 mm, an outer diameter of 180 mm, and an inclusion adhering layer inner diameter of about 100 to 110 mm. Inclusion adhesion layer thickness is 5 mm at the minimum and 15 mm at the maximum
Met. The composition of the immersion nozzle body was 50% by weight of Al ₂ O ₃ , 25% by weight of SiO _{2 and} 25% by weight of C, and the composition of the inclusion adhering layer of the inner tube was 90% by weight of Al ₂ O ₃ and 10% by weight of granular iron. %. The thickness of the inclusion adhering layer is about 12
mm.

Example 2 As an immersion nozzle to be reused, an Al ₂ O ₃ -C type immersion nozzle used for continuous casting of Al-Ti deoxidized steel was used. The composition of the inclusion adhering layer of the inner tube was 80% by weight of Al ₂ O ₃ , 10% by weight of titanium oxide and 10% by weight of granular iron, and the thickness of the inclusion adhering layer was about 10 mm. Other than that is the same as that of the first embodiment.

Example 3 As an immersion nozzle to be reused, an Al ₂ O ₃ -C type immersion nozzle used for continuous casting of Al-Si deoxidized steel was used. The composition of the inclusion adhering layer of the inner tube was 80% by weight of Al ₂ O ₃ and Si.
It was composed of 10% by weight of O _{2 and} 10% by weight of granular iron, and the thickness of the inclusion adhering layer was about 10 mm. Otherwise, Example 1
Is the same as

COMPARATIVE EXAMPLE 1 As materials for the immersion nozzle, 50% by weight of Al ₂ O ₃ , 25% by weight of SiO _{2 and} 25% by weight of C were used, and the structure shown in FIG. 3 was used as a comparative product. .

A continuous casting test was carried out using the immersion nozzle according to the present invention and the comparative product shown in Examples 1 to 3 above.
The durability of the immersion nozzle was evaluated by examining the damage of the immersion nozzle body. In the continuous casting test, C: 0.
02% by weight, Si: 0.3% by weight, Mn: 0.31% by weight, P: 0.008% by weight, S: 0.017% by weight, O:
A high oxygen content steel having a composition of 510 ppm was used and the molten steel temperature was 1565 ° C. FIG. 4 shows the amount of damage to the inner tube of each immersion nozzle during the casting time of 210 minutes. From FIG. 4, the damage amount of the Al ₂ O ₃ —C-based immersion nozzle of Comparative Example 1 was 12 mm.
On the other hand, the damage amounts of the immersion nozzles of Examples 1 to 3 were 0.5 mm, 2 mm and 3 mm, respectively, and it was found that the damage amounts were significantly reduced.

[0020]

EFFECTS OF THE INVENTION According to the method of the present invention, the immersion nozzle after being used for continuous casting of Al deoxidized steel or Al composite deoxidized steel can be reused, which reduces the steelmaking cost and causes environmental pollution. Can be reduced. The method of the present invention also enables stable continuous casting of high oxygen content steel.

[Brief description of drawings]

Figure 1: Al ₂ O ₃ after use in continuous casting of aluminum killed steel
It is a figure which shows the state of the inclusion | attachment inclusion in the inner pipe | tube of the C type immersion nozzle main body.

FIG. 2 is a diagram showing a configuration of a reuse immersion nozzle used for an actual machine test.

FIG. 3 is a view showing a configuration of a conventional continuous casting immersion nozzle.

FIG. 4 is a diagram showing the amount of damage to the inner pipe of the immersion nozzle body when the reused immersion nozzles of Examples 1, 2 and 3 and the immersion nozzle of the comparative product were subjected to continuous casting of high oxygen content steel.

Claims (5)

[Claims] 1. A used immersion nozzle, which is used for continuous casting of Al deoxidized or Al composite deoxidized steel and has an inclusion adhesion layer over the entire inner tube surface of the immersion nozzle body, is continuously cast of high oxygen content steel. A method for reusing an immersion nozzle for continuous casting of steel, which is used as an immersion nozzle for steel. 2. The main body of the used immersion nozzle is made of Al ₂ O ₃
The method for reusing an immersion nozzle for continuous casting of steel according to claim 1, which is made of a -SiO ₂ -C material. 3. The method for reusing the immersion nozzle for continuous casting of steel according to claim 1 or 2, wherein the thickness of the inclusion adhering layer of the inner pipe of the used immersion nozzle body is in the range of 2 to 15 mm. 4. The continuous steel according to claim 1, wherein the inclusion adhering layer of the inner tube of the used immersion nozzle body is substantially composed of Al ₂ O ₃ and granular iron which is an unavoidable impurity. Reusing method of dipping nozzle for casting. 5. The inclusion adhering layer of the inner tube of the used dipping nozzle body contains 15 parts by weight in total of one or two components selected from the group consisting of Al ₂ O ₃ , SiO ₂ and TiO _2. % Or less and inevitable impurities consisting of granular iron.
4. A method for reusing the immersion nozzle for continuous casting of steel according to any one of 1 to 3.