JP3124421B2 - Immersion nozzle for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle used for casting molten steel from a tundish into a mold in continuous casting of steel.

[0002]

2. Description of the Related Art At present, in continuous casting, an immersion nozzle is used to supply molten steel from a tundish into a mold without oxidizing the molten steel. The material of the immersion nozzle is mainly composed of Al ₂ O ₃ and C.
What contains about ₂ % by weight of SiO ₂ is mainly used. In such an immersion nozzle, as the casting time elapses, the precipitates in steel, such as alumina and metal, adhere to the inner wall of the nozzle, and in severe cases, the nozzle may be clogged and the casting may be stopped.

[0003] Further, the nozzle blockage causes disturbance of the flow of molten steel in the mold, so that inclusion defects due to powder entrainment are increased. As means for solving this problem, as described in JP-Sho 64-40154, the use of a nozzle consisting of ZrO ₂ -CaO-C material have been attempted. By using this ZrO ₂ —CaO—C material for the inner wall of the nozzle, CaO in the refractory and A
React with l ₂ O ₃ to form a low melt of calcium aluminate. This low melt is washed away by a molten steel stream to give a small amount of erosion, thereby preventing adhesion.

[0004]

SUMMARY OF THE INVENTION However, ZrO
_{In the case of a 2-} CaO-C material nozzle, if the casting time is long or the cleanliness of molten steel deteriorates, sufficient CaO to lower the melting point of alumina attached to the inner wall of the nozzle is used.
Cannot be supplied, so that nozzle blockage occurs. For this reason, at present, the ZrO ₂ -CaO-C quality nozzle is not a reliable blockage prevention measure. Furthermore, ZrO ₂
Since the -CaO-C-based nozzle is used to wash away the inclusions once deposited on the inner wall of the nozzle by the molten steel flow, there is a problem that coarse inclusions flow into the mold and deteriorate the quality of the slab. In view of these problems, an object of the present invention is to provide a continuous casting immersion nozzle capable of always casting a working steel sheet material without inclusion defects while preventing nozzle blockage. is there.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a dipping nozzle for continuous casting of steel, which removes 5 to 50 wt. % Of SiO ₂ , 50 to 95 wt% of Al ₂ O ₃ , and a refractory having a C content of 1 to 4 wt% .

[0006]

In order to establish a technique for preventing the adhesion of the immersion nozzle, it is necessary to first clarify the mechanism of alumina adhesion to the inner wall of the nozzle. The present inventors have found from the investigation of the immersion nozzle after the actual casting that the adhesion and deposition of the inclusions in the molten steel progress from the reaction alumina layer generated by the reaction between the immersion nozzle refractory and the molten steel. Furthermore, the basic mechanism of the reaction mechanism between the immersion nozzle refractory and the molten steel was studied, and it was found that the reactive alumina layer, which is the starting point of the adhesion, was formed through the following reaction process.

First, as shown in equation (1), SiO ₂ in the nozzle refractory is reduced by C, and SiO gas, C
O gas is generated. SiO ₂ (s) + C (s) = SiO (g) + CO (g) (1) These gases diffuse inside the nozzle refractory and are present in the molten steel at the nozzle / molten steel interface according to the equations (2) and (3). Reacts with Al. 3SiO (g) +2 Al = Al 2 O 3 (s) +3 Si (2) 3CO (g) +2 Al = Al 2 O 3 (s) +3 C (3)

At this time, the oxide film formed at the interface between the nozzle and the molten steel is a reactive alumina layer. Since this reactive alumina layer is formed by the reaction between the nozzle and the molten steel, it is very active alumina and easily becomes a starting point for the inclusion of inclusions in the molten steel. From the above results, it is important to prevent a reactive alumina layer from being formed on the inner wall of the nozzle in order to prevent the inclusion of inclusions.

The present inventors considered that in order to prevent the formation of a reactive alumina layer from the above-described reaction mechanism, it is effective to reduce C in the nozzle refractory to a level that does not cause a problem. That is, if C does not exist in the nozzle refractory, the C reduction reaction of SiO _{2 represented by} the formula (1) does not occur. Therefore, at the nozzle / molten steel interface, equation (2)
The reaction alumina layer based on the reaction of the formula (3) is not generated, and the adhesion of alumina can be prevented.

In the present invention, it is preferable that C is not contained in the inner wall refractory, but if necessary, it may be added in an amount of 1 to 4 wt% . This is because when the C content exceeds 4 wt% , the C reduction reaction rate of SiO ₂ rapidly increases,
This is because the adhesion of alumina proceeds. In addition, low-expansion SiO ₂ is excellent in spalling resistance improvement, and 5 w
By adding t% or more, it is possible to compensate for a decrease in spalling resistance due to the C-less formation. However, SiO ₂ in the inner wall refractory
If the content exceeds 50% by weight, on the contrary, the corrosion resistance decreases. Therefore, the content of SiO ₂ in the refractory on the inner wall is 5 to 5
It is necessary to be in the range of 0 wt%. Further, Al ₂ O ₃
Has a function of increasing the corrosion resistance, the material of the immersion nozzle must contain more than 50 wt%, Al ₂ O Conversely
_If the content of ₃ exceeds 95 wt%, the spalling resistance is reduced. Therefore, the proper content of Al ₂ O ₃ is 5
0 to 95 wt%.

Although the basic components of the immersion nozzle are as described above, other materials which are already known as additives to the material of the nozzle may be contained as long as the effects of the present invention are not impaired. . For example, to improve the strength, metal S
It is also possible to combine i with MgO or the like to improve corrosion resistance. Also, considering the original purpose, it is not necessary that the entire inner wall of the nozzle be made of the material of the present invention, and the material is applied only to a portion where the adhesion easily proceeds, and the conventional material is used in combination with the other portions. Is also possible.

[0012]

The present invention will be described below with reference to examples and comparative examples. A binder was added to the raw material contents shown in Table 1 in an amount of 10 wt% in an external manner, kneaded, and formed into a nozzle shape shown in FIG. 1 at a pressure of 1.0 t / cm ² using an isostatic press. 1 is an inner wall, 2 is a powder line portion, 3 is a discharge hole, and 4 is a nozzle body. A: ZrO ₂
-C _{material, B ... Al 2 O 3 -C} -SiO 2 material (conventional _{material), C ... Al 2 O 3} -SiO 2 material (the present invention material). The refractory in the powder line portion was ZrO ₂ 75 wt.
% And C in a ZrO ₂ -C material containing 25 wt%.

[0013]

[Table 1]

Further, the molded body is reduced and fired at a temperature of 1200 ° C., and is immersed in a continuous casting immersion nozzle (outer diameter: 185 mm).
φ, an inner diameter of 90 mmφ, a discharge hole diameter of 70 mmφ, a discharge hole angle of 35 degrees, and an inner hole body thickness of 15 mm). Using the immersion nozzle thus obtained, Ti
Was cast at 400 ppm for 30 minutes. In both the examples and comparative examples of the present invention, the casting dimensions were 245 mm thick × 1500 mm wide, and 8 mm.
It was cut into 500 mm lengths to make one coil unit. The slab was hot-rolled and cold-rolled by a conventional method to finally form a cold-rolled steel sheet having a coil of 0.7 mm in thickness and 1500 mm in width.
Regarding the evaluation of the immersion nozzle clogging, after the immersion nozzle was recovered after casting, the maximum adhesion thickness immediately above the discharge hole was measured, and this was divided by the casting time to calculate the adhesion speed. Also,
The slab quality was visually observed on an inspection line after cold rolling, and evaluated by the number of inclusion defects generated per coil.

As shown in Table 1, in the embodiment, at least the entire inner wall of the immersion nozzle is coated with 5 to 50 wt% of SiO ₂ , 50 wt%.
It includes Al ₂ O ₃ of and 95 wt%, and 1 to the C content
By using the refractory having the composition of 4 wt% , the nozzle clogging could be always stably prevented. In addition, not only in operation but also in quality, there was no occurrence of inclusion defects, and an extremely good slab could be obtained.

On the other hand, in Comparative Example 1, the C content was 4 w
Since the amount exceeded t% , the effect of preventing nozzle blockage was not sufficiently obtained, and the casting was stopped 300 minutes after the start of casting. In Comparative Example 2, the SiO ₂ content was less than 5 wt% and Al ₂ O
_{(3) Since the} content exceeds 95 wt%, the spalling resistance was reduced, and a crack was generated in the immersion nozzle 180 minutes after the start of casting, and the casting was stopped. Furthermore, in Comparative Example 3, the SiO ₂ content exceeded 50 wt% and the Al ₂ O ₃ content was 50 wt%.
%, The corrosion resistance was reduced, and the casting was stopped 230 minutes after the start of casting due to erosion nozzle erosion. In addition, although the example is a result of a test performed on the structural nozzle of FIG. 1, a similar effect was obtained with the structural nozzle of FIG. 2.

[0017]

As described above, according to the immersion nozzle for continuous casting of the present invention, the clogging of the slab is extremely stable because the nozzle clogging can be reliably prevented and no inclusion defect occurs. , And the yield is significantly improved. Further, since various unsteady operations due to nozzle blockage are eliminated, an effective immersion nozzle can be provided in operation.

[Brief description of the drawings]

FIG. 1 is a view for explaining the material of each part of the immersion nozzle of the present invention.

FIG. 2 is a view for explaining a material of each part of another immersion nozzle of the present invention.

[Explanation of symbols]

1 inner wall 2 powder line portion 3 discharge hole 4 nozzle body A ZrO ₂ -C material _{B Al 2 O 3 -C-SiO} 2 material (conventional material) C Al ₂ O ₃ -SiO ₂ material (invention material)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-243258 (JP, A) JP-A-61-276753 (JP, A) JP-A-60-148649 (JP, A) 114639 (JP, A) JP-A-57-206557 (JP, A) JP-A-6-179056 (JP, A) JP-A-5-228591 (JP, A) JP-A-5-123840 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/10 330 B22D 41/54 C04B 35/101

Claims (1)

(57) [Claims] 1. In an immersion nozzle for continuous casting of steel, 5% to 50% by weight of S is added to the entire inner wall of the nozzle in contact with molten steel or a portion where adhesion is likely to proceed, excluding industrially inevitable components.
iO ₂ , containing 50 to 95 wt% of Al ₂ O ₃ and C
An immersion nozzle for continuous casting, comprising a refractory having a composition having a content of 1 to 4 wt% .