JPH0631410A - Long stopper for continuous casting - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a non-alumina adherent long stopper used for continuous casting of steel. [Structure] ZrO ₂ 30 ~ on the outer layer of the long stopper
By having the refractory composition for continuous casting having a composition of 90% by weight, CaO 3 to 28% by weight and C 5 to 40% by weight in the outer layer of the molten steel contact portion in a range of 3 to 13 mm, alumina adhesion can be effectively prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long stopper for flow rate control, which is used for pouring molten steel from a tundish into a mold in continuous casting of steel.

[0002]

2. Description of the Related Art In recent years, in continuous casting of steel, a long stopper has been mentioned as a method for controlling the flow rate of molten steel. However, this long stopper is subject to thermal shock during preheating and contact with molten steel after the end of preheating. A single-layer structure made of alumina-graphite or alumina-graphite-fused silica refractory having high impact resistance is used. In order to solve the problem of alumina adhesion in the immersion nozzle, a nozzle material containing CaZrO ₃ has recently been developed (Japanese Patent Application Laid-Open No. 57-71860) and has been used.
CaZrO ₃ reacts with alumina to form a low melting point material. Since this substance does not stay on the surface but melts, alumina is not adhered and nozzle clogging can be prevented. Also,
Japanese Examined Patent Publication No. 47-44321 discloses a two-layer structure in which the outer peripheral surface of a main body material having a high spalling resistance is lined with an outer lining material having a high corrosion resistance.

[0003]

The problem to be solved in the present invention is to solve the problem of clogging due to adhesion of alumina and long stopper material generated during long-time casting with alumina-graphite or alumina-graphite-fused siliceous long stopper. The purpose is to find a means for preventing inclusion of inclusions in steel by elution of alumina.

[0004]

SUMMARY OF THE INVENTION The present invention uses ZrO ₂
0 to 90% by weight, CaO 3 to 28% by weight, and C 5
A long stopper for continuous casting having a refractory composition of -40% by weight on the outer surface of 3 to 13 mm.

[0005]

The ZrO ₂ —CaO—C system is mentioned as the non-alumina system refractory composition which is difficult to adhere to alumina. ZrO
_{The 2-} CaO-C material has a higher coefficient of thermal expansion than the alumina-graphite material system or the alumina-graphite-fused silica material, so the rate of occurrence of cracks and breakage when subjected to the above-mentioned thermal shock. Will increase.

CaO reacts with alumina particles which are inclusions in molten steel to form a low melting point compound of Al ₂ O ₃ -CaO. Since the melting point of this reaction product is 1450 to 1500 ° C. and is liquid at the molten steel temperature, it melts without adhering to the outer wall of the refractory.

In the present invention, the content of C is set to 5 to 40% by weight because it is excellent in thermal shock resistance, slag infiltration resistance and oxidation resistance. On the other hand, when C is less than 5% by weight, thermal shock resistance and slag infiltration resistance are poor, and when it exceeds 40% by weight, corrosion resistance is significantly reduced. As a raw material of C, natural or artificial graphite, mesophase carbon, coke,
It refers to carbon black and the like, and a high purity of 80% or more is desirable.

The amount of ZrO ₂ compounded is 30 to 90% by weight because it is excellent in corrosion resistance and slag infiltration resistance.
On the other hand, when ZrO ₂ is less than 30% by weight, the corrosion resistance is poor, and 9
If it exceeds 0% by weight, the compounding amount of C and CaO decreases, and the alumina adhesion preventing function and spall resistance are poor.

The content of CaO is set to 3 to 28% by weight because it has an excellent function of preventing adhesion of alumina. on the other hand,
If CaO is less than 3% by weight, it is inferior in prevention of adhesion of alumina.
If it exceeds 8% by weight, the corrosion resistance is poor.

As a raw material, Z is used to prevent the digestion of CaO.
A compound with rO ₂ , Al ₂ O ₃ , or SiO ₂ or a salt containing Ca is preferable, and ZrO ₂ —CaO, A
_{l 2 O 3 -CaO, SiO 2} -CaO, CaCO 3, CaO
Stabilized ZrO _{2 and the} like can be mentioned, and it is desirable that the purity is as high as possible at 80% or more. Electrofused products, sintered products and the like can be used, but the crystal size is used as a normal refractory raw material, It is preferably 200 μm or less.

In the long stopper 1 having a two-layer structure as shown in FIG. 1, the main body 2 is made of alumina-graphite or alumina-graphite-fused silica, and the outer cover 3 is made of ZrO ₂ -CaO-C. In the long stopper having the two-layer structure arranged, the layers may be peeled off due to the difference in expansion between the materials when subjected to thermal shock.

Table 1 shows alumina-graphite materials and ZrO _2-.
Table 2 shows the physical property values of CaO-C based materials,
The result of the spalling test is shown. For the stress generated in Table 2, the physical properties shown in Table 1 were used, and the stress generated between layers was calculated by the finite element method. The larger the index, the larger the generated stress. As the conditions of the spalling test, a two-layer structure product was prepared, preheated at 600 ° C. for 1 hour, immersed in hot metal at 1600 ° C. for 20 minutes, and the cut surface of the air-cooled sample was observed to confirm the presence or absence of peeling.

Alumina having physical properties as shown in Table 1
As the thickness of the graphite-based material and the ZrO ₂ —CaO—C-based material increases, the stress generated between the layers increases as shown in Table 2.

The thickness t of the ZrO ₂ --CaO--C system material is 1
When it exceeds 5 mm, the phenomenon of delamination between layers is recognized in the immersion spalling test, so ZrO ₂ -CaO-
The thickness of the C-based material is preferably 3 to 13 mm.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

【Example】

(Embodiment 1) Hereinafter, the present invention will be described based on embodiments. Table 3 shows the blending ratio and the quality measurement results of the blended mixture which was molded by an isostatic press and fired in a reducing atmosphere.

[0018]

[Table 3]

The erosion test conditions in Table 3 are 20 × 20 × 15.
The 0 mm rod-shaped sample was immersed in electrolytic iron at 1600 ° C. for 1 hour, and then the melt loss dimension was measured. The melting loss of Example 1 is 1
The larger the index, the worse the melt resistance is.

The spalling test conditions are 30 × 30 × 2
A 00 mm rod-shaped sample was immersed in 1600 ° C. pig iron for 10 minutes without preheating and then water cooling was repeated 5 times for 1 minute, and the timing of crack initiation was observed.

The adhesion test condition is 20 × 20 × 150 mm
The rod-shaped sample of 1600 ℃ aluminum killed steel (Al =
(0.05%) molten steel was soaked in molten steel for 60 minutes and then pulled up to observe the presence or absence of alumina adhesion. ◎ indicates no adhesion, ○ indicates adhesion 2
Less than mm, x is 2 mm or more of adhesion.

The materials 1 to 4 of Example 1 all have strength, melting resistance, and thermal shock resistance that can withstand use, and have good adhesion test results.

On the other hand, Comparative Examples 1 and 2 in which the amount of C is less than the range of the present invention are inferior in the result of the spalling test and are poor in thermal shock resistance, and Comparative Example 3 in which the amount of C is large is inferior in melt damage resistance. .

Comparative Example 4 in which ZrO ₂ is more than the range of the present invention has poor thermal shock resistance. Comparative Example 5 in which CaO is less than the range of the present invention has an alumina adhesion as a result of the adhesion test,
Does not achieve the purpose. On the other hand, Comparative Example 1, which has a large amount of CaO, has a poor erosion resistance.

Example 2 As shown in FIGS. 2A and 2B, a refractory material having the composition of the present invention was used as a long stopper 1.
As a result of continuously casting a product having a surface of 13 mm on a surface of 13 mm in a 300-ton ladle 10 times and casting for 500 minutes, it was confirmed that there was no adhesion of alumina, and there was no problem in terms of melting loss and spalling. The main body (1-a) is an alumina-graphite-fused silica material, and the outer coating (1-b) is ZrO ₂ -CaO-.
C-based material, (1-c) is a porous plug.

[0026]

As described above, by using the long stopper for continuous casting according to the present invention, the adhesion of alumina to the long stopper can be effectively prevented, and the casting cost of steel and the refractory cost can be reduced, and It enables stable long-term casting of steel, which can greatly contribute to the improvement of steel productivity.

[Brief description of drawings]

[Figure 1] Long stopper for continuous casting.

FIG. 2 (a) Another continuous casting stopper. (B) Other continuous casting stoppers.

[Explanation of symbols]

1 Long stopper for continuous casting 2 Long stopper main body (alumina-graphite material) 3 Long stopper outer coating (ZrO ₂ -CaO-C
Quality) 1-a Long stopper body (alumina-graphite-fused silica system) 1-b Long stopper outer coating (ZrO ₂ -CaO
-C material) 1-c Porous plug

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Yamada 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division (72) Inventor Hideaki Kawabe 1-1, Higashihama-cho, Hachimansai-ku, Kitakyushu, Fukuoka Kurosaki Ceramics Co., Ltd.

Claims (1)

[Claims] 1. A long stopper for continuous casting having a refractory composition containing 30 to 90% by weight of ZrO ₂ , 3 to 28% by weight of CaO, and 5 to 40% by weight of C on the outer surface portion thereof for 3 to 13 mm.