JP2627473B2 - Long stopper 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 a flow control long stopper 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 proposed as a method for controlling the flow rate of molten steel. However, this long stopper receives a thermal shock at the time of preheating and at the time of contact with molten steel after the completion of preheating. A single layer structure made of alumina-graphite or alumina-graphite-fused silica-based refractory which is rich in impact properties is used. In the immersion nozzle, in order to solve the alumina deposition problem, it developed a nozzle material containing recently CaZrO ₃ (JP 57-71860 JP), was to be used.
CaZrO ₃ reacts with the alumina to produce a low melting point material. Since this substance flows without staying on the surface, the adhesion of alumina does not occur and the nozzle can be prevented from being clogged. Also,
Japanese Patent Publication No. 47-44321 introduces a two-layer structure in which a spalling-resistant body material is lined with an outer lining material having a high erosion resistance.

[0003]

The problem to be solved in the present invention is that the alumina-graphite or alumina-graphite-fused silica-based long stopper causes a blockage due to the adhesion of alumina and a material of the long stopper which occur during long-time casting. It is an object of the present invention to find a means for preventing inclusion of inclusions into steel due to elution of alumina.

[0004]

SUMMARY OF THE INVENTION According to the present invention, ZrO ₂
0-90% by weight, 3-28% by weight of CaO, and 5% of C
About 40% by weight of the refractory composition from the surface
It is a long stopper for continuous casting arranged in layers with a thickness of about 13 mm .

[0005]

SUMMARY OF flame alumina adherence, non-alumina based refractory composition, ZrO ₂ -CaO-C systems. ZrO
_2- CaO-C-based materials have a higher coefficient of thermal expansion than alumina-graphite materials or alumina-graphite-fused silica materials, so the rate of occurrence of cracks and breakage when subjected to the aforementioned thermal shock Increase.

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

In the present invention, the compounding amount of C is set to 5 to 40% by weight because heat resistance, slag infiltration resistance and oxidation resistance are excellent. On the other hand, when C is less than 5% by weight, thermal shock resistance and slag infiltration resistance are inferior. When C exceeds 40% by weight, corrosion resistance is significantly reduced. Raw materials for C include natural or artificial graphite, mesophase carbon, coke,
It refers to carbon black or the like, and preferably has a high purity of 80% or more.

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

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

The raw material is Z for preventing digestion of CaO.
It is desirable to use a compound with rO ₂ , Al ₂ O ₃ , SiO ₂ or a salt containing Ca, and ZrO ₂ —CaO, A
l ₂ O ₃ -CaO, SiO ₂ -CaO, CaCO ₃ , CaO
Stabilized ZrO _{2 and the} like are preferable, and it is desirable that the purity is as high as possible of 80% or more, and an electrofused product, a sintered product and the like can be used, but the crystal size is usually used as a refractory raw material. Those having a size of 200 μm or less are desirable.

In a long stopper 1 having a two-layer structure as shown in FIG. 1, an alumina-graphite or alumina-graphite-fused silica material is used for the main body 2 and a ZrO ₂ —CaO—C material is used for the outer lining 3. In the disposed long stopper having the two-layer structure, there is a possibility that delamination between layers occurs due to a difference in expansion between materials when subjected to a thermal shock.

Table 1 shows alumina-graphite materials and ZrO _2-
Table 2 shows the physical properties of the CaO-C-based materials,
Shows the results of the spalling test. The stresses generated in Table 2 were calculated by using the physical properties shown in Table 1 and by the finite element method. The larger the index, the greater the generated stress. The spalling test conditions were as follows: a two-layer structure 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 material is 1
When the thickness exceeds 5 mm, a peeling phenomenon between the layers is observed in the immersion spalling test, so that ZrO ₂ -CaO-
The thickness of the C-based material is desirably 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 results of quality measurement of the compounded mixture and the kneaded compound, which were molded by an isostatic press and fired in a reducing atmosphere.

[0018]

[Table 3]

The erosion test conditions in Table 3 were 20 × 20 × 15.
A 0 mm rod-shaped sample was immersed in electrolytic iron at 1600 ° C. for 1 hour, and then the erosion dimension was measured. The amount of erosion of Example 1 was 1
As 00, the larger the index, the lower the erosion resistance.

The spalling test condition is 30 × 30 × 2
A 00 mm rod-shaped sample was immersed in pig iron at 1600 ° C. for 10 minutes without preheating, and then water-cooled for 1 minute five times to observe the time of crack generation.

The adhesion test condition is 20 × 20 × 150 mm
The bar-shaped sample was made of aluminum killed steel (Al =
(0.05%) of molten steel for 60 minutes and then pulled up to observe whether alumina had adhered. ◎ indicates no adhesion, ○ indicates adhesion 2
mm, x is 2 mm or more.

Each of the materials 1 to 4 of Example 1 has strength enough to withstand use, erosion resistance, and thermal shock resistance, and has good adhesion test results.

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

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

Example 2 As shown in FIGS. 2A and 2B, a refractory having the composition of the present invention was used as a long stopper 1
As a result of continuously casting 500 times for 500 minutes in a 300-t molten steel pot, it was confirmed that there was no adhesion of alumina, and there was no problem in terms of erosion and spalling. The main body (1-a) is an alumina-graphite-fused silica-based material, and the outer lining (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, it is possible to effectively prevent alumina from adhering to the long stopper, thereby reducing the cost of casting steel and the cost of refractories, and Stable long-time casting of steel becomes possible, which can greatly contribute to improvement in productivity of steel.

[Brief description of the drawings]

FIG. 1 is a long stopper for continuous casting.

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

[Explanation of symbols]

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

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Yamada 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Hideaki Kawabe 1-Higashihama-machi, Yawatanishi-ku, Kitakyushu-shi, Fukuoka 1. Inside Kurosaki Ceramics Co., Ltd. (56) References JP-A-1-130857 (JP, A) JP-A-4-158896 (JP, A) JP-A-3-138805 (JP, A) JP-A-5-154627 (JP, A)

Claims (1)

(57) [Claims] 1. A refractory composition containing 30 to 90% by weight of ZrO2, ₃ to 28% by weight of CaO, and 5 to 40% by weight of C is formed into a layer with a thickness of 3 to 13 mm from the surface of a molten steel immersion part.
Long stopper for continuous casting placed .