JPH04114957A - Refractory for continuous casting and production thereof - Google Patents

Abstract

PURPOSE:To obtain the continuous casting refractory having high strength and excellent spool resistance by employing an Al2O3-C composition containing carbon or a mixture of the carbon and boron nitride and alumina having specific small particle diameters as a fundamental composition. CONSTITUTION:A refractory for continuous casting comprises an Al2O3-C composition containing 5-30wt.% of carbon alone or a mixture of the carbon and boron nitride and 95-70wt.% of alumina having particle diameters of <=0.15mm as a fundamental composition. The particle diameter distribution of the alumina comprises preferably 10-40wt.% of particle diameters of 0.044mm-0.15mm, 30-60wt.% of particle diameters of 0.010-0.04mm and 20-40wt.% of particle diameters of <=0.019mm. The particle diameter distribution of the carbon comprises preferably 40-70 wt.% of particle diameters of >=0.15mm, 10-40wt.% of particle diameters of 0.15-0.044 and 10-40wt.% of <=0.04mm. The refractory raw materials of the fundamental composition are mixed with 0.1-3wt.% of boron carbide, 0.5-10wt.% of metal silicon and a binder, kneaded, molded and baked in a nonoxidative atmosphere to provide the refractory for the continuous casting.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a refractory for continuous casting of steel and a method for producing the same, and in particular to a refractory lining of a mold solidified below the surface of the molten metal in the continuous casting stage O1η. A12 (h-C refractory for continuous casting and its manufacturing method) which has high strength and excellent spalling resistance and is suitable for use in break rings for horizontal continuous casting, etc. be.

(Prior art) Refractories for continuous casting, such as nozzles and sliding nozzles that transfer molten steel from the ladle to the tundish or from the tundish to the mold, are used to prevent oxidation and turbulence of /8 steel, and to prevent molten steel flow. It is an important component because the quality of the material greatly affects the quality of steel products. Conventionally, refractories for these parts were required to have spalling resistance in addition to corrosion resistance, so Al2
O:l-C based materials are often used. In recent years, the range of use of refractories in continuous casting equipment has expanded, and they are now being used not only in GJs, which are the parts that come into contact with molten steel, but also in parts that come into contact with steel that has begun to solidify, such as heating molds and break rings for horizontal continuous casting. The properties of the refractories used in these parts include moderate corrosion resistance and spalling resistance, as well as abrasion resistance, lubricity, and workability. Up to now, silicon carbide (Special Publication No. 6m-4622) has been used as a refractory for heating molds.
9), silicon nitride-boron nitride (Japanese Patent Application Laid-open No. 56wt20) is used as a refractory for break ring materials for horizontal continuous casting.
Non-oxide materials have been proposed, such as silicon nitride (Japanese Patent Publication No. 57-36057), materials containing aluminum nitride and boron nitride with the remainder being silicon nitride (Japanese Patent Application Laid-open No. 56WT2057), Its usefulness has been attracting attention. However, these materials are mainly non-oxide materials called new ceramics, and their manufacturing costs are high, making it difficult for them to be widely used industrially. On the other hand A]
Regarding 203-C quality materials, for example, Japanese Patent Publication No. 63-48
In Publication No. 828, alumina 4 of 80 mesh or less
0-65 t%, silica 1-30 t%, carbon 10-4
5-t%, boron carbide 0.05-211t%, and has a bending strength of 93-99 kg/cffl at room temperature.

(Problem to be Solved by the Invention) However, in the old 03-C material, which has been conventionally widely used in immersion nozzles, etc., the maximum particle size of the alumina and silica, which are the aggregates, is usually 0.5 to 0. .3+nn+, and its bending strength was also about 100 kg/cf at maximum. Therefore, when used as a mold lining material, refractory aggregate particles fall out of the structure due to abrasion of the solidified slab, causing the surface roughness of the working surface of the material to become rough and causing damage to the slab. It was alive.

(Means for Solving the Problems) Therefore, the present invention uses relatively inexpensive alumina-carbon material as a basic material and improves surface area, wear resistance, lubricity, and strength, thereby making it possible to perform heating molding and horizontal continuous casting. The present invention provides a refractory that can be applied to refractories such as pre-clinging. That is, in the present invention, the structure is made finer and the strength is increased by using alumina having a smaller particle size than the conventional one. Carbon, another basic material, contributes to flexibility, lubricity and spall resistance.

It is also possible to replace part of this carbon with boron nitride. Therefore, the refractory of the present invention comprises: a) carbon alone or a combination of carbon and boron nitride;
~30 t% and b) 95-70 alumina with a particle size of 0°15 mm or less
The basic composition is Al2O, -C containing % wt%. It is also possible to add boron carbide to this basic composition for the purpose of improving oxidation resistance, and metal silicon for the purpose of increasing strength and wear resistance.

The alumina used in the present invention preferably has a particle size distribution in which: a) particle size 0.044;
m+++~0.15mm is 10~40wt%, b)
Particle size 0.010 mm-0, CN3 mm is 30-60
wt%, C) Particle size 0.010 +++ m or less is 20~
It is 40wt%.

Further, graphite is suitable as a raw material for carbon contained in the refractory of the present invention, and it is effective that this graphite also has a particle size distribution.

In this particle size distribution, a) particle size of 0.15 mm or more is 40 to 70 wt%, b)
Particle size 0.15mm ~ 0.044mm is 10~40
wt%, C) Particle size of 0.044 mm or less is ICl-4 (
ht%.

The refractory of the present invention can be obtained as follows. First, additives such as boron carbide and metal silicon are added to the basic composition of carbon (or carbon and boron nitride) and alumina, and then an organic binder such as pitch and resin is mixed and kneaded.

It is then pressure molded, dried and fired in a non-oxidizing atmosphere.

(Function) As described above, in the present invention, the structure of the refractory is refined by using alumina mainly in fine powder having a particle size of 0.15 mm or less. As a result, for example, the bending strength is 1
The strength of the refractory is increased, such as 50 kg/c+ll or more, and the surface precision and lubricity are also improved. Furthermore, if this fine alumina has a particle size distribution, greater strength will be imparted. In this particle size distribution, the particle size is 0.044
mm ~0.15mm is 10~40wt%, particle size is 0.0
10 to 0.044 mm is 30 to 60 wt%, particle size is 0.
It is effective to have a particle size distribution in which 20 to 40 wt% of the particle size is 0.010 mm or less.

Graphite, especially phosphorous graphite, is generally used as the carbon constituting the refractory of the present invention. The carbon content is 5 to 30 carbon alone or a combination of carbon and boron nitride.
wt% is appropriate. If it is less than 5 wt%, spall resistance will be poor, and if it exceeds 30 wt%, strength and corrosion resistance will be reduced. In addition, in cases where carbon in refractories is absorbed into molten steel, so-called carbon big amplifier of steel, it is possible to replace some of the carbon with boron nitride without impairing spall resistance. It is possible to reduce carbon emissions. Boron nitride is called white carbon and has properties similar to graphite in terms of thermal conductivity, corrosion resistance, and lubricity, so it can be replaced with carbon.

In the present invention, graphite such as phosphorous graphite that can be used as a carbon raw material is flexible, has high lubricity, and smoothness, so there is no problem in that respect even if the particle size is large. However, if fine particles are blended and used, the dispersion becomes more uniform, resulting in the effect of improving spall resistance. Furthermore, by providing a particle size distribution, it is possible to improve molding and filling properties.

That is, since graphite such as phosphorous graphite has a lower specific gravity than alumina, and therefore occupies a relatively large volume, its particle size or particle size distribution greatly influences the moldability as a refractory material. In terms of the relationship between the particle size distribution of carbon and mold filling properties, it is important that the particle size is at least 0.15 mm or more (
Although the maximum diameter is not particularly limited, it is preferably 0.5 mm or less. ) is 40 to 70 wt%, particle size is 0.15 to 0.
044 mm is 10 to 40 wt%, particle size is 0.044 mm
In the case of a particle size distribution of 10 to 40 wt%, the molding and filling properties are improved, and as a result, the porosity is reduced and the strength is improved.

In the refractory of the present invention, boron carbide or metallic silicon can be added to the basic composition of 1□03-C. Among these, boron carbide is added mainly for the purpose of improving oxidation resistance, and metallic silicon is added for the purpose of improving strength and wear resistance. The amount of these additions is the total weight of the aforementioned alumina and carbon, or if part of the carbon is replaced with boron nitride, the weight of the boron nitride added to alumina and carbon is the total weight. weight of 100
In the case of boron carbide, a ratio of 0.1 to 3 is appropriate. When this ratio is less than 0.1, almost no effect is observed, and when it exceeds 3, the corrosion resistance and spalling resistance deteriorate significantly. The amount of metal silicon added is suitably within a range of 0.5 to 10% of the total weight. If the content is less than this range, the effect of addition will hardly be recognized, and if it exceeds this range, corrosion resistance and spalling resistance will deteriorate significantly.

In the refractory of the present invention, it is also possible to add silicon carbide at a ratio of 10 or less to 100 of the total weight in order to improve spall resistance and oxidation resistance.

In the refractory manufacturing process of the present invention, the raw materials described above are fired in a non-oxidizing atmosphere. This is to prevent structural deterioration due to carbon oxidation and to maintain high strength. Also, increase the firing temperature to 1000-1500"
If C is used, silicon carbide can be generated by the reaction between carbon and metal silicon, thereby increasing spall resistance and strength.

Further, as the organic binder used here, pitch or phenol resin is suitable, but it is effective to use both in combination to impart strength and spall resistance. The amount of organic binder added is 100% of the total weight as described above.
A ratio of 2 to 20 is appropriate; if it is too small, sufficient strength will not be developed, and if it is too large, the molded body will swell due to volatile matter that dissociates from the binder during firing, leading to weakening of the structure. There are concerns.

(Example) Using the carbon shown in Table 1 and the alumina shown in Table 2,
The raw material composition shown in Table 3 is used as a refractory raw material, and after mixing and kneading this refractory raw material, the raw material is pressure-formed and fired in a non-oxidizing atmosphere.
Obtained refractory bricks. Then, the refractory brick of the present invention (N
o,] to 7) are shown in Table 3 along with the physical properties of comparative fasteners outside the scope of the present invention. In addition, phosphorous graphite A in Table 1
has been conventionally used, and phosphorous graphite B is obtained by crushing phosphorous graphite A into fine particles.

The alumina shown in Table 2 is obtained by crushing sintered alumina and sifting it into various particle sizes.

Table 1 Properties of carbon Table 2 Properties of alumina Also, Fig. 1 (8) shows No. 3 refractory bricks according to the present invention, and Fig. 1 (B) shows the refractory bricks used in conventional immersion nozzles. Microscopic photographs of the particle structure of Monobrick (10 wt % of fused silica with a particle size of 0.5 mm or less are added) are shown. From the above, it was confirmed that the refractory brick of the present invention had a fine structure and significantly improved strength.

Next, face 1 large brick No. 1, N according to the present invention
.

No. 4, No. 5, and No. 5 were used in the heating mold shown in FIG. In FIG. 2, a heating mold 2 made of the refractory material of the present invention and having a rectangular cylindrical cross section and a thickness of 30 mm is placed on top of a metal mold 1. . Note that 3 is a high-frequency heater for heating that is wound around the outer periphery of the heating mold 2, and 4 is molten steel. After preheating the heating mold 2 using a gas burner so that the temperature of the inner surface thereof reached approximately 800° C., molten steel was poured into the mold and casting was performed. As a result, no cracking occurred in the firebrick 3 due to thermal shock, and there was little wear and tear.

(Effect of the invention) In the refractory of the present invention, the particle size of alumina is mainly 0.15.
By making the thickness less than mm, the Mi weave of the refractory was made finer and the strength was increased by 11 times compared to the conventional one. In other words, the bending strength of the F1□03-C refractory nozzle conventionally used for immersion nozzles was approximately 100 kg/c4 at room temperature, but the refractory of the present invention has a bending strength of approximately 150 kg/c4.
Al1 or higher, large ones 240 kg/cfl or higher.”
It showed a high strength of 2, and a remarkable effect was obtained. Surface precision, wear resistance, and lubricity were also greatly improved by making the structure finer. As a result, 4. (The refractory of the present invention can now be used in areas where molten steel begins to solidify, such as the lining of submerged solidification molds, heating molds, and break rings in horizontal continuous casting. Another big advantage is that it is made of 1□O, -C material, which is cheaper and easier to obtain than minx.Al2O3-〇 refractories have traditionally been used for long nozzles, sliding nozzles, immersion nozzles, etc. High strength and high durability are also required in the parts, and the refractory of the present invention naturally has these high strength and high durability.
It can be applied as a material that satisfies high durability.

In the manufacturing method of the present invention, since the firing is performed in a non-oxidizing atmosphere, there is no structural deterioration due to carbon oxidation.
It has become possible to provide high-quality refractories without sacrificing the effects described above.

[Brief explanation of drawings]

Figures 1 (A) and (B) are micrographs of the grain structure of the refractory according to the present invention and the grain structure of a conventional product, respectively. Figure 2 is a photograph of the refractory of an embodiment of the present invention applied to heated malt. FIG. 1...metal mold, 3...heater, 2...heating mold, 4...? Yong Steel.

Claims (1)

[Claims] 1 a) 5 to 30 wt % of carbon alone or carbon and boron nitride in combination; and b) 95 to 70 w of alumina with a particle size of 0.15 mm or less.
A refractory for continuous casting, characterized in that its basic composition is Al_2O_3-C containing t%. 2 The alumina has a particle size distribution, and at least in this particle size distribution, a) particle size of 0.044 mm to 0.15 mm is 10 to 40 w;
t% b) Particle size 0.010mm to 0.044mm is 30 to 60
The refractory for continuous casting according to claim 1, characterized in that wt% c) particle size of 0.010 mm or less is 20 to 40 wt%. 3 Carbon has a particle size distribution, and at least in this particle size distribution, a) 40 to 70 wt% of particles with a particle size of 0.15 mm or more b) 10 to 40 wt% of particle sizes of 0.15 mm to 0.044 mm
The refractory for continuous casting according to claim 1, characterized in that c) particle size of 0.044 mm or less is 10 to 40 wt%. 4 a) 5 to 30 wt% of carbon alone or a combination of carbon and boron nitride and b) 95 to 70 w of alumina with a particle size of 0.15 mm or less
c) 0.1 to 3 wt% of boron carbide on the outside, 0.5 to 1
A method for producing a refractory for continuous casting, which comprises adding 0 wt% of metal silicon and a binder, kneading and shaping the product, and then firing the product in a non-oxidizing atmosphere.