JPH0812451A - Carbon-containing refractory - Google Patents

Abstract

PURPOSE:To provide a carbon-containing refractory having good spalling property, corrosion resistance and oxidation resistance and effective as a material for refractory member of a continuous casting apparatus by relaxing change in volume accompanied by transformation and suppressing thermal expansion to a low value. CONSTITUTION:This carbon-containing refractory contains 3-40wt.% carbon raw material and 2-97wt.% zirconia-silicon carbide composite raw material having a molar ratio of ZrO2/SiC is in the range of (50/1) to (1/5) as essential components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon-containing refractory suitable as a refractory member for a continuous casting apparatus such as a long nozzle, a submerged nozzle, a slide gate valve plate, and the like.

It is widely known that zirconia is chemically stable, and it has been shown that even in refractory materials, slag dissolution loss is extremely small compared to other oxides. The immersion part of a continuous casting nozzle such as a long nozzle or an immersion nozzle is largely melted by tundish slag or mold powder, and a zirconia raw material is often used. In addition, a zirconia raw material is also applied to the slide gate valve plate in order to improve the corrosion resistance. Since the zirconia raw material has a large coefficient of thermal expansion, it is often used as a zirconia-carbon material in combination with a carbon raw material.

With this zirconia-carbonaceous material, the greater the amount of carbon, the better the spalling resistance, but on the contrary, the corrosion resistance decreases, so the mixing ratio of the zirconia raw material and the carbon raw material is naturally limited. Within this range, various studies have been made to further improve corrosion resistance while maintaining high spall resistance. For example, Japanese Patent Publication No. 59-12
No. 29 discloses that ZrO ₂ : 70 to 9 is added to the powder line portion.
It is disclosed that a powder line portion is coated with a refractory comprising 3% by weight, C: 2 to 10% by weight, and 5 to 30% by weight of at least one of SiC and fused silica. JP-A-63-97344 discloses that ZrO ₂ : 55
~ 87% by weight, graphite: 10 ~ 30% by weight, SiC: 3 ~
Disclosed is a continuous casting immersion nozzle extrapolated refractory comprising 20% by weight of Si and 0 to 5% by weight of Si.

[0004]

However, zirconia changes from a monoclinic type to a tetragonal type at about 1100 ° C. with heating. At this time, the volume of the refractory changes greatly, and the spalling resistance of the refractory is significantly impaired. When monoclinic zirconia is applied to a refractory, the thermal expansion of the entire system can be reduced to some extent by devising the particle size composition or using it together with a carbon material or SiC as described in the above two publications. It is not relaxation.

Further, in order to prevent a change in volume due to the transition, a method in which calcia, magnesia, or the like is dissolved in solid form and used as a refractory raw material in a stabilized state has been widely used. But,
The thermal expansion coefficient of stabilized zirconia is larger than that of other oxides such as alumina, and it is difficult to say that even a zirconia-garbon material is a material having excellent thermal spalling properties.

Accordingly, an object of the present invention is to utilize a zirconia-silicon carbide composite raw material having a structure in which monoclinic zirconia and silicon carbide crystals are uniformly dispersed in one particle to obtain a volume accompanying the transition. An object of the present invention is to provide a carbon-containing refractory which has good spalling resistance, corrosion resistance, and oxidation resistance and is effective as a material for a refractory member of a continuous casting apparatus by reducing the change and suppressing the thermal expansion.

[0007]

[SUMMARY OF Namely, the carbon-containing refractory of the present invention, 3 to 40 wt% of carbon material as essential components and the molar ratio of ZrO ₂ / SiC in the range of 50 / 1-1 / 5 -97% by weight zirconia-silicon carbide composite material
It is characterized by containing.

Furthermore, the carbon-containing refractory of the present invention may contain a stabilized zirconia raw material and / or an unstabilized zirconia raw material in an amount of 95% by weight or less.

The carbon-containing refractory of the present invention comprises 95% by weight of one or more refractory raw materials selected from the group consisting of silica, mullite, alumina and spinel.
It can be contained in the following amounts.

[0010] The carbon-containing refractory of the present invention may contain one or more selected from the group consisting of carbides, borides, metals and alloy powders in an amount of 10% by weight or less.

[0011]

The zirconia-silicon carbide composite raw material used in the present invention absorbs the volume change due to the transition of monoclinic zirconia by uniformly dispersing it with silicon carbide in one particle, and the thermal expansion of the particle. It itself can be suppressed to a lower level than monoclinic zirconia. The zirconia-carbon silicon composite material is obtained by firing zirconium silicate mixed well with carbon in a non-oxidizing atmosphere such as Ar, N ₂ , CO, etc., and pulverizing it to a predetermined particle size. The zirconia-silicon carbide composite raw material is composed of monoclinic zirconia and silicon carbide as essential components, and is composed of SiO ₂ , Si.
It may contain a small amount of ₃ N ₄ , ZrN, ZrC and the like.

ZrO _{2 as a} zirconia-silicon carbide composite raw material
The molar ratio of / SiC is substantially determined by the molar ratio of ZrO ₂ / SiO ₂ of zirconium silicate which is a starting material. For example, ideally using zircon as the starting material,

## STR1 ## ZrSiO ₄ (solid) + 3C (solid) → ZrO ₂ (solid) + SiC (solid) + 2CO (gas) and ZrO ₂ / SiO
_The molar ratio becomes 1/1.

The mixing ratio between zirconium silicate and the carbon raw material may be basically equimolar. However, in general S
In the reaction between iO ₂ and C, the formation of SiO (gas) occurs first, so that the composition of the zirconia-silicon carbide composite material is liable to shift to the ZrO ₂ rich direction due to the scattering, Therefore, the mixing ratio can have a certain range.

As a starting material, zirconium silicate can be a natural material such as zircon, or a synthetic zirconium silicate gel.

The carbon may be either amorphous carbon such as coke, activated carbon or carbon black, or crystalline carbon such as graphite. Carbon-containing materials such as carbon fibers and pitch, organic resins that generate carbon by heating such as phenolic resins can also be used (however, carbon in carbon-containing materials or organic resins is
(Converted as the carbon content after removing components that evaporate below 1000 ° C.). From the viewpoint of reaction with SiO (gas), those having a high specific surface area, a low degree of graphitization, and high reactivity are preferred.

In order to obtain a high-purity zirconia-silicon carbide composite raw material, it is preferable that the starting materials, zirconium silicate and carbon, contain as few impurities as possible.

In order to prevent the scattering of SiO during firing,
After or at the same time as mixing, granulation is preferably performed with an aqueous solution of CMC, PVA, gum arabic, starch or the like as the primary binder, and more preferably pelletized. The granulated particle size is preferably 2 mm or more from the viewpoint of preventing scattering of SiO (gas).

The firing temperature is 1400 ° C. in view of the reaction rate.
The above is necessary, and about 1700 ° C. is desirable. However,
When the temperature exceeds 1800 ° C., zirconium carbide is remarkably generated. Since the carbon material starts oxidizing at 450 ° C. or more, zirconium carbide at 600 ° C. or more, and silicon carbide at 800 ° C. or more, it is 450 ° C. to remove the excess carbon material while leaving the zirconium carbide in the zirconia-silicon carbide composite material. At 600 ° C. to remove excess carbon material and fix zirconium carbide as zirconia, 6
Annealing (annealing) may be performed at a temperature of 00 to 800 ° C.

The zirconia-silicon carbide composite raw material obtained as described above has low volume expansion due to phase transition and low thermal expansion coefficient as compared with zirconia, and is suitable for use as a raw material of zirconia-carbon refractory material. Shows sex. In addition, by using a zirconia-silicon carbide composite material, oxidation resistance and corrosion resistance can be improved.

It is known that silicon carbide forms an oxide film, functions as an effective antioxidant, and has good wettability and corrosion resistance against slag. Here, in the zirconia-silicon carbide composite raw material used in the present invention, silicon carbide is evenly distributed in the composite raw material,
Zirconia, silicon carbide, carbon, and the like can be easily dispersed in a carbon-containing refractory without special consideration for the dispersion of silicon carbide and can effectively contribute to the improvement of oxidation resistance and corrosion resistance. Is significantly different from the carbon-containing refractory obtained by mixing the above.

The amount of the zirconia-silicon carbide composite material in the second invention of the present invention is in the range of 2 to 97% by weight, preferably 10 to 90% by weight. Addition amount is 2
If the content is less than 10% by weight, the contribution to the improvement of spalling resistance, oxidation resistance, and corrosion resistance is small, so that it is not preferable.
If the content exceeds 10% by weight, the carbon material cannot be sufficiently added to the refractory, and spalling resistance is significantly impaired, which is not preferable.

The molar ratio of zirconia / silicon carbide in the zirconia-silicon carbide composite material can be any ratio. However, from the viewpoint of balance of spalling resistance, oxidation resistance, and corrosion resistance, it is preferably 50/1 to 1/1.
5, more preferably a ratio of 20/1 to 1/5. When the ratio of zirconia is larger than 50/1, the spalling resistance and the function as an antioxidant become insufficient, which is not preferable, and when the ratio of silicon carbide is larger than ⅕, it is not preferable. It is not preferable because the strength is lowered and the corrosion resistance is reduced accordingly.

The compounding amount of the carbon material in the carbon-containing refractory of the present invention is in the range of 3 to 40% by weight, preferably 10 to 20% by weight. If the amount is less than 3% by weight, spall resistance and slag resistance are lost, and if it exceeds 40% by weight, corrosion resistance is lost. As the carbon material, various graphite materials such as scale graphite, earth graphite, artificial graphite, etc., and amorphous carbon materials such as pitch and carbon black can be used.

The carbon-containing refractory of the present invention may contain a stabilized zirconia raw material and / or an unstabilized zirconia raw material. The crystal phase of the zirconia raw material includes isotropic, square, and monoclinic, and any of these may be used. The stabilized zirconia raw material may be a solid solution with magnesia and / or calcia and / or yttria.

The amount of the stabilized zirconia raw material and / or the unstabilized zirconia raw material blended in the carbon-containing refractory material of the present invention is 95% by weight or less, preferably 80% by weight in total.
% By weight or less. When the amount exceeds 95% by weight,
The amount of the zirconia-silicon carbide composite material and the amount of the carbon material are reduced, and good corrosion resistance and spalling resistance may not be obtained.

Further, oxides such as silica, mullite, alumina, and spinel can be used as other refractory raw materials that can be blended with the carbon-containing refractory of the present invention. As is well known, these refractory raw materials have a sufficiently low coefficient of thermal expansion and are useful raw materials in view of spalling resistance. However, as compared with the zirconia-silicon carbide composite raw material and the zirconia raw material used in the present invention, the corrosion resistance is considerably reduced.
It is at most 5% by weight, preferably at most 80% by weight.

Further, a carbide such as silicon carbide, a boride, a metal or an alloy powder, which is a conventional raw material, may be appropriately added to the carbon-containing refractory as long as the characteristics of the carbon-containing refractory of the present invention are not impaired. it can. When blending these raw materials, the blending amount of these raw materials is at most 10% by weight or less, preferably 5% by weight or less.
% By weight or less. 10% by weight
If it exceeds, spalling resistance is impaired, which is not preferable. These raw materials are commonly used as antioxidants for carbon-containing refractories.

The compound having the above compounding ratio is kneaded together with a binder to be molded into a predetermined shape, and then the obtained molded product is fired in a non-oxidizing atmosphere, for example, in a coke breeze under a nitrogen atmosphere to continuously produce It is possible to make a refractory member used in a continuous casting apparatus such as a casting nozzle. Organic resins such as phenolic resins, tar, pitch, etc. can be used as the binder,
Phenolic resins having excellent moldability are preferred. In addition, the addition compounding amount of the binder is 5 to 5
It is in the range of 20% by weight, preferably 7-15% by weight. The kneading may be performed at room temperature or may be performed by heating and kneading. For forming into a predetermined shape, an equal pressure press is desirable in order to obtain uniformity of the material. However, other conventional means such as extrusion molding and a uniaxial press may be used. The firing temperature is 700 to 1400 ° C, preferably 900 to 1400 ° C.
And the firing time is in the range of 10 minutes to 24 hours, preferably 1 to 12 hours.

[0029]

EXAMPLES The carbon-containing refractory material of the present invention will be further described with reference to the following examples. Production of zirconia-silicon carbide composite material: ZrO ₂ / SiC molar ratio = 1/1 5 parts by weight of a 3% by weight aqueous solution of polyvinyl alcohol (PVA) is added as a binder to 100 parts by weight of zircon and 19.7 parts by weight of carbon black. After kneading, 2mmφ × 2m
m pellets. This is baked at 1700 ° C. for 1 hour in an Ar atmosphere to obtain a zirconia-silicon carbide composite raw material,
This was used in the following examples by pulverizing it to a predetermined particle size and adjusting the particle size.

ZrO ₂ / SiC molar ratio = 1/5, 20
/ 1,100 / 1 zirconium silicate gel (ZrO ₂ / SiO ₂ molar ratio = 1 / 5,20 / 1,100 / 1) and 100 parts by weight, 37.8 parts by weight of carbon black, respectively, 1.43 parts by weight , 0.29 parts by weight, and the resulting mixture is mixed with CO 2
The zirconia-silicon carbide composite material was calcined at 1700 ° C. for 1 hour in an atmosphere to obtain a zirconia-silicon carbide composite material, which was crushed to a predetermined particle size, and used in the following examples.

Example 1 Using the zirconia-silicon carbide composite material obtained as described above, a phenol resin (10% by weight based on the weight of the composition) was added to a composition having the composition shown in Table 1 below. Was kneaded as a binder. Then, it is molded to a size of 100 mm x 30 mm x 30 mm with an isostatic press,
The test sample was obtained by firing at 1000 ° C. in powder coke.
Next, a spalling test, a erosion test, and an oxidation resistance test were performed on these test samples. The spalling test is Ar
The sample was immersed in molten steel at 1600 ° C for 120 seconds in an atmosphere, and then subjected to water quenching.
The sample was immersed in molten steel at 1600 ° C. for 60 minutes in an r atmosphere, and the oxidation resistance test was evaluated based on the oxidation state when the sample was held in an electric furnace at 1300 ° C. for 60 minutes in air. . The obtained results are also shown in Table 1.

[0032]

[Table 1]

Example 2 A compound shown in Table 2 below was kneaded with a phenolic resin (10% by weight on the basis of the compound) as a binder, and then kneaded with an isostatic press to obtain 100 mm × 30 mm.
Molded into a size of × 30mm, 1000 ℃ in powder coke
The sample was fired at. For the obtained test sample,
A spalling test, a melting test, and an oxidation resistance test were performed in the same manner as in Example 1.

[0034]

[Table 2]

Example 3 A phenol resin (10% by weight based on the weight of the composition) was kneaded with the composition shown in Table 3 below as a binder, and then 100 mm × 30 mm by isostatic pressing.
Molded into a size of × 30mm, 1000 ℃ in powder coke
The sample was fired at. For the obtained test sample,
A spalling test, a melting test, and an oxidation resistance test were performed in the same manner as in Example 1. The zirconia-silicon carbide composite material used in this example had a ZrO ₂ / SiC molar ratio of 1:
It is one.

[0036]

[Table 3]

Example 4 Using the product 2 of the present invention and the comparative product 2, an immersion nozzle for continuous casting was prepared and tested with a continuous casting machine for bloom. As a result, about 20% of the comparative product 2 was cracked by thermal shock, whereas the invention product 2 was not cracked by thermal shock. In addition, the erosion condition of the product 2 of the present invention was about 10% better.

[0038]

Carbon-containing refractory of the present invention exhibits, ZrO ₂ / SiC molar ratio of zirconia in the range of 50 / 1-1 / 5 as an essential component - since the blended silicon carbide composite material, spalling It is possible to provide a material suitable for a refractory member of a continuous casting apparatus having excellent heat resistance and corrosion resistance.

Claims (4)

[Claims] 1. A carbon raw material is contained as an essential component in an amount of 3 to 40% by weight and a ZrO ₂ / SiC molar ratio in the range of 50/1 to 1/5 is contained in an amount of 2 to 97% by weight of a zirconia-silicon carbide composite raw material. A refractory material containing carbon, which is characterized by: 2. The carbon-containing refractory according to claim 1, comprising a stabilized zirconia raw material and / or an unstabilized zirconia raw material in an amount of 95% by weight or less. 3. The carbon-containing material according to claim 1, wherein one or more refractory raw materials selected from the group consisting of silica, mullite, alumina and spinel are contained in an amount of 95% by weight or less. Refractory. 4. The method according to claim 1, wherein one or more selected from the group consisting of carbides, borides, metals and alloy powders are contained in an amount of 10% by weight or less. Carbon-containing refractories.