JPH05148006A - Carbon-containing refractory - Google Patents

Abstract

PURPOSE:To provide a carbon-containing refractory capable of holding its high strength in a wide temperature range and reduced in the lowering of the strength even under an oxidative atmosphere condition. CONSTITUTION:The refractory comprises 100 pts.wt. of a fire-resistant aggregate comprising 50-97wt.% of a mixture of one kind or more of fire-resistant oxides, nitrides, borides and carbides and 3-50wt.% of a carbon material, 0.3-10 pts.wt. of boron carbide, and 0.3-15 pts.wt. of a mesophase pitch containing an optically anisotropic mesophase pitch in an amount of >=60% and giving a carbonization yield of >=70%, and the refractory can, if necessary, further contain 0.5-5 pts.wt. of a thermosetting resin.

Description

Detailed Description of the Invention

[0001]

The present invention has a high high temperature strength,
The present invention relates to a carbon-containing refractory having excellent thermal shock resistance and hot abrasion resistance as well as excellent oxidation resistance.

[0002]

2. Description of the Related Art Refractory materials containing carbon materials such as graphite have a high thermal conductivity of carbon, are difficult to wet with molten metal and slag, and prevent excessive sintering of refractory materials. In the coexistence with wood, it complements the advantages of the refractory aggregate and is widely used as a refractory for metallurgy such as a refractory for pig making and a refractory for steelmaking.

In recent years, due to severer operating conditions such as strong agitation operation, demands for improvement of hot wear resistance, high temperature strength and thermal shock resistance of carbon-containing refractories have become stronger and stronger, especially high temperature strength. Is desired.

For carbon-containing refractories, natural scaly graphite is generally used as a carbon material.
Since it does not melt up to a temperature of 00 ° C., it is difficult to expect strength improvement due to sintering of scaly graphite particles or sintering of scaly graphite particles and other aggregate particles. Therefore, the quality of carbon bond formation derived from the binder is an important factor that determines the strength of the refractory.

Conventionally, carbon-containing refractory binders have been
Liquid phenol resin or powder resin with carbonization yield of 40% or more,
Tar compatible resin and carbonization yield 50-60% and softening point 8
Pitch binder of 0 ~ 90 ℃ is used,
None of them are satisfactory in terms of strength.

As a method of strengthening carbon bonding, for example, in Japanese Patent Laid-Open No. 2-268953, a method of increasing hot strength by adding mesophase carbon powder having a high carbonization yield to an alumina-zirconia-silicon carbide type refractory material is disclosed. However, the effect of improving the strength is not yet sufficient.

The above binders all release volatile matter and carbonize as the temperature rises, but the carbon joints produced are inferior in oxidation resistance to the carbon materials used as fire-resistant aggregates. The carbon joint preferentially reacts with oxygen and disappears, and the strength of the refractory material decreases.

Therefore, in order to improve the high temperature strength of the carbon-containing refractory material, increasing the bonding strength of the carbon bonding and preventing the preferential oxidation and disappearance of the carbon bonding remain as problems to be solved. There is.

Further, as a means for improving the oxidation resistance of the carbon-containing refractory, a metal powder such as Al, Si, Cr, Mg, or Ti, or an alloy powder of two or more kinds thereof is added to have a high affinity with oxygen. A method of suppressing the oxidation of a carbon material by utilizing the properties is known. Further, a boride is added to the carbon-containing refractory to suppress the oxidation of the carbon material due to its high affinity with oxygen, and the generated B ₂ O ₃ forms a coating of the refractory aggregate and the low melting point compound, A method for preventing the oxidation of a carbon material is disclosed, for example, in JP-A-57-5811 as a magnesia-graphite refractory to which boron nitride or boron carbide is added, and JP-A-58-74579. The official gazette discloses a carbon-containing refractory to which metallic Al powder, metallic Si powder and boron carbide are added.

[0010]

However, none of the above-mentioned oxidation preventing methods has been able to solve the problem that the binder-derived carbon joint is more easily oxidized than the carbon material used as the refractory aggregate. However, there is still no provision for a means for preventing strength reduction due to preferential oxidation and disappearance of carbon joints.

The strength of the carbon-containing refractory using a phenol resin as a binder is high up to 200 to 300 ° C. due to the development of resin strength, but the strength is lowered due to the decomposition of the resin as the temperature rises, and 400 to 1000 ° C. Between 2
It is about 1/4 of the strength at 00 ° C. Moreover, resin-derived carbon is a non-graphitizable carbon that exhibits a glassy structure, and since it is difficult for graphitization to proceed due to temperature rise, it has lower oxidation resistance than the carbon material used as a fire-resistant aggregate, Easily oxidize and disappear. Such an intermediate temperature range (400-1
(000 ° C) The strength of the carbon joint easily deteriorates and the carbon joint easily oxidizes and disappears. Promotes wear damage due to.

[0012] A tar-compatible resin is used to improve the drawbacks of the phenol resin binder, but the properties of the resin remain strongly and the effect of improving the strength in the intermediate temperature range is small.

Further, since the conventional pitch binder has a large amount of volatile components and expands during the heat treatment at 200 to 500 ° C., it is difficult to obtain a dense brick structure.

Mesophase pitch has a low volatile content,
Since the obtained carbon joint is dense, it has a large effect of improving strength in the intermediate temperature range, and since it is easily graphitizable carbon, it has excellent oxidation resistance. However, even graphitizable carbon has a high degree of crystallinity and is inferior in oxidation resistance as compared with an extremely stable carbon material. Therefore, it is unavoidable that the carbon joint derived from the mesophase pitch is preferentially oxidized in the structure of the carbon-containing refractory used under the oxidizing atmosphere condition, the structure of the refractory becomes brittle, and the strength is reduced. Get up.

Therefore, an object of the present invention is to provide a carbon-containing refractory which can maintain high strength in a wide temperature range and has a small strength reduction even under oxidizing atmosphere conditions.

[0016]

Means for Solving the Problems As a result of intensive investigations by the present inventors to develop a carbon-containing refractory material having high high-temperature strength, a carbon-containing refractory material to which mesophase pitch and boron carbide are added has excellent high-temperature strength. The inventors have found that they have the above characteristics and completed the present invention.

That is, according to the present invention, the high temperature strength of the carbon-containing refractory is remarkably increased by using the mesophase pitch and the boron carbide together to form a carbon joint having high joint strength and excellent oxidation resistance. It has succeeded in improving it.

The carbon-containing refractory material according to the present invention comprises 50 to 97% by weight of a mixture of one or more of refractory oxides, nitrides, borides and carbides and 3 to 50% by weight of carbon material.
100 parts by weight of fire-resistant aggregate, boron carbide 0.3 to 10
60% by weight and mesophase having optical anisotropy
It is characterized by containing 0.3 to 15 parts by weight of mesophase pitch having a carbonization yield of 70% or more.

Further, the carbon-containing refractory according to the present invention is one or two of refractory oxides, nitrides, borides and carbides.
50 to 97% by weight of a mixture of one or more kinds and 3 to 50 carbon materials
100 parts by weight of refractory aggregate made up by weight, boron carbide 0.3
10 parts by weight, 6 mesophases having optical anisotropy
It is characterized by containing 0.3 to 15 parts by weight of mesophase pitch having a carbonization yield of 70% or more containing 0% or more and 0.5 to 5 parts by weight of thermosetting resin.

[0020]

The mesophase pitch in the carbon-containing refractory material of the present invention functions as a high-strength bonding agent when added together with boron carbide. The mechanism is that boron reacts with carbon as a solid solution by the reaction between boron carbide and mesophase pitch to form a carbon joint having high strength and excellent oxidation resistance.

The mesophase pitch is 200 to 500 ° C.
It softens and flows, spreads around the aggregate, and adheres. Furthermore,
Although the carbonization reaction proceeds as the temperature rises, a dense carbon joint can be obtained because the volatile content is small. The carbon joint is a graphitizable carbon with anisotropy developed, and graphitization proceeds as the temperature further rises to form a stronger joint.

In this series of carbonization and graphitization processes, boron carbide reacts with the mesophase pitch. Boron in boron carbide diffuses into carbon bond derived from mesophase pitch,
As a solid solution, the carbon bond becomes extremely strong. Furthermore, the presence of boron promotes graphitization and further strengthens the carbon bond.

It is known that boron carbide reacts with carbonaceous substances to form a solid solution of boron in the carbon body [Kenji Miyazaki et al .: Carbon; No. 128, pp. 2-6 (1987)]. However, in the present invention, the mesophase pitch is more reactive than the carbon material, and the boron carbide is highly dispersed in the carbonaceous material derived from the mesophase pitch. It reacts with the pitch.

Further, it is known that a carbon body containing a solid solution of boron has excellent oxidation resistance, and a carbon joint containing a solid solution of boron produced by a reaction between boron carbide and mesophase pitch also has an oxidation resistance. It has excellent properties.

Therefore, according to the present invention, the carbon bond has high strength in a wide temperature range due to the existence of the strong carbon bond, and the carbon bond is preferentially used even when used under the condition of high temperature and oxidizing atmosphere. It is possible to provide a carbon-containing refractory which is not oxidized and whose refractory structure is extremely weakened.

Furthermore, while boron carbide reacts with the mesophase pitch, it also acts as an antioxidant for carbon materials. Boron carbide reacts with oxygen to form B ₂ O ₃ , which forms a highly viscous melt composed of refractory raw materials and coats the refractory surface,
Prevents oxidation of carbon materials.

As the boron carbide used in the present invention, those commercially available as abrasives may be used, and it is preferable to use those having a particle size of 0.149 mm or less in view of reactivity and uniform dispersibility. The blending ratio of the boron carbide is
The content is 0.3 to 10 parts by weight with respect to 100 parts by weight of the refractory aggregate, but if less than 0.3 parts by weight, the effect of addition is small, and if it exceeds 10 parts by weight, high temperature strength and corrosion resistance decrease. And durability is reduced.

The mesophase pitch used in the present invention may be added and blended as a powder, or may be mixed with a refractory aggregate or boron carbide at a temperature at which the mesophase pitch is softened and melted, and further melted. It is also possible to dissolve the mesophase pitch in oil and add it by mixing with the refractory aggregate or boron carbide.

The properties of the mesophase pitch are not particularly limited, but 60% or more of mesophase having optical anisotropy is contained from the viewpoint of the strength, oxidation resistance and denseness of the formed joint. Those are preferable.

Further, the carbonization yield of the mesophase pitch is preferably 70% or more in view of the amount of volatile matter and the denseness and purity of the carbon joint to be formed. The higher the carbonization yield, the better, but it is also necessary that suitable fluidity is obtained at 200 to 500 ° C. and that it has good reactivity with boron carbide.

From the viewpoint of corrosion resistance, it is not preferable that the amount of the mesophase pitch added exceeds 15 parts by weight with respect to 100 parts by weight of the refractory aggregate. If the amount is less than 0.3 part by weight, the effect of strength development becomes small. When both mesophase pitch and thermosetting resin are used, the addition amount of mesophase pitch is about 0.3 to 10 parts by weight, and the addition amount of thermosetting resin is about 0.5 to 5 parts by weight. Preferably.

Further, as refractory raw materials which can be used in the present invention, oxides of magnesia, spinel, calcia, dolomite, alumina, silica, zirconia, zircon and the like, and silicon carbide, silicon nitride, boron nitride, boron carbide and zirconium boride are used. Non-oxides such as

Examples of the carbon material usable in the present invention include natural graphite or artificial graphite such as scaly graphite and earth-like graphite, electrode scrap, carbon fiber, and pyrolytic graphite.

The mixing ratio of the carbon material varies depending on the kind of the refractory raw material and the purpose of use of the carbon-containing refractory material of the present invention, but is 3 to 5 of the refractory aggregate comprising the carbon material and the refractory raw material.
It preferably constitutes 0% by weight. The reason for setting the blending ratio within the above range is that if the carbon material is less than 3% by weight, the characteristics that the carbon material is difficult to wet with molten metal or slag cannot be sufficiently exhibited. Further, the refractory as a whole is easily wet with slag, and the slag resistance is insufficient. On the other hand, if it exceeds 50% by weight, it is difficult to obtain a sufficient strength, and it is difficult to obtain a dense structure.

The above-mentioned refractory raw material and carbon material are not particularly limited, and it is preferable to use magnesia, calcia, dolomite, spinel and alumina as a main component, and natural graphite, although it depends on the purpose of use.

The carbon-containing refractory of the present invention is prepared by preparing these particle-size-adjusted refractory aggregates and boron carbide and mesophase pitch powder at a predetermined mixing ratio, or by preliminarily preparing refractory aggregates and boron carbide at the melting temperature of mesophase pitch. Prepare a mixture of mesophase pitch at a prescribed mixture ratio, or dissolve mesophase pitch in dissolved oil and mix it with refractory aggregate or boron carbide in advance at a prescribed mixture ratio, and knead and mold at high temperature. If this is done, an unfired product can be obtained. Further, a phenol resin may be added, and in this case, a non-sintered product can be obtained by kneading and molding at room temperature and drying at about 200 ° C. Further, it can be fired in a reducing atmosphere at about 900 to 1500 ° C. and used as a fired refractory.

[0037]

EXAMPLES The carbon-containing refractory material of the present invention will be described below with reference to examples. Example 1 A phenol resin was prepared by kneading a mixture adjusted to have a blending ratio shown in Table 2 below at room temperature or high temperature and press-molded at a pressure of 1500 kgf / cm ² to a size of 230 × 114 × 65 mm at room temperature or high temperature. 20 for those with
It was dried at 0 ° C. for 5 hours. In addition, xylene was used as the dissolved oil shown in Table 2. The various properties of the mesophase pitch shown in Table 2 are shown in Table 1 below.

[0038]

[Table 1] Softening point (° C) Anisotropic content (%) Carbonization yield (%) Mesophase pitch 1 218 100 85 Mesophase pitch 2 252 90 80 Mesophase pitch 3 400 60 60 82

[0039]

[Table 2]

As shown in Table 2 above, the properties of the obtained unburned carbon-containing refractory product are that the product of the present invention has higher strength in a wider temperature range than that of the comparative product and is heat-treated under the oxidizing atmosphere condition. It can be seen that the high strength is maintained even after the heat treatment and the oxidation resistance is excellent.

Example 2 As a gas injection nozzle for a molten metal container, 3 parts by weight of mesophase pitch, 1 part by weight of boron carbide and 3 parts by weight of phenolic resin were added to the compound containing magnesia and graphite as the aggregate of the present invention 1 in Table 2 above. A non-fired gas injection nozzle was manufactured in which a stainless steel tube having an inner diameter of 1.5 mm and an outer diameter of 3.5 mm was loaded into a refractory having parts added thereto. 180 ton converter placed on the bottom of the converter,
Refining was performed by blowing argon gas of 7 kgf / cm ² at a rate of 8 Nm ³ / min. The wear rate was reduced by about 15% with respect to the comparative product 7 to which 3 parts by weight of the phenol resin and 3 parts by weight of the mesophase pitch were added, and no abnormal damage due to peeling due to heat spalling or gas leakage was observed.

Example 3 A mixture of 50% by weight of mesophase pitch and 50% by weight of boron carbide was added to 300 to 400 in the compound containing alumina and graphite as the aggregate of the present invention 3 in Table 2 as a plate brick for sliding nozzle. After melt mixing at ℃, after cooling,
4 parts by weight of pulverized powder and 4 parts by weight of phenol resin were added, and kneaded, molded and dried by a conventional method to produce an unfired plate. A two-strand 60 ton tundish was compared to an unfired plate with the addition of 4 parts by weight phenolic resin. Both of them completed the continuous casting of 6 charges, but the product of the present invention in which the mesophase pitch and boron carbide were added had a slight decarburization around the nozzle holes as compared with the conventional non-added product, and a corner defect of the nozzle hole, The roughness of the sliding surface was small and the effect was confirmed.

[0043]

The carbon-containing refractory material of the present invention has a high carbonization yield and uses a combination of mesophase pitch with advanced optical anisotropy and boron carbide, so that it softens at 200 to 400 ° C.
After the molten mesophase pitch is dispersed around the refractory aggregate, it reacts with boron carbide to form a carbon joint having extremely strong and excellent oxidation resistance, and a very strong refractory structure can be formed. The carbon-containing refractory can maintain high strength even at a temperature of 400 to 1000 ° C. in which strength is significantly reduced by conventional resin bonding, and further, even when used under an oxidizing atmosphere condition, a carbon bonding part is formed. Since it does not preferentially oxidize and disappear to weaken the refractory structure, high strength can be maintained. Therefore, when the carbon-containing refractory is used under repeated heating conditions in an oxidizing atmosphere, oxidative loss of the carbon material and abrasion damage due to molten metal or the like are significantly reduced.

Claims (2)

[Claims] 1. 100 parts by weight of a refractory aggregate comprising 50 to 97% by weight of a mixture of one or more of refractory oxides, nitrides, borides and carbides and 3 to 50% by weight of a carbon material, boron carbide Carbonization yield 70% containing 0.3 to 10 parts by weight and 60% or more of mesophase having optical anisotropy
A carbon-containing refractory material characterized by containing 0.3 to 15 parts by weight of the above mesophase pitch. 2. 100 parts by weight of a refractory aggregate consisting of 50 to 97% by weight of a mixture of one or more of refractory oxides, nitrides, borides and carbides and 3 to 50% by weight of a carbon material, boron carbide 0.3 to 10 parts by weight, 0.3 to 15 parts by weight of mesophase pitch containing 60% or more of mesophase having optical anisotropy and carbonization yield of 70% or more, and 0.5 to 5 parts by weight of thermosetting resin. A refractory material containing carbon, which comprises: