JPH0782003A - Carbon-containing refractory - Google Patents

Abstract

PURPOSE:To obtain a carbon-containing refractory having excellent hot strength without reducing thermal shock resistance by adding an improved pitch as a binder to a refractory raw material composed of carbon and magnasia, kneading, molding and burning. CONSTITUTION:A solution obtained by dissolving 2-15wt.% of an improved pitch in a heterocyclic compound (e.g. quinoline) is added to 100wt.% of a refractory raw material composed of 5-30wt.% of carbon and 70-95wt.% of magnesia. Then, the mixture is kneaded, molded and burnt in a nonoxidizing atmosphere at >=500 deg.C. The composition can further be mixed with 0.5-3wt.% Al or an Al alloy based on 100wt.% of the refractory raw material. Consequently, oxidation resistance and strength of carbon-containing refractory can be bettered.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a container for treating molten metal,
In particular, it relates to a refractory material containing carbon such as a converter.

[0002]

As a binder for carbon-containing refractory materials,
Phenolic resins have been used (for example, Japanese Patent Laid-Open No. Sho 5).
4-16161).

Further, in order to improve the thermal shock resistance of the carbon-containing refractory, a binder to which pitch and a phenol resin are added in combination is used (for example, JP-A-2-180).
753, JP-A-4-55361, JP-A-4-36755
No. 6).

[0004]

When a phenolic resin is used as a binder, curing proceeds due to a polycondensation reaction of a functional group bonded to a benzene ring or a crosslinking reaction with an adjacent benzene ring due to addition of a curing agent. Develops strength.

However, when heated in a non-oxidizing atmosphere, thermal decomposition occurs from the binding site formed by polycondensation or cross-linking reaction, it becomes difficult for condensation between adjacent benzene rings to occur, and the yield remaining as carbon after heating is increased. Get lower.

As a result, the weight loss due to thermal decomposition causes
When a phenol resin is used as a binder for a carbon-containing refractory, the strength is reduced during hot working.

The pitch is composed of various compounds having different molecular weights such as aliphatic compounds and aromatic compounds.

Therefore, when heated in a non-oxidizing atmosphere, the low molecular weight compound contained in the pitch undergoes thermal decomposition, resulting in weight reduction.

As a result, when pitch is used as a binder for a carbon-containing refractory, the weight of the low-molecular weight compound is greatly reduced by thermal decomposition, resulting in a decrease in strength during hot working.

In order to solve this problem, a metal has been added to the carbon-containing refractory to improve the hot strength, but the thermal shock resistance is deteriorated (for example, Japanese Patent Laid-Open Publication No. Sho. 54-163913).

The present invention is to provide a carbon-containing refractory having excellent hot strength without lowering the thermal shock resistance which is an excellent feature of the carbon-containing refractory.

[0012]

The present invention is based on carbon 5-30.
After adding a solution prepared by dissolving 2 to 15 wt% of modified pitch in a heterocyclic compound to 100 wt% of a refractory raw material composed of 70 wt% and 70 to 95 wt% of magnesia, after kneading and molding, a non-oxidizing atmosphere is obtained. It is a carbon-containing refractory characterized by being fired at a temperature of 500 ° C. or higher.

Further, according to the present invention, the refractory raw material 10 is composed of 5 to 30 wt% of carbon and 70 to 95 wt% of magnesia.
To 0 wt%, 0.5 to 3 wt% of Al or Al alloy is added together with a solution in which 2 to 15 wt% of modified pitch is dissolved in a heterocyclic compound, and after kneading and molding, in a non-oxidizing atmosphere. It is a carbon-containing refractory characterized by being fired at a temperature of 500 ° C. or higher.

The above-mentioned modified pitch is soluble in a heterocyclic compound, is a crystalline phase or a mixed phase consisting of a crystalline phase or an amorphous phase, and is fired at 800 ° C. in a non-oxidizing atmosphere. The pitch has a weight reduction rate of 30% or less when performed.

Further, the heterocyclic compound dissolves the modified pitch, and its addition amount is 100 v of the bulk volume of the refractory raw material.
It is 2 to 10 vol% with respect to ol%.

The present invention will be described in detail below. The present inventors have found that the modified pitch has an extremely low weight reduction rate of 30% or less when fired at 800 ° C. in a non-oxidizing atmosphere, and a heterocyclic compound, compared to a phenolic resin and pitch. Focusing on the property that it dissolves in, it is thought that adding the modified pitch to the magnesia-carbonaceous refractory after dissolving it in the heterocyclic compound has the effect of improving hot strength and thermal shock resistance. Invented.

The carbon content is set to 5 to 30 wt% because it is excellent in thermal shock resistance and slag infiltration resistance.

This is because if the carbon content is less than 5 wt%, the thermal shock resistance and slag infiltration resistance will be poor, and if the carbon content exceeds 30 wt%, the oxidation resistance will be significantly reduced.

As the carbon, natural or artificial graphite, anthracite, mesophase carbon, carbon black or the like can be used, and the purity is preferably 90% or more.

The magnesia content is set to 70 to 95 wt% because it is excellent in corrosion resistance and thermal shock resistance.

This is because if the magnesia is less than 70 wt%, the corrosion resistance is poor, and if the magnesia exceeds 95 wt%, the thermal shock resistance is poor.

Sintered products and electro-melted products can be used as magnesia, and the purity is preferably 95% or more.

The reason why the modified pitch is added in an amount of 2 to 15 wt% is that it is excellent in hot strength and thermal shock resistance.

If the amount of modified pitch added is less than 2 wt%,
Inferior in hot strength and thermal shock resistance, the addition amount of modified pitch is 1
This is because if it exceeds 5 wt%, cracking occurs due to shrinkage of the refractory during firing, resulting in poor strength.

The case of using quinoline as an example of the heterocyclic compound will be described. The amount of quinoline added is 2 to 10 vol with respect to 100 vol% of the bulk volume of the refractory raw material.
% Is because the dispersibility of the modified pitch during kneading and the filling property during molding are excellent.

When the amount of quinoline added is less than 2 vol%,
This is because the dispersibility of the modified pitch during kneading and the filling property during molding are poor, and molding becomes impossible when the amount of quinoline added exceeds 10 vol%.

The atmosphere for firing the carbon-containing refractory is preferably a non-oxidizing atmosphere such as Ar, N ₂ , CO or CO ₂ . The atmosphere is made non-oxidizing in order to prevent the oxidation of graphite.

The firing temperature of the carbon-containing refractory material is set to 500 ° C. or higher because the modified pitch is softened and melted at a temperature of 300 ° C. or higher, and is semi-coke at a temperature of 500 ° C. or higher.
This is to prevent remelting of the modified pitch.

If the firing temperature of the carbon-containing refractory is less than 500 ° C., a creep phenomenon occurs during use, and the stability of the structure lined with the refractory cannot be ensured.

The amount of Al or Al alloy added is 0.5 to 3 w.
The reason for setting t% is that it is excellent in hot strength, corrosion resistance, and oxidation resistance.

Addition amount of Al or Al alloy is 0.5 wt%
If it is less than 1, the hot strength, corrosion resistance and oxidation resistance are poor, and if the addition amount of Al or Al alloy exceeds 3 wt%, the thermal shock resistance is poor.

The modified pitch used in the present invention is soluble in quinoline, is a crystalline phase or a mixed phase composed of a crystalline phase or an amorphous phase, and is fired at 800 ° C. in a non-oxidizing atmosphere. It is desirable that the weight reduction rate be 30% or less.

Further, the crystalline content in the modified pitch is
It is preferably 60% or more. This is because when the crystalline content in the modified pitch is less than 60%, the strength developed when used as a binder is poor.

Further, the modified pitch is set to 8 in a non-oxidizing atmosphere.
This is because if the weight loss rate exceeds 30% when fired at 00 ° C, the hot strength becomes poor.

The modified pitch becomes a carbonized product having a layered structure with a highly developed carbon hexagonal net surface by heating in a non-oxidizing atmosphere, forms a strong carbon bond, and is compared with a phenol resin or pitch. Since the rate of weight loss due to thermal decomposition is extremely low, when the modified pitch is used as the binder of the carbon-containing refractory, the strength is less decreased due to thermal decomposition and the hot strength is improved.

By dissolving the modified pitch in quinoline and adding it to the refractory raw material, it becomes possible to uniformly disperse the modified pitch, thereby improving the hot strength.

As described above, the use of the modified pitch as the binder of the carbon-containing refractory material improves the hot strength of the carbon-containing refractory material. However, the carbonized product of the modified pitch is higher than that of the phenol resin. Has high thermal conductivity,
In addition, the thermal shock resistance is improved because a layered structure capable of relaxing the thermal stress generated by the thermal shock inside the carbon-containing refractory is provided.

Further, the carbon-containing refractory material of the present invention has oxidation resistance due to the following mechanism of added Al or Al alloy,
Brings strength improvement.

Here, description will be made by taking metal Al as an example.
Since metal Al has a higher oxygen affinity than carbon in the temperature range of 600 ° C. or higher, it is more easily oxidized than carbon and Al ₂
It becomes O ₃ and prevents the oxidation of carbon.

Then, the pores in the refractory structure are closed by the volume expansion when Al ₂ O _{3 is} generated, so that the inflow of the oxidizing gas into the refractory is suppressed and the oxidation resistance is improved.

Further, during the firing in a non-oxidizing atmosphere or the preheating of the furnace, the metallic Al is converted into A by the reaction of the formula (1).
It generates a _{l 4 C 3, Al 2 O} 3 , and MgO · Al ₂ O _3, and accompanied by volume expansion at the time of generation.

[0042]

Embedded image MgO + C → MgO + C + Al ₄ C ₃ + Al ₂ O ₃ + MgO.Al ₂ O ₃ (1)

Due to this volume expansion, the pores in the refractory structure are closed, the structure is densified, and the strength is improved.

[0044]

EXAMPLES The present invention will be described below based on examples.

[0045]

Example 1 As a refractory lining for a molten metal processing container,
Table 1 shows examples of magnesia-carbonaceous refractories in which the modified pitch of the present invention is dissolved in quinoline and added as a binder.

[0046]

[Table 1]

Electromagnetic fused magnesia was used as magnesia, and natural graphite was used as carbon. The modified pitch used was a coal tar pitch that had been heat-treated and then fractionated with a solvent.

The presence or absence of the crystalline phase contained in the modified pitch was confirmed by X-ray diffraction. The weight reduction rate of the modified pitch was calculated from the weight change before and after firing at 800 ° C. in an Ar atmosphere.

The dissolution of the modified pitch in quinoline was 44 μm.
The modified pitch powder pulverized to m or less was dissolved in quinoline heated to 80 ° C.

A predetermined amount of each quinoline solution in which modified pitch was dissolved was added to the raw material composition shown in Table 1 and kneaded.

Thereafter, this mixture was vacuum friction molded, dried at about 100 ° C. for 24 hours, and then calcined under the conditions shown in Table 1 to obtain a magnesia-carbonaceous refractory material.

For comparison, Table 1 also shows the manufacturing conditions of the magnesia-carbonaceous refractory when a phenol resin is used as a binder.

The obtained magnesia-carbonaceous refractory material was subjected to bulk specific gravity, apparent porosity measurement, hot strength evaluation test and thermal shock resistance evaluation test.

The hot strength evaluation test was carried out at 1000 in Ar gas flow.
It was carried out by measuring the bending strength during hot at 1400C.

The thermal shock resistance test was conducted on molten steel at 1600 ° C.
After dipping for 0 second, water cooling was performed for 30 seconds, and then air cooling was repeated for 10 minutes to evaluate thermal shock resistance.

Regarding the evaluation of thermal shock resistance, the one in which the refractory was cracked in one thermal shock test was bad, and the one in which the refractory was cracked in the repeated thermal shock test two to four times was good. The case where the refractory did not crack in the thermal shock test was rated as excellent.

The magnesia-carbonaceous refractory obtained by dissolving the modified pitch of the present invention in quinoline and adding it as a binder exhibited excellent thermal shock resistance and excellent hot strength.

On the other hand, Comparative Example 5 was inferior in hot strength because the amounts of carbon and modified pitch added were not appropriate.

Comparative Example 6 was inferior in hot strength and thermal shock resistance because the added amounts of magnesia, modified pitch and quinoline were not proper. Comparative Example 7 was inferior in hot strength because the modified pitch used as the binder had a large weight reduction rate.

In Comparative Example 8, the refractory material after molding was processed in air at 800
Since it was fired at ℃, the apparent porosity increased and the hot strength was poor.

Comparative Example 9 was inferior in hot strength because it used a phenol resin as a binder.

[0062]

Example 2 As a refractory lining for a molten metal processing container,
Table 2 shows examples of magnesia-carbonaceous refractories in which the metal and the modified pitch of the present invention are dissolved in quinoline and added as a binder.

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

[Table 5]

Electromagnetic fused magnesia was used as magnesia, and natural graphite was used as carbon. The modified pitch used was prepared under the same conditions as in Example 1, and the modified pitch was dissolved in quinoline under the same conditions as in Example 1.

To the raw material compositions shown in Table 2, a predetermined amount of quinoline solution in which modified pitch was dissolved was added and kneading was performed.

Thereafter, this mixture was vacuum friction molded, dried at about 100 ° C. for 24 hours, and then fired under the conditions shown in Table 2 to obtain a magnesia-carbonaceous refractory material.

For comparison, Table 2 also shows the production conditions of the magnesia-carbonaceous refractory when a phenol resin is used as a binder.

The magnesia-carbonaceous refractory thus obtained was subjected to measurement of bulk specific gravity and apparent porosity, hot strength evaluation test and thermal shock resistance evaluation test under the same conditions as in Example 1, and further oxidation resistance test. , A corrosion resistance test was conducted. The oxidation resistance test was performed by firing in air at a temperature of 1400 ° C. for 3 hours.

For the oxidation resistance index, the thickness of the decarburized layer after firing was measured, and the refractory to which the metal and the phenol resin were added was set to 100.

The smaller the oxidation resistance index, the better the oxidation resistance. The corrosion resistance test was performed by a high frequency lining method at 1650 ° C. for 3 hours. The composition of slag is CaO / Si
O ₂ = 3.3, T. Fe = 18%.

The corrosion resistance index was measured by measuring the amount of erosion in the maximum erosion portion after the erosion test, and showing the refractory to which metal and phenol resin were added as 100. The smaller the corrosion resistance index, the better the corrosion resistance.

The magnesia-carbonaceous refractory obtained by dissolving the metal of the present invention and the modified pitch in quinoline and adding it as a binder exhibited excellent thermal shock resistance and excellent hot strength, oxidation resistance and corrosion resistance.

On the other hand, Comparative Example 16 was inferior in hot strength and oxidation resistance because the amounts of carbon, modified pitch and metal added were not appropriate.

Comparative Example 17 was inferior in hot strength, corrosion resistance and thermal shock resistance because the added amounts of magnesia, metal, modified pitch and quinoline were not proper.

Comparative Example 18 was inferior in hot strength, oxidation resistance, corrosion resistance, and thermal shock resistance because the modified pitch used as a binder had a large weight reduction rate.

In Comparative Example 19, the fire extinguishing material after molding was heated in air at 80
Since it was fired at 0 ° C., the apparent porosity increased, and the hot strength, oxidation resistance, corrosion resistance, and thermal shock resistance were poor.

In Comparative Example 20, since the phenol resin was used as the binder, the hot strength, oxidation resistance, corrosion resistance and thermal shock resistance were poor.

[0081]

Industrial Applicability According to the present invention, the thermal shock resistance, hot strength, oxidation resistance, and corrosion resistance are dramatically improved as compared with conventional phenol resins or carbon-containing refractories containing phenol resins and metals. It has become possible to extend body life and reduce furnace material costs.

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location // B22D 41/02 A (72) Inventor Atsushi Nakao 20-1 Shintomi, Futtsu City Nippon Steel Corp. Within the development headquarters

Claims (4)

[Claims] 1. Carbon 5 to 30 wt% and magnesia 7
After adding a solution in which 2 to 15 wt% of modified pitch is dissolved in a heterocyclic compound to 100 wt% of refractory raw material consisting of 0 to 95 wt%, after kneading and molding, 500 ° C. in a non-oxidizing atmosphere. A carbon-containing refractory characterized by being fired at the above temperature. 2. Carbon 5-30 wt% and magnesia 7
With respect to 100 wt% of the refractory raw material consisting of 0 to 95 wt%, 0.5 to 3 wt% of Al or Al alloy is added together with a solution in which 2 to 15 wt% of modified pitch is dissolved in a heterocyclic compound, and kneading, After molding, 500 in non-oxidizing atmosphere
A carbon-containing refractory characterized by being baked at a temperature of ℃ or higher. 3. The modified pitch is soluble in a heterocyclic compound, is a crystalline phase or a mixed phase composed of a crystalline phase or an amorphous phase, and is fired at 800 ° C. in a non-oxidizing atmosphere. The carbon-containing refractory material according to claim 1 or 2, wherein the weight reduction rate is 30% or less when it is performed. 4. The carbon-containing refractory material according to claim 1, wherein the amount of the heterocyclic compound added is 2 to 10 vol% with respect to 100 vol% of the bulk volume of the refractory raw material.