JPH04362067A - Carbon-containing basic refractories - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to carbon-containing basic refractories with improved oxidation resistance and hot strength used in various steelmaking containers such as converters, ladles, tundishes, and RH. be.

0002

BACKGROUND OF THE INVENTION In recent years, with advances in steelmaking technology, MgO--C bricks have been widely used as refractories for steelmaking containers. However, recently, various types of molten steel processing have come to be carried out in these containers, and therefore, even higher corrosion resistance, spalling resistance, and wear resistance under extremely high temperatures are required.

[0003] Various methods have been proposed in the past as means for imparting oxidation resistance to the carbon material of MgO-C bricks, but the method of adding metal powder such as aluminum or magnesium has been widely and generally adopted. (For example, Japanese Patent Application Laid-open No. 107749/1983).

[0004] Recently, a method has been proposed in which oxidation is prevented by adding calcium hexaboride instead of the above-mentioned metal powder and coating the carbon material with boron oxide produced by the oxidation (Japanese Unexamined Patent Application Publication No. 1999-3) -45553).

[0005]

[Problems to be Solved by the Invention] However, although the method of adding metal powder improves oxidation resistance, hot strength, and structural stability, the stress relaxation function decreases, resulting in poor corrosion resistance.
There is a problem with ringability. Furthermore, further improvement in oxidation resistance at high temperatures is desired.

Further, when a method of adding calcium hexaboride was studied in detail, it was found that although it does provide oxidation resistance, it significantly lowers corrosion resistance. Therefore, a method is required to obtain oxidation resistance without impairing the corrosion resistance of bricks by adding calcium hexaboride.

The present invention has been made to solve the above-mentioned conventional problems, and provides a carbon-containing base that exhibits excellent corrosion resistance, hot strength, structural stability, oxidation resistance, and spalling resistance under ultrahigh temperatures. The purpose is to provide durable refractories.

[0008]

[Means for Solving the Problems] The inventors studied various performances of MgO-C bricks for steel making containers, and after intensive research, they found that by using metal powder and calcium hexaboride together, they added both. This invention was completed by discovering a synergistic effect that could not be seen with the addition of each substance alone.

That is, the present invention provides basic refractory materials 60 to
It is a carbon-containing basic refractory consisting of 97 parts by weight, 3 to 40 parts by weight of carbon material, 0.5 to 5 parts by weight of aluminum or/and magnesium, and 0.5 to 5 parts by weight of calcium hexaboride.

The basic refractory material used in this invention is mainly clinker such as fused magnesia, sintered magnesia, calcia, dolomite, and magcalcia. Further, other refractory materials can be used in combination as necessary. The amount of basic refractory material used is 60 to 97 parts by weight.

[0011] Carbon materials include natural graphite, artificial graphite,
Known carbon materials such as electrode scraps, petroleum coke, and carbon black can be used, but high-purity graphite is suitable from the viewpoint of corrosion resistance at high temperatures. The amount of this carbon material used is 3 to 40 parts by weight. If the basic refractory material is less than 60 parts by weight and the carbon material exceeds 40 parts by weight, the strength of the brick will decrease, and if the carbon material is less than 3 parts by weight and the basic refractory material is more than 97 parts by weight, the spalling resistance will decrease. Both are unfavorable.

As the metal powder, which is one of the characteristics of the present invention, a single powder of aluminum or magnesium, or a mixed powder or alloy powder of both is used.

Another feature of the present invention is that calcium hexaboride is a fine powder with a particle size of 44 μm or less, preferably an ultrafine powder with a particle size of 10 μm or less. The use of fine powder contributes to the improvement of hot strength as described below.

[0014] The amount of metal powder used in this invention is 0.
5 to 5 parts by weight. This is because if the amount of metal powder is less than 0.5 parts by weight, the effect of adding it will not be exhibited, and if it exceeds 5 parts by weight, the spalling resistance will decrease due to a decrease in stress relaxation function.

[0015] Also, the amount of calcium hexaboride used is 0.5
~5 parts by weight. This is because if the amount of calcium hexaboride is less than 0.5 parts by weight, the effect of adding it will not be exhibited, and if it exceeds 5 parts by weight, the corrosion resistance will decrease.

Further, the content of both the metal powder and calcium hexaboride is preferably 1 to 6 parts by weight. The amount of each addition can be adjusted depending on the required performance of the part where the brick is used to adjust various performances and make the overall wear and tear uniform. For example, the amount of calcium hexaboride used is increased in areas that require higher oxidation resistance, and the metal powder and calcium hexaboride are used in larger amounts in areas that are in contact with hot water where hot strength is required. Reduce the amount of calcium hexaboride in the slag line area. Furthermore, when spalling resistance is important, the amount of metal powder is reduced and the amount of calcium hexaboride is increased.

[0017] In the method for producing a carbon-containing basic refractory of the present invention, a binder is added to each material whose particle size has been adjusted, and the mixture is kneaded and then pressure-formed, which is then used as an unfired refractory that is heat-treated. It is. The binder used is a common one, such as tar, pitch, or phenolic resin.

[0018]

[Operation] Since the metal powder used in this invention is easily oxidized, it prevents the oxidation of the carbonaceous material generated from the carbon material and binder, and at the same time, the produced aluminum oxide reacts with the basic material magnesia to form the spinel. MgO・Al2
The volumetric expansion during the production of O3) closes the pores, and the densification of the structure further increases the oxidation resistance, and at the same time improves the hot strength. When calcium hexaboride coexists in this system, the boron promotes spinel formation, resulting in further significant improvements in oxidation resistance and hot strength.

Furthermore, when calcium hexaboride is added to MgO--C bricks, boron oxide produced by oxidation reacts with magnesia to form 3MgO.B2 O3, which forms a coating of carbon material and exhibits an antioxidant effect. Furthermore, when metal powder and calcium hexaboride are used together, when calcium hexaboride is reduced to a reduced state by the metal powder, it becomes more likely to react with carbon materials, and furthermore CaC
2, new bonds are generated between the carbon materials, strengthening the bonds in the matrix portion and blocking the easily reactive terminal groups of the carbon materials. This serves to improve strength and oxidation resistance. This carbide formation does not occur in the absence of metal powder, or occurs only at a small rate and amount. This bond formation due to carbonization of calcium hexaboride is a surface reaction, and becomes more pronounced as the particle size of calcium hexaboride becomes smaller.

[0020] Regarding the effect of preventing oxidation of carbon materials by the coating caused by boron oxide produced by the oxidation of calcium hexaboride, the same effect can be seen by adding boron carbide or boron oxide itself, but the corrosion resistance A decline is seen. This is because when calcium hexaboride is oxidized, the calcium oxide produced increases the viscosity of the slag and prevents it from penetrating into the bricks.On the other hand, when boron carbide or boron oxide is added, it melts into the slag. This is because it leads to tissue deterioration.

[0021]

[Example] Metal powder with a particle size of 0.5 mm or less and calcium hexaboride ultrafine powder with a particle size of 10 μm or less were added to magnesia clinker and scale graphite having the usual particle size composition shown in Table 1 to form a phenolic resin. After kneading and molding with 2.5 parts by weight, the mixture was heat-treated at 300°C for 3 hours. Measured values of physical properties and various test results are also shown in Table 1. The oxidation resistance index is the decarburized area after heating in air at 1400°C for 10 hours compared to the conventional standard product with metal aluminum addition (Comparative Example 1).
It is expressed as an index that is set to 0. The corrosion resistance index was expressed as an index in which the amount of corrosion loss after treatment at 1750°C for 5 hours using converter slag (C/S=3.4) was set as 100 for Comparative Example 1. The spalling resistance index was determined by repeating the operation of immersion in hot metal at 1650 DEG C. three times, and the ratio of the elastic modulus before and after was expressed as an index, with Comparative Example 1 being 100. Regarding the comprehensive evaluation, Comparative Example 1 was used as the standard (C), and various characteristics were evaluated in five grades from A to E in descending order of overall judgment.

[0022]

[Table 1]

According to Table 1 above, Comparative Example 1 corresponds to the currently used MgO--C brick, in which metal powder was used alone. This Comparative Example 1 was used as the standard (C
), Examples 1 to 11 all had (A
) or (B).

First, in Examples 1 to 4, 6, and 8 to 11, in which aluminum and calcium hexaboride were used in combination in the range of 0.5 to 5.0 parts by weight, the corrosion resistance was either fair or improved. is observed, as well as oxidation resistance,
It can be seen that remarkable effects are exhibited in both spalling resistance and hot strength. In particular, in Examples 1 and 2, even if the amounts of aluminum and calcium hexaboride used were small, by using both together, the oxidation resistance was good, and the hot strength and spalling resistance were improved. Excellent in that respect.

[0025] Also, Example 5 in which magnesium and calcium hexaboride were used together in a range of 0.5 to 5 parts by weight each
Significant improvements were seen in corrosion resistance, oxidation resistance, spalling resistance, and hot strength. Furthermore, it can be seen that even in Example 7, in which an aluminum-magnesium alloy and calcium hexaboride were used in combination, corrosion resistance and the like were even more excellent.

As described above, a synergistic effect is obtained by the combined use of metal powder and calcium hexaboride, proving the superiority of the present invention.

On the other hand, in Comparative Example 2 in which calcium hexaboride is used alone, the oxidation resistance and spalling resistance are fair, but the hot strength and corrosion resistance are reduced. In addition, the metal powder and calcium hexaboride were added in Example 1 to
In Comparative Examples 3 to 6, in which oxidation resistance, corrosion resistance,
A significant decrease is observed in at least one of spalling resistance and hot strength. Further, in Comparative Example 7 in which magnesium and boron carbide were used in combination, a decrease in corrosion resistance was observed.

[0028]

[Effects of the Invention] As explained above, according to the present invention, the metal powder prevents the oxidation of carbonaceous substances generated from carbon materials and binders, and at the same time, the produced aluminum oxide reacts with the basic material magnesia. The pores are closed by the volumetric expansion when spinel is produced, and the densification of the structure further increases oxidation resistance and improves hot strength at the same time. Further, by adding calcium hexaboride, the interaction with the metal powder strengthens the bond in the matrix portion and prevents oxidation of the carbon material. In this way, the combined use of metal powder and calcium hexaboride has the extraordinary effect of further improving oxidation resistance and hot strength.

Claims (1)

[Claims] Claim: 1. 60 to 97 parts by weight of basic refractory material, 3 to 40 parts by weight of carbon material, 0.5 to 5 parts by weight of aluminum or/and magnesium, and 0.5 parts by weight of calcium hexaboride.
5 to 5 parts by weight of a carbon-containing basic refractory.