KR19990059266A - High Magnesium-Carbon Refractory - Google Patents

Abstract

The present invention relates to a high resistance magnesia-carbon refractory material, at least one metal selected from 75 to 90% by weight of magnesia refractory material, 10 to 25% by weight of graphite graphite, metal powder Al, Mg-Al alloy, Al-Si alloy Metal powder containing 1 to 6% by weight, 0.1 to 0.8% by weight of a mixture of boron carbide (B ₄ C) and calcium boride (CaB ₆ ), and 4 to 5% by weight of a waste phenol compound binder; The mixing ratio of B ₄ C) and calcium boride (CaB ₆ ) is characterized by having a composition ratio of 1: 1.

The magnesia-carbon refractory material according to the present invention has the effect that the refractory is resistant to the penetration and erosion of slag, that is, corrosion resistance and oxidation resistance can be extended to extend the life of the furnace.

Description

High Magnesium-Carbon Refractory

The present invention relates to high-resistance magnesia-carbon refractory, and more particularly, to the refractory of magnesia-carbon (MgO-C) used for the walls of furnaces, that is, resistance to oxidation and resistance to slag penetration and erosion. The present invention relates to a high-content magnesia-carbon refractory material having an increased content of magnesia-carbon refractory material.

In general, the walls of converters and electric furnaces used in the steelmaking process are frequently exposed to the atmosphere, and the graphite in the magnesia-carbon refractory is easily oxidized by the surrounding oxygen, which is the most susceptible to slag. In recent years, as the parts other than the wall are advanced, in particular, the life of the magnesia-carbon refractory material is influenced.

That is, the wall part of the furnace is accompanied by abrasion by molten steel together with oxidation of graphite by the atmosphere, and spalling, which is a peeling phenomenon of the surface deterioration layer due to the erosion reaction of the surface by the penetration of slag and molten steel and the penetration of slag. As a phenomenon occurs, especially, high oxidation resistance, high corrosion resistance and high strength are required.

The magnesia-carbon refractory material is a brick material. In general, in the magnesia-carbon refractory material, at least one metal powder such as aluminum powder, magnesium powder, silicon powder, magnesium aluminum alloy, and aluminum-silicon alloy is used to prevent oxidation. Although it is mixed and added, the operating conditions are severe, so the resistance to oxidation is poor, so oxidation resistance and corrosion resistance can not be exhibited, and thus the furnace is damaged early. Korea Patent Publication No. 86-1649 discloses boron carbide. By adding 0.3 to 5% to at least one metal powder, there is an effect of improving the oxidation resistance to the amount used, but there is a problem in that the corrosion resistance is lowered due to the increase in the low melting point material with the increase in the amount of boron carbide.

The present invention has been made to solve the problems of the prior art as described above, by significantly improving the corrosion resistance, oxidation resistance and hot strength of the magnesia-carbon (MgO-C) refractory used in the walls of the furnace to magnesia-car It is an object to provide a high content magnesia-carbon refractories with improved solvent resistance.

The present invention for achieving the above object is a metal powder containing at least one metal selected from magnesia refractory material 75 to 90% by weight, graphite graphite 10 to 25% by weight, metal powder Al, Mg-Al alloy, Al-Si alloy 1 to 6% by weight, 0.1 to 0.8% by weight of a mixture of boron carbide (B ₄ C) and calcium boride (CaB ₆ ), and 4 to 5% by weight of a phenol-based compound binder.

In addition, the mixing ratio of the boron carbide (B ₄ C) and calcium boride (CaB ₆ ) is characterized by having a composition ratio of 1: 1.

Hereinafter, the present invention will be described in detail.

Magnesia-carbon refractory according to the present invention is a metal powder containing at least one metal selected from magnesia refractory material 75 to 90% by weight, graphite graphite 10 to 25% by weight, metal powder Al, Mg-Al alloy, Al-Si alloy Boron carbide (B ₄ C) and calcium boride (CaB ₆ ) are mixed in an amount of 1 to ₆ % by weight, and the compound is added in an amount of 0.1 to 0.8% by weight.

And, the mixing amount of the boron carbide (B ₄ C) and calcium boride (CaB ₆ ) is maintained at 0.1 to 0.8% by weight, but the mixing ratio is to have a composition ratio of 1: 1.

Here, the above-mentioned Korean Patent Publication No. 86-1649 shows the effect of improving the oxidation resistance by adding 0.3 to 5% by weight of boron carbide to one or more existing metal powders, but depending on the amount of boron carbide used, The effect on the corrosion resistance of the magnesia-carbon refractory material is unclear, and suggests that when boron carbide is used at 0.3 weight% or less, the addition effect is not.

However, boron carbide is represented by the following reaction formula,

B ₄ C (s) + 6CO = 2B ₂ O ₃ (l) + 7C (s) -------------- (1)

3MgB (s) + B ₂ O ₃ (l) = 3MgOB ₂ O ₃ (s) ------------- (2)

(s: solid phase, l: liquid phase)

It covers the surface of the refractory brick in the form of liquid boron (B ₂ O ₃ , melting point: 700 ℃) oxide at a relatively low temperature to suppress the oxide of graphite, and tightly binds the tissues, so the effect on oxidation resistance is excellent. Liquid B ₂ O ₃ reacts with magnesia (melting point: 2,800 ° C.) to form 3MgO.B ₂ O ₃ (melting point: 1,313 ° C.), a low melting point reaction product.

In addition, as the amount of boron carbide used increases, the reaction product moves toward a low melting point chemical such as 3MgO · B ₂ O ₃ (melting point: 988 ° C.), rather than 3MgO · B ₂ O ₃ , so that the solid solution phase of the reaction product is magnesia. -Corrosion of carbon refractory itself has a fatal effect on corrosion resistance.

Therefore, in the case where the amount of boron carbide is to be suppressed to the minimum, the result of the present inventors added 0.25 to 1% by weight in order to grasp the quality characteristics according to the amount of boron carbide used (Comparative Examples A to F). Oxidation resistance, hot strength and corrosion resistance increase as the amount used increases, but the corrosion resistance tends to decrease slightly when it exceeds 0.5% by weight, resulting in a decrease in corrosion resistance when it exceeds 1% by weight. This is because Magnesia-carbon (MgO-C) brick to which 1% by weight of boron carbide was added was left at 1,400 ° C. for 5 hours under oxidizing conditions, and then 3MgO · B ₂ O ₃ was added as a reaction product. When the boron carbide is 1% by weight or more, it is expected that the corrosion resistance is lowered due to the increase of the low melting point B ₂ O ₃ -based compound. Therefore, to satisfy the corrosion resistance and the oxidation resistance, which are excellent properties of the magnesia-carbon refractory, boron carbide is 1 It is preferable to set it as weight% or less.

In addition, magnesia used in the present invention can be used both molten magnesia and sintered magnesia, but in order to improve the corrosion resistance, the molten magnesia having a large crystal size prepared by melting at a high temperature of 2,000 ℃ or more is preferable, the amount used is 75 to 90% by weight to be.

In addition, the graphite used may also be a Kish impression graphite produced by refining the natural graphite and carbon dust collected from the forced preparation, it is preferable to use a high-purity crystalline graphite with almost no impurities to improve the corrosion resistance.

Although the use amount of the graphite to raise the magnesia-carbon refractory is 10 to 25% by weight, the most preferred amount to the slag penetration resistance of the electric furnace and converter is 20% by weight.

In the above case, when the amount of the drawn graphite is less than 10% by weight, the erosion resistance and the thermal shock resistance to slag are inferior. In addition, when the drawn graphite exceeds 25% by weight, the kneading becomes difficult to be uniform, resulting in poor closeness during molding and lowering of physical properties, resulting in lowering of corrosion resistance and oxidation resistance due to deterioration of physical properties.

On the other hand, the reason for using a mixture of boron carbide and calcium boride is to improve the corrosion resistance and oxidation resistance of the magnesia-carbon refractory in small amounts, and to contribute to the improvement of the wear resistance by improving the hot strength.

Although the mixing amount of the boron carbide and calcium boride is 0.1 to 0.8%, the mixing amount is preferably 0.5% by weight and the mixing ratio is used one by one. When the amount of the boron carbide and calcium boride mixed is less than 0.1% by weight, there is no enhancement effect of erosion resistance and oxidation prevention against slag, and when the amount exceeds 0.8% by weight, the corrosion resistance is deteriorated.

In addition, in order to uniformly disperse boron carbide and calcium boride, it is preferable to make the maximum particle size smaller than 0.075 mm.

As the metal powder, it is preferable to use 1 to 6% by weight of one or more mixtures selected from Al, Mg-Al alloys and Al-Si alloys in combination. Exceeding this would lower the erosion resistance to slag.

On the other hand, the use of a phenolic binder is for producing a refractory of excellent quality by increasing the bonding strength of the aggregate portion and the matrix portion of the refractory.

The amount of the phenolic compound binder used is 4 to 5% by weight, but most preferably 4.4% by weight. When the amount of the phenolic compound binder used is less than 4% by weight, the physical properties intended by the present invention cannot be obtained and 5% by weight. A larger number adversely affects the physical properties and corrosion resistance of the overall refractory.

Table 1 shows examples and comparative examples according to various raw material configurations of the magnesia-carbon refractory material according to the present invention.

Invention Example Comparative Example One 2 3 4 5 A B C D E F Raw material composition Molten Magnesia 80 80 80 80 80 80 80 80 80 80 80 Impression graphite (98%) 20 20 20 20 20 20 20 20 20 20 20 Metal Al 3 3 3 3 - 3 3 3 3 4 4 Alloy Mg-Al 2 2 2 2 2 2 2 2 2 - - Alloy Al-Si - - - - 3 - - - - - - Boron Carbide (B ₄ C) 0.1 0.25 0.3 0.3 0.1 - 0.25 0.5 0.8 One - Calcium boride (CaB ₆ ) 0.1 0.25 0.2 0.5 0.3 - - - - - One Phenolic binder 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 General property Volume specific gravity 2.88 2.88 2.89 2.87 2.89 2.89 2.87 2.89 2.88 2.89 2.87 Porosity (%) 2.1 1.9 2.2 2.3 2.0 2.0 2.1 2.2 1.9 2.1 2.3 Compressive strength (㎏ / ㎠) 380 367 348 365 362 359 368 360 371 365 369 Oxidation Test Weight loss rate (%) 10.4 7.8 8.0 6.0 10.9 13.6 10.3 9.4 6.1 6.0 7.5 After oxidation 137 169 164 188 134 62 138 160 187 189 185 Bending strength (㎏ / ㎠) Room temperature 154 149 152 150 162 150 151 153 151 148 150 1,400 ℃ 135 145 143 148 140 120 135 140 147 149 150 High frequency induction Erosion Length (mm) 10.4 8.85 9.1 9.5 10.0 11.1 10.3 9.74 10.0 11.2 11.5 Erosion Index 94 80 82 85 90 100 93 88 90 101 104

Examples 1-5

As shown in Table 1, the examples are boron carbide and calcium boride in 5% by weight of 80% by weight of molten magnesia refractory material, 20% by weight 98% grade graphite, Al, Mg-Al alloy, Al-Si alloy The mixture was added 0.2 to 0.8% by weight, and the phenolic compound binder was mixed with 4.4% by weight and molded under a pressure of 1,200 kg / cm 2 to make a standard brick (230 × 114 × 65mm), which was then used at 180 ° C. for 48 hours. After drying, the quality characteristics were measured as shown in Table 1.

Comparative Examples A to F

As shown in Table 1, Comparative Example was prepared by mixing and molding in the same manner as in Example, and prepared a standard brick. Unlike Examples, boron carbide and calcium boride were not used alone or added to the metal powder in the raw material composition. Did.

The quality analysis result according to the present invention was measured based on the test standard according to the Korean Industrial Standard and the Japanese Industrial Standard, and the experimental conditions of the high frequency induction furnace were carried out 10 times for 1/2 hour at 1,650 to 1,700 ° C. Has a CaO / SiO ₂ ratio of 1.

Therefore, as shown in Table 1, when the boron carbide and calcium boride are used in two kinds of mixed metal powders, 0.2 to 0.8% by weight alone (Comparative Examples B to D) or complex (Examples 1 to 5) are used. As the amount of use increases, the weight reduction rate and the erosion index decrease compared to the additive-free (Comparative Example A), resulting in the improvement of the hot bending strength along with the oxidation resistance and corrosion resistance, and when it is 1 wt% or more (Comparative Examples E, F) The result is a decrease.

If the boron carbide and calcium boride are used in an amount of not less than 1% by weight, the low melting point oxidation reaction product is formed in an excessive amount to promote the penetration and erosion of the slag, thereby lowering the corrosion resistance of the magnesia-carbon refractory.

Therefore, what is important in the present invention is to use a mixture of boron carbide and calcium boride. As shown in Examples (1 to 5) and Comparative Examples (B to F) of Table 1, it is possible to oxidize the surface of the refractory brick faster than using only boron carbide by using a mixture of trace amounts of boron carbide and calcium boride. By preventing the oxidation of the graphite to cover the oxidation resistance and corrosion resistance is improved, and the hot strength is improved by densification of the tissue by the various reaction products and the formation of high viscosity melt. In addition, the mixing ratio of boron carbide and calcium boride, as can be seen in Examples 2 and 3, the use of 1: 1 shows a good result.

Therefore, according to the above-described quality test results, according to the present invention, thermal characteristics such as corrosion resistance, oxidation resistance, hot strength, etc. are remarkably improved, and thus the life of the furnace can be extended.

As described above, the highly resistant magnesia-carbon refractory according to the present invention has the effect of improving the corrosion resistance and oxidation resistance to extend the life of the furnace.

Claims (2)

Magnesia refractory material 75 to 90% by weight, graphite 10 to 25% by weight, metal powder 1 to 6% by weight of metal powder containing at least one metal selected from Al, Mg-Al alloy, Al-Si alloy, boron carbide (B A highly resistant magnesia-carbon refractory comprising 4 to 5% by weight of a mixture of ₄ C) and calcium boride (CaB ₆ ) and 4 to 5% by weight of a phenolic compound binder. The method of claim 1, Mixing ratio of the boron carbide (B ₄ C) and calcium boride (CaB ₆ ) is a high content magnesia-carbon refractory, characterized in that having a composition ratio of 1: 1.