JPS6324947B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an alumina-chromium refractory used as a lining for pig iron mixers, steelmaking ladles, etc. Traditionally, high-grade chamomile bricks or high-alumina bricks were used for the lining of pig iron mixed cars, but recently, desulfurization treatment has been carried out on mixed pig iron cars, and as a result, the basicity of the slag has decreased. As a result of increasing the amount of heat or stirring the hot metal, the wear and tear of refractories is increasing. As a countermeasure to this problem, it is possible to use basic refractories, but basic refractories have excellent slag resistance but have a large coefficient of thermal expansion, so they may cause cracking due to expansion stress, pure thermal spalling, or slag attack. Structural spalling due to transparent material is likely to occur, and this causes a peeling phenomenon, resulting in a surprisingly high rate of wear and tear. In addition, pig iron mixing cars are often cooled down after discharging hot metal until the next pig iron is received.
Basic bricks with large thermal expansion often develop so-called joint openings. Next, high silicic acid bricks and zircon bricks were commonly used as the lining for molten steel ladle, but as a recent trend, continuous casting, vacuum degassing treatment, etc. have become widely used, and the temperature of molten steel has increased. As the temperature rises, the residence time of molten steel becomes longer, and the erosion of refractories becomes more severe than before. Alumina-chromium bricks have been developed as one of the measures to address the changes in properties required of refractories for pig iron mixers or molten steel ladles. Normally, alumina-chromium bricks have very good corrosion resistance, and when used in mixed pig iron cars, alumina-chromium bricks have a lower coefficient of thermal expansion than basic bricks, but their corrosion resistance is lower than that of basic bricks. As a result, slag is difficult to penetrate and does not show any flaking phenomenon, and the rate of wear and tear is reduced.Also, when used in ladle for molten steel, this alumina-chromium brick has excellent corrosion resistance, but In the high-temperature range where the temperature exceeds 1650°C, the disadvantage was that the steel was susceptible to wear and tear due to the abrasive action of molten steel. The following proposals have been made as conventional techniques for alumina-chromium refractories, including improvements to these drawbacks. In other words, Special Public Interest Publication No. 44-8995
The publication states that 5% or more (substantially 10 to 20%) of chromite in fine powder of 40 μ or less is added to silicate alumina-based raw materials such as siyamoto and waxite, and the SiO ₂ in the mixture is reduced.
A chromium-alumina refractory suitable for molten steel ladles has been shown to have a content of 45 to 80%. In this case, alumina silicate raw materials are also used in fine particles, but these tend to become dense during long-term use and reduce spalling resistance, and corrosion resistance also deteriorates.
This is inferior to the case where alumina silicate raw material is used only for coarse grains. To improve this point, JP-A-51-102006
According to the disclosure in the publication, 50 to 80% of the alumina-silicate raw material is coarse particles, and 50 to 20% of chromite, which is fine particles or smaller, is combined. However, since this composition is not adaptable depending on the application, Japanese Patent Application Laid-Open No. 51-127108 was disclosed as an improvement.
According to the description in the publication, a mixture of alumina-silica-based raw materials and chromite in a ratio of 4:1 to 4:6 is 85~
99%, 15 to 1% of alumina, zircon, magnesia, spinel, clay, silicon carbide, or titanium oxide is added as a third component. It is recognized that these conventional bricks have better corrosion resistance than high silicic acid or zircon materials when used in molten steel ladles, but when receiving molten steel at a particularly high temperature of 1650℃ or higher, Although the wear resistance is good in the parts that come into contact with the slag, there have been cases where the parts that come into contact with the molten steel suffer from increased wear and tear. The present invention was created in consideration of the current situation,
The purpose of this project is to propose a refractory that solves the problems of conventional alumina/ _{chromium refractories} as described above. The fine particulate part to be mixed with Al ₂ O ₃ purity
A method for manufacturing an alumina-chromium refractory that has a high softening point under load and improved resistance to high-temperature molten steel flow by comprising approximately 30% of high-purity alumina of 98% or higher and 30 to 35% of chromite. The purpose is to provide Next, the material type, application conditions, etc. of the refractory in the method of the present invention will be explained in detail with examples.
Al ₂ O ₃ 50-90%, i.e. sillimanite,
Calcined bauxite, andalusite, and calcined shale are used. If the content of Al ₂ O ₃ is less than 50%, the highly corrosion-resistant brick that is the object of the present invention cannot be obtained.
When a raw material containing 90% or more of Al ₂ O ₃ is used, there is no significant difference in corrosion resistance, but spalling resistance decreases. The blending ratio of this high alumina raw material containing 50 to 90% Al ₂ O ₃ is preferably 35 to 45%. If the content is less than 35%, the spall resistance of the brick will decrease, and if it is more than 45%, the corrosion resistance will tend to decrease. It is desirable to use all high alumina raw materials containing 50 to 90% Al ₂ O ₃ as coarse particles with a particle size of 1 mm or more, but up to about 20% of them are coarse particles with a particle size of 1 mm or more.
It is also possible to mix the following: However, in general, if high alumina raw materials are blended as fine particles, sintering will progress during long-term use and there will be a tendency for them to peel off, so it is preferable that the fine particles be 20% or less, and the particle size is 1.
If it is less than 20%, there will be too few coarse particles in the particle size structure, and the filling property during molding will be poor. For chromite chromite, Cr ₂ O ₃ 30 ~
40%, SiO ₂ 6% or less is used as fine powder of 1 mm or less, and the blending amount of this chromite is 30~
It shall be 35%. If chromite is less than 30%, it is susceptible to chemical erosion by slag, and if it is more than 35%, the amount of high alumina raw material is relatively reduced, resulting in a decrease in spall resistance or a decrease in the amount of alumina. Resistance to mechanical wear from molten steel is reduced. All high-purity alumina containing 98% Al ₂ O ₃ or more shall be fine particles with a particle size of 1 mm or less. The amount of this stuff is 25
If it is less than 35%, the resistance to wear of high-temperature molten steel is insufficient, and if it is more than 35%, and the amount of chromite is relatively reduced, the chemical corrosion resistance will be reduced, and the resistance to wear of high-temperature steel will be insufficient. When the amount of alumina raw material decreases, there is a tendency for spall resistance to decrease. The above raw materials are mixed, and a binder such as sulfite pulp waste liquid, molasses, CMC,
Add appropriate amounts of PVA etc. and water and knead,
After being appropriately shaped and dried, the bricks are fired at 1,350 to 1,400°C. The bricks obtained in this way can be used in slag lines of ladles, etc. where high-temperature steel tapping is carried out at temperatures above 1650℃, and exhibit excellent wear resistance.
Good results were also obtained when it was used for the lining of pig iron mixer cars that undergo a lot of desulfurization treatment. A specific example of the method for producing an alumina-chromium refractory of the present invention is as follows:
Using raw materials with chemical components as shown in the table, cup clay with the mixing ratio shown in Table 2 is kneaded and molded.
It was dried at 1350°C for 24 hours and then fired for 3 days including holding at 1350°C for 5 hours. The physical properties of the refractory brick thus obtained are as shown in Table 3.
Nos. 1 to 5 in Table 2 or 3 are refractories obtained by the method of the present invention (hereinafter referred to as the products of the present invention).
Nos. 6 and 7 show respective values for comparative products. Among the comparative products, No. 6 has a fine particle portion entirely composed of chromite, and No. 7 has alumina added to the fine powder portion, but the amount is smaller than the range of the present invention product. It is. A typical physical property value of the product of the present invention is that the softening point under load is higher than that of the comparative product. When these bricks were used in the slag line of a 100-ton ladle with a tapping temperature of 1650 to 1700°C, all of them were good with little melting damage, but comparative products No. 6 and No. There was a large amount of melt damage in the parts that were in contact with the molten steel, and the results were as shown in the bottom column of Table 3. In addition, it is applied to the slag line, which is the most severe operating condition in a 600t pig iron mixer car that performs desulfurization treatment,
The erosion rate at that time was verified and was as shown in Table 4. In other words, in the actual use of the product of the present invention, good results were obtained, with the erosion rate being only about 1/3 that of Shamoto bricks and about 2/3 that of high alumina bricks.

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[Table] As stated above, the alumina-chromium refractories obtained by the method of the present invention have many superior properties compared to conventional alumina-chromium bricks, and can be used in accordance with the purpose of the present invention. It goes without saying that the technical ideas encompassed herein are not limited to the above-mentioned embodiments, and that all applications, diversions, etc. derived from these are included within the technical scope of the present invention. .

Claims (1)

[Claims] 1 Contains 50 to 90% Al ₂ O ₃ , of which
Less than 20% is fine particles with a particle size of 1 mm or less, and the rest is high alumina raw material sized into coarse particles with a particle size of 1 mm or more.
30-45% fine-grained chromite with a particle size of 1 mm or less30
-35% and 25-35% of fine particles of high purity alumina with a particle size of 1 mm or less containing 98% or more of Al ₂ O ₃ are mixed with appropriate additives such as a binder and water, then kneaded, molded, and dried. , a method for producing an alumina-chromium refractory, characterized by firing.