JPH10212159A - Alumina-magnesia-carbon refractory for hearth electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an unfired brick for a hearth electrode having higher corrosion resistance than the conventional magnesia-carbon brick by using alumina, magnesia and carbon in a specified ratio and blending a specified amt. of the magnesia in the form of periclase. SOLUTION: This brick for a hearth electrode is an unfired alumina- magnesia-carbon or alumina-spinel-magnesia-carbon brick contg. 45-90wt.% alumina, 5-30wt.% magnesia and 5-25wt.% carbon, contg. >=5wt.%, preferably 5-30wt.% of the magnesia in the form of periclase and having electric conductivity represented by <=2×10<-4> Ω.m specific resistance. The brick further contains 0.5-10wt.% powder of Al, Mg, Si or an alloy of them as an antioxidant. An org. resin binder such as phenolic resin is added at the time of blending starting materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory used for a hearth electrode brick of a DC electric furnace for steelmaking.

[0002]

2. Description of the Related Art Electroconductive magnesia-carbon bricks are generally used as hearth electrode bricks, but further improvement in durability is required.

[0003]

The operating surface side of the hearth electrode brick is exposed to wear damage due to the flow of molten steel and oxidation of carbon due to oxygen during blowing, and in order to improve the durability, it is necessary to use these materials. A refractory with strong resistance is required.

[0004]

SUMMARY OF THE INVENTION The present invention relates to an alumina 45.
~ 90% by weight, magnesia 5 ~ 30% by weight, carbon 5
The content of magnesia is at least 5% by weight or more, and alumina-magnesia-carbon and alumina-spinel-magnesia-carbon bricks containing at least 5% by weight of periclase are used as hearth electrode bricks. Has been found to be improved.

[0005]

The present invention relates to a refractory obtained by adding a magnesia material and carbon to an alumina material,
The alumina-based material and the magnesia-based material react during preheating and use, causing pores to close due to volume expansion due to spinel formation, blocking the flow of air from the outside into the refractory, and the constituents in the refractory. In addition, the refractory is prevented from being oxidized, and at the same time, the refractory is densified to prevent wear due to the flow of molten steel.

In addition to the addition of carbon, the addition of carbon can reduce slag infiltration and reaction due to reduction in wettability, and reduce wear due to its excellent spalling resistance.

[0007]

The alumina raw material used in the present invention can be fused alumina, sintered alumina, bauxite and other high alumina raw materials containing at least 80% by weight of alumina. Alumina-rich to magnesia-rich electrofused and sintered clinker containing up to 20% by weight, 10-80% by weight, and a total of alumina and magnesia of 80% by weight or more can be used. It is possible to use electrofused magnesia, seawater, and natural magnesia clinker containing at least 10% by weight.

[0008] In the magnesia component, the compounding amount of the periclase crystal is preferably 5 to 30% by weight, and 5% by weight.
If it is less than 10, the pores are not sufficiently closed due to small expansion,
If the content is more than 30% by weight, the swelling becomes too large, the structure is deteriorated, and the wear resistance is poor.

As the carbon raw material, in addition to natural graphite and artificial graphite, electrode scrap, coke, carbon black, and the like can be used. However, phosphorous graphite is preferably used because it greatly affects the conductivity, and filling during molding is preferable. Excellent in terms of sex.

The amount of the carbon raw material is preferably 5 to 25% by weight. If the amount is less than 5% by weight, even if a treatment such as reduction firing is carried out, the electric conductivity is so low that it cannot be used as an electrode brick. Due to such factors, peeling damage due to structural spalling increases and wear increases. When the content of carbon is 25% by weight or more, conductivity and structural spalling are good, but resistance to oxidation is reduced and wear is increased.

[0011] A resin binder is added to the mixture containing the above-mentioned raw materials and kneaded. The resin-based binder is not particularly limited as long as it can be cured by heat treatment, but a phenol resin or the like is preferably used.

[0012] As an antioxidant measure, the present invention also provides that the total addition of one or more selected from aluminum powder, magnesium powder, silicon metal powder or an alloy powder thereof is 0.5 to 10% by weight. included.

[0013]

Example 1 A kneaded clay obtained by kneading the compounds shown in Table 1 was formed by a friction press, and heat-treated at 250 ° C. for 12 hours to obtain an unfired brick. For conductivity,
After heating and cooling at 1000 ° C. in a reducing atmosphere, the specific resistance was measured. Generally, as a conductive refractory, 2 × 10 ⁻⁴ Ω ·
m or less is required.

The damage condition was evaluated by a rotary erosion test method, using a slag having a composition shown in Table 2 at 1600 ° C. to 16 ° C.
An erosion test was performed at a temperature of 50 ° C. for 10 hours, and the amount of erosion was compared.

The oxidation test uses a silicon carbide heating element electric furnace,
After heating at 1400 ° C. for 3 hours in an air atmosphere, it was taken out of the furnace, cooled, cut, and the thickness of the oxide layer was measured and compared.
The results of the erosion test and the results of the oxidation test are indicated by an index with Comparative Example 12 in Table 1 being 100.

[0016]

By using the hearth electrode brick of the present invention, corrosion resistance is about 1.4 times higher than that of the conventional magnesia-carbon brick, and the service life can be extended. In addition, the work environment can be improved by extending the replacement time of the hearth and reducing the number of replacement times.

[Table 1]

[Table 2]

Claims (3)

[Claims] In a refractory whose hearth brick serves as an electrode (hereinafter referred to as hearth electrode brick), alumina 45 to 90 is used.
Wt%, magnesia 5-30 wt%, carbon 5-25
% By weight, and the magnesia content is at least 5%.
% By weight or more in the form of periclase, characterized by using a phenolic resin or another organic resin-based binder and a combination thereof, and having an electrical resistivity of 2 × 10 ⁻⁴ Ω · m or less. Alumina-magnesia-carbon and alumina-spinel having properties
Magnesia-carbon brick. 2. One or two or more selected from aluminum powder, magnesium powder, silicon powder, or an alloy powder thereof are used as an antioxidant with respect to 100% by weight of the refractory material according to claim 1. Hearth electrode bricks using a total of 0.5 to 10% by weight of powder. 3. A direct current electric furnace for steel making, wherein the hearth brick serves as an electrode, wherein the refractory according to claim 1 or 2 is used as a hearth electrode brick.