JP2001192259A - Spinel-carbonaceous brick for hearth of direct current electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means capable of stably executing melting of scrap, etc., by improving the corrosion resistance of a corrosive brick for the hearth of a direct current electric furnace. SOLUTION: This means is attained by using a spinel carbonaceous brick for the hearth of the direct current electric furnace consisting of an aggregate consisting of Al2O3-MgO based spinel, magnesia and alumina and in which the weight ratio of respective components are (Al2O3-MgO based spinel >= magnesia) and (Al2O3-MgO based spinel >= alumina) and 5-25 wt.% carbon per the sum of the aggregate and the carbon and moreover containing a binder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION As a bottom electrode of a DC electric furnace for melting scrap, there are a multi-pin type and a steel rod type in which an electric current flows through steel, and a method in which an electric current flows through a conductive refractory. The present invention relates to the latter refractory for a conductive bottom electrode.

[0002]

2. Description of the Related Art As a conductive material refractory for a furnace bottom of a DC electric furnace,
MgO-C bricks, which are usually used also in converters, are generally used. Carbon is effective in preventing erosion by slag and permeation and exfoliation of slag in bricks, but imparts conductivity, which is an essential property as an electrode. M
The gO-based aggregate has excellent corrosion resistance to slag.

However, the conventional MgO-C brick has a high wear rate, so that the amount of repair material used increases, and adoption of a new refractory material can reduce the material cost and construction cost of the refractory material. Has been requested.

[0004] In order to solve such a problem, spinel-
Carbon bricks have been developed (JP-A-54-125).
209). This brick is mainly for a furnace wall such as a hot spot portion, and has a weight ratio of MgO / Al ₂ O ₃ of 75 /
The spinel-based molten aggregate having a composition of 25 to 28/72 is 65 to 95% by weight, and the carbon or carbon-containing material is 35 to 5% by weight in terms of C.

As refractories used in the hearth of an electric furnace for steel making, 45 to 90% by weight of alumina,
-30% by weight and 25-25% by weight of carbon, wherein at least 5% by weight or more of the above magnesia is blended in the form of periclase, and alumina-spinel-magnesia made of a phenolic resin or another organic resin binder is used. Carbon bricks are also known (JP-A-10-25)
No. 1055). This brick has a problem in slag corrosion resistance.

JP-A-10-212159 discloses an alumina-magnesia-carbon refractory for a hearth electrode. This refractory is made of alumina 45 to 90 wt.
%, Magnesia 5-30wt%, carbon 5-25wt
%, The antioxidant is 0 to 10% by weight, and 5% by weight or more is an alumina-spinel-magnesia-carbon refractory of Vericlace, and has an electric resistivity of 2 × 10 ⁻⁴ Ω · m or less.

[0007]

The MgO-C refractory used for the bottom electrode of the DC electric furnace is heated to 1700 due to the heat generated by the Joule heat of the current flowing through the brick itself and the high temperature of the furnace atmosphere.
℃ or higher. It is known that when MgO-C bricks are used at a high temperature, magnesia and carbon of the bricks themselves react with each other to weaken the structure of the bricks and promote wear. Therefore, a furnace using MgO-C bricks as a furnace bottom is known. This reaction is considered to be one of the causes of damage at the bottom electrode. Disassembly investigation of the bottom electrode after use showed that MgO-C
It was confirmed that the brick was decarburized by the oxidation-reduction reaction of MgO and C of the brick itself and embrittled due to the thinning of the MgO aggregate, and slag and metal penetrated there, and it was confirmed that wear was progressing. It is an object to prevent the oxidation-reduction reaction of the refractory itself at a high temperature of the MgO-C brick described above.

The refractory disclosed in Japanese Patent Application Laid-Open No. Hei 10-212159 is composed of alumina as a main aggregate and 5 wt% or more of periclase. The purpose of spinel is to densify the structure and stabilize the volume at the time of formation.

[0009]

The analysis of the MgO-C brick after being used for the furnace bottom electrode confirmed that the brick was damaged more by the reaction of the magnesia and carbon of the brick itself at the periphery of the pin. Was done. In order to reduce the damage caused by the reaction between the aggregate and the carbon of the brick itself, in the carbon-containing brick, the material was changed from magnesia clinker to another clinker to reduce the damage caused by the reaction with carbon.

Inexpensive and excellent in corrosion resistance instead of magnesia,
And alumina as a strong aggregate against reduction by carbon at high temperatures, there are Al ₂ O ₃ -MgO based spinel, mainly a spinel so towards the spinel is excellent in corrosion resistance against slag electric furnace Spinel-magnesia-alumina-C and spinel-alumina-magnesia-C bricks were developed and applied as aggregates.

Although magnesia causes an oxidation-reduction reaction with carbon, and alumina has poor corrosion resistance to slag, it is not desirable. However, when used as the second and third components, the amount thereof is small and the above-mentioned disadvantages are reduced. . Also, about 1
When the temperature exceeds 200 ° C., the problem further disappears because alumina and magnesia react to start generating spinel. Further, as is generally known, an effect that the structure is made dense by the expansion accompanying spinel generation and the corrosion resistance is improved can be expected.

The spinel material has a weight ratio of 71.7: 28.3 when Al ₂ O ₃ and MgO are equimolar. Commercial products have a wide range of weight ratios and small amounts of Ti
It also contains impurities such as O ₂ , SiO ₂ , and FeO ₃ .
The spinel to which the present invention is applied has a weight ratio of Al ₂ O ₃ : MgO of about 60:40 to 90:10. The spinel aggregate used may be a fired product, but an electrofused product is denser and has excellent durability. The maximum particle size of spinel is 5m
m is preferable.

Magnesia preferably has a maximum particle size of about 5 mm. Al ₂ O ₃ -MgO spinel: ratio of Magunashia a weight ratio of 1: 0 to 1: about 1 is appropriate.
The preferred addition amount of magnesia is 0.1 to 35% by weight.

The alumina preferably has a maximum particle size of about 5 mm. Al ₂ O ₃ -MgO spinel: the ratio of alumina in a weight ratio of 1: 0 to 1: about 1 is appropriate. The preferable addition amount of alumina is 0.1 to 35% by weight.

In the present invention, the structure can be further densified by adding magnesia or alumina.

As the carbon raw material, scaly graphite, artificial graphite, earthy graphite, quiche graphite, anthracite, etc. can be used, but those having high purity have good durability. The particle size is preferably about 1 mm or less. If the amount is less than 5%, thermal spalling often occurs, and if it is more than 25%, oxidation is increased, which is not desirable. The preferred amount is 6 to 2
It is about 0% by weight.

As the binder, a usual organic binder can be used, and it is common to use a phenol resin or a pitch used for MgO-C bricks alone or in combination. This binder binds and integrates aggregate, carbon, and the like, and after firing, carbonizes and continuously exhibits a binder function. The amount of the binder is 2 to 7 based on 100 parts by weight of the aggregate and carbon in total.
A suitable amount is about parts by weight.

In the present invention, in addition to the above-mentioned aggregate component, A
It is preferable to add 1, Si, Mg or B. These can be added in the form of simple substance (Al, Si), alloy (Al-Mg or the like) or compound (B4C or the like).

The method of kneading, molding and drying at the time of brick production is the same as that of ordinary MgO-C brick. Usually, heat treatment is performed at about 150 to 300 ° C. to secure the strength of the resin after drying. Further, heat treatment may be performed at a high temperature, followed by baking until the resin is decomposed or carbon bonds are formed.

Since the carbon is not changed even if the material of the aggregate is changed, there is no problem regarding the conductivity of the newly developed brick.

[0021]

EXAMPLE For the trial production of brick, Al was used as spinel aggregate.₂O
₃Baked spinel with a weight ratio of 68% (maximum particle size 4 mm)
A and 85% (maximum particle size 4mm) electrofused spinel B
Used. MgO aggregate is 98% pure (maximum particle size 0.5
mm) electrofused product, Al₂O ₃Aggregate is 99% pure (maximum grain
Electrolyte with a diameter of 2 mm), purity of carbon (scale graphite) 98
% By weight (maximum particle size: 1 mm) of scale graphite was used.

To these raw materials, 3% by weight of a phenolic resin was added, kneaded, molded, dried, and then heat-treated at 250 ° C. for 10 hours to produce 11 types of bricks 1 to 11 as shown in the table.

Comparative MgO-C brick M and Al ₂ O
MgO, Al ₂ O ₃ , carbon raw material and manufacturing method of the _3- C brick A are the same as those of the prototype brick.

The durability of the prototype brick was changed to the conventional MgO-C brick.
1700 ° C, 2 hours in Ar atmosphere for comparison with M
Heat treatment during the oxidation and reduction of the brick itself
The weight loss rate before and after the treatment was determined. Also, at 1700 ° C
Rolling drum erosion tests were performed to compare the erosion rates. used
The components of the slag are CaO: 35, SiO₂: 20, Al ₂
O₃: 6, MgO: 8, FeO: 31 (wt%)
You.

According to the test results, the magnesia-based brick has good corrosion resistance but is weak to the oxidation-reduction reaction, and the alumina-based brick is strong to the oxidation-reduction reaction but has poor corrosion resistance, and the spinel-based brick has both properties. You can see that they are well-balanced.

[0026]

[Table 1]

The brick 2 and the brick 6 'obtained by adding 2% and 1% of metal powders Al and Si to the brick 6 at the furnace bottom electrode portion of a conductive hearth type 80-ton DC electric furnace, respectively, are made of a conventional material, MgO-C.
The effect was confirmed by partially separating the inside of the quality comparison brick M.

According to the disassembly investigation after use, it was found that MgO
-C brick and M are oxidized to a depth of about 15mm from the working surface-
Embrittlement occurs due to a reduction reaction, and slag and metal partially penetrate. On the other hand, the bricks 2, 6 'according to the invention have a brittleness depth of 2 mm. The length of the brick is initially 500m
m, but the remaining thickness of the conventional material M was 200 mm, the brick 2 was 260 mm, and the brick 6 ′ was 280 mm, confirming high durability.

[0029]

According to the present invention, it is possible to improve the corrosion resistance of bricks at the bottom of a DC electric furnace at a high temperature, prolong the brick replacement time of the electric furnace, and stably dissolve scraps and the like.

Claims (3)

[Claims] 1. A brick for a DC electric furnace comprising a furnace bottom electrode using a conductive refractory, comprising an oxide aggregate, carbon, a binder and an antioxidant, and having a carbon content of 5 to 25. wt%, magnesia aggregate to another as main components _Al 2 _O 3 -MgO spinel, spinel of alumina - magnesia - alumina -C bricks or spinel - alumina - magnesia -C bricks _{2. An} aggregate comprising Al ₂ O ₃ —MgO-based spinel, magnesia and alumina, wherein the weight ratio of each component is Al ₂ O ₃ —MgO-based spinel ≧ Magnesia Al ₂ O ₃ —MgO-based spinel ≧ Alumina. And carbon is 5 to 5 times the sum of the aggregate and carbon.
Spinel-C brick for DC electric furnace hearth comprising 25% by weight and further containing a binder 3. Al, Si, M not more than 10 parts by weight based on 100 parts by weight of the sum of the aggregate of claim 1 or 2 and carbon.
g or B containing spinel-C brick for furnace bottom of DC electric furnace