JPH07291710A - Graphite containing refractory - Google Patents

Abstract

PURPOSE:To produce a low conductive graphite-containing refractory by incorporating an oxide aggregate of one or more kind of Al2O3, MgO and spinel, a flake graphite having specific average particle diameter and metal powder in a specific ratio. CONSTITUTION:A blended material is obtained by blending <=6wt.% Sic (hereinafter %), 85-94% oxide aggregate of one or more kind of Al2O3, MgO and spinel and 6-15% natural flake graphite 75-15mum in average particle diameter and >=90% in 44-200mum particle diameter. Next, 2-4% Al metal powder or alloy powder containing >=60% Al is added into the blended material in external multiplication and further an adequate quantity of blender is mixed. After that, the mixed material is press molded and fired in a reducing atmosphere to obtain the low heat conductive graphite containing refractory.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory brick lined in a hot metal pretreatment vessel, and more particularly to a refractory brick used in a portion requiring heat insulation.

[0002]

2. Description of the Related Art The desiliconization, dephosphorization, and desulfurization processes have been divided with the upgrading of steel, and hot metal pretreatment is carried out between the blast furnace and the converter. As a kiln for pre-treatment of molten pig iron, there are a mixed pig wheel and a ladle, and a slag corrosion resistance is a characteristic required for a refractory brick lining.

The slag from the blast furnace has a basicity (C / S) of about 1, but the slag basicity rises to about 5 by the hot metal pretreatment.

Therefore, the refractory brick of the hot metal pretreatment container is required to have corrosion resistance against a wide range of slag basicity.

Generally, since acidic refractory bricks are easily eroded by basic slag and basic refractory bricks are easily eroded by acid slag, neutral alumina is used as an aggregate for refractory bricks of a hot metal pretreatment vessel.

Graphite is used to suppress the infiltration of slag into this refractory brick. Graphite has an advantage of further improving thermal shock resistance, but has a drawback of being easily oxidized and decarburized in a high temperature atmosphere. Therefore, silicon carbide or the like is further added as an antioxidant of graphite.

Thus, as a refractory brick for a hot metal pretreatment container, an alumina-graphite-silicon carbide based brick has come to be generally used.

The main wear of these graphite-containing refractory bricks is oxidation of graphite or dissolution in steel, and the type and content of graphite have been studied in order to improve durability.

For example, Japanese Patent Application Laid-Open No. 59-169968 discloses the form and content of scaly graphite used to improve the corrosion resistance and spalling resistance of graphite-containing refractory bricks.

Further, Japanese Patent Laid-Open No. 62-56354 discloses the particle size and the addition amount of graphite for improving the oxidation resistance and durability of graphite-containing refractory bricks.

[0011]

By the way, graphite-containing refractory bricks have high thermal conductivity due to the high thermal conductivity of graphite. Therefore, there are problems such as a decrease in hot metal temperature and a decrease in reaction efficiency of hot metal pretreatment.

In view of this problem, in operation, the hot metal temperature is secured by the secondary combustion heat by the gas acid treatment in which oxygen is blown, but in the case of refractory bricks, an attempt was made to use a heat insulating material, etc. There is not enough heat insulation to meet.

On the other hand, it can be considered that the refractory brick lowers its own thermal conductivity. However, the conventional technology focuses on improving corrosion resistance, oxidation resistance, and spalling resistance, and little consideration is given to heat conduction, or rather the advantage of improving spalling resistance by high heat conductivity is emphasized. It had been.

Therefore, the present invention has an object to reduce the thermal conductivity without impairing the durability of the refractory lining lined in the hot metal pretreatment container, particularly in the graphite-containing refractory brick used in a portion requiring heat insulation.

[0015]

In order to solve this problem, the present invention provides a graphite-containing refractory brick having an average particle size of from 75 to 75.
If it is 150 μm and 44 to 200 μm,
It is characterized by containing 6 to 15% by weight of natural scaly graphite containing 0% by weight or more.

The present invention uses scaly graphite obtained by crushing natural minerals as a graphite source.

Since the main cause of wear of the graphite-containing refractory brick is oxidation of graphite, scaly graphite having high crystallinity is used so as not to deteriorate the oxidation resistance.

By the way, the scaly graphite is in the form of scales (foil pieces), has a layered structure in the thickness direction of the scales, and has a high thermal conductivity in the layer surface direction. The higher the crystallinity, the higher the thermal conductivity.

The size of the scaly graphite can be defined by the spread and thickness of its layer surface, but the thermal conductivity is determined by the spread dimension of the layer surface.

Therefore, in the refractory brick of the present invention, the spreading dimension of the layer surface of the scaly graphite is defined as the particle size, and the thermal conductivity can be lowered without impairing the oxidation resistance by controlling the particle size and the addition amount. .

The inventors examined the effect of the particle size and addition amount of scaly graphite on the thermal conductivity, and found that the smaller the particle size and the smaller the addition amount, the lower the thermal conductivity.

However, it was also found that the moldability of bricks becomes worse as the particle size becomes smaller and the addition amount becomes smaller.

Therefore, when the moldability was examined, when the content was less than 6% by weight, the graphite was not sufficiently filled between the aggregates and the molding strength was lowered to deteriorate the spall resistance.

On the other hand, if the content exceeds 15% by weight, the particle size of graphite must be considerably reduced in order to lower the thermal conductivity, resulting in poor moldability and low strength. Therefore, it should contain 6 to 15% by weight of scaly graphite, and more preferably 8
~ 12 wt% was required.

Next, in order to reduce the thermal conductivity in this content range, it was considered that the particle size may be made smaller when the content is large and may be slightly larger when the content is small.

Experiments were carried out while changing the average particle size to 30, 100 and 300 μm. When the content was 15% by weight, the thermal conductivity was higher than that of the conventional one when the particle size exceeded about 200 μm.

On the other hand, the oxidation resistance was worse than before when the particle size was smaller than about 44 μm. Therefore, the particle size of scaly graphite is 44
It was optimal for the purpose of the present invention to be in the range of ˜200 μm.

Although it is difficult to classify the particle size completely within the above range industrially, it is sufficient if the content is 90% by weight or more and the average particle size is 74 to 150 μm.

The present invention has been made with respect to a refractory brick lining for a hot metal pretreatment container, and the components of bricks other than graphite will be described below.

As the brick aggregate, it is preferable to use alumina, magnesia and spinel, which is a compound of alumina and magnesia, which have high corrosion resistance to the hot metal pretreatment material, or a mixture of two or more kinds.

The blending amount of the brick component is basically 100% in total of the aggregate and the graphite, but as described above, if the aggregate exceeds 94% by weight, the graphite cannot be sufficiently filled between the aggregates and the resistance is increased. If the spalling property becomes poor and the aggregate content is less than 85% by weight, the particle size of graphite must be made sufficiently small in order to lower the thermal conductivity, resulting in poor moldability.

Metal powder is added to prevent oxidation of graphite. The addition amount is 2 to 4% by weight in the above-mentioned graphite compounding range.
Is preferred.

If it is less than 2% by weight, the oxidation resistance effect cannot be obtained, and if it exceeds 4% by weight, the structure is densified after the metal is oxidized and the spall resistance is lowered.

Further, in the present invention, the metal powder is Al metal,
Alternatively, an Al-based alloy containing 60% by weight or more of Al is preferable.

As a result of experiments, the inventors have found that the Al-based metal is the best for preventing the oxidation of graphite of the graphite-containing refractory brick for pretreatment of hot metal.

When the Al metal was oxidized, it became the same alumina as the aggregate component, and the structure was not densified. Further, in order to prevent oxidation at low temperatures, it was effective to lower the melting point of the metal by alloying and close the pores that cause oxidation.

The alloy component may be any element contained in the aggregate component, but the major components of the aggregate, such as Mg and Si.
Is more preferable.

When the Al content in the alloy is 60% by weight or less,
The reaction product of the product after oxidation and the aggregate easily forms slag and the low melting point compound, and the corrosion resistance is lowered.

In order to utilize the graphite-containing refractory brick according to the present invention as a refractory lining brick for a hot metal pretreatment container having a high gas acid treatment, silicon carbide is further added to prevent oxidation of graphite at high temperatures.

The addition of silicon carbide is done in replacement with aggregate. That is, it is preferably 94 to 85% by weight together with the aggregate, and 6% by weight is preferable in order not to increase the thermal conductivity.

[0041]

Example 1 Table 1 shows bricks according to the present invention (Nos. 5, 6, 7, 12, 13, 16, 17, 1) used in Examples.
9), the bricks that deviate from the features of the invention, and the comparative brick compositions according to the prior art are given in% by weight.

The scaly graphite is characterized by the present invention and has an average particle size of 100 μm, larger than 300 μm, and smaller than 3.
Three types of 0 μm were used.

The aggregate was made of a combination of three kinds of alumina, magnesia and spinel, and the particle diameters were all 2 mm or less.

The additives used are four kinds of metals or alloys and silicon carbide, each having a particle size of 44 μm or less. The metal is added to the mixture of scaly graphite and the aggregate in an external weight%, and the silicon carbide is added internally. It was added as a weight percentage.

After mixing the raw materials having the formulations shown in Table 1 with a phenol resin as a binder for 30 minutes, 230 mm × 1 at 1000 kg / cm ³ under a uniaxial press molding machine.
It was molded into a shape of 10 mm × 65 mm.

Then, a brick was made by firing at 230 ° C. for 24 hours in a reducing atmosphere. The test pieces were cut out from the prototype bricks and evaluated as follows.

The thermal conductivity was measured by a steady heat flow method by cutting out a cylinder having a length of 150 mm and a diameter of 20 mm in the direction of 230 mm of a brick, punching thermocouple insertion holes at 5 positions on the side surface.

The evaluation result is shown as a relative value when the comparative brick is 100. The smaller the value is, the smaller the thermal conductivity is.

Melt loss was evaluated by a rotary erosion test. Slag having a basicity (C / S) of 3.4 and total Fe of 5% was used and eroded at 1700 ° C. for 4 hours.

The erosion length of each brick was measured, and the relative value when the comparative brick was set to 100 was taken as the melt loss index. The smaller the value, the better the corrosion resistance.

In the thermal spall test, a prism having a length of 230 mm and a cross section of 30 × 30 mm was cut out in the 230 mm direction of the brick, and the brick was immersed in 1500 ° C. hot metal for 90 seconds and cooled for 30 seconds with water for 5 seconds.
Repeated times.

The elastic moduli E ₁ and E ₂ were measured before and after the test, and the ratio (E ₂ / E ₁ ) was evaluated as a spall resistance index. The larger the value, the better the spall resistance.

In the oxidation test, the thickness of the oxide layer was measured when a 30 × 30 × 30 mm test piece was oxidized at 1400 ° C. for 10 hours in the atmosphere.

The relative value with the comparative brick as 100 was evaluated as the oxidation index. The smaller the value is, the more excellent the oxidation resistance is.

Table 1 shows the evaluation results. Further, FIGS. 1 to 4 show the relationship between the particle size and the addition amount of scaly graphite and each characteristic, and the upper limit value and the lower limit value of the target characteristic value of the present invention.

Since the purpose of the present invention is to set the thermal conductivity index to 100 or less, it is preferable that the graphite content is 15% by weight or less and the particle size is 200 μm or less.

It is preferable that the melting loss index is smaller, and the brick according to the present invention of 100 or less is sufficiently durable to use.

On the other hand, the spall resistance index decreased as the graphite content decreased, and required 6% by weight or more, preferably 8% by weight or more. Further, the oxidation index increases when the particle size of graphite is small, so the particle size is preferably 44 μm or more.

From the above results, the graphite-containing refractory bricks according to the present invention have lower thermal conductivity than the conventional comparative bricks, and have comparable corrosion resistance, spalling resistance and oxidation resistance.

[0060]

Second Embodiment No. 1 of the first embodiment of the present invention. 6 bricks were applied to the towed car lining. The number of times of gas acid treatment was twice as many as usual, but the brick of the present invention had a low thermal conductivity, so a large amount of slag adhered, and the wear rate was not different from that of the conventional material. The average decrease in hot metal temperature was reduced by about 5 ° C compared to the past.

[0061]

[Table 1]

[0062]

By applying the graphite-containing refractory brick of the present invention to the refractory lining refractory brick of the hot metal pretreatment vessel, the hot metal temperature drop is reduced by 5 to 10 ° C, and the heat compensation cost is greatly improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average particle size and addition amount of scaly graphite and the thermal conductivity index.

FIG. 2 is a graph showing the relationship between the average particle size and addition amount of scaly graphite and the melt damage index.

FIG. 3 is a graph showing the relationship between the average particle size and addition amount of scaly graphite and the spall resistance index.

FIG. 4 is a graph showing the relationship between the average particle size and addition amount of scaly graphite and the oxidation index.

Claims (4)

[Claims] 1. An average particle diameter of 75 to 150 μm,
A graphite-containing refractory brick characterized by containing 6 to 15% by weight of natural scaly graphite containing 90% by weight or more of particles having a particle size of 44 to 200 μm. 2. An oxide aggregate made of at least one of alumina, magnesia and spinel 94 to 85% by weight.
And graphite to 6 to 15% by weight, and the outer powder to the metal powder 2 to 4
The graphite-containing refractory brick according to claim 1, wherein the refractory brick contains graphite in a weight percentage. 3. The metal powder is Al metal or 60 Al.
The graphite-containing refractory brick according to claim 2, wherein the refractory brick contains an Al-based alloy containing at least 5% by weight. 4. A total of 94 to 85% by weight, a total of 6 to 15% by weight of graphite, 6 to 15% by weight of graphite, and a metal powder of 2 in total, together with 6% by weight or less of silicon carbide and an oxide aggregate composed of at least one of alumina, magnesia and spinel. The graphite-containing refractory brick of claims 1 and 3 having a composition of ˜4% by weight.