JP2604002B2 - Carbon containing refractories - Google Patents

Description

The present invention relates to a carbon-containing refractory, and more particularly to an oxidation-resistant refractory.
The present invention relates to a carbon-containing refractory having improved spalling resistance, slag resistance and hot strength.

[Conventional technology and its problems]

Since carbon-containing refractories have relatively excellent spalling resistance and slag resistance, the range of use has been rapidly expanded in recent years. In particular, unburned bricks combining MgO clinker and scale graphite are used in converters, secondary refining furnaces, and other steelmaking furnaces, and have dramatically increased furnace life.

However, the bonding of carbon-containing refractories mainly depends on carbon bonds, and in an oxidizing atmosphere, the bonding strength is lost with the oxidative consumption of carbon, so that the wear rate of the refractory becomes extremely large. Has been pointed out.

In order to remedy this drawback, it has been proposed to add an oxidizable metal powder, and aluminum, silicon, magnesium and their alloys are mentioned as examples of the oxidizable metal powder.

However, when silicon powder or silicon alloy powder is added, oxidation resistance and hot strength are increased, but there is a problem that slag resistance is reduced. Also, when magnesium powder or magnesium alloy powder is added, slag resistance does not decrease, but there is a problem that magnesium evaporates at a high temperature to form voids in the structure, resulting in insufficient hot strength. . Therefore, among these easily oxidizable metal powders, the hot strength at 1000 ° C. or higher can be enhanced,
It is considered optimal to use an aluminum powder or an aluminum alloy powder capable of obtaining an effect such as a significant increase in corrosion resistance.

However, MgO-C bricks to which aluminum or an aluminum alloy has been added have the problem that, for example, bricks that have been expanded by being heated to 1000 ° C. or more by baking or using an actual furnace are decomposed and disintegrated by moisture in the air after cooling. There is a problem that dissatisfaction is left in enhancing the chemical property. In addition, refractory bricks to which aluminum or an aluminum alloy is added have a large coefficient of thermal expansion at a high temperature of 1000 ° C. or higher, and when used for lining of a refining furnace or the like, they tend to be pressed against each other due to thermal expansion and to cause spalling wear,
Furnace life may be significantly shortened.

Further, it has been pointed out that aluminum powder or aluminum alloy powder is liable to cause dust explosion and has a large risk in handling.

The present invention has been made in view of the above circumstances, and a problem caused by the addition of aluminum powder or aluminum alloy powder is to add aluminum or aluminum alloy in coarse particles and to add boron nitride (hereinafter referred to as BN). The present invention has been completed based on the finding that it can be eliminated by the addition of a carbon-containing refractory having improved oxidation resistance, spalling resistance, slag resistance and hot strength. It is the purpose.

[Means for solving the problem]

In order to achieve the above object, the carbon-containing refractory according to the present invention comprises 1 to 97% by weight of a carbonaceous raw material,
Coarse particles having a particle size of 0.5 to 20 mm, which are one or two or more metals selected from aluminum or an alloy containing 20% by weight or more of aluminum in 100 parts by weight of a refractory composition consisting of up to 99% by weight. 1 to 30 parts by weight and BN powder 0.1
-10 parts by weight.

[Action]

The refractory blend used in the present invention is composed of a carbonaceous raw material and a refractory raw material, and the blending ratio of the carbonaceous raw material therein is preferably 1 to 97% by weight. If the compounding ratio of the carbonaceous raw material is less than 1% by weight, sufficient spalling resistance cannot be obtained, so that it is not preferable.

Although the carbonaceous raw material used in the present invention is not particularly limited, scaly graphite, earthy graphite, coke, carbon black, artificial graphite, quiche graphite, carbon fiber, calcined anthracite and the like can be used.

Further, the type of refractory raw material used in the present invention is not particularly limited, but oxides such as magnesia, calcia, dolomite, magdro, spinel, alumina, mullite, silica, etc., non-oxides such as silicon carbide, silicon nitride, etc. It is preferred to use

One or two selected from aluminum or an alloy containing aluminum added to the refractory composition
Coarse particles of more than one kind of metal (hereinafter referred to as aluminum coarse particles)
Basically, aluminum carbide (Al ₂ C ₃ ) and aluminum oxide (Al ₂ O ₃ ) or aluminum oxide powder
Increase in hot strength due to the formation of MgO-C brick spinel MgO · Al ₂ O ₃ in the shows the effect of such improvement in corrosion resistance. In the present invention, since aluminum or aluminum alloy in the form of coarse particles is added, aluminum is unevenly distributed in the structure of the brick, and portions having different coefficients of thermal expansion are scattered in the structure. Then, a minute crack is generated due to the partial difference in thermal expansion coefficient, the thermal expansion coefficient of the brick as a whole is reduced, and the force of pressing adjacent bricks with each other is reduced.
Therefore, for example, even when used as a lining brick, it is possible to reduce spalling wear and to prevent a decrease in furnace life.

The aluminum used in the present invention does not necessarily have to be high-purity aluminum, as long as it has aluminum as a main component. However, when an aluminum alloy is used in the present invention, the aluminum content is 20%.
% Or more, and the balance can be an alloy containing one or more of various metals such as magnesium, silicon, calcium, boron, iron, chrome, and zirconium. An alloy having an aluminum content of less than 20% by weight is not preferable because the effect of improving the hot strength and corrosion resistance by the aluminum component becomes insufficient.

The particle size of the aluminum coarse particles in the present invention is preferably 0.5 to 20 mm, and less than 0.5 mm is not preferable because aluminum cannot be sufficiently unevenly distributed as coarse particles. This is not preferable because it easily occurs. The optimum range of the particle size depends on the size of the refractory molded product, and the minimum size of the brick (for example, 200 mm for a 200 mm x 300 mm x 800 mm rectangular brick)
Most preferably, aluminum coarse particles having a particle diameter of 1/50 to 1/200 (1 to 4 mm in this example) are used. In addition, as long as such aluminum coarse particles are used, aluminum powder or aluminum alloy powder can be used in addition to the aluminum coarse particles. In this case, the aluminum powder or aluminum alloy powder needs to be within 50% by weight of the total of the aluminum powder and the aluminum coarse particles. The effect of using aluminum coarse particles is not preferable because the effect is extremely thin, and the possibility of dust explosion increases.

The aluminum coarse particles having the above-mentioned particle size do not contain fine powder floating in the air, and are less likely to cause a dust explosion.

In the present invention, the addition amount of the aluminum coarse particles is preferably 1 to 30 parts by weight based on 100 parts by weight of the refractory composition. If the addition amount of the aluminum coarse particles is less than 1 part by weight, it is not preferable because the hot strength cannot be sufficiently increased,
On the other hand, if the amount exceeds 30 parts by weight, the coefficient of thermal expansion becomes excessively large and the brick structure is disintegrated, which is not preferable.

The BN added to the refractory formulation is stable in the coexistence with carbon below about the service temperature of the refractory of about 1800 ° C., and most of the BN is present in the refractory. Part of the BN is oxidized by oxygen contained in the pores of the refractory to form B ₂ O ₃
This is considered to have the effect of promoting the sintering of the refractory raw material and forming a dense and strong connecting structure. When the carbon-containing refractory with BN added is exposed to a highly oxidizing atmosphere, the BN near the operating surface is oxidized to B ₂ O ₃ , forming a high-viscosity melt with the refractory raw material and forming a refractory material. It will coat the surface and prevent carbon oxidation. Further, nitrogen generated by the oxidation of BN reacts with aluminum carbide (Al ₄ C ₃ ) generated between the aluminum coarse particles and carbon to produce aluminum nitride (AlN) and carbon. Aluminum nitride is mainly oxidized by carbon monoxide, like aluminum carbide, and becomes aluminum oxide (Al ₂ O ₃ ) or spinel (MgO · Al ₂ O ₃ ) in MgO-C brick, increasing the hot strength. This contributes to the improvement of corrosion resistance. Here, aluminum carbide is decomposed by water or air in the vicinity of room temperature to cause tissue collapse, whereas aluminum nitride has extremely low reactivity with water or the water in the air. It does not bring about any disruption of the organization.

Even if BN is a fine powder, it is an extremely stable substance and is not oxidized at room temperature. Therefore, even if BN is used, dust explosion does not occur.

Further, in the present invention, the amount of the BN powder added is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the refractory composition. If the amount of the BN powder is less than 1 part by weight, the antioxidant effect becomes insufficient, which is not preferable. If it exceeds 10 parts by weight, the corrosion resistance is remarkably reduced due to the formation of boron oxide, which is not preferable.

The use of an appropriate amount of binder in the present invention does not hinder at all, but in consideration of the carbon bond and the reactivity with aluminum, the amount of the fixed carbon measured according to the fixed carbon measurement method of JISK-2425 is 20% by weight or more. It is preferred to use certain binders. Typical examples of such a binder include coal tar pitch, petroleum pitch, phenolic resin, and furan resin.

The carbon-containing refractory according to the present invention is the above carbonaceous raw material,
The refractory raw material, the aluminum coarse particles and the BN powder were kneaded using the above-mentioned binder according to a conventional method, and were molded.
By drying at a temperature of 0 ° C. or less, a carbon-containing refractory as an unfired refractory is obtained, and the molded body is 800 to 1
By firing in a reducing atmosphere at about 500 ° C., a carbon-containing refractory as a fired refractory can be obtained.

〔Example〕

As shown in Examples 1 to 7 in Table 1, a carbonaceous raw material (scale graphite), a refractory raw material (magnesia, spinel, alumina) and a binder were used, and aluminum coarse particles and BN powder were added. The kneaded material is kneaded for 1 hour to obtain a kneaded material, and the kneaded material is pressurized with a hydraulic press at a pressure of 1000 kgf / cm ^{2 to} form a 230 mm × 114 mm × 65 mm rectangular solid, which is heated at 200 ° C. for 24 hours. And dried to obtain unfired refractories having different amounts of components.

(Comparative example)

As shown in Comparative Examples 1 to 6 in Table 1 in the same manner as in the examples, using carbonaceous raw materials (scale graphite), refractory raw materials (magnesia, spinel, alumina) and a binder, aluminum powder, aluminum Magnesium alloy powder was added, and in Comparative Examples 2 and 4, BN powder was added and kneaded with a roll pan for 1 hour to obtain a kneaded material. The kneaded material was subjected to a pressure of 1000 kgf / cm ² by a hydraulic press. To form a rectangular parallelepiped molded body of 230 mm × 114 mm × 65 mm, and dried by heating at 200 ° C. for 24 hours to obtain unfired refractories having different amounts of components.

(Measurement of physical property values)

With respect to the bricks of Examples 1 to 7 and Comparative Examples 1 to 6 obtained as described above, apparent porosity, bulk specific gravity, hot bending strength, oxidation test, slag erosion index, and coefficient of linear expansion under load Was measured. The measurement results of these physical properties are as shown in Table 1.

In Table 1, the oxidation test was performed by measuring the thickness of a decarburized layer after holding a cubic sample of 50 × 50 × 50 mm in an electric furnace at 1500 ° C. for 1 hour, and the slag erosion index was 1750 ° C. Synthetic slag (CaO / SiO ₂ = 2, T.Fe = 20%
Example 1 when contacted for 2 hours.
Alternatively, the amount of erosion of each of Comparative Examples 1 and 2 is shown assuming that the amount of erosion is 100, and the coefficient of linear expansion under load is 0.1 kgf / c.
It shows the coefficient of thermal expansion from room temperature to 1400 ° C. under a load of m ² and 20 kgf / cm ² .

As is clear from Table 1, Examples 1 to 7 using aluminum coarse particles or aluminum-magnesium alloy coarse particles and BN powder have higher hot strength and corrosion resistance than Comparative Examples 1, 2, 5, and 6. Is about the same, but since the coefficient of thermal expansion under load is reduced, it can be seen that microcracks are formed inside and the stress absorbing ability is improved.

Moreover, since the oxidation resistance of Comparative Examples 1, 3, 5, and 6 in which BN was not used was remarkably inferior, it can be seen that the oxidation resistance of each of the examples was significantly increased.

Furthermore, since the hot strength of Comparative Example 4 is remarkably low, it can be said that the hot strength of each example is remarkably increased.

[Practical test] The bricks of Examples 1, 2, and 5 and Comparative Examples 1 to 3 were used in a slag line section of a 90-ton ladle, and the wear rate was calculated from the remaining size after the furnace shut down. did. Table 2 shows the results.

In Examples 1, 2, and 5, there is no decarburized layer, and the wear is smooth. On the other hand, in Comparative Example 1, oxidation wear and peeling of the working surface layer of 20 to 50 mm occurred, and the wear rate was extremely high. In Comparative Example 2, although the oxidative wear was small, the operating surface layer was peeled off by 20 to 50 mm, and the wear rate was increased. Further, in Comparative Example 3, the operating surface layer was not peeled off, but the wear rate was increased due to oxidation wear. in addition,
In Comparative Examples 1 and 3, the recovered brick after use in the actual furnace collapsed after about one week due to moisture in the air.
In Examples 1, 2, 5 and Comparative Example 2 to which BN was added, the recovered brick did not collapse even after being released for one month.

〔The invention's effect〕

According to the carbon-containing refractory of the present invention, as described above, since the aluminum component is added, the hot strength can be increased and the corrosion resistance can be enhanced.
In addition, since the aluminum component is added in the form of coarse particles, the coefficient of thermal expansion of the refractory as a whole can be reduced, and the stress absorption capacity is increased, for example, when used as a lining of a steelmaking furnace. The pressing stress between adjacent bricks is reduced, and peeling wear is reduced. Furthermore, by adding BN, oxidation resistance is enhanced, and at the high temperature, aluminum carbide can be converted to aluminum nitride to suppress the collapse of the brick after heating or after use in a real furnace, thereby reducing oxidation loss and It is possible to prevent a decrease in furnace life due to brick collapse during intermediate repair.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ichiro Tsuchiya 1576 Nakahiro, Higashioki, Ako City, Hyogo Prefecture 2 Inside Kawasaki Furnace Materials Co., Ltd. No. 2 in Kawasaki Furnace Materials Co., Ltd. (72) Inventor Tatsuo Kawakami 1576 No. 2, east offshore of Naka-hiroji, Ako-shi, Hyogo Prefecture In Kawasaki Furnace Materials Co., Ltd. (56) References )

Claims (1)

(57) [Claims] 1 to 97% by weight of a carbonaceous raw material and a refractory raw material 3
Coarse particles having a particle size of 0.5 to 20 mm, which are one or two or more metals selected from aluminum or an alloy containing 20% by weight or more of aluminum in 100 parts by weight of a refractory composition consisting of up to 99% by weight. 1 to 30 parts by weight and 0.1 to 10 parts by weight of boron nitride powder.