JPH07300360A - Magnesia refractory - Google Patents

Abstract

PURPOSE:To inhibit slag from penetrating into refractories and improve them in their thermal spalling and structural spalling properties by using a refractory material mairily comprising spinel type whiskers and magnesia. CONSTITUTION:A starting substance containing aluminum, magnesia and a carbonaceous material is placed in a tubular furnace heated at 1,300 to 1,700 deg.C and carbon monoxide gas and carbon dioxide gas are introduced into the furnace to effect oxidation and reduction reactions to form spinel type whiskers of 0.5-10mum diameter, 0.5-10mm length and 100-10,000 aspect ratio. Then, 0.1-10wt.% of this spinel type whiskers, a refractory material mainly containing magnesia and a binder are kneaded and press-molded, heat-treated at 200-800 deg.C to give refractory bricks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia refractory used as a lining material for various molten metal containers such as a converter, a molten steel ladle, a smelting ladle and a RH in a steelmaking process.

[0002]

2. Description of the Related Art In recent years, refractory linings for molten metal containers such as ladles have changed from high-temperature refractory mainly composed of wax stone to zircon and high-alumina with high slag erosion resistance. Alumina / spinel amorphous refractory materials, which are hard to penetrate slag, are now commonly used, but they have not yet been able to achieve satisfactory durability. . Therefore, under particularly severe conditions of use, basic refractory materials such as magnesia-carbon bricks and magnesia-chromic direct-bond bricks mainly composed of magnesia materials are used.

As the refractory for the converter, dolomite or magnesia brick has been used for many years since the introduction of the converter, but higher quality refractory is required due to severe operating conditions. Nowadays, magnesia carbon bricks, which are excellent in sponging resistance, are generally used.

[0004]

As a lining material for a molten metal container, a basic refractory material mainly containing a magnesia material is excellent in slag erosion resistance. However, this basic refractory has the following defects in addition to the property that it is prone to cause thermal sporing. Since refractories using magnesia materials have excellent slag erosion resistance, if the low-viscosity slag that penetrates into the refractory penetrates deep into the refractory and solidifies, the thermal expansion of the magnesia part and the slag infiltration part Due to the difference in the ratio, structural sparking occurs and the refractory material peels off. The penetration of slag into this basic refractory is particularly remarkable in unfired bricks and amorphous refractories having a higher porosity than in fired bricks.

The magnesia-carbon refractory bricks and the magnesia-chromium direct bond bricks as described above are intended to prevent the penetration of slag of the magnesia refractory material and to improve the thermal spooling characteristics. . Magnesia-carbon brick is a lining material for converters and refining ladles, because it has significantly improved sponging resistance and slag penetration resistance due to the difficulty of wetting carbon material with slag, low thermal expansion, and high thermal conductivity. Widely used as. Recently, however, the use of carbon-containing bricks has become unfavorable because it causes carbon pickup due to the increasing grade of steel and the increase in the melting ratio of ultra-low carbon steel. In addition, magnesia-chromium direct bond bricks are used as lining materials for smelting pots and RH because they have excellent slag erosion resistance and slag penetration resistance. However, the anti-spooling property was not always satisfactory.

[0006]

SUMMARY OF THE INVENTION The inventors of the present invention have mainly used magnesia-based materials so that they can be used for melting ultra-low carbon steel, and have a refractory sponge and a heat-resistant sponge containing as little carbon material as possible. As a result of studying the slag permeability, it was found that the above object can be achieved by using a magnesia-based material containing aluminum-magnesium spinel whiskers as the material of the refractory material, and has reached the present invention. That is, the present invention is a magnesia refractory material containing 0.1 to 10% by weight of spinel whiskers and the balance being a refractory material mainly containing magnesia.

The magnesia refractory material used in the present invention may be a known magnesia refractory material such as an electrofused magnesia clinker, a sintered magnesia clinker, or a natural magnesia clinker, or a combination of these materials with a magnesia-alumina spinel. It is also possible to use it as a mixture with one or more of chromium oxide, magnesia and chromium spinel.

The spinel whisker is MgO-A.
It is made of 1 ₂ O ₃ and is pre-synthesized and added to the refractory composition. The amount of this spinel whisker added is 0.1 to 10% by weight, preferably 0.3 to 3.0% by weight. If this amount is less than 0.1% by weight, the effect of addition cannot be obtained, and thus heat resistant spooling resistance and slag penetration resistance cannot be obtained. On the other hand, if it exceeds 10% by weight, the refractory structure loosens, and on the contrary, slag easily penetrates, which causes structural spooling, which is not preferable.

The spinel whisker used in the present invention is
For example, it is prepared by oxidation-reduction reaction by heating aluminum, magnesia and a carbonaceous material as starting materials in a carbon monoxide gas atmosphere and intermittently introducing carbon dioxide gas. That is, the starting raw material powder is 1300 to 1700
It is placed in a tubular furnace heated to ℃ and atmospheric gas of carbon monoxide gas and carbon dioxide gas is introduced to generate whiskers. The shape of the whisker is 0.5 to 10 μm in diameter and length.
It is preferably 0.5 to 10 mm and an aspect ratio of 100 to 10,000.

As the constituent material of the present invention, in addition to the above, if necessary, one kind or two or more kinds of materials such as alumina, zirconia, aluminum nitride and silicon carbide can be used. It is preferable that 50% by weight or more of MgO is MgO from the viewpoint of slag erosion resistance. Also, if the amount is less than 5% by weight, natural graphite, carbon
Carbonaceous materials such as bon black can also be added. Further, when a carbonaceous material is used, a metal or alloy such as Al, Si or Al-Mg can be used as an antioxidant.

The magnesia refractory material of the present invention is used not only as a standard refractory material such as fired bricks and non-fired bricks but also as an irregular shape refractory material such as cast molding materials and spray repair materials. be able to.
In the case of producing a brick, a magnesia material, a spinel whisker, and other raw materials as needed are weighed according to a conventional method, a binder is added, and the mixture is kneaded and then press-molded. This molded body is heat-treated at a temperature of 200 to 800 ° C. to be used as an unfired brick, or is fired at a temperature of 1000 ° C. or more to be used as a fired brick. As the binder, any of organic binders such as phenol resin and inorganic binders such as sodium silicate and bitter juice can be used.

The amorphous refractory is mainly used as a casting material and a spray repair material. Also in this case, a binder, a dispersant, a plasticizer, a curing modifier and the like are appropriately selected for a predetermined refractory material in a conventional manner, and the mixture is used with water or another solvent. Alumina cement as a binder,
In addition to sodium silicate, phosphate, etc., phenol resin can also be used.

[0013]

By adding the spinel whisker to the magnesia material, the stress concentration at the crack tip can be relaxed by pulling out the whisker even when a crack is generated by thermal shock. The presence of whiskers also causes the crack growth path to be deflected in a zigzag manner. As a result, the heat-resistant spooling property is remarkably improved. In addition, when using refractory, the spinel whiskers suppress the penetration of slag into the refractory by increasing the viscosity of the slag by reacting with the slag component on the operating surface, and Prevent occurrence. Further, the spinel-like whiskers have a shape close to that of a single crystal and have high strength, and have thermally stable characteristics. Therefore, when added to a magnesia refractory, the hot strength is remarkably improved due to the reinforcing effect.

Spinel whiskers used in the present invention
Besides, whiskers such as alumina, silica-alumina, silicon carbide and silicon nitride are known as ceramic whiskers. However, for example SiO
_Use of whiskers such as silica / alumina, silicon carbide, and silicon nitride containing ₂ for the purpose of the present invention is not preferable because heat-resistant spooling property can be improved, but slag erosion resistance decreases. . That is, in operation during use, the SiO ₂ component in the whisker reacts with the slag to reduce the viscosity of the slag, so that the corrosion of the refractory is promoted. Further, when an alumina whisker is used, when Al ₂ O ₃ reacts with MgO in the refractory to generate spinel at a high temperature during use, a volume change occurs and the whisker shape is lost at the same time. No effect such as anti-spooling property can be obtained by adding the spinel whisker of the invention.

[0015]

【Example】

Preparation of Spinel Whiskers 5 g of aluminum powder having a purity of 95% and a particle size of 149 μm or less and 5 g of graphite powder having a purity of 99% were placed in a first alumina boat, and 1 g of the same aluminum powder and 4.5 g of graphite powder, and a purity of 99 were used. %, And 4.5 g of magnesia powder having a particle size of 149 μm or less was placed in a second alumina boat, and the tubular electric furnace was arranged so that the inlet side was the first alumina boat and the outlet side was the second alumina boat. Before heating, Ar gas was flowed in advance to remove air in the furnace. 50 at a rate of 600 ℃ / h
Stop the flow of Ar gas at 0 ° C, and then add 0.1 l / m of CO gas.
Immediately after reaching a predetermined temperature (1500 ° C.), CO ₂ started to be mixed in and heated at a predetermined temperature for 8 hours. When observed after cooling in the furnace, whiskers were found to have formed on the periphery of the outflow side boat. As a result of X-ray diffraction analysis of this whisker, it was confirmed to be spinel (MgO.Al ₂ O ₃ ).

Preparation of Refractory Material Samples were prepared using materials and binders having the compositions shown in Table 1. All the formulations in Table 1 are shown in parts by weight. Further, the molding method "P" in Table 1 was
It was press-molded, and “V” was vibration-cast molded after water was added to the material. “Heat” in the firing column means that the kneaded product was press-molded and then heat-treated at 300 ° C. for 15 hours. Also, "dry" means 2 at 150 ° C after casting the compound.
It was dried for 4 hours. Table 1 shows the physical properties of the sample thus produced.

The slag test also serves as a spooling test, using a rotary slag test furnace and heating with oxygen-propane burner at 1600 to 1650 ° C. for 3.5 hours in total, and reaching the set temperature on the way for 1 hour. After that, the burner was turned off and forced air cooling with a fan was performed for 30 minutes three times. The slag composition was Al ₂ O ₃ 13.9%, SiO ₂ 16.0%, Fe ₂
O ₃ 20.3%, CaO 40.1%, MnO ₂ 4.5%, MgO
A C / S 2.5 of 5.2% was used. The results of the slag test are shown in Table 1. In the results of Table 1, "no" indicates that almost no cracks were found by visual observation of the cut surface of the sample after the test, "large" indicates that the sample was separated by large cracks, "medium", “Small” indicates that medium and small cracks were observed.

[0018]

[Table 1]

The sample to which the spinel-like whiskers of the present invention were added (Example 1) had significantly improved sponging resistance and less slag penetration as compared with the sample without addition (Comparative Example 1). There is. This is also the case when a small amount of graphite is added (Example 2 and Comparative Example 4). In addition, the addition of alumina or silicon carbide whiskers (Comparative Examples 2 and 3) does not provide such an effect. The effect of the present invention is the same for the irregular refractory (Example 3 and Comparative Example 5).

[0020]

According to the present invention, in a basic refractory material mainly containing a magnesia material, by incorporating a predetermined amount of spinel whiskers, it becomes clear that the penetration of slag into the refractory material is clear from the examples. It is possible to minimize damage to refractories due to structural spooling. In addition, damage to the refractory due to thermal spooling is suppressed due to the stress relaxation effect by pulling out the whiskers.

Claims (1)

[Claims] 1. 0.1-10% by weight of spinel whisker
A magnesia refractory material containing, and the balance being a refractory material mainly containing magnesia.