JP6348071B2 - Magnesia refractory - Google Patents

Description

  The present invention relates to a magnesia refractory. In particular, the present invention relates to a magnesia refractory having low thermal conductivity, excellent spall resistance and corrosion resistance, and high durability.

  In the steel process, refractories containing carbon such as alumina-carbonaceous, alumina-silicon carbide-carbonaceous, and magnesia carbonaceous are used as the lining material of molten steel containers. As the carbon source, scaly graphite is mainly used. This is because scaly graphite has the property of absorbing the thermal expansion of refractory aggregates such as alumina and magnesia, and greatly contributes to the improvement of heat-resistant spalling properties. In addition, since scaly graphite has poor wettability with slag, it also has a function of suppressing infiltration of the slag component into the refractory.

On the other hand, carbon-containing refractories containing scaly graphite have a high thermal conductivity due to the presence of scaly graphite, and thus cause thermal energy loss due to the dissipated heat of the molten metal. Further, when used in an oxidizing atmosphere such as a converter or a secondary refining facility, the carbon component of the refractory containing carbon is oxidized and lost due to vapor phase oxidation. There is a problem that wear of the refractory itself progresses because the slag component infiltrates into pores formed with the disappearance of graphite and the aggregate dissolves.
From these facts, it is desired that the carbon raw material in the carbon-containing refractory, particularly the scaly graphite content, is small. However, as described above, scaly graphite contributes to the improvement of the spall resistance of the refractory, so that the problem of a decrease in the spall resistance occurs due to a decrease in the graphite content.

Various means have been proposed for preventing the decrease in spall resistance associated with the reduction of scaly graphite.
For example, Patent Document 1 describes that a highly durable refractory can be obtained by using an organic binder, pitch, or carbon black alone or in combination as an alternative carbon raw material for scaly graphite.

  Patent Document 2 describes that a highly durable refractory containing no scaly graphite can be obtained by adding a mesophase pitch / thermosetting resin.

  Furthermore, Patent Document 3 discloses that magnesia-based raw material having a particle size of more than 10 μm to 500 μm is 20 to 50% by mass of the refractory raw material composition, and particles having a particle size of 10 μm or less are 0 to 5 mass of the refractory raw material composition. It is described that, after kneading and molding with an organic binder, tar or pitch can be impregnated to a deep part by impregnation with tar or pitch, and a high-resistance magnesia refractory can be obtained. .

Japanese Patent Laid-Open No. 11-322405 JP 2005-139062 A JP 2002-12914 A

The invention described in Patent Document 1 has a problem that the strength and elastic modulus after oxidation firing are high, and the spall resistance is insufficient depending on the conditions of the kiln used.
The invention described in Patent Document 2 has a problem that the carbon content is as large as 4% by mass or more, and the structure deterioration after oxidation and firing of carbonaceous matter is large.
In the invention described in Patent Document 3, a carbon component such as tar is added, and the total carbon content is large, and the problems such as increase in thermal conductivity and carbon pickup have not been solved.
An object of the present invention is to provide a magnesia refractory that suppresses thermal energy loss from molten steel, has excellent corrosion resistance and spall resistance, and has sufficient durability.

The gist of the present invention is as follows.
(1) Contains magnesia-based raw material, 0.2% to 0.9% by weight of carbon black, and 0.1% to less than 0.5% by weight of powdered metal Al, and other thermosetting A magnesia refractory characterized by using a refractory raw material mixture formed by adding a functional resin and an antioxidant for a carbon component.

  Since the magnesia refractory of the present invention does not contain scaly graphite, it has low thermal conductivity and high corrosion resistance. Furthermore, it shows high spall resistance due to fine pores caused by carbon black. Therefore, when it is used as a lining material for a molten steel container, a heat energy loss from the molten steel can be suppressed, and the durability is improved.

It is a figure which shows the derivation method of a spall damage index. It is a figure which shows the spall damage index at the time of carbon black addition. It is a figure which shows the outline | summary of a rotational erosion test method. It is a figure which shows the refractory sample shape used for a rotation erosion test. It is a figure which shows the erosion index at the time of carbon black addition. It is a figure which shows the spall damage index at the time of powdery metal Al addition. It is a figure which shows the erosion index at the time of powdery metal Al addition.

Hereinafter, embodiments of the present invention will be described in detail. In the present invention, a refractory raw material mixture in which carbon black is added to a magnesia-based raw material as a carbon raw material in an amount of 0.2% by mass to 0.9% by mass and powdered metal Al is added in an amount of 0.1% by mass to less than 0.5% by mass. By using a magnesia refractory using the refractory, a refractory having a low thermal conductivity and excellent corrosion resistance and spall resistance can be obtained as compared with a graphite-containing magnesia refractory.
A refractory raw material mixture was prepared by adding carbon black, powdered metal Al, other thermosetting resin, and carbon component antioxidant to the magnesia-based raw material described above as a carbon raw material.
Here, the magnesia-based raw material is magnesia alone or a mixture of refractory raw materials containing 95% by mass or more of magnesia. The magnesia may be a magnesia clinker having a particle size of about 100 μm to 3 mm, which is usually used for magnesia carbon bricks.

First, the effect of carbon black will be described.
Specimens made of magnesia refractories using a mixture of refractory raw materials containing 0.7% by mass of scaly graphite or carbon black in magnesia-based raw materials (referred to as scaly graphite-containing refractories and carbon black-containing refractories, respectively). As described above, the thermal conductivity was measured by a steady heat flow method. Here, the steady heat flow method is a method for obtaining a thermal conductivity by applying a one-dimensional axial or radial steady heat flow to a sample and acquiring a temperature gradient of the sample. The sample was molded into Φ20 × 150 mm, the end in the longitudinal direction was maintained at 600 ° C., and the amount of heat transferred to the opposite end was measured to calculate the thermal conductivity.

As a result of the measurement, the heat conductivity of the scaly graphite-containing refractory was 12.3 W / mK, and the heat conductivity of the carbon black-containing refractory was 10.3 W / mK. The amount of heat dissipated when these two refractories were applied to an actual RH lower tank was calculated under the conditions of a molten steel temperature of 1600 ° C., an atmospheric atmosphere of 30 ° C., a refractory thickness of 480 mm, and an iron skin thickness of 25 mm. As a result, the scaly graphite-containing refractory 17271W / ^{m 2,} carbon black in refractories containing can reduce 8.3% heat energy loss by changing the carbon black 15948W / ^{m 2,} and the carbon component from the vein graphite there were.

  Carbon black has a particle size of about 100 nm, which is smaller than that of scaly graphite, and forms many fine pores after disappearance of oxidation. Therefore, the elastic modulus of the refractory is lowered and the spall resistance is improved. A magnesia refractory in which the amount of carbon black added was changed between 0% by mass and 1.2% by mass, and a magnesia refractory to which 1.0% by mass of scaly graphite was added for comparison were 40 mm × 40 mm × It was prepared with a size of 160 mm, and a spall resistance evaluation test was performed. In the spall resistance evaluation test, each refractory was immersed in hot metal at 1600 ° C. for 3 minutes, and then extracted from the hot metal and air-cooled for 10 minutes three times. Thereafter, the crack length generated by observing the cross section of the refractory was measured, the measurement result of the scaly graphite-containing refractory was indexed as 100, and the spall resistance was evaluated as a spalling damage index. It can be said that the smaller this value, the better the spall resistance. The outline of the crack length measurement method is shown in FIG. 1, and the result is shown in FIG. When the carbon black addition amount is 0% by mass, the spalling damage index is 115 and the spall resistance is inferior. However, as the carbon black addition amount is increased, the spall resistance is improved. By adding 0.2% by mass of carbon black, the spalling damage index is 99, and the spall resistance is higher than that of the refractory spalling damage index (100, black square mark) containing 1.0% by mass of scaly graphite. improves. Therefore, the lower limit of the carbon black addition amount was set to 0.2% by mass.

On the other hand, since the porosity increases due to an increase in the amount of carbon black added, there is a concern about deterioration of corrosion resistance. Therefore, a corrosion resistance evaluation test was performed. Corrosion resistance was evaluated by the rotary erosion method. The rotary erosion method is a test in which a sample having a shape shown in FIG. 4 is lined inside a cylindrical test apparatus as shown in FIG. 3, an erosion material is put in the sample, and the sample is rotated and heated. The immersion ingredients CaO: 30 _{wt% · SiO 2: 30% ·} Al 2 O 3: 20% · FeO: using slag composition is 20%. The test temperature is 1650 ° C, and the slag is replaced 10 times every 30 min. The refractory residual dimension after the erosion test is measured at 7 points, and the average value is calculated as the erosion dimension. Was indexed as 100 and evaluated as a melting index. It can be said that the smaller this value, the better the corrosion resistance. As a result, as shown in FIG. 5, the corrosion resistance decreases as the porosity increases when 0.7% by mass or more is added, the erosion index is 99 when 0.9% by mass is added, and the scale increases when the amount is further added. By containing 1.0% by mass of graphite, the corrosion resistance is lower than that of the refractory. Therefore, the upper limit of the amount of carbon black added is set to 0.9% by mass.

As described above, from the evaluation results of the spall resistance / corrosion resistance, the addition amount of carbon black is preferably 0.2 to 0.9 mass%, particularly preferably 0.5 to 0.7 mass%.
The powdered metal Al is generally added as an antioxidant for the carbon raw material, and is used in the form of a powder to increase the reactivity. The particle size is preferably about the same as or smaller than that of magnesia clinker. Further, in the present invention, it is considered that in addition to the characteristics of the carbon component as an antioxidant, it contributes to the formation of fine pores.
Generally, metal Al added to a carbon-containing refractory plays a role as an antioxidant for a carbon component. That is, by the reaction of 2Al (l) + 3CO (g) = Al ₂ O ₃ (s) + 3C (s), Al (l) reduces CO (g), precipitates C (s), and carbon as a whole. Contributes to the suppression of component reduction. Furthermore, since Al can be a vapor species such as Al (g), this reaction occurs not only around the metal Al but also anywhere in the refractory to form Al ₂ O ₃ .
However, in the case of a refractory with a very small carbon content as in the present invention, the CO partial pressure in the refractory is low, and Al is in a state in which Al (l) or Al (g) is more stable than Al ₂ O _3. Thus, it is presumed that outflow and evaporation occur at high temperatures, resulting in the formation of many pores in the refractory structure. The observation of the structure after firing confirmed the formation of fine pores between the magnesia raw material aggregates, and the Al component was detected around the pores.

When the spalling damage index is evaluated using the same method as described above, the structure becomes rough due to pore formation accompanying the addition of metallic Al. Therefore, as shown in FIG. The index decreases, that is, the spall resistance improves. Here, the spalling damage index of the scaly graphite-containing refractory was set to 100. The spalling damage index was improved by adding 0.1% by mass or more of metal Al. Contrary to the improvement of the spall resistance, the amount of slag infiltration increases with the formation of pores, so that the corrosion resistance deteriorates as the amount of metal Al added increases as shown in FIG. When the melting loss index of the scaly graphite-containing refractory is 100, the addition amount of metal Al becomes 100 when the addition amount is 0.5% by mass, and when it is added more, the corrosion resistance deteriorates. The amount was less than 5% by mass.
As described above, from the evaluation results of the spall resistance and the corrosion resistance, the amount of metal Al added is preferably 0.1% by mass or more and less than 0.5% by mass, and the addition of 0.3 to 0.4% by mass is more preferable.

In the present invention, as described above, the antioxidant effect is obtained by adding metal Al. As an antioxidant for other carbon components, one or more metal powders such as Mg, Si, and B and their alloys are generally added.
Metal Si, like metal Al, can obtain an antioxidation effect by reduction reaction of CO gas, but it is known that a high antioxidation effect is exhibited when used together with metal Al. The anti-oxidation effect by Si is reduced by the reaction of Si (s) + C (s) = SiC (s) SiC (s) + 2CO (g) = SiO ₂ (s) + 3C (s). However, it is reported that SiC formation is promoted by the combined use with metal Al, and as a result, the antioxidant effect is increased.
Furthermore, boron carbide reduces CO gas by the reaction of B ₄ C + 6CO (g) = 2B ₂ O ₃ (l) + 7C (s), and the liquid phase of the generated boron oxide becomes a dense layer on the refractory surface. By preventing the intrusion of oxygen, a high antioxidant effect can be obtained.

Further, a thermosetting resin for expressing the strength during pressure molding and heat treatment, and a pitch are also added to bond the magnesia refractory raw material with carbon bonds to enhance the structure strength.
The refractory raw material mixture according to the present invention is kneaded, press-molded by a press or the like, and then baked at 120 to 400 ° C. to produce an unfired magnesia refractory. The magnesia refractory obtained as described above can be fired in a reducing or non-oxidizing atmosphere at about 500 to 1500 ° C. to produce a “baked product”, which is also included in the present invention. is there.

Examples of the present invention are listed in Table 1 together with comparative examples.
The test materials were kneaded with the composition shown in the table, pressed into a parallel shape of 230 mm × 114 mm × 65 mm by a friction press, and then heated at 250 ° C. for 10 hours. The raw material usage ratio in the table is mass%. The obtained specimens were subjected to a spall resistance evaluation test and a corrosion resistance evaluation test by the methods described above to evaluate the spalling damage index and the melting index.

Sample No. 1 to 10 are examples of the invention, and both show good characteristics in which both the spalling damage index and the melting index are less than 100.
Sample No. 11 is a comparative example, and since it does not contain a carbon raw material, it is inferior in spall resistance.
Sample No. No. 12 is a comparative example, and since the amount of carbon black added exceeds the upper limit, the corrosion resistance is poor.
Sample No. Reference numerals 13 and 14 are comparative examples, and since the metal Al is excessively added, the corrosion resistance is poor.
Samples Nos. 15 and 16 are comparative examples, which do not contain metal Al and have changed the additive metal species, but they cannot achieve both corrosion resistance and spalling resistance.
Sample No. Reference numeral 17 is a comparative example, does not contain carbon black, contains 1% by mass of scaly graphite, and is used as a reference material for the spalling damage index / melting index 100.

  The magnesia refractory according to the present invention is applicable as a liner for molten metal containers such as converters, electric furnaces, ladles, vacuum degassing furnaces, and the like.

Claims (1)

  Containing magnesia-based raw material, carbon black 0.2 mass% or more and 0.9 mass% or less, and powdered metal Al 0.1 mass% or more and less than 0.5 mass%, and other thermosetting resins, A magnesia refractory characterized by using a refractory raw material mixture to which an antioxidant of a carbon component is added.

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