JP6215409B1 - Mug carbon brick and molten steel pan using this - Google Patents

Abstract

[PROBLEMS] To improve the oxidation resistance of a magcarbon brick, particularly a magcarbon brick used in a slag line portion of a molten steel pan. An electrofused magnesia containing 0.3 to 3% by mass of CaO and 0.4 to 3% by mass of SiO2 is 65 to 97% by mass, graphite is 1 to 30% by mass, and silicon carbide is 1 to 3% by mass. A refractory raw material composition containing 6% by mass is kneaded and molded together with an organic binder, and then dried and the magcarbon brick 3 obtained by drying is placed in the slag line portion 2 of the molten steel pan 1. [Selection] Figure 1

Description

  The present invention relates to a magnesia carbon brick used for a molten metal container or the like, that is, a magcarbon brick and a molten steel pan using the same.

  Mug carbon brick is frequently used as a lining material for molten metal containers. Magcarbon bricks contain carbon, are not easily wetted by slag, and are excellent in thermal shock resistance, so there is little peeling damage and stable durability can be obtained. However, since it contains a carbon material such as graphite, it has a drawback that it is easily oxidized. To compensate for this, it is known to add an antioxidant such as aluminum, aluminum magnesium alloy or silicon carbide. In applications where phase oxidation is likely to occur, for example, in the slag line portion of a molten steel pan, particularly the uppermost stage of the brick in the slag line portion, the effect was not sufficient.

For example, Patent Document 1 discloses a magcarbon brick containing 1 to 6% of silicon carbide as an antioxidant. In this document, silicon carbide (SiC) is oxidized to SiO ₂ and CO, and CO is released as a gas, but SiO ₂ melts into a film and covers the working surface, so that oxygen bricks are covered. It is described as blocking intrusion. Moreover, although oxidation resistance improves with the addition amount of SiC, when the addition amount of SiC exceeds 6%, the oxidation resistance improvement effect is saturated and the durability (melting resistance) is also reduced. Yes. However, the melting point of SiO ₂ itself is 1600 ° C. or higher, and it is difficult to obtain sufficient oxidation resistance even if only SiC is added.

In Patent Document 2, the CaO content is 1.3 to 2.7% by weight, the SiO ₂ content is 0.1 to 0.3% by weight, and the CaO / SiO ₂ ratio (C / S) is 6 to 20. A mag-carbon brick using MgO-CaO refractory raw material is disclosed. And in the Table 2A, a magcarbon brick containing 2.0% by weight of CaO and 0.2% by weight of SiO ₂ and 1 to 3% by weight of SiC ultrafine powder (<10μ). It is disclosed that the addition of SiC ultrafine powder is extremely effective in improving the hot strength and wear resistance. However, as in Patent Document 2, when the content of SiO ₂ in the magnesia clinker used is small, the hot strength and the wear resistance are improved, but the oxidation resistance is still insufficient.

Patent Document 3 describes a MgO-C brick for lining that is lined on a slag line part of a ladle, and metal Al, which has been added as an antioxidant and a strength developing material for MgO-C brick, is conventionally used. It describes that one or two or more selected from Si, SiC and B ₄ C are added as an alternative to Al without addition. In Patent Document 3, although the antioxidant effect is obtained to some extent by adding SiC, the wear of brick due to oxidation becomes a bottleneck of the life of the ladle, particularly in the slag line portion of the ladle, and further improvement is desired. It is rare.

Japanese Patent Laid-Open No. 3-208862 Japanese Patent Laid-Open No. 9-2441067 JP 2011-184217 A

  The problem to be solved by the present invention is to improve the oxidation resistance of the magcarbon brick, particularly the magcarbon brick used in the slag line portion of the molten steel pan.

The inventors of the present invention found that fusing magnesia containing specific amounts of CaO and SiO ₂ is produced by a decomposition reaction of SiC + 2CO → SiO ₂ + 3C at a high temperature when using brick when used in combination with a specific amount of silicon carbide (SiC). It has been found that the reaction with SiO ₂ is promoted to produce an MgO—CaO—SiO ₂ low melting point substance, so that the effect of suppressing gas phase oxidation is remarkably improved.

That is, according to the present invention, the following (1) to (5) magcarbon bricks and the molten steel pan (6) using the same are provided.
(1) CaO 0.3 to 3% by weight and 65 to 97 wt% of fused magnesia of SiO ₂ containing 0.4 to 3 wt%, 1 to 30 wt% of graphite, and 1 to silicon carbide A mag-carbon brick for a slag line part of a molten steel pan, obtained by kneading and molding a refractory raw material composition containing 6% by mass together with an organic binder and then drying.
(2) The magnesium carbide brick according to (1), wherein the silicon carbide in the refractory raw material composition has a particle size of 0.074 mm or less and 80% by mass or more.
(3) fused magnesia of the refractory raw material formulation is, CaO content is 1.1 to 2.0 mass%, and SiO ₂ content of 0.6 to 2.1 wt% (1) or The mug carbon brick described in (2).
(4) The mug carbon brick according to any one of (1) to (3), wherein the content of silicon carbide in the refractory raw material composition is 1 to 3% by mass.
(5) The said refractory raw material composition contains 0.5-5 mass% of aluminum and / or an aluminum alloy, The mug carbon brick in any one of (1) to (4).
(6) A molten steel pan in which the magcarbon brick according to any one of (1) to (5) is installed in a slag line portion.

Hereinafter, the present invention will be described in detail.
In order to promote the production of the low melting point material of MgO-CaO-SiO ₂ system by SiO ₂ produced by the above-described decomposition reaction of SiC + 2CO → SiO ₂ + 3C, CaO and SiO _{2 in} electrofused magnesia are important. If the CaO content is 0.3% by mass or less or the SiO ₂ content is 0.4% by mass or less, the amount of low-melting substance produced is insufficient, so that the antioxidant effect is insufficient. On the other hand, if there is too much SiO ₂ in the electrofused magnesia, it will easily react with slag and the corrosion resistance will decrease, so the upper limit of the SiO ₂ content is 3 mass% from the viewpoint of the balance between oxidation resistance and corrosion resistance. In addition, when there is too much CaO in electrofused magnesia, bricks are easily digested, so the CaO content is 3 mass% as the upper limit from a practical aspect. Further, in the case of a more oxidation resistance and high corrosion resistance mug carbon brick, CaO content in the fused magnesia 1.1 to 2.0 wt%, SiO ₂ content of 0.6 to 2.1 It can be made into the mass%.

  The reason why electrofused magnesia is used as magnesia in the present invention is that electrofused magnesia has a dense particle structure and exhibits higher oxidation resistance and higher corrosion resistance than other magnesia when used in magcarbon bricks. is there.

In the present invention, silicon carbide is used as an antioxidant. As described above, silicon carbide generates SiO ₂ by a decomposition reaction of SiC + 2CO → SiO ₂ + 3C at a high temperature during use of a brick, and reacts with MgO, CaO, and SiO ₂ in electrofused magnesia, so that MgO—CaO— An SiO ₂ -based low melting point material is produced. Since the gap between the magnesia particles is filled with this low melting point substance, the intrusion of air into the brick is suppressed and the gas phase oxidation of graphite (carbon) is suppressed. As a result, the strength reduction of the brick structure is suppressed, and the wear resistance and corrosion resistance are improved. In addition, the formation of carbon at the same time as the decomposition reaction described above results in densification of the brick structure, thereby further improving the oxidation resistance.

If the amount of silicon carbide used in the refractory raw material composition (compounding amount) is less than 1% by mass, a sufficient antioxidant effect cannot be obtained, and if it exceeds 6% by mass, the amount of SiO ₂ produced by the above decomposition reaction increases. As a result, the amount of low-melting substance produced becomes excessive and the corrosion resistance is lowered. The amount of silicon carbide used in the refractory raw material composition is preferably 1 to 3% by mass.

In addition, when silicon carbide is used as a fine powder, the above-described decomposition reaction is promoted, and the reactivity between SiO ₂ produced by the above-described decomposition reaction and CaO and SiO _{2 in} electrofused magnesia is increased, so that oxidation resistance is achieved. Can be further enhanced. Therefore, it is preferable that 0.074 mm or less is 80 mass% or less as for the particle size structure of silicon carbide. However, if the particle size is too small, the activity becomes too high and the corrosion resistance may be lowered. Therefore, the content of 10 μm or less is more preferably 70% by mass or less.

In addition to aluminum carbide, aluminum, aluminum alloy, silicon, and B ₄ C are well known as antioxidants for magcarbon bricks. Aluminum and aluminum alloys are oxidized to produce Al ₂ O ₃ , but Al ₂ O ₃ reacts with MgO to form spinel. Therefore, if the amount used is large, the volume stability problem and elastic modulus increase, resulting in thermal shock. There is a problem that the performance decreases. Silicon produces SiO ₂ in the same way as silicon carbide, but has little effect of densifying the structure of carbon like silicon carbide. When B ₄ C is also oxidized, a low melting point substance is formed, but the melting point is low and the corrosion resistance is lowered.

However, aluminum and aluminum alloys can be used in combination with silicon carbide to improve the strength and oxidation resistance of the magcarbon brick, and preferably 0.5 to 5% by mass in the refractory raw material composition. 3% by weight can be used. Silicon can be used in combination with silicon carbide to prevent oxidation and can be used in an amount of 0.5 to 3% by mass in the refractory raw material composition. Aluminum, aluminum alloy, and silicon can be used in combination, and in that case, 0.5 to 5% by mass in total can be used in the refractory raw material composition. B ₄ C can be used in a small amount in order to enhance the antioxidant effect. For example, 0.1 to 1% by mass can be used in the refractory raw material composition.

  If the amount of graphite used in the refractory raw material composition is less than 1% by mass, thermal shock resistance cannot be obtained, and if it exceeds 30% by mass, the strength decreases. Moreover, when it is desired to increase the corrosion resistance of the brick, the amount of graphite used may be 10 to 20% by mass.

  In addition, the particle size as used in the field of this invention is shown with the sieve opening (mm) in a JIS standard sieve. For example, a raw material particle having a particle size of 1 mm or less is a raw material particle that has passed through a sieve when the sieve opening is sieved with a 1 mm sieve.

According to the present invention, at a high temperature at the time of brick used, specific amounts of CaO and CaO-MgO-SiO ₂ system formed by the reaction between the fused magnesia and SiO ₂ produced by the decomposition reaction of silicon carbide containing SiO ₂ The low melting point material and the carbon generated simultaneously by the above-described decomposition reaction make the brick structure dense, thereby suppressing gas phase oxidation and improving oxidation resistance. In addition, the strength reduction of the brick structure is suppressed, and the wear resistance and corrosion resistance are improved. In particular, the magcarbon brick according to the present invention can be remarkably improved in the durability of the molten steel pan by being installed at the slag line portion of the molten steel pan, which is likely to cause vapor phase oxidation, particularly at the uppermost stage of the brick.

It is a notional longitudinal cross-sectional view of the molten steel pan using the mug carbon brick of this invention.

The electrofused magnesia used for the refractory raw material composition of the magcarbon brick of the present invention is a commercially available electrofused magnesia whose content of SiO ₂ and CaO is within the range of the present invention, or of SiO ₂ and CaO. Fused magnesia produced by an electrofusion method so that the content falls within the range of the present invention can be used.

  Silicon carbide can be used without any problem as long as it is generally used for refractories, and specifically has a SiC content (purity) of 80% or more.

  Graphite can be used as long as it is usually used in magcarbon bricks, and specifically, it is scale-like graphite, graphitized carbon black, artificial graphite and the like.

  Aluminum, aluminum alloy, and silicon are used for densifying the brick structure and as an aid for preventing oxidation, and can be used without any problem as long as they are generally used for magcarbon bricks.

  In addition to these refractory raw materials, pitch and carbon black can be used in the present invention to improve thermal shock resistance. Pitch and carbon black can be used without problems as long as they are generally used for mag-carbon bricks. The usage-amount can be 0.5-2 mass% in a refractory raw material compound.

  The magcarbon brick of the present invention can be produced by a general method for producing magcarbon brick. That is, the magcarbon brick of the present invention can be obtained by kneading and forming the refractory raw material composition together with an organic binder and then drying (heat treatment). The drying temperature (heat treatment temperature for drying) can be 200 to 500 ° C.

  As an organic binder, the organic binder currently used with the usual mag-carbon brick can be used, for example, a furan resin, a phenol resin, etc. can be used. Further, the organic binder can be used in any form of powder or liquid dissolved in an appropriate solvent, or a combination of liquid and powder. The method and conditions of kneading, molding and drying (heat treatment) are also in accordance with a general method for producing magcarbon bricks.

  The magcarbon brick of the present invention thus obtained can be used as a lining material for molten metal processing furnaces such as converters, electric furnaces, hot metal pots, molten steel pots, vacuum degassing furnaces, etc. By using it as the uppermost lining material of the bricks arranged in the slag line part of the molten steel pan where oxidation is a problem, particularly in the slag line part, it is possible to significantly extend the life of the molten steel pan.

As described above, the magcarbon brick of the present invention is obtained by kneading and forming a refractory raw material composition together with an organic binder and then drying (heat treatment), and is a so-called non-fired brick. In non-fired brick, it is impossible to directly specify the content of the organic binder in the brick. Further, the magcarbon brick of the present invention is characterized by using electrofused magnesia containing specific amounts of CaO and SiO ₂ , but in the state of magcarbon brick, CaO derived from electrofused magnesia. and it is extremely difficult to identify and distinguish between CaO and SiO ₂ derived from SiO ₂ and other refractory raw material, also from this point, it is not possible to identify directly the product due to its structure, or characteristic Or roughly impractical. Thus, the present invention has a so-called “impossible / impractical circumstances”.

  Magcarbon bricks were produced using the refractory raw material formulations shown in Tables 1 and 2. That is, by adding an appropriate amount of a phenolic resin as an organic binder to each refractory raw material composition shown in Tables 1 and 2 and kneading and forming, and then heat-treating (drying) at 250 ° C., a magcarbon brick is obtained. It was. And about the obtained mag-carbon brick, oxidation resistance, corrosion resistance, and compressive strength were evaluated. The chemical components of electrofused magnesia A to I shown in Tables 1 and 2 are as shown in Table 3. The silicon carbide used as a raw material had a SiC content of 95% by mass, and a particle size of 0.074 mm or less and a content of 10 μm or less of 50% by mass.

  In the evaluation of oxidation resistance, a test piece cut out to 50 mm × 50 mm × 50 mm was heated in an oxidizing atmosphere at 1400 ° C. × 5 hours in an electric furnace, and then the size of the oxidation depth was measured. The evaluation results were indexed with the oxidation depth dimension of Comparative Example 1 as 100. The larger the value of this oxidation resistance index, the better the oxidation resistance.

  In the evaluation of corrosion resistance, a combination of steel pieces: converter slag at a mass ratio of 1: 1 was melted at 1650 ° C. in an induction furnace, the test pieces were immersed in this melt for 3 hours, and the remaining dimensions of the test pieces were measured. Was measured. The evaluation results were indexed with the remaining dimension of Comparative Example 2 as 100. The larger the value of this corrosion resistance index, the better the corrosion resistance.

  The compressive strength was measured according to JIS-R2206 after each brick was fired at 1400 ° C. for 3 hours in coke breeze.

Examples 1 to 6 shown in Table 1 use fused magnesia in which the contents of CaO and SiO ₂ are within the scope of the present invention. It can be seen that the balance between corrosion resistance and corrosion resistance is excellent, and the oxidation resistance of the magcarbon brick is effectively improved in practice.

Looking specifically at each example shown in Table 1, in Examples 1 to 3, although the oxidation resistance improves as the SiO ₂ content in the electrofused magnesia increases, the corrosion resistance may decrease. Recognize. Example 4 is the case where the upper limit of the SiO ₂ content in the electrofused magnesia is excellent in oxidation resistance, but the corrosion resistance is the lowest in the examples. In Example 5, the CaO content in the electrofused magnesia is 0.3 mass%, which is the lower limit, but sufficient oxidation resistance is obtained. Example 6 has the best balance between oxidation resistance and corrosion resistance.

On the other hand, Comparative Example 1 is an example in which fusing magnesia having a SiO ₂ content of 0.1% by mass, which is lower than the lower limit of the present invention, was used. In Example 1, the SiO ₂ content was 0.4% by mass. Compared to the case of using fused magnesia, the oxidation resistance index is as low as 100, which is not practical. Comparative Example 2 is an example in which fusing magnesia having a SiO ₂ content of 3.5% by mass and exceeding the upper limit of the present invention was used, but fusing magnesia having a SiO ₂ content of 3% by mass in Example 4 was used. However, the oxidation resistance is equivalent to that of the case, but the corrosion resistance index is too low as 100, which is not a practical level. Comparative Example 3 is an example in which fusing magnesia having a CaO content of 0.1% by mass and lower than the lower limit of the present invention was used. In Example 5, a fusing magnesia having a CaO content of 0.3% by mass was used. However, the oxidation resistance index is as low as 90 compared to the case.

Examples 7 to 11 shown in Table 2 use metal Al (aluminum) and metal Si (silicon) together with fused magnesia whose CaO and SiO ₂ contents are within the scope of the present invention. The amount used was changed, and the balance between oxidation resistance and corrosion resistance was superior to Comparative Examples 4 and 5. Moreover, Examples 8-10 which added metal Al have a large compressive strength after baking, and are excellent in an intensity | strength characteristic.

  In Comparative Example 4, the amount of silicon carbide used is 0.5 mass%, which is lower than the lower limit of the present invention, and the oxidation resistance is inferior to that in the case where the amount of silicon carbide used in Example 7 is 1 mass%. Yes. In Comparative Example 5, the amount of silicon carbide used is 7% by mass, which exceeds the upper limit of the present invention, and the corrosion resistance index is as small as 104 compared to the case where the amount of silicon carbide used in Example 11 is 6% by mass. It is inferior in corrosion resistance.

  The longitudinal cross-sectional view of the molten steel pan 1 which uses the mag carbon brick of an Example and a comparative example for FIG. 1 is shown. Magcarbon brick 3 is installed on the upper five stages, and an alumina magnesia-based castable 4 is constructed in addition to this part. In addition, the slag line portion is a portion that is in contact with the slag for a long time during operation. In FIG. 1, the slag line portion 2 is a four-stage portion excluding the uppermost brick. Further, the uppermost brick of the slag line portion of the molten steel pan in FIG. 1 is 31 which is the uppermost step of the four bricks arranged in the slag line portion. In this molten steel pan 1, the molten steel pan using the magcarbon brick of Example 6 was compared with the molten steel pan using the magcarbon brick of Comparative Example 1. In the molten steel pan in which the magcarbon brick of Comparative Example 1 was arranged, the wear of the uppermost stage 31 of the brick of the slag line portion was the largest, and the slag line portion had to be replaced with a new one after 70 times of use. On the other hand, in the molten steel pan in which the magcarbon brick of Example 6 was arranged, the slag line portion was similarly damaged most in the uppermost stage 31, but could be used up to 100 times. From this, it can be seen that the mag-carbon brick of the present invention can significantly improve the durability of the molten steel pan at least by installing it at the top of the brick in the slag line portion of the molten steel pan.

DESCRIPTION OF SYMBOLS 1 Molten steel pan 2 Slag line part 3 Mag carbon brick 4 Castable 31 The top of the brick of a slag line part

Claims (6)

The CaO 0.3 to 3% by weight and 65 to 97 wt% of fused magnesia of SiO ₂ containing 0.4 to 3 wt%, graphite 30 wt%, and silicon carbide 1-6 wt% Mug carbon brick for slag line part of molten steel pan, obtained by kneading and molding the refractory raw material composition including organic binder and drying.   The magnesium carbide brick according to claim 1, wherein the silicon carbide in the refractory raw material composition has a particle size of 0.074 mm or less and 80 mass% or more. The refractory raw material fused magnesia in the formulation is, CaO content is 1.1 to 2.0 wt%, and claim 1 or claim SiO ₂ content of 0.6 to 2.1 wt% 2 Mug carbon brick described in 1.   The magcarbon brick according to any one of claims 1 to 3, wherein a content of silicon carbide in the refractory raw material composition is 1 to 3 mass%.   The said refractory raw material mixture is a mag-carbon brick in any one of Claims 1-4 containing 0.5-5 mass% of aluminum and / or aluminum alloy.   A molten steel pan in which the magcarbon brick according to any one of claims 1 to 5 is installed in a slag line portion.

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