Manufacturing method of magnesia carbon bricks
By optimizing the particle size and content of compressed and expanded graphite, and magnesia in the refractory raw material mixture, the method produces magnesia-carbon bricks with improved corrosion and spalling resistance for use in secondary refining equipment, addressing the limitations of existing technologies.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- KROSAKI HARIMA CORP
- Filing Date
- 2024-11-22
- Publication Date
- 2026-06-03
AI Technical Summary
Existing methods for producing low-carbon magnesia-carbon bricks face challenges in achieving both improved corrosion resistance and spalling resistance due to issues with particle size and content of compressed and expanded graphite, leading to poor filling during molding, high porosity, and insufficient resistance in secondary refining equipment like RH-type vacuum degassing furnaces.
Incorporating 0.5% to 8% by mass of compressed and expanded graphite with a particle size of less than 5 mm, along with specific proportions of magnesia with varying particle sizes, into the refractory raw material mixture, followed by kneading, molding, and heat-treating, to enhance the brick's density and resistance properties.
The method results in magnesia-carbon bricks with enhanced corrosion resistance and spalling resistance, suitable for use in secondary refining equipment, while minimizing carbon pickup and heat loss, and improving steel quality.
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for producing magnesia-carbon bricks suitably used in secondary refining equipment such as a vacuum degassing furnace in steelmaking equipment.
Background Art
[0002] For example, in a RH type vacuum degassing furnace, magnesia-carbon bricks are used as the lining material. Under operating conditions with a large amount of oxygen injection, iron oxide is generated, so the magnesia-carbon bricks need to have corrosion resistance against slag containing a large amount of iron oxide. To enhance the iron oxide resistance of magnesia-carbon bricks, reducing the carbon content is effective. This is because the carbon (C) component of the magnesia-carbon bricks is oxidized in the liquid phase by the iron oxide in the slag, so reducing the carbon content acts effectively. Here, in the present invention, a low carbon content means that the content of graphite in the refractory raw material blend used in the method for producing magnesia-carbon bricks is 8% by mass or less. Thus, to achieve low carbonization of magnesia-carbon bricks, the content of graphite in the refractory raw material blend is reduced, but this will result in a decrease in spalling resistance.
[0003] One method for improving the spalling resistance of low-carbon magnesia carbon bricks is to use compressed and expanded graphite instead of ordinary scaly graphite. For example, in Example 2 of Patent Document 1, 2% by mass of compressed and sheet-formed graphite, which has been crushed and classified to a particle size of 2 to 7 mm after expansion treatment, is used. According to Patent Document 1, it is possible to improve corrosion resistance while maintaining spalling resistance by including such compressed and expanded graphite. However, the compressed and expanded graphite used in Patent Document 1 has a particle size of 2 to 7 mm, and since it includes large particles, when used in the manufacturing method of low-carbon magnesia carbon bricks, there is a problem of poor filling during molding, high porosity and reduced corrosion resistance, and in regions with a low content of compressed and expanded graphite, the distance between compressed and expanded graphite particles in the structure becomes large, so sufficient spalling resistance cannot be obtained.
[0004] Furthermore, Patent Document 2 describes the use of compressed expanded graphite, which is obtained by compressing expanded graphite at a pressure of 10 MPa or more and then crushing it to a particle size of 1 mm or less. In Example 3, 4% by mass of compressed expanded graphite was used, and it was shown to have excellent corrosion resistance and spalling resistance. However, even when using the compressed expanded graphite disclosed in Patent Document 2, the corrosion resistance and spalling resistance of the resulting magnesia-carbon brick were still insufficient. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2021-59482 [Patent Document 2] Japanese Patent Application Publication No. 8-81256 [Overview of the project] [Problems that the invention aims to solve]
[0006] The problem that this invention aims to solve is to provide a method for manufacturing magnesia carbon bricks that can further improve the corrosion resistance and corrosion spalling resistance of low-carbon magnesia carbon bricks. [Means for solving the problem]
[0007] The inventors of the present invention have focused on the particle size composition and content of compressed-expand graphite and magnesia in the refractory raw material mixture used in the method for producing low-carbon magnesia carbon bricks and have conducted various studies. As a result, they have found that by including 0.5% to 8% by mass of compressed-expand graphite with a particle size of less than 5 mm in the refractory raw material mixture, and further including 35% to 60% by mass of magnesia with a particle size of 1 mm to less than 5 mm and 30% to 60% by mass of magnesia with a particle size of less than 1 mm, a low-carbon magnesia carbon brick can be obtained that has improved corrosion resistance and spalling resistance due to a denser structure compared to when conventional compressed-expand graphite is used.
[0008] In other words, according to one aspect of the present invention, the following method for manufacturing a magnesia-carbon brick is provided. A method for producing magnesia carbon bricks, comprising adding an organic binder to a refractory raw material mixture containing 0.5% to 8% by mass of compressed and expanded graphite with a particle size of less than 5 mm, 35% to 60% by mass of magnesia with a particle size of 1 mm to less than 5 mm, and 30% to 60% by mass of magnesia with a particle size of less than 1 mm, wherein the total amount of graphite is 8% by mass or less and the total amount of graphite and magnesia is 91% by mass or more, kneading and molding the mixture, and then heat-treating it.
[0009] Here, compressed and expanded graphite is obtained by crushing expanded graphite that has been compressed into a sheet, as disclosed in Patent Documents 1 and 2. [Effects of the Invention]
[0010] According to the present invention, the corrosion resistance and spalling resistance of low-carbon magnesia carbon bricks can be simultaneously improved. For example, sufficient durability can be obtained when used in secondary refining equipment such as RH-type vacuum degassing furnaces, while also suppressing carbon pickup, improving steel quality, and minimizing heat loss. [Modes for carrying out the invention]
[0011] In this invention, compressed and expanded graphite with a particle size of less than 5 mm is used. If compressed and expanded graphite with a particle size of 5 mm or more is used, the packing performance of the clay during molding will be poor, resulting in a higher porosity after firing (hereinafter simply referred to as "firing") in a reducing atmosphere at 1400°C, which is the environment in which it is used in an actual furnace, and a decrease in corrosion resistance. If compressed and expanded graphite with a particle size of less than 3 mm is used, the packing performance of the clay during molding will be further improved, resulting in an even lower porosity after firing and improved corrosion resistance. When compressed and expanded graphite with a particle size of less than 3 mm is used, it is preferable that the particle size composition is such that particles with a particle size of 1 mm or more and less than 2 mm make up 25% by mass or more and 70% by mass or less. In other words, in this invention, it is preferable to use compressed and expanded graphite with a particle size of less than 3 mm that contains 25% by mass or more and 70% by mass or less particles with a particle size of 1 mm or more and less than 2 mm. When compressed and expanded graphite with such a particle size composition is used, the structure becomes even denser, and corrosion resistance is further improved.
[0012] In this invention, the content of compressible and expandable graphite is 0.5% by mass or more and 8% by mass or less in proportion to 100% by mass of the total amount of refractory raw material formulation. If the content of compressible and expandable graphite is less than 0.5% by mass, the spalling resistance is insufficient, and if it exceeds 8% by mass, the filling performance during molding deteriorates, resulting in a higher porosity after firing and a decrease in corrosion resistance.
[0013] In this invention, graphite other than compressible / expandable graphite can be used in combination with compressible / expandable graphite, provided that the total amount with compressible / expandable graphite is 8% by mass or less. Examples include scaly graphite and expanded graphite. The content of graphite other than compressible / expandable graphite can be 1% by mass or less (including 0) if higher corrosion resistance is desired.
[0014] In this invention, the content of magnesia with a particle size of 1 mm or more and less than 5 mm is 35% by mass or more and 60% by mass as a percentage of the total mass of the refractory raw material mixture. If the content of magnesia with a particle size of 1 mm or more and less than 5 mm is less than 35% by mass, the content of magnesia with a particle size of less than 1 mm becomes relatively high, resulting in poor packing of the clay during molding, and consequently, a higher porosity after firing and a decrease in corrosion resistance. Similarly, if the content of magnesia with a particle size of 1 mm or more and less than 5 mm exceeds 60% by mass, the packing of the clay during molding also becomes poor, resulting in a higher porosity after firing and a decrease in corrosion resistance.
[0015] In this invention, the content of magnesia with a particle size of less than 1 mm is 30% to 60% by mass in proportion to 100% by mass of the total amount of refractory raw material formulation. In both cases, if the content of magnesia with a particle size of less than 1 mm is less than 30% by mass or more than 60% by mass, the packing performance of the clay during molding deteriorates, resulting in a higher porosity after firing and a decrease in corrosion resistance. Furthermore, in this invention, by setting the content of magnesia with a particle size of 3 mm to less than 5 mm to 15% to 40% by mass, corrosion resistance and spalling resistance can be further improved. In this invention, in order to ensure sufficient corrosion resistance, the total amount of magnesia is 91% by mass or more. As for the magnesia used in this invention, those commonly used as raw materials for refractories can be used, such as electrofused magnesia and sintered magnesia.
[0016] In the present invention, in addition to the graphite and magnesia mentioned above, one or more of the following can be included in a total amount of 5% by mass or less: carbon black, fiber, glass, aluminum, aluminum alloy, silicon, boron carbide, silicon carbide, pitch, spinel, and alumina.
[0017] Here, the particle size referred to in the present invention is the size of the sieve mesh when refractory raw material particles are sieved and separated. For example, magnesia with a particle size of less than 1 mm refers to magnesia that passes through a sieve with a mesh size of 1 mm, and magnesia with a particle size of 1 mm or more refers to magnesia that does not pass through a sieve with a mesh size of 1 mm.
[0018] The magnesia carbon brick of the present invention can be manufactured by a general method for manufacturing unburned magnesia carbon bricks. That is, the magnesia carbon brick of the present invention can be obtained by adding an organic binder to the above-mentioned refractory raw material mixture, kneading, molding, and then performing heat treatment. The heat treatment temperature can be, for example, 150 to 600 °C, preferably 150 to 400 °C.
[0019] As described above, according to the method for manufacturing a magnesia carbon brick of the present invention, a low-carbon magnesia carbon brick excellent in spalling resistance and corrosion resistance can be obtained. Therefore, the magnesia carbon brick obtained by the present invention is particularly suitable for use in an RH type vacuum degassing furnace for treating extra-low carbon steel.
Examples
[0020] Table 1 shows the composition of the refractory raw material mixture in the examples and comparative examples of the present invention, and the physical properties of the obtained bricks. As the refractory raw materials used, magnesia was electrically fused magnesia with a MgO purity of 98% by mass, and the expanded graphite was sheet-shaped expanded graphite with a fixed carbon content of 95% by mass, which was pulverized and then classified into a predetermined particle size range by a sieve. Flaky graphite with a fixed carbon content of 95% was used. Table 2 shows the particle size composition of the expanded graphite used in Table 1.
[0021]
Table 1
[0022]
Table 2
[0023] Magnesia-carbon bricks were produced by adding 2% by mass of phenolic resin as an organic binder to the refractory raw material formulations shown in Table 1, kneading the mixture, molding it into a shape of 230 mm × 114 mm × 100 mm using an oil press, and then heat-treating it at a maximum temperature of 250°C for 5 hours. For each example of magnesia-carbon brick, the apparent porosity was measured, and its corrosion resistance and spalling resistance were evaluated.
[0024] For the measurement of apparent porosity, samples calcined under a reducing atmosphere at 1400°C were used. Specifically, a 50×50×50 mm sample was buried in coke breeze, heated to 1400°C in an electric furnace, held for 5 hours, and then allowed to cool naturally. After that, white kerosene was used as the solvent and the measurement was performed in accordance with JIS R2205.
[0025] Corrosion resistance was evaluated by a rotary erosion test. In the rotary erosion test, the inner surface of a drum with a horizontal rotation axis was lined with the test bricks, slag was added and heated to erode the brick surface. The heat source was an oxygen-propane burner, the test temperature was 1700°C, and the slag composition was CaO: 30% by mass, SiO2: 30% by mass, Al2O3: 20% by mass, FeO + Fe2O3: 20% by mass. The discharge and addition of slag was repeated 10 times every 30 minutes. After the test, the amount of erosion (mm) was determined from the difference in thickness (mm) before and after the test at the maximum erosion point of each brick. After the test, the erosion dimension (mm) of the maximum erosion point of each test brick was measured and expressed as an erosion index with the erosion dimension of the brick in "Comparative Example 1" listed in Table 1 set to 100. A erosion index of 90 or higher but less than 100 was rated as ◎ (Excellent), 100 or higher but less than 110 as ○ (Good), and 110 or higher as × (Poor).
[0026] Spalling resistance was evaluated using a 40 x 40 x 190 mm sample fired at 1400°C for 5 hours in a reducing atmosphere. This sample was then immersed in molten iron heated to 1600°C for 90 seconds, followed by 30 seconds of water cooling. This cycle was repeated five times. After the test, the sample was cut and the cross-section was observed to evaluate the degree of cracking. Specifically, a sample with no cracks or only very minor cracks after the test was evaluated as ◎ (Excellent), a sample with moderate cracks deemed to have sufficient heat spalling resistance for practical use was evaluated as ○ (Good), and a sample with significant cracking or spalling that prevented it from withstanding the five repeated tests and was deemed unsuitable for actual use was evaluated as × (Poor).
[0027] The overall evaluation was based on the evaluation results for corrosion resistance and spalling resistance. Specifically, if both corrosion resistance and spalling resistance evaluation results were ◎, it was evaluated as ◎ (Excellent); if at least one evaluation result was ○ and there were no × evaluation results, it was evaluated as ○ (Good); and if at least one evaluation result was ×, it was evaluated as × (Poor).
[0028] Examples 1 to 3, Example 5, and Example 9 all had different compression-expand graphite content, but they were within the scope of the present invention, resulting in low apparent porosity after firing, excellent corrosion resistance, and good spalling resistance. In contrast, Comparative Example 1 had a compression-expand graphite content of 0.1 mass%, which is below the lower limit of the present invention, resulting in poor spalling resistance. Comparative Example 2 had a compression-expand graphite content of 10 mass%, which is above the upper limit of the present invention, resulting in high apparent porosity after firing and poor corrosion resistance. Comparative Example 3 had a particle size of less than 7 mm for the compression-expand graphite, which is above the upper limit of the present invention, resulting in high apparent porosity after firing and poor corrosion resistance.
[0029] Examples 4 to 8 show cases where the particle size of the compressed and expanded graphite differs, but they fall within the scope of the present invention, and the apparent porosity after firing is low, the corrosion resistance is excellent, and the spalling resistance is also good. Of these, Examples 5 to 7 show cases where the particle size of the compressed and expanded graphite is less than 3 mm, and the composition contains 25% to less than 70% by mass of particles with a particle size of 1 mm or more and less than 2 mm, resulting in even better corrosion resistance.
[0030] Examples 10 to 12 differed in their magnesia content (1 mm to less than 5 mm), but all fell within the scope of the present invention, resulting in excellent corrosion resistance and spalling resistance. In contrast, Comparative Example 4 had a magnesia content (1 mm to less than 5 mm) below the lower limit of the present invention, resulting in poor corrosion resistance. Comparative Example 5 had a magnesia content (1 mm to less than 5 mm) above the upper limit of the present invention, resulting in poor corrosion resistance.
[0031] Examples 13 and 14 showed different magnesia content of less than 1 mm, but were within the scope of the present invention and yielded good results. Comparative Example 6 showed a magnesia content of less than 1 mm exceeding the upper limit of the present invention, resulting in poor corrosion resistance. Comparative Example 5, mentioned above, also showed a magnesia content of less than 1 mm below the lower limit of the present invention, resulting in poor corrosion resistance.
[0032] Example 15 did not contain magnesia in the form of 3 mm or more but less than 5 mm, but it was within the scope of the present invention and yielded good results. Example 16 contains pitch and boron carbide, and Example 17 further contains scaly graphite, but both were within the scope of the present invention and yielded good results.
Claims
1. A method for producing magnesia carbon bricks, comprising adding an organic binder to a refractory raw material mixture containing 0.5% to 8% by mass of compressed and expanded graphite with a particle size of less than 5 mm, 35% to 60% by mass of magnesia with a particle size of 1 mm to less than 5 mm, and 30% to 60% by mass of magnesia with a particle size of less than 1 mm, wherein the total amount of graphite is 8% by mass or less and the total amount of graphite and magnesia is 91% by mass or more, kneading and molding the mixture, and then heat-treating it.
2. A method for producing a magnesia-carbon brick according to claim 1, wherein the particle size of the compressed and expanded graphite is less than 3 mm.
3. The method for producing a magnesia carbon brick according to claim 2, wherein the compressed and expanded graphite contains 25% to 70% by mass of particles with a particle size of 1 mm or more and less than 2 mm, in proportion to 100% by mass of the total amount of compressed and expanded graphite.
4. A method for producing a magnesia carbon brick according to any one of claims 1 to 3, wherein the content of graphite other than compressed and expanded graphite is 1% by mass or less (including 0) in proportion to 100% by mass of the total amount of refractory raw material formulation.
5. A method for producing a magnesia carbon brick according to any one of claims 1 to 3, wherein the content of magnesia with a particle size of 3 mm or more and less than 5 mm is 15% by mass or more and 40% by mass or less, in proportion to 100% by mass of the total amount of refractory raw material compound.
6. A method for producing a magnesia carbon brick according to claim 4, wherein the content of magnesia with a particle size of 3 mm or more and less than 5 mm is 15% by mass or more and 40% by mass or less, in proportion to 100% by mass of the total amount of refractory raw material compound.