Multi-phase ceramic side sealing plate for twin-roll thin-strip continuous casting and preparation method of multi-phase ceramic side sealing plate

Abstract

The invention belongs to the technical field of high-temperature structural ceramics, and particularly relates to a multiphase ceramic side sealing plate for twin-roll thin-strip continuous casting and a preparation method of the multiphase ceramic side sealing plate. The invention discloses a multiphase ceramic side sealing plate for twin-roll thin-strip continuous casting. The multiphase ceramic side sealing plate is characterized by being prepared from the following raw materials in percentage by weight: 50-60% of boron nitride, 30-35% of aluminum oxide, 3-5% of calcium carbonate and 5-10% of boron carbide, wherein boron nitride has two sizes, the large particle size d50 is greater than 10 [mu] m, the addition amount is 40-50%, the small particle size BN scale d50 is greater than 1 [mu] m, and the addition amount is 10-15%; the aluminum oxide is nano aluminum oxide, and d50 is less than 1 [mu] m; the d50 of the nano calcium carbonate is less than 1 [mu] m, and the boron carbide is 1000 meshes. The side sealing plate has the advantages of being low in firing temperature, excellent in high-temperature mechanical property and good in oxidation resistance, particularly can solve the problem that the side sealing plate is poor in initial blank shell oxidation wear resistance, and meanwhile meets the service requirements of thin-strip continuous casting on molten steel erosion resistance, molten steel thermal shock resistance, self-lubrication and the like of the side sealing plate.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature structural ceramics, and in particular relates to a multiphase ceramic side sealing plate for twin-roller thin strip continuous casting and a preparation method thereof. Background Art

[0002] Thin strip continuous casting is an important means for the steel industry to achieve carbon reduction. Shagang Group has made further innovations based on the introduction of Nucor Steel's twin-roll thin strip technology. It now has 4 production lines with the best production indicators in the world and has achieved commercial operation. At the same time, functional refractory materials support the efficient operation of modern metallurgy, especially the thin strip continuous casting process. The flow distributor and side sealing plates greatly support the operation of the thin strip continuous casting process. The thin strip continuous casting side sealing plate is the core of the side sealing technology. Its main function is to cooperate with the casting rollers to form a molten pool to prevent the side leakage of molten steel. It is required to have excellent self-lubrication and thermal shock resistance, and must also be resistant to erosion by molten steel and resistance to friction and wear of the strip.

[0003] The material of the side sealing plate has undergone a series of evolutions. At present, BN-ZrO2-SiC hot-pressed ceramics have become the mainstream for the side sealing plate, because it has both thermal shock resistance, steel liquid corrosion resistance, and friction and wear resistance. However, there are still the following problems: (1) The sintering temperature of the material is high. Although zirconium oxide can reduce the sintering temperature of BN, the effect is not obvious. However, the sintering temperature is generally 1600°C, and the preparation cost is high.

[0004] (2) Although the introduction of liquid phase sintering aids can significantly reduce the sintering temperature of the material, some residues can still remain in the BN ceramic material, thereby affecting the high temperature service performance, especially the resistance to erosion by molten steel.

[0005] (3) The thermal conductivity of the side sealing plate is high, and the thickness of the side sealing plate is (25~35mm). The temperature gradient between the cold surface and the hot surface is large, which makes it easy for cold steel and slag to form on the hot surface.

[0006] (4) Studies have shown that the oxidation of BN is a key step in steel liquid corrosion and strip wear. The oxidation resistance of the current BN ceramic side sealing plate needs to be improved.

[0007] At present, the number of continuous casting furnaces of thin strip continuous casting is significantly lower than that of traditional slab continuous casting, which is mainly restricted by the service life of the side sealing plates. Therefore, improving the service performance of the side sealing plates is of great significance to the development of the thin strip continuous casting industry. Summary of the invention

[0008] The present invention proposes a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting and a preparation method thereof, which have the characteristics of low firing temperature, excellent high-temperature mechanical properties and good anti-oxidation performance. In particular, it can solve the problem that the side sealing plate has insufficient resistance to oxidation and wear of the primary billet shell, and at the same time meet the service requirements of thin strip continuous casting for the side sealing plate to resist erosion by molten steel, resist thermal shock of molten steel, and self-lubrication.

[0009] The present invention adopts the following technical solutions to achieve the above-mentioned invention objectives: A composite ceramic side sealing plate for twin-roller thin strip continuous casting, the raw materials and weight percentages of the composite ceramic side sealing plate are: 50-60% boron nitride, 30-35% alumina, 3-5% calcium carbonate, and 5-10% boron carbide; wherein the boron nitride has two sizes, wherein the largest particle size is d 50 >10μm, addition amount 40%~50%, small particle size BN flake d 50 >1μm, added in an amount of 10% to 15%; the alumina is nano alumina, d 50 <1μm; nano calcium carbonate, d 50 <1μm, boron carbide is 1000 mesh.

[0010] The dispersants used for boron nitride and aluminum oxide are GLYDOL N1055 and FS20 respectively, and the added amounts of the two account for 0.5% and 0.1% of the weight of the dispersed raw materials respectively.

[0011] A method for preparing a composite ceramic side sealing plate for twin-roller thin strip continuous casting comprises: mixing small-particle boron nitride, nano-aluminum oxide, nano-calcium carbonate, GLYDOL N1055, FS20, and deionized water accounting for 45-55% of the total mass of the above solids and large-particle boron nitride are put into a stirring ball mill for stirring ball milling: the ball-to-material weight ratio is greater than 2, and the ball milling time is 5-10 hours to ensure that the raw materials can be dispersed, especially the dispersion of nano-alumina and calcium carbonate, and then large-particle boron nitride is added to the stirring ball mill for ball milling, and the ball milling time is 30-60 minutes; then the above-dispersed slurry is dried by a spray dryer to obtain a powder of ≤0.5mm; then the above-mentioned raw materials are placed in a steel mold for briquetting, and the pre-pressing pressure of the initial cold pressing is 60-70MPa, and the pressure surface is turned to perform cold pressing again, with a pressure of 120-150Mpa, and finally the pressure surface is turned again to place the green body into a corresponding graphite mold for hot pressing sintering, and the vacuum degree in the hot pressing furnace is less than 100pa.

[0012] The hot pressing sintering system of the composite ceramic side sealing plate is as follows: the first stage: heating time 30-60min, the temperature is raised to 200℃ and then kept warm for 2-4h; the second stage: heating time 50-150min, the temperature is raised to 1000℃ and then kept warm for 2-4h, the pressure is 10MPa; the third stage: heating time 50-150min, the temperature is raised to 1400-1500℃ and then kept warm for 1-4h, the pressure is 20-30MPa.

[0013] The present invention proposes a composite ceramic side sealing plate for twin-roll thin strip continuous casting and a preparation method thereof, which adopts a method of cold pressing first and then hot pressing to avoid directional arrangement of boron nitride; because flaky boron nitride will produce layered arrangement during the sintering process, especially the larger the scale, the more obvious the layered effect, so the side sealing plate usually has cracks in the layered direction when subjected to thermal shock; directional arrangement occurs during cold pressing, and the force-bearing surface is regulated during hot pressing, so that the original directional arrangement is effectively broken to avoid the layer effect; When the composite ceramic side sealing plate is hot-pressed and sintered at 800-900°C, the calcium carbonate contained in it decomposes in stages. The CaO formed after the decomposition forms a low-melting product with a small amount of B2O3 in BN. The amount of liquid phase is significantly increased compared with the original amount of B2O3. The liquid phase can further promote the dissolution and precipitation of small-particle boron nitride flakes, and precipitate around large-particle boron nitride flakes, continuously promoting the sintering and growth of boron nitride; a large number of large-particle flaky boron nitride are staggered and interspersed, which effectively improves the toughness of the BN-based ceramic side sealing plate, thereby improving the thermal shock resistance.

[0014] When the composite ceramic side sealing plate is hot-pressed and sintered at a temperature above 1300°C, the calcium boron glass phase significantly decomposes and volatilizes in a reducing atmosphere, and a large amount of CaO in the system undergoes a solid solution reaction with corundum: CaO+Al2O3= CaO*6Al2O3 (abbreviated as CA6), which is the binary compound with the best hydration resistance and the highest melting point in the CaO-Al2O3 binary system; the anisotropy of CA6 grain growth and the average thermal expansion coefficient similar to Al2O3, its lamellar crystal shape is similar to boron nitride, and they are interlaced with each other, which can improve the mechanical properties and toughness of the material; at the same time, due to the high melting point of CA6 (melting temperature is about 1830°C), it has a series of excellent properties such as good stability in a high-temperature reducing atmosphere and low solubility in iron oxide-containing slag; secondly, the thermal conductivity of CA6 is low, and the large amount of calcium hexaaluminate formed inside the composite ceramic side sealing plate can effectively reduce the thermal conductivity of the side sealing plate, thereby inhibiting the formation of cold steel or slag on the hot surface (contact surface with molten steel) of the side sealing plate.

[0015] The present invention introduces a large number of large-particle boron nitride flakes to improve the ceramic toughness and resistance to thermal shock of molten steel of the side sealing plate, and adopts multi-directional pressing to make the boron nitride flakes interpenetrate with each other and eliminate the layered effect; the introduced B4C improves the oxidation resistance of the side sealing plate, and during the service process, the BN or B4C on the hot surface of the side sealing plate (the contact area between the molten steel and the strip) is oxidized to form B2O3, and when the system contains more Al2O3, aluminum borate can be formed, which can effectively slow down the volatilization of B2O3, thereby slowing down or inhibiting the continuous oxidation, especially forming 9Al2O3 with a high melting point. *2B2O3 can enhance the resistance of the metamorphic layer to erosion or scouring caused by molten steel; the temperature of the solidified shell area of ​​the primary strip is relatively low, and BN and B4C exist in the form of molten B2O3 after oxidation. The composite ceramic side sealing plate of the present invention contains a large amount of 9Al2O3. After the formation of high-melting-point boroaluminate, the mechanical wear resistance can be further improved. Once 9Al2O3 *2B2O3 is formed in the side sealing plate strip area, the mechanical wear resistance can be significantly improved, thereby reducing the wear rate and thereby increasing the service life of the side sealing plate, so that the service life of the side sealing plate is increased from the existing 6 furnaces to more than 9 furnaces; it can be seen from the above that the composite ceramic side sealing plate has a low sintering temperature and excellent high-temperature service performance, and has a value for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of pressing the composite ceramic side sealing plate in the preparation method of the present invention.

[0017] Figure 2 This is the B2O3-Al2O3 phase diagram. DETAILED DESCRIPTION

[0018] The present invention is described in detail with reference to the accompanying drawings and specific embodiments: Embodiment 1:

[0019] A method for preparing a composite ceramic side sealing plate for twin-roll thin strip continuous casting is as follows: first, the proportions are made according to the following table:

[0020] According to the proportion in the table, small-particle boron nitride, nano-alumina, nano-calcium carbonate, GLYDOL N1055, FS20 and deionized water are put into a stirring ball mill for stirring ball milling (ball-to-material weight ratio 2) for 5 hours, and then large-particle boron nitride is added to the stirring ball mill for ball milling for 30 minutes; then the dispersed slurry is dried by a spray dryer to obtain a powder of ≤0.5 mm; then the above raw materials are placed in a steel mold for briquetting, and cold pressed twice in different directions, with pre-pressures of 60 MPa and 120 MPa respectively, and finally the green body is placed in a corresponding graphite mold (the other direction during hot pressing) for hot pressing sintering, the vacuum degree in the hot pressing furnace is <100 pa, the maximum firing temperature is 1450°C, the insulation time, and the pressure is 30 MPa; after cooling with the furnace, CNC machining is performed according to the size to finally obtain a composite ceramic side sealing plate product. Embodiment 2:

[0021] The method for preparing the composite ceramic side sealing plate for twin-roll thin strip continuous casting is as follows: firstly, the proportions are made according to the following table:

[0022] According to the proportion in the table, small-particle boron nitride, nano-alumina, nano-calcium carbonate, GLYDOL N1055, FS20, and deionized water are put into a stirring ball mill for stirring ball milling (ball-to-material weight ratio 3), the ball milling time is 10h, and then large-particle boron nitride is added to the stirring ball mill for ball milling, and the ball milling time is 60min; then the above-dispersed slurry is dried by a spray dryer to obtain a powder of ≤0.5mm; then the above-mentioned raw materials are placed in a steel mold for block pressing, cold pressing twice in different directions, the pre-pressure is 70MPa and 150Mpa respectively, and finally the green body is placed in the corresponding graphite mold (the other direction surface during hot pressing) for hot pressing sintering, the vacuum degree in the hot pressing furnace is <100pa, the maximum firing temperature is 1400℃, the heat preservation time, and the pressure is 20Mpa. After cooling with the furnace, CNC machining is performed according to the size to finally obtain a composite ceramic side sealing plate product. Embodiment 3:

[0023] The method for preparing the composite ceramic side sealing plate for twin-roll thin strip continuous casting is as follows: firstly, the proportions are made according to the following table:

[0024] According to the proportion in the table, small-particle boron nitride, nano-alumina, nano-calcium carbonate, GLYDOL N1055, FS20, and deionized water are put into a stirring ball mill for stirring ball milling (ball-to-material weight ratio 4), ball milling time 8h, and then large-particle boron nitride is added to the stirring ball mill for ball milling, and the ball milling time is 40min; then the above-dispersed slurry is dried by a spray dryer to obtain a powder of ≤0.5mm; then the above-mentioned raw materials are placed in a steel mold for block pressing, cold pressing twice in different directions, the pre-pressure is 65MPa and 130Mpa respectively, and finally the green body is placed in the corresponding graphite mold (the other direction surface during hot pressing) for hot pressing sintering, the vacuum degree in the hot pressing furnace is <100pa, the maximum firing temperature is 1500℃, the insulation time, and the pressure is 25Mpa. After cooling with the furnace, CNC machining is performed according to the size to finally obtain a composite ceramic side sealing plate product.

Claims

1. A composite ceramic side sealing plate for twin-roller thin strip continuous casting, characterized in that: The raw materials and weight percentages of the composite ceramic side plate sealing plate are: 50-60% boron nitride, 30-35% alumina, 3-5% calcium carbonate, and 5-10% boron carbide; the boron nitride has two sizes, the largest of which is d 50 >10μm, addition amount 40%~50%, small particle size BN flake d 50 >1μm, added in an amount of 10% to 15%; the alumina is nano alumina, d 50 <1μm; nano calcium carbonate, d 50 <1μm, boron carbide is 1000 mesh.

2. A composite ceramic side sealing plate for twin-roll thin strip continuous casting as claimed in claim 1, characterized in that: The dispersants used for boron nitride and aluminum oxide are GLYDOL N1055 and FS20 respectively, and the added amounts of the two account for 0.5% and 0.1% of the weight of the dispersed raw materials respectively.

3. A method for preparing a composite ceramic side sealing plate for twin-roll thin strip continuous casting according to any one of claims 1 to 2, characterized in that: According to the proportion, small-particle boron nitride, nano-alumina, nano-calcium carbonate, GLYDOL N1055, FS20, and deionized water accounting for 45-55% of the total mass of the above solids and large-particle boron nitride are put into a stirring ball mill for stirring and ball milling: the ball-to-material weight ratio is greater than 2, and the ball milling time is 5-10 hours to ensure that the raw materials can be dispersed, especially the dispersion of nano-alumina and calcium carbonate, and then the large-particle boron nitride is added to the stirring ball mill for ball milling, and the ball milling time is 30-60 minutes; then the above-dispersed slurry is dried by a spray dryer to obtain a powder of ≤0.5mm; then the above-mentioned raw materials are placed in a steel mold for briquetting, the initial cold pressing pre-pressing pressure is 60-70MPa, the pressure surface is turned around for cold pressing again, the pressure is 120-150Mpa, and finally the pressure surface is turned around to place the green body into a corresponding graphite mold for hot pressing and sintering, and the vacuum degree in the hot pressing furnace is less than 100pa.

4. A method for preparing a composite ceramic side sealing plate for twin-roll thin strip continuous casting as claimed in claim 3, characterized in that: The hot pressing sintering system of the composite ceramic side sealing plate is as follows: the first stage: heating time 30-60min, the temperature is raised to 200℃ and then kept warm for 2-4h; the second stage: heating time 50-150min, the temperature is raised to 1000℃ and then kept warm for 2-4h, the pressure is 10MPa; the third stage: heating time 50-150min, the temperature is raised to 1400-1500℃ and then kept warm for 1-4h, the pressure is 20-30MPa.

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