A multiphase ceramic side sealing plate for twin-roll thin strip continuous casting and its preparation method

Abstract

This invention belongs to the field of high-temperature structural ceramics technology, specifically relating to a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting and its preparation method. The multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is characterized by the following raw materials and weight percentages: boron nitride 50-60%, alumina 30-35%, calcium carbonate 3-5%, and boron carbide 5-10%; wherein the boron nitride is available in two sizes, with the larger particle size d... 50 >10μm, addition amount 40%~50%, small particle size BN flakes d 50 >1μm, added at 10%–15%; the alumina is nano-alumina, d 50 <1μm; Nano calcium carbonate, d 50 <1μm, boron carbide is 1000 mesh. This invention gives it the characteristics of low firing temperature, excellent high-temperature mechanical properties, and good oxidation resistance. In particular, it can solve the problem of insufficient resistance to oxidation and wear of the initial billet shell in the side sealing plate, while meeting the service requirements of thin strip continuous casting for the side sealing plate to resist molten steel erosion, resist molten steel thermal shock, and self-lubrication.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature structural ceramics technology, specifically relating to a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting and its preparation method. Background Technology

[0002] Thin strip continuous casting is an important means for the steel industry to achieve carbon reduction. Shagang Group has further innovated based on the introduction of Nucor Steel's twin-roll thin strip technology and now has four production lines with the best production indicators in the world, which have been commercially operated. At the same time, functional refractory materials support the efficient operation of modern metallurgy, especially in the thin strip continuous casting process. The flow distributor and side sealing plate greatly support the operation of the thin strip continuous casting process. The side sealing plate of thin strip continuous casting is the core of the side sealing technology. Its main function is to cooperate with the casting roll to form a molten pool, prevent the side leakage of molten steel, and requires excellent self-lubricating properties and thermal shock resistance, as well as resistance to molten steel corrosion and strip friction and wear.

[0003] The materials used for side sealing plates have undergone a series of evolutions. Currently, BN-ZrO2-SiC hot-pressed ceramic has become the mainstream material for side sealing plates because it combines thermal shock resistance, molten steel corrosion resistance, and friction and wear resistance. However, the following problems still exist:

[0004] (1) The material has a high firing temperature. Although zirconium oxide can reduce the firing temperature of BN, the effect is not obvious. However, the firing temperature is generally 1600℃, and the preparation cost is high.

[0005] (2) Although the introduction of liquid phase sintering aid can significantly reduce the sintering temperature of the material, it can still remain in BN ceramic materials, thus affecting the high-temperature service performance, especially the resistance to molten steel corrosion.

[0006] (3) The side sealing plate has a high thermal conductivity and a thickness of (25~35mm). The temperature gradient between the cold and hot surfaces is large, which makes it easy for cold steel and slag to form on the hot surface.

[0007] (4) Studies show that the oxidation of BN is a key step in the corrosion of molten steel and the wear of strip. The oxidation resistance of BN ceramic side sealing plates needs to be improved.

[0008] Currently, the number of consecutive casting cycles for thin strip continuous casting is significantly lower than that for traditional slab continuous casting, mainly due to the limited 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

[0009] This invention proposes a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting and its preparation method, which has the characteristics of low firing temperature, excellent high-temperature mechanical properties and good oxidation resistance. In particular, it can solve the problem of insufficient resistance to oxidation and wear of the initial billet shell of the side sealing plate, and at the same time meet the service requirements of thin strip continuous casting for the side sealing plate to resist steel erosion, resist steel thermal shock and self-lubrication.

[0010] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0011] A multiphase ceramic side sealing plate for twin-roll thin strip continuous casting, wherein the raw materials and weight percentages for preparing the multiphase ceramic side sealing plate are: boron nitride 50-60%, alumina 30-35%, calcium carbonate 3-5%, and boron carbide 5-10%; wherein the boron nitride is available in two sizes, with the larger particle size d 50 >10μm, addition amount 40%~50%, small particle size BN flakes d 50 >1μm, added at 10%–15%; the alumina is nano-alumina, d 50 <1μm; Nano calcium carbonate, d 50 <1μm, boron carbide is 1000 mesh.

[0012] The dispersants used for boron nitride and alumina are GLYDOL N1055 and FS20, respectively, and the amount of each is 0.5% and 0.1% of the weight of the dispersed raw materials, respectively.

[0013] A method for preparing a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is as follows: small-particle boron nitride, nano-alumina, nano-calcium carbonate, and GLYDOL are mixed according to a specified ratio. N1055, FS20, and deionized water comprising 45-55% of the total mass of the above solids and large-particle boron nitride were added to a stirred ball mill for ball milling: ball-to-material weight ratio >2, milling time 5-10 hours to ensure dispersion of raw materials, especially nano-alumina and calcium carbonate. Then, large-particle boron nitride was added to the stirred ball mill for ball milling for 30-60 minutes. The dispersed slurry was then dried in a spray dryer to obtain powder with a particle size ≤0.5mm. The raw materials were then placed in a steel mold for briquetting. The initial cold pressing pressure was 60-70 MPa. The pressure surface was then reversed for another cold pressing at 120-150 MPa. Finally, the pressure surface was reversed again and the green body was placed into a corresponding graphite mold for hot pressing and sintering. The vacuum degree in the hot pressing furnace was <100 Pa.

[0014] The hot-pressing sintering process for multiphase ceramic side sealing plates is as follows: First stage: heating time 30-60 min, temperature rise to 200℃ and hold for 2-4 h; Second stage: heating time 50-150 min, temperature rise to 1000℃ and hold for 2-4 h, pressure 10 MPa; Third stage: heating time 50-150 min, temperature rise to 1400-1500℃ and hold for 1-4 h, pressure 20-30 MPa.

[0015] This invention proposes a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting and its preparation method. It adopts a method of cold pressing followed by hot pressing to avoid the directional arrangement of boron nitride. Because the flake-like boron nitride will produce a layered arrangement during the sintering process, especially the larger the flakes, the more obvious the layered effect. Therefore, the side sealing plate usually cracks in the layered direction when subjected to thermal shock. The directional arrangement occurs during cold pressing, but the stress surface is controlled during hot pressing, and the original directional arrangement is effectively broken, avoiding the layered effect.

[0016] During hot-pressing sintering at 800–900℃, the calcium carbonate in the multiphase ceramic side sealing plate undergoes phased decomposition. The resulting CaO forms a low-melting-point substance with a small amount of B2O3 in BN. The amount of liquid phase is significantly increased compared to the original amount of B2O3. The liquid phase can further promote the dissolution and precipitation of small-diameter boron nitride flakes and precipitate around large-diameter boron nitride flakes, continuously promoting the sintering and growth of boron nitride. The large number of large-diameter flake-shaped boron nitride particles are interspersed and interwoven, effectively improving the toughness of the BN-based ceramic side sealing plate, thereby enhancing its thermal shock resistance.

[0017] During the hot-pressing sintering stage above 1300℃ in the multiphase ceramic side sealing plate, under a reducing atmosphere, the calcium borosilicate glass phase significantly decomposes and volatilizes, while 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 resistance to hydration and the highest melting point in the CaO-Al2O3 binary system. The anisotropy of CA6 grain growth and the average coefficient of thermal expansion similar to Al2O3, and its lamellar crystal form similar to boron nitride, interpenetrating each other, can improve the mechanical properties and toughness of the material. At the same time, due to the high melting point of CA6 (melting temperature of about 1830 ℃), it has good stability under high-temperature reducing atmosphere and low solubility in iron oxide slag, among other excellent properties. Secondly, CA6 has a low thermal conductivity, and the large amount of calcium hexaaluminate formed inside the multiphase ceramic side sealing plate can effectively reduce the thermal conductivity of the side sealing plate, thereby inhibiting the formation of cold steel or slag clumps on the hot surface (the surface in contact with molten steel) of the side sealing plate.

[0018] This invention introduces a large number of large-particle-size boron nitride flakes to improve the ceramic toughness and resistance to thermal shock from molten steel in the side sealing plate. Simultaneously, multi-directional pressing allows the boron nitride flakes to interweave, eliminating the layered effect. The introduction of B4C enhances the oxidation resistance of the side sealing plate. During service, the BN or B4C on the hot surface of the side sealing plate (the contact area between molten steel and strip) oxidizes to form B2O3. When the system contains a significant amount of Al2O3, it can form aluminoborate, effectively slowing down the volatilization of B2O3, thereby mitigating or inhibiting the continued oxidation process, particularly the formation of high-melting-point 9Al2O3. *2B2O3 can enhance the resistance of the modified layer to erosion or impact caused by molten steel. The temperature of the solidified shell area of ​​the initial strip is relatively low. After oxidation, BN and B4C exist in the form of molten B2O3. The multiphase ceramic side sealing plate of the present invention contains a large amount of 9Al2O3. After forming high-melting-point borosilicate, it can further improve the resistance to mechanical wear. Once 9Al2O3 *2B2O3 is formed in the strip area of ​​the side sealing plate, it can also significantly improve the resistance to mechanical wear. Therefore, it can reduce the wear rate and thus increase the service life of the side sealing plate, increasing the service life of the side sealing plate from the current 6 heats to more than 9 heats. It can be seen from the above that the multiphase ceramic side sealing plate has a low firing temperature and excellent high-temperature service performance, and has promotion and application value. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the pressing of the multiphase ceramic side sealing plate in the preparation method of the present invention.

[0020] Figure 2 The diagram shows the B2O3-Al2O3 phase. Detailed Implementation

[0021] The present invention will be described in detail with reference to the accompanying drawings and specific embodiments: Example 1:

[0022] A method for preparing a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is as follows: First, the proportions are prepared according to the table below:

[0023]

[0024] According to the proportions in the table, small-particle boron nitride, nano-alumina, nano-calcium carbonate, GLYDOL N1055, FS20, and deionized water are added to a stirred ball mill for stirring and ball milling (ball weight ratio 2) for 5 hours. Then, large-particle boron nitride is added to the stirred ball mill for ball milling for 30 minutes. The dispersed slurry is then dried in a spray dryer to obtain powder with a particle size ≤0.5mm. The raw materials are then placed in a steel mold for pressing, with cold pressing twice on different surfaces at pre-pressures of 60MPa and 120MPa. Finally, the green body is placed in a corresponding graphite mold (on the other surface during hot pressing) for hot pressing and sintering. The vacuum degree in the hot pressing furnace is <100Pa, the maximum firing temperature is 1450℃, the holding time is 30MPa, and the pressure is 30MPa. After cooling in the furnace, the product is CNC machined to the required dimensions to obtain the multiphase ceramic side sealing plate. Example 2:

[0025] The preparation method of the multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is as follows: First, the proportions are prepared according to the following table:

[0026]

[0027] According to the proportions in the table, small-particle boron nitride, nano-alumina, nano-calcium carbonate, GLYDOL N1055, FS20, and deionized water are added to a stirred ball mill for ball milling (ball-to-material weight ratio 3) for 10 hours. Then, large-particle boron nitride is added to the stirred ball mill and milled for 60 minutes. The dispersed slurry is then dried in a spray dryer to obtain powder with a particle size ≤0.5mm. The raw materials are then placed in a steel mold for pressing, with cold pressing twice on different sides at pre-pressures of 70MPa and 150MPa respectively. Finally, the green body is placed in a corresponding graphite mold (with the other side facing up during hot pressing) for hot pressing and sintering. The vacuum degree in the hot pressing furnace is <100Pa, the maximum firing temperature is 1400℃, the holding time is 20MPa, and the pressure is 20MPa. After cooling in the furnace, the product is CNC machined to the required dimensions to obtain the multiphase ceramic side sealing plate. Example 3:

[0028] The preparation method of the multiphase ceramic side sealing plate for twin-roll thin strip continuous casting is as follows: First, the proportions are prepared according to the following table:

[0029]

[0030] According to the proportions in the table, small-particle boron nitride, nano-alumina, nano-calcium carbonate, GLYDOL N1055, FS20, and deionized water are added to a stirred ball mill for stirring and ball milling (ball-to-material weight ratio 4) for 8 hours. Then, large-particle boron nitride is added to the stirred ball mill and milled for 40 minutes. The dispersed slurry is then dried in a spray dryer to obtain powder with a particle size ≤0.5mm. The raw materials are then placed in a steel mold for pressing, with cold pressing twice on different sides at pre-pressures of 65MPa and 130MPa respectively. Finally, the green body is placed in a corresponding graphite mold (with the other side facing up during hot pressing) for hot pressing and sintering. The vacuum degree in the hot pressing furnace is <100Pa, the maximum firing temperature is 1500℃, the holding time is 25MPa, and the pressure is 25MPa. After cooling in the furnace, the product is CNC machined to the required dimensions to obtain the multiphase ceramic side sealing plate.

Claims

1. A multiphase ceramic side sealing plate for twin-roll thin strip continuous casting, characterized in that: The raw materials and weight percentages for preparing the multiphase ceramic side plate sealing plate are: boron nitride 50-60%, alumina 30-35%, calcium carbonate 3-5%, and boron carbide 5-10%; among which, the boron nitride comes in two sizes, with the larger particle size d... 50 >10μm, addition amount 40%~50%, small particle size BN flakes d 50 >1μm, added at 10%–15%; the alumina is nano-alumina, d 50 <1μm; Nano calcium carbonate, d 50 <1μm, boron carbide is 1000 mesh; the above raw materials are placed in a steel mold for pressing, the initial cold pressing pre-pressing pressure is 60-70MPa, the pressure surface is turned over and cold pressing is performed again, the pressure is 120-150MPa, and finally the pressure surface is turned over again and the green blank is placed into the corresponding graphite mold for hot pressing and sintering, the vacuum degree in the hot pressing furnace is <100Pa.

2. The multiphase ceramic side sealing plate for twin-roll thin strip continuous casting as described in claim 1, characterized in that: The dispersants used for boron nitride and alumina are GLYDOL N1055 and FS20, respectively, and the amount of each is 0.5% and 0.1% of the weight of the dispersed raw materials, respectively.

3. The method for preparing a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting as described in any one of claims 1-2, characterized in that: According to the specified ratio, small-particle-size 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-size boron nitride are added to a stirred ball mill for stirring and ball milling: ball-to-material weight ratio > 2, ball milling time 5-10 hours, to ensure the dispersion of raw materials, especially nano-alumina and calcium carbonate. Then, large-particle-size boron nitride is added to the stirred ball mill for ball milling for 30-60 minutes. The dispersed slurry is then dried in a spray dryer to obtain powder with a particle size ≤ 0.5 mm. The raw materials are placed in a steel mold for briquetting. The initial cold pressing pressure is 60-70 MPa. The pressure surface is then reversed for cold pressing again at a pressure of 120-150 MPa. Finally, the pressure surface is reversed again and the green body is placed into a corresponding graphite mold for hot pressing and sintering. The vacuum degree in the hot pressing furnace is < 100 Pa.

4. The method for preparing a multiphase ceramic side sealing plate for twin-roll thin strip continuous casting as described in claim 3, characterized in that: The hot-pressing sintering process for multiphase ceramic side sealing plates is as follows: First stage: heating time 30-60 min, temperature rise to 200℃ and hold for 2-4 h; Second stage: heating time 50-150 min, temperature rise to 1000℃ and hold for 2-4 h, pressure 10 MPa; Third stage: heating time 50-150 min, temperature rise to 1400-1500℃ and hold for 1-4 h, pressure 20-30 MPa.

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