High-strength refractory material for VD furnace and preparation process of high-strength refractory material
By introducing zirconia-coated sapphire composite and gradient pore structure into the refractory materials for VD furnaces, the problems of thermal shock damage and insufficient strength of the refractory materials for VD furnaces have been solved. This has achieved a synergistic effect of high strength, low thermal conductivity, thermal shock resistance and erosion resistance, thus extending the furnace lining life and improving the operational stability of the VD furnace.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI PENGPU SPECIAL REFRACTORY MATERIAL FACTORY
- Filing Date
- 2026-02-12
- Publication Date
- 2026-05-12
AI Technical Summary
Existing refractory materials for VD furnaces are prone to thermal shock damage when subjected to frequent fluctuations in high and low temperatures, have insufficient thermal insulation performance, and lack strength under complex working environments. This results in a short service life of the furnace cover, unstable molten steel temperature, and affects the quality of the steel.
Using zirconia-zirconia composite material as aggregate, combined with sodium silicate-treated sisal fiber and nano-silica-coated ammonium oxalate, a gradient pore structure is formed through a composite pore-forming agent to improve the material's thermal shock resistance and corrosion resistance.
It achieves synergistic optimization of high strength, low thermal conductivity, thermal shock resistance and erosion resistance, which extends the furnace lining life, reduces energy consumption, and ensures the stable operation of the VD furnace.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of refractory materials technology, and relates to a high-strength refractory material for VD furnaces and its preparation process. Background Technology
[0002] Vacuum distillation (VD) is an important method in modern steel refining technology. It involves placing molten steel, partially melted in an electric furnace or converter, into a sealed vacuum vessel. Through vacuuming and bottom-blowing argon agitation, impurities and gases are removed from the molten steel, improving its purity and the quality of the finished steel. During VD refining, the furnace lid plays a crucial role. On one hand, it must protect other equipment inside the furnace from damage caused by the high-temperature radiation of the molten steel and slag splashing. On the other hand, it must minimize heat loss, maintain a stable furnace temperature, and prevent excessive temperature drops in the molten steel during degassing.
[0003] However, existing refractory materials for VD furnaces have many problems. For example, when traditional refractory materials experience frequent fluctuations in high and low temperatures, the thermal stress changes can easily cause thermal shock damage to the furnace cover castable lining, affecting its long-term stability. Furthermore, insufficient insulation performance leads to significant heat energy waste, exacerbates furnace temperature instability, increases energy consumption, and causes uneven steel temperature and composition fluctuations, affecting the final steel quality. In addition, some refractory materials lack sufficient strength, and when subjected to complex working environments such as high-temperature airflow, high-temperature slag splashing, chemical gas erosion, and mechanical vibration, they are prone to steel shell deformation, internal refractory material detachment, and spalling, reducing the furnace cover's service life and resulting in longer VD furnace downtime and reduced utilization. Therefore, there is an urgent need to develop a high-strength refractory material for VD furnaces and its preparation process. Summary of the Invention
[0004] The purpose of this invention is to provide a high-strength refractory material for VD furnaces and its preparation process, which has the characteristics of high strength, excellent thermal shock resistance and good slag erosion resistance.
[0005] The objective of this invention can be achieved through the following technical solutions: A high-strength refractory material for VD furnaces, the formulation of which is as follows (in parts by weight): 65-75 parts of sintered mullite aggregate, 10-12 parts of fused alumina-zirconia composite material 8-10 parts of alumina micro powder 4-6 parts of calcium aluminate cement 2-3 parts of silica powder 0.05~0.1 parts of composite pore-forming agent, Water-reducing agent 0.12~0.25 parts, The preparation method of the fused alumina-zirconia composite is as follows: S1-1: Place the fine powder of premium slag and the micro powder of zirconium oxide in a mixer and mix for 30-60 min to obtain a mixed powder. Add a polyvinyl alcohol solution with a mass concentration of 4-8% to the mixed powder and granulate in a granulator to obtain wet granules. S1-2: After drying the wet particles at 100~120 ℃ for 2~4 h, the temperature is raised to 1100~1300 ℃ at a rate of 2~5 ℃ / min and held for 1~3 h, and then naturally cooled to room temperature to obtain the fused alumina-zirconia composite material.
[0006] As a preferred technical solution of the present invention, the high-grade sapphire fine powder and zirconium oxide micro powder in S1-1 are mixed at a mass ratio of (95~97):(3~5).
[0007] As a preferred embodiment of the present invention, the amount of polyvinyl alcohol solution added in S1-1 is 4-8% of the mass of the mixed powder.
[0008] As a preferred embodiment of the present invention, the method for preparing the composite pore-forming agent is as follows: S4-1: Immerse sisal fibers in a sodium silicate solution with a concentration of 3-5 wt%, stir at 60-80 ℃ for 1-2 h, then wash with deionized water and dry at 60 ℃ for 10-12 h to obtain pretreated sisal fibers. S4-2: Ammonium oxalate and nano-silica are mixed at a mass ratio of (97~99):(1~3) and pulverized together in an air jet mill to obtain powder A; S4-3: Mix the pretreated sisal fiber with powder A for 10-20 min at a mixing speed of 1000-2000 rpm, add polystyrene microspheres, mix for 5-15 min at a mixing speed of 600-800 rpm, add liquid paraffin, and continue mixing for 3-5 min to obtain the composite pore-forming agent.
[0009] As a preferred embodiment of the present invention, the sisal fibers in S4-1 have a length of 0.5~2.0 mm and a diameter of 10~30 μm.
[0010] As a preferred technical solution of the present invention, the mass ratio of pretreated sisal fiber, powder A and polystyrene microspheres in S4-3 is (30~40):(40~60):(10~15).
[0011] As a preferred embodiment of the present invention, the amount of liquid paraffin added in S4-3 is 2-3% of the total mass of the pretreated sisal fiber, powder A and polystyrene microspheres.
[0012] As a preferred embodiment of the present invention, the water-reducing agent is one or both of sodium tripolyphosphate and sodium hexametaphosphate.
[0013] A preparation process for a high-strength refractory material for VD furnaces, the specific steps of which are as follows: S9-1: Add sintered mullite aggregate, calcined gemstone-zirconia composite material, alumina micro powder, calcium aluminate cement, silica micro powder, composite pore-forming agent and water-reducing agent to the mixer for dry mixing according to the formula ratio. S9-2: Add deionized water to the dry mixture and mix again to obtain a casting material. Inject the mixed casting material into the mold to form a shape, then cure and demold, and then bake at 450℃ for 4 hours to obtain the high-strength refractory material for VD furnace.
[0014] As a preferred embodiment of the present invention, the curing temperature in S9-2 is 35~45 ℃ and the curing time is 24~36 h.
[0015] After being calcined at 1100~1300℃, the sintering shrinkage of the zirconia-zirconia composite material significantly reduces secondary shrinkage of the product during high-temperature service when used as aggregate, giving the material excellent high-temperature volume stability and preventing structural loosening of the lining due to repeated thermal cycling. Secondly, the dispersed zirconia can induce stress-induced phase transformation when the material is subjected to typical thermal stress in a VD furnace. The volume expansion generated by the phase transformation can form a uniformly distributed microcrack network in the matrix. These microcracks can effectively disperse and absorb crack propagation energy, thereby greatly improving the fracture toughness and thermal shock resistance of the material. Finally, the composite material is tightly bonded to the matrix, and the microcrack formation process brought about by the zirconia phase transformation can inhibit the propagation of large cracks, making the material more resilient when subjected to molten steel scouring or slag erosion, delaying spalling damage, and comprehensively improving the service life and safety reliability of the lining under harsh conditions of vacuum high temperature and rapid heating and cooling.
[0016] Pretreatment of sisal fibers with sodium silicate solution in an alkaline environment partially hydrolyzes hemicellulose and lignin on the fiber surface, removing impurities, increasing surface roughness and reactive sites, and significantly improving its specific surface area and bonding ability with inorganic powders. Some silicate ions are adsorbed and deposited on the fiber surface and in the micropores, forming an amorphous silica coating after drying. During the high-temperature sintering of refractory materials, the silica coating on the treated fibers reacts with components such as alumina in the matrix, promoting localized sintering or the formation of a mullite phase. This not only improves the structural stability of the fiber remnant at high temperatures, preventing premature collapse, but also transforms it from a simple sacrificial template for pore formation into one that combines pore-forming and micro-area reinforcement functions, thereby enhancing the strength of the final material.
[0017] Ammonium oxalate and nano-silica are co-pulverized in an air jet mill. The intense collision and shearing forces generated by the high-speed airflow achieve nanoparticle coating of the ammonium oxalate particles. The nano-silica particles uniformly adhere to the surface of the ammonium oxalate, forming a physical barrier that effectively slows its contact with moisture in the environment, improving stability during storage and mixing. The nano-silica coating slows down the decomposition rate of ammonium oxalate, allowing for a more gradual release of the gases produced during decomposition. This promotes the formation of finer, more uniform closed micropores and avoids the formation of destructive large pores. After complete decomposition of ammonium oxalate, the in-situ network of nano-silica coating acts as a framework for the micropores, preventing pore collapse at high temperatures and maintaining the stability of the pore structure.
[0018] High shear force causes powder A to adhere mechanically to the surface of pretreated sisal fibers, forming a fiber-powder structure. Subsequent medium-speed mixing disperses polystyrene microspheres within the fiber network gaps, creating a three-dimensional network structure. These polystyrene microspheres act as a high-temperature pore-forming agent, forming macropores during subsequent heat treatment. Liquid paraffin acts as a binder, coating the particle surface during mixing to obtain a composite pore-forming agent.
[0019] During the sintering of refractory materials, ammonium oxalate decomposes first in the low-temperature stage, creating micropores around the fibers; in the medium-temperature stage, the fibers carbonize and shrink, leaving narrow channels along the fiber direction; in the high-temperature stage, polystyrene microspheres decompose, forming larger spherical pores in the gaps of the skeleton. Ultimately, a composite pore structure combining micropores, mesopores, and macropores in a gradient distribution is formed, effectively reconciling the inherent contradictions between high strength and insulation, and between thermal shock resistance and erosion resistance in VD furnace refractory materials. First, the stable micropores of nano-silica significantly reduce the thermal conductivity, while the reinforcing network formed by fiber carbonization synergistically enhances high strength and thermal insulation performance. Second, the gradient pores, acting as an elastic buffer layer, effectively disperse thermal stress, and, combined with the crack deflection mechanism induced by fiber channels, improve thermal shock resistance. Third, the tortuous pores with low connectivity greatly increase the slag penetration resistance, and, combined with the dense gradient naturally formed on the working surface, effectively improve the material's erosion resistance. Thus, the material achieves synergistic optimization of high strength, low thermal conductivity, thermal shock resistance, and erosion resistance under the conditions of high temperature, strong erosion, and rapid heating and cooling in a VD furnace, providing key conditions for extending furnace lining life and reducing energy consumption.
[0020] The beneficial effects of this invention are: In this invention, the dispersed zirconium oxide in the zirconia-zirconia composite material generates a microcrack network in the matrix through stress-induced phase transformation, endowing the material with excellent thermal shock resistance and fracture toughness. In the composite pore-forming agent, the sisal fibers, after pretreatment with sodium silicate solution, form an amorphous silica coating on their surface. This coating reacts with the matrix at high temperatures to generate a reinforcing phase, transforming the fibers from simple pore-forming templates into a stable framework with micro-area reinforcement functions. Ammonium oxalate, after being coated with nano-silica, exhibits improved storage stability. Its controlled decomposition forms uniform micropores, and the residual silica network serves as a microporous framework to prevent collapse. Through a stepwise mixing process, the above components are combined with polystyrene microspheres and liquid paraffin to form a pore-forming agent with a specific structure, ensuring that each component decomposes sequentially during sintering: ammonium oxalate forms micropores at low temperatures, fibers carbonize at medium temperatures leaving long channels, and microspheres generate spherical macropores at high temperatures, ultimately constructing a composite pore structure with a gradient distribution of micropores, mesopores, and macropores. The structure exhibits significant synergistic effects: the micropores and reinforcing skeleton effectively reduce thermal conductivity while ensuring strength; the gradient pores and fiber channels act as stress buffer layers and crack deflection paths, greatly improving thermal shock resistance; and the tortuous and low-connectivity pores significantly hinder slag penetration. Therefore, the material prepared by this invention simultaneously achieves synergistic optimization of high stability, high strength, excellent thermal shock resistance, and erosion resistance, thereby effectively extending furnace lining life and ensuring safe operation. Detailed Implementation
[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.
[0022] It should be noted that, unless otherwise specified, the present invention does not specifically limit the source of the raw materials used in the following embodiments. Commercially available products or products prepared by conventional preparation methods that are well known to those skilled in the art can be used. Experimental methods that do not specify specific conditions are all conventional methods and conventional conditions well known in the art.
[0023] Example 1 A high-strength refractory material for VD furnaces, the formulation of which is as follows (in parts by weight): 70 parts of sintered mullite aggregate 11 parts of fused alumina-zirconia composite material 9 parts of alumina micro powder 5 parts of calcium aluminate cement 2.5 parts of silica powder 0.08 parts of composite pore-forming agent, 0.2 parts sodium tripolyphosphate, The preparation method of the fused alumina-zirconia composite is as follows: S1-1: High-grade coke fine powder and zirconium oxide micro powder are mixed in a mixer at a mass ratio of 96:4 for 45 min to obtain a mixed powder. A 6% polyvinyl alcohol solution is added to the mixed powder, and the amount of polyvinyl alcohol solution added is 6% of the mass of the mixed powder. The mixture is then granulated in a granulator to obtain wet granules. S1-2: The wet particles are dried at 110 °C for 3 h, then heated to 1200 °C at a rate of 3 °C / min and held for 2 h, and then naturally cooled to room temperature to obtain the fused alumina-zirconia composite material.
[0024] The preparation method of the composite pore-forming agent is as follows: S4-1: Sisal fibers with a length of 0.5~2.0 mm and a diameter of 10~30 μm are immersed in a sodium silicate solution with a concentration of 4 wt%. The solution is stirred at 70 ℃ for 1.5 h, then washed with deionized water and dried at 60 ℃ for 11 h to obtain pretreated sisal fibers. S4-2: Ammonium oxalate and nano-silica are mixed at a mass ratio of 98:2 and pulverized together in an air jet mill to obtain powder A; S4-3: Mix the pretreated sisal fiber with powder A for 15 min at a mixing speed of 1500 rpm, add polystyrene microspheres and mix for 5-15 min. The mass ratio of pretreated sisal fiber, powder A and polystyrene microspheres is 35:50:12. Mix at a mixing speed of 700 rpm. Add liquid paraffin, the amount of which is 2.5% of the total mass of pretreated sisal fiber, powder A and polystyrene microspheres. Continue mixing for 4 min to obtain the composite pore-forming agent.
[0025] A preparation process for a high-strength refractory material for VD furnaces, the specific steps of which are as follows: S9-1: Add sintered mullite aggregate, calcined gemstone-zirconia composite material, alumina micro powder, calcium aluminate cement, silica micro powder, composite pore-forming agent and water-reducing agent to the mixer for dry mixing according to the formula ratio. S9-2: Add deionized water to the dry mixture and mix again to obtain a casting material. Inject the mixed casting material into the mold to form a shape, then cure and demold. The curing temperature is 40 ℃ and the curing time is 30 h. Then bake at 450 ℃ for 4 h to obtain the high-strength refractory material for VD furnace.
[0026] Example 2 A high-strength refractory material for VD furnaces, the formulation of which is as follows (in parts by weight): 65 parts of sintered mullite aggregate 10 parts of fused alumina-zirconia composite material 8 parts of alumina micro powder 4 parts of calcium aluminate cement 2 parts of silica powder 0.05 parts of composite pore-forming agent, Sodium hexametaphosphate 0.12 parts, The preparation method of the fused alumina-zirconia composite is as follows: S1-1: High-grade coke fine powder and zirconium oxide micro powder are mixed in a mixer at a mass ratio of 95:5 for 30 min to obtain a mixed powder. A polyvinyl alcohol solution with a mass concentration of 4% is added to the mixed powder. The amount of polyvinyl alcohol solution added is 4% of the mass of the mixed powder. The mixture is then granulated in a granulator to obtain wet granules. S1-2: The wet particles are dried at 100 °C for 2 h, then heated to 1100 °C at a rate of 2 °C / min and held for 1 h, and then naturally cooled to room temperature to obtain the fused alumina-zirconia composite material.
[0027] The preparation method of the composite pore-forming agent is as follows: S4-1: Sisal fibers with a length of 0.5~2.0 mm and a diameter of 10~30 μm are immersed in a 3 wt% sodium silicate solution. The fibers are stirred at 60 ℃ for 1 h, then washed with deionized water and dried at 60 ℃ for 10 h to obtain pretreated sisal fibers. S4-2: Ammonium oxalate and nano-silica are mixed at a mass ratio of 97:3 and pulverized together in an air jet mill to obtain powder A; S4-3: Mix the pretreated sisal fiber with powder A for 10 min at a mixing speed of 1000 rpm, add polystyrene microspheres and mix for 5 min. The mass ratio of pretreated sisal fiber, powder A and polystyrene microspheres is 30:40:10. The mixing speed is 600 rpm. Add liquid paraffin, the amount of which is 2% of the total mass of pretreated sisal fiber, powder A and polystyrene microspheres. Continue mixing for 3 min to obtain the composite pore-forming agent.
[0028] A preparation process for a high-strength refractory material for VD furnaces, the specific steps of which are as follows: S9-1: Add sintered mullite aggregate, calcined gemstone-zirconia composite material, alumina micro powder, calcium aluminate cement, silica micro powder, composite pore-forming agent and water-reducing agent to the mixer for dry mixing according to the formula ratio. S9-2: Add deionized water to the dry mixture and mix again to obtain a casting material. Inject the mixed casting material into the mold to form a shape, then cure and demold. The curing temperature is 35 ℃ and the curing time is 36 h. Then bake at 450℃ for 4 h to obtain the high-strength refractory material for VD furnace.
[0029] Example 3 A high-strength refractory material for VD furnaces, the formulation of which is as follows (in parts by weight): 75 parts of sintered mullite aggregate. 12 parts of fused alumina-zirconia composite material 10 parts of alumina micro powder 6 parts of calcium aluminate cement 3 parts silica powder 0.1 parts of composite pore-forming agent, 0.25 parts sodium tripolyphosphate, The preparation method of the fused alumina-zirconia composite is as follows: S1-1: High-grade coke fine powder and zirconium oxide micro powder are mixed in a mixer at a mass ratio of 97:3 for 60 min to obtain a mixed powder. A polyvinyl alcohol solution with a mass concentration of 8% is added to the mixed powder. The amount of polyvinyl alcohol solution added is 8% of the mass of the mixed powder. The mixture is then granulated in a granulator to obtain wet granules. S1-2: The wet particles are dried at 120 °C for 4 h, then heated to 1300 °C at a rate of 5 °C / min and held for 3 h, and then naturally cooled to room temperature to obtain the fused alumina-zirconia composite material.
[0030] The preparation method of the composite pore-forming agent is as follows: S4-1: Sisal fibers are immersed in a 5wt% sodium silicate solution. The length of the sisal fibers is 0.5~2.0 mm and the diameter is 10~30 μm. The solution is stirred at 80 ℃ for 2 h, then washed with deionized water and dried at 60 ℃ for 12 h to obtain pretreated sisal fibers. S4-2: Ammonium oxalate and nano-silica are mixed at a mass ratio of 99:1 and pulverized together in an air jet mill to obtain powder A; S4-3: Mix the pretreated sisal fiber with powder A for 20 min at a mixing speed of 2000 rpm, add polystyrene microspheres and mix for 15 min. The mass ratio of pretreated sisal fiber, powder A and polystyrene microspheres is 40:60:15. The mixing speed is 800 rpm. Add liquid paraffin, the amount of which is 3% of the total mass of pretreated sisal fiber, powder A and polystyrene microspheres. Continue mixing for 5 min to obtain the composite pore-forming agent.
[0031] A preparation process for a high-strength refractory material for VD furnaces, the specific steps of which are as follows: S9-1: Add sintered mullite aggregate, calcined gemstone-zirconia composite material, alumina micro powder, calcium aluminate cement, silica micro powder, composite pore-forming agent and water-reducing agent to the mixer for dry mixing according to the formula ratio. S9-2: Add deionized water to the dry mixture and mix again to obtain a casting material. Inject the mixed casting material into the mold to form a shape, then cure and demold. The curing temperature is 45 ℃ and the curing time is 24 h. Then bake at 450 ℃ for 4 h to obtain the high-strength refractory material for VD furnace.
[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that premium grade sapphire powder is used instead of sapphire-zirconia composite material; otherwise, they are the same as in Example 1.
[0033] Comparative Example 2 The difference between this comparative example and Example 1 is that the fine powder of premium sapphire and the micro powder of zirconium oxide are mechanically mixed to replace the sapphire-zirconia composite material; otherwise, they are the same as in Example 1.
[0034] Comparative Example 3 The difference between this comparative example and Example 1 is that no pretreatment of sisal fibers is performed in the preparation of the composite pore-forming agent; otherwise, it is the same as Example 1.
[0035] Comparative Example 4 The difference between this comparative example and Example 1 is that nano-silica is not added to S4-2 in the preparation of the composite pore-forming agent; otherwise, they are the same as in Example 1.
[0036] Comparative Example 5 The difference between this comparative example and Example 1 is that a single polystyrene microsphere is used instead of the composite pore-forming agent; otherwise, they are the same as in Example 1.
[0037] Performance testing The number of thermal shock cycles was determined according to the test method in GB / T30873-2014 "Test Method for Thermal Shock Resistance of Refractory Materials", the compressive strength was determined according to the test method in GB / T 5072-2008 "Test Method for Compressive Strength of Refractory Materials at Room Temperature", and the flexural strength was determined according to the test method in GB / T3001-2017 "Test Method for Flexural Strength of Refractory Materials at Room Temperature". The specific test results are shown in the table below.
[0038] As can be seen from the examples and comparative data, the refractory material prepared by the present invention has good compressive strength, flexural strength and thermal shock resistance.
[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention are still within the scope of the present invention.
Claims
1. A high-strength refractory material for VD furnaces, characterized in that, The formulation of the refractory material is as follows, calculated in parts by weight. 65-75 parts of sintered mullite aggregate, 10-12 parts of fused alumina-zirconia composite material 8-10 parts of alumina micro powder 4-6 parts of calcium aluminate cement 2-3 parts of silica powder 0.05~0.1 parts of composite pore-forming agent, Water-reducing agent 0.12~0.25 parts, The preparation method of the fused alumina-zirconia composite is as follows: S1-1: Place the fine powder of premium slag and the micro powder of zirconium oxide in a mixer and mix for 30-60 min to obtain a mixed powder. Add a polyvinyl alcohol solution with a mass concentration of 4-8% to the mixed powder and granulate in a granulator to obtain wet granules. S1-2: After drying the wet particles at 100~120 ℃ for 2~4 h, the temperature is raised to 1100~1300 ℃ at a rate of 2~5 ℃ / min and held for 1~3 h, and then naturally cooled to room temperature to obtain the fused alumina-zirconia composite material.
2. The high-strength refractory material for VD furnaces according to claim 1, characterized in that, The S1-1 mixture of premium slag powder and zirconium oxide powder is prepared at a mass ratio of (95~97):(3~5).
3. The high-strength refractory material for VD furnaces according to claim 1, characterized in that, The amount of polyvinyl alcohol solution added in S1-1 is 4-8% of the mass of the mixed powder.
4. The high-strength refractory material for VD furnaces according to claim 1, characterized in that, The preparation method of the composite pore-forming agent is as follows: S4-1: Immerse sisal fibers in a sodium silicate solution with a concentration of 3-5 wt%, stir at 60-80 ℃ for 1-2 h, then wash with deionized water and dry at 60 ℃ for 10-12 h to obtain pretreated sisal fibers. S4-2: Ammonium oxalate and nano-silica are mixed at a mass ratio of (97~99):(1~3) and pulverized together in an air jet mill to obtain powder A; S4-3: Mix the pretreated sisal fiber with powder A for 10-20 min at a mixing speed of 1000-2000 rpm, add polystyrene microspheres, mix for 5-15 min at a mixing speed of 600-800 rpm, add liquid paraffin, and continue mixing for 3-5 min to obtain the composite pore-forming agent.
5. The high-strength refractory material for VD furnaces according to claim 4, characterized in that, The sisal fibers in S4-1 have a length of 0.5~2.0 mm and a diameter of 10~30 μm.
6. The high-strength refractory material for VD furnaces according to claim 4, characterized in that, The mass ratio of pretreated sisal fiber, powder A and polystyrene microspheres in S4-3 is (30~40):(40~60):(10~15).
7. The high-strength refractory material for VD furnaces according to claim 4, characterized in that, The amount of liquid paraffin added in S4-3 is 2-3% of the total mass of the pretreated sisal fiber, powder A and polystyrene microspheres.
8. The high-strength refractory material for VD furnaces according to claim 1, characterized in that, The water-reducing agent is one or both of sodium tripolyphosphate and sodium hexametaphosphate.
9. A preparation process for a high-strength refractory material for a VD furnace as described in any one of claims 1 to 8, characterized in that, The specific steps of the preparation process are as follows. S9-1: Add sintered mullite aggregate, calcined gemstone-zirconia composite material, alumina micro powder, calcium aluminate cement, silica micro powder, composite pore-forming agent and water-reducing agent to the mixer for dry mixing according to the formula ratio. S9-2: Add deionized water to the dry mixture and mix again to obtain a casting material. Inject the mixed casting material into the mold to form a shape, then cure and demold, and then bake at 450℃ for 4 hours to obtain the high-strength refractory material for VD furnace.
10. The preparation process of a high-strength refractory material for a VD furnace according to claim 9, characterized in that, The curing temperature in S9-2 is 35~45 ℃, and the curing time is 24~36 h.