Carbon-free composite spinel material for refining special steel of aircraft carrier and preparation method of carbon-free composite spinel material

Abstract

The invention discloses a carbon-free composite spinel material for refining special steel of an aircraft carrier and a preparation method of the carbon-free composite spinel material. The carbon-free composite spinel material comprises the following components in percentage by mass: 20-30% of activated alumina micro powder, 5-12% of yttria-stabilized zirconia micro powder, 1-3% of a rare earth oxide composite additive and the balance of fused magnesite particles, wherein the rare earth oxide is formed by compounding Y2O3 and La2O3 according to the mass ratio of (2-3): 1; the preparation method comprises the steps of raw material high-energy ball milling pretreatment, vacuum mulling and aging treatment, isostatic compaction and gradient drying, and segmented controllable atmosphere sintering. Through the synergistic effect of zirconium oxide phase change toughening and rare earth oxide grain boundary purification, the high-temperature strength, thermal shock resistance and erosion resistance of the material are remarkably improved at the same time under the completely carbon-free condition, and the method is particularly suitable for the vacuum refining process of aircraft carrier special steel; the technical problems that a traditional carbon-containing material pollutes molten steel and a traditional carbon-free material is insufficient in performance are solved.

Description

Technical Field

[0001] This invention relates to the field of carbon-free composite spinel material preparation technology, specifically to a carbon-free composite spinel material for refining special steel for aircraft carriers and its preparation method. Background Technology

[0002] Carbon-free composite spinel material for refining special steel for aircraft carriers belongs to the field of high-end refractory materials and auxiliary materials for steelmaking in metallurgical engineering. It is mainly used in the secondary refining process of special steels such as aircraft carrier deck steel and hull structural steel. This material is usually placed in the ladle or tundish in the form of prefabricated components. Through physicochemical action at high temperatures, it adsorbs non-metallic inclusions in the molten steel and controls the cleanliness and compositional uniformity of the molten steel. It is one of the key functional materials to ensure the high toughness, high strength and fatigue resistance of special steels.

[0003] Currently, magnesia, magnesia-calcium, or carbon-containing composite refractories are mainly used for refining materials both domestically and internationally. Among them, magnesia-alumina spinel is widely used due to its excellent thermal shock resistance and slag erosion resistance. Existing technologies often introduce aluminum sources into the magnesia matrix and react them at high temperatures to generate the spinel phase, or directly use pre-synthesized spinel particles as aggregate, combined with carbonaceous materials such as graphite to improve erosion resistance and thermal conductivity. However, these carbon-containing materials are prone to introducing carbon contamination during the refining of ultra-low carbon steel, especially oxygen-sensitive steel, affecting the purity of the steel. Some carbon-free spinel materials rely on high-purity synthetic raw materials or complex sintering processes, resulting in problems such as high cost, insufficient thermal stability, or poor impermeability.

[0004] Traditional carbon-free spinel materials often suffer from weak bonding between aggregate and matrix due to insufficient microstructure design, and poor matching of thermal expansion coefficients. This makes the materials prone to microcracks and propagation during the drastic temperature changes in the refining process. At the same time, they soften and peel off under the long-term scouring of high-temperature molten steel, affecting service life and the stability of refining effect. Summary of the Invention

[0005] A problem with existing technologies is that they cannot synergistically improve the high-temperature structural strength and thermal shock resistance of materials under completely carbon-free conditions. To address this problem, this invention provides a carbon-free composite spinel material for refining special steel for aircraft carriers and its preparation method.

[0006] The technical solution of the present invention is: a carbon-free composite spinel material for refining special steel for aircraft carriers, comprising, by mass percentage, 20-30% activated alumina micro powder, 5-12% yttrium oxide stabilized zirconium oxide micro powder, 1-3% rare earth oxide composite additives, and the balance being fused magnesia particles; wherein the rare earth oxide composite additives are powders composed of Y2O3 and La2O3 in a mass ratio of 2-3:1.

[0007] Explanation: By controlling high-energy ball milling, bidirectional pressure isostatic pressing, gradient drying, and segmented sintering, the high uniformity of component distribution, the forming stability of the green body, and the reliability of the final product's microstructure were ensured. This resulted in good production repeatability and a high yield. Precise use of each component refined the material grains, further improving its high-temperature mechanical properties.

[0008] Furthermore, the MgO content in the fused magnesia particles is greater than 97.5%, and the particle size distribution is as follows: 15-25% of the particles are 1-3 mm, 10-20% of the particles are 0.5-1 mm, 15-25% of the particles are 0.088-0.5 mm, and the remainder is fine powder of 0.1 μm to 0.088 mm.

[0009] Explanation: By precisely controlling the purity and particle size distribution of fused magnesia particles, the microstructure of the material was optimized. This ensured the high-temperature chemical stability of the material system, avoided the formation of low-melting-point impurity phases, and achieved the densest packing of the powder through three-level particle size distribution. This significantly improved the forming density of the green body, reduced sintering shrinkage, and ultimately enabled the material to obtain higher bulk density, strength, and impermeability, laying the structural foundation for the material's excellent resistance to molten steel erosion.

[0010] This invention also provides a method for preparing a carbon-free composite spinel material for refining special steel for aircraft carriers, comprising the following steps: S1. Raw material pretreatment and composite powder preparation According to the formula, fused magnesia particles, activated alumina micro powder, yttrium oxide stabilized zirconia micro powder, and rare earth oxide composite additives are placed together in a planetary ball mill. Anhydrous ethanol is used as the grinding medium, and high-energy ball milling is carried out for 4 to 10 hours at a ball-to-material ratio of 3 to 5:1 and a rotation speed of 280 to 400 r / min to obtain a uniformly distributed composite powder. S2, Vacuum mixing and aging treatment The composite powder described in S1 is placed in a vacuum plow, and a composite binder of 4-6% of the total powder mass is added. The mixture is then kneaded for 30-60 minutes under vacuum conditions of -0.08 to -0.1 MPa and temperature of 40-60℃ to obtain vacuum-degassed clay. The clay is then placed in a sealed container and aged at room temperature for 24-48 hours to obtain clay for use as a green body. The composite binder is composed of hydroxypropyl methylcellulose and polyethylene glycol in a mass ratio of 1:0.5-1. S3, Isostatic pressing and gradient drying The blank material described in S2 is loaded into a rubber mold and cold isostatically pressed at a pressure of 150~250MPa for 5~15 min. The molded blank is then placed in a humidity-controlled drying oven and pretreated at a temperature of 30~40℃ and a humidity of 80~90% for 12~24 h. The temperature is then increased to 110~120℃ at a rate of 0.5~1℃ / min and dried for 24~48 h to obtain a dried blank. S4, segmented controlled atmosphere sintering The dried green body described in S3 is placed in a high-temperature sintering furnace and sintered under a slightly positive pressure oxygen atmosphere. First, the temperature is increased to 600-800℃ at a rate of 1-2℃ / min and held for 2-4 hours to remove the organic binder. Then, the temperature is increased to 1200-1400℃ at a rate of 3-5℃ / min and held for 2-4 hours to complete the initial formation of the spinel phase. Next, the temperature is increased to 1700-1780℃ at a rate of 2-3℃ / min and held for 6-12 hours to complete the densification of the material and the purification of grain boundaries. Finally, the temperature is decreased to 1450-1550℃ at a rate of 2-3℃ / min and held for 1-2 hours to relieve stress. Then, the material is cooled to room temperature in the furnace to obtain a carbon-free composite spinel material.

[0011] Description: This invention achieves defect-free molding through high-energy ball milling for nano-dispersion, vacuum hot mixing and aging to regulate plasticity, isostatic pressing and gradient drying, and a systematic combination of long-term high-temperature sintering and stress-controlled cooling under a micro-oxygen atmosphere. For the first time, it synergistically achieves the unity of ultra-high strength, excellent thermal shock resistance and extreme corrosion resistance of spinel materials under carbon-free conditions, meeting the extreme working conditions required for the refining of special steel for aircraft carriers, and forming a completely new preparation process route.

[0012] Furthermore, the high-energy ball mill described in S1 uses zirconia grinding balls, and the ball mill is filled with high-purity nitrogen for protection. The temperature is controlled at 20~50℃ during the ball milling process; the specific surface area of ​​the composite powder is 5~15m². 2 / g, with a particle size distribution D50 of 0.5~2μm.

[0013] Note: Zirconia grinding balls were used in a temperature-controlled ball mill under nitrogen protection, effectively preventing iron contamination and material oxidation during the grinding process, thus ensuring the chemical purity of the raw materials. By controlling the ball milling parameters, a specific surface area of ​​5~15m² was ultimately obtained. 2 The composite powder with a density of / g and D50 of 0.5~2μm greatly increases the reactivity of the raw materials, promotes the solid-phase reaction during sintering, and provides a crucial raw material guarantee for obtaining sintered bodies with uniform microstructure.

[0014] Furthermore, the composite binder in S2 also includes 0.5-1% of a plasticizer by total powder mass, wherein the plasticizer is one of glycerol or dibutyl phthalate; during the mixing process, the material temperature is maintained at 40-60℃ and the vacuum degree is maintained at -0.09--0.1MPa.

[0015] Explanation: The addition of specific plasticizers and strict control of mixing temperature and vacuum significantly improve the molding performance of the clay. The addition of plasticizers enhances the lubrication of the powder, giving the clay better extensibility and plasticity. The precise control of temperature and vacuum ensures that the binder is evenly distributed and air bubbles are fully eliminated, thereby avoiding stress concentration defects in the green body, providing a uniform and dense green body for subsequent molding, and greatly improving the yield.

[0016] Furthermore, the isostatic pressing described in S3 adopts a bidirectional pressurization method, first pre-pressing at 50~100MPa for 2~5 min, and then raising to the final pressure of 150~250MPa and holding for 5~15 min; during the drying process, the humidity gradually decreases from 90% to 30%, and the temperature gradually increases from 40℃ to 120℃.

[0017] Explanation: The use of bidirectional pressure isostatic pressing combined with gradient drying is a key innovation to ensure high density and defect-free products. The bidirectional pressure method, with pre-pressing followed by high pressure, achieves optimal powder arrangement and significantly improves the density of the green body. The innovative gradient drying process, through precise control of the coordinated changes in humidity and temperature, achieves safe and uniform moisture removal, completely solving the technical problem of easy cracking during the drying process of large green bodies.

[0018] Furthermore, the sintering process described in S4 is carried out in a slightly oxidizing atmosphere with an oxygen partial pressure of 5~15 kPa, and the pressure inside the sintering furnace is maintained 1~5 kPa higher than the outside pressure; during the heat preservation stage at 1700~1780℃, the oxygen flow rate is adjusted every 1~2.5 h, and the flow rate varies from 10~50 L / min.

[0019] Explanation: The precise atmosphere control strategy greatly improved the sintering quality of the material; the micro-positive pressure oxygen atmosphere prevented the reduction reaction of the material components at high temperatures, ensuring the stability of the material composition; the innovative method of periodically adjusting the oxygen flow rate during the heat preservation stage created a dynamically balanced sintering environment, which promoted the densification process and grain boundary purification reaction, ultimately obtaining an ideal microstructure with fine grains and a dense structure.

[0020] Furthermore, after S4, a heat treatment step is also included: the sintered carbon-free composite spinel material is annealed at 1400~1500℃ for 4~8 h, with argon gas introduced for protection during the annealing process, and then cooled to 600~800℃ at a rate of 1~2℃ / min after annealing, and then cooled to room temperature in the furnace.

[0021] Note: The annealing heat treatment step added after S4 effectively eliminates the internal stress generated during rapid cooling of the material through precision annealing under a protective atmosphere, stabilizes the phase composition of the material, and in particular ensures the existence state of the zirconia toughening phase, thereby significantly improving the fracture toughness, thermal stability and service life of the material, making the product performance more stable and reliable.

[0022] The beneficial effects of this invention are: This invention utilizes a multi-component composite and optimized preparation process to produce a high-performance carbon-free composite spinel material. By introducing a specific proportion of yttrium oxide-stabilized zirconia micropowder, the material's fracture toughness and thermal shock resistance are significantly enhanced through its unique phase transformation toughening mechanism. This allows it to withstand severe temperature fluctuations in refining environments without cracking or peeling, resulting in a significantly extended lifespan. Furthermore, the use of rare earth oxide composite additives, a specific ratio of Y₂O₃ and La₂O₃, achieves both grain boundary purification and sintering fluxing effects. Rare earth elements preferentially react with low-melting-point impurities in the raw materials to form high-melting-point stable compounds, purifying the grain boundaries and thus significantly strengthening the material. The high-temperature strength and resistance to slag penetration and erosion ensure that the molten steel is not contaminated by refractory materials. At the same time, the additive promotes the sintering densification process, enabling the material to achieve extremely high bulk density and strength at a relatively low sintering temperature. The completely carbon-free design of the material fundamentally eliminates carbon contamination of ultra-high purity special steel, making it particularly suitable for vacuum refining processes of steel grades such as aircraft carrier steel, where the control of interstitial elements such as hydrogen, oxygen, and carbon is extremely strict. The material of this invention also possesses comprehensive excellent properties such as carbon-free, high density, high strength, high thermal shock resistance, and high erosion resistance, meeting all the stringent requirements of aircraft carrier special steel refining for key refractory materials, with outstanding technological advancement and economic benefits. Detailed Implementation

[0023] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0024] Example 1: A carbon-free composite spinel material for refining special steel for aircraft carriers, comprising, by mass percentage, 25% activated alumina micropowder, 8% yttrium oxide-stabilized zirconia micropowder, 2% rare earth oxide composite additives, and the balance being fused magnesia particles; the rare earth oxide composite additives are powders composed of Y₂O₃ and La₂O₃ in a mass ratio of 2.5:1; the fused magnesia particles contain 99.2% MgO, and their particle size distribution is as follows: 20% particles of 1~3mm, 15% particles of 0.5~1mm, 20% particles of 0.088~0.5mm, and the balance being fine powder of 0.1μm~0.088mm; the yttrium oxide-stabilized zirconia micropowder is yttrium oxide-stabilized zirconia powder produced by Shenyang Shihua Micro-Nano Materials Technology Co., Ltd. Example 2: This example is a method for preparing carbon-free composite spinel material for refining special steel for aircraft carriers, as described in Example 1, and includes the following steps: S1. Raw material pretreatment and composite powder preparation According to the formula, fused magnesia particles, activated alumina micro powder, yttrium oxide-stabilized zirconia micro powder, and rare earth oxide composite additives were placed together in a planetary ball mill and subjected to high-energy ball milling for 7 hours at a ball-to-material ratio of 4:1 and a rotation speed of 350 r / min using anhydrous ethanol as the grinding medium, to obtain a uniformly distributed composite powder. The high-energy ball milling used zirconia grinding balls, and the mill was filled with high-purity nitrogen for protection. The temperature was controlled at 35℃ during the ball milling process. The specific surface area of ​​the composite powder was 10~12 m². 2 / g, particle size distribution D50 is 0.8~1.5μm; S2, Vacuum mixing and aging treatment The composite powder described in S1 is placed in a vacuum ply mill, and a composite binder of 5% of the total powder mass is added. The mixture is then kneaded for 45 minutes under a vacuum of -0.09 MPa and a temperature of 50°C to obtain vacuum-degassed ply. The ply is then placed in a sealed container and aged at room temperature for 36 hours to obtain ply for use as a blank. The composite binder is composed of hydroxypropyl methylcellulose and polyethylene glycol in a mass ratio of 1:0.75. The composite binder also contains a plasticizer of 0.75% of the total powder mass, which is glycerin. During the kneading process, the material temperature is maintained at 50°C and the vacuum is maintained at -0.095 MPa. S3, Isostatic pressing and gradient drying The blank material described in S2 is loaded into a rubber mold and cold isostatically pressed at 200 MPa for 10 min. The pressed blank is then placed in a humidity-controlled drying oven and pretreated at 35°C and 85% humidity for 18 h. The temperature is then increased to 115°C at a rate of 0.75°C / min and dried for 36 h to obtain a dried blank. The isostatic pressing is performed using a bidirectional pressurization method, first pre-pressed at 75 MPa for 3.5 min, and then increased to the final pressure of 200 MPa and held for 10 min. During the drying process, the humidity gradually decreases from 90% to 30%, and the temperature gradually increases from 40°C to 120°C. S4, segmented controlled atmosphere sintering The dried green body described in S3 was placed in a high-temperature sintering furnace and sintered under a slightly positive pressure oxygen atmosphere. First, the temperature was increased to 700℃ at a rate of 1.5℃ / min and held for 3 hours to remove the organic binder. Then, the temperature was increased to 1300℃ at a rate of 4℃ / min and held for 3 hours to complete the initial formation of the spinel phase. Next, the temperature was increased to 1740℃ at a rate of 2.5℃ / min and held for 10 hours to complete the densification of the material and the purification of grain boundaries. Finally, the temperature was decreased to 1500℃ at a rate of 2.5℃ / min and held for 1.5 hours to relieve stress. The material was then cooled to room temperature with the furnace to obtain a carbon-free composite spinel material. The sintering process was carried out in a slightly oxidizing atmosphere with an oxygen partial pressure of 10 kPa, and the pressure inside the sintering furnace was maintained 3 kPa higher than the outside pressure. During the 1740℃ holding stage, the oxygen flow rate was adjusted every 2 hours, with the flow rate varying from 10 to 50 L / min.

[0025] Example 3: This example is basically the same as Example 1, except that, by mass percentage, it includes 20% activated alumina micro powder, 5% yttrium oxide stabilized zirconia micro powder, 1% rare earth oxide composite additive, and the balance being fused magnesia particles; the rare earth oxide composite additive is a powder composed of Y2O3 and La2O3 in a mass ratio of 2:1; the fused magnesia particles contain more than 97.5% MgO, and their particle size distribution is as follows: 15% of particles are 1~3mm, 10% are 0.5~1mm, 15% are 0.088~0.5mm, and the balance is fine powder of 0.1μm~0.088mm.

[0026] Example 4: This example is basically the same as Example 1, except that, by mass percentage, it includes 30% activated alumina micro powder, 12% yttrium oxide stabilized zirconium oxide micro powder, 3% rare earth oxide composite additive, and the balance being fused magnesia particles; the rare earth oxide composite additive is a powder composed of Y2O3 and La2O3 in a mass ratio of 3:1; the fused magnesia particles contain more than 97.5% MgO, and their particle size distribution is as follows: 1~3mm particles account for 25%, 0.5~1mm particles account for 20%, 0.088~0.5mm particles account for 25%, and the balance is fine powder of 0.1μm~0.088mm.

[0027] Example 5: This example is basically the same as Example 2, except that S1, raw material pretreatment and composite powder preparation are different. According to the formula, fused magnesia particles, activated alumina micro powder, yttrium oxide stabilized zirconia micro powder, and rare earth oxide composite additives are placed together in a planetary ball mill. Anhydrous ethanol is used as the grinding medium, and high-energy ball milling is carried out for 4 hours at a ball-to-material ratio of 3:1 and a rotation speed of 280 r / min to obtain a uniformly distributed composite powder. S2, Vacuum mixing and aging treatment The composite powder described in S1 is placed in a vacuum pug mill, and a composite binder of 4% of the total powder mass is added. The mixture is then kneaded for 30 minutes under a vacuum of -0.1 MPa and a temperature of 40°C to obtain vacuum-degassed pug material. The pug material is placed in a sealed container and aged at room temperature for 24 hours to obtain pug material for use as a blank. The composite binder is composed of hydroxypropyl methylcellulose and polyethylene glycol in a mass ratio of 1:0.5. S3, Isostatic pressing and gradient drying The blank material described in S2 is loaded into a rubber mold and cold isostatically pressed at a pressure of 150 MPa for 5 min. The molded blank is then placed in a humidity-controlled drying oven and pretreated at 30°C and 80% humidity for 12 h. The temperature is then increased to 110°C at a rate of 0.5°C / min and dried for 24 h to obtain a dried blank. S4, segmented controlled atmosphere sintering The dried green body described in S3 was placed in a high-temperature sintering furnace and sintered under a slightly positive pressure oxygen atmosphere. First, the temperature was increased to 600℃ at a rate of 1℃ / min and held for 2 hours to remove the organic binder. Then, the temperature was increased to 1200℃ at a rate of 3℃ / min and held for 2 hours to complete the initial formation of the spinel phase. Next, the temperature was increased to 1700℃ at a rate of 2℃ / min and held for 6 hours to complete the densification of the material and the purification of grain boundaries. Finally, the temperature was decreased to 1450℃ at a rate of 2℃ / min and held for 1 hour to relieve stress. The material was then cooled to room temperature in the furnace to obtain a carbon-free composite spinel material.

[0028] Example 6: This example is basically the same as Example 2, except that S1, raw material pretreatment and composite powder preparation are different. According to the formula, fused magnesia particles, activated alumina micro powder, yttrium oxide stabilized zirconia micro powder, and rare earth oxide composite additives are placed together in a planetary ball mill and high-energy ball milling is carried out for 10 h with anhydrous ethanol as the grinding medium at a ball-to-material ratio of 5:1 and a rotation speed of 400 r / min to obtain uniformly distributed composite powder. S2, Vacuum mixing and aging treatment The composite powder described in S1 is placed in a vacuum pug mill, and a composite binder of 6% of the total powder mass is added. The mixture is then kneaded for 60 min under a vacuum of -0.08 MPa and a temperature of 60°C to obtain vacuum-degassed pug material. The pug material is placed in a sealed container and aged at room temperature for 48 h to obtain pug material for use as a blank. The composite binder is composed of hydroxypropyl methylcellulose and polyethylene glycol in a mass ratio of 1:1. S3, Isostatic pressing and gradient drying The blank material described in S2 is loaded into a rubber mold and cold isostatically pressed under a pressure of 250 MPa for 15 min. The molded blank is then placed in a humidity-controlled drying oven and pretreated at 40°C and 90% humidity for 24 h. The temperature is then increased to 120°C at a rate of 1°C / min and dried for 48 h to obtain a dried blank. S4, segmented controlled atmosphere sintering The dried green body described in S3 was placed in a high-temperature sintering furnace and sintered under a slightly positive pressure oxygen atmosphere. First, the temperature was increased to 800℃ at a rate of 2℃ / min and held for 4 h to remove the organic binder. Then, the temperature was increased to 1400℃ at a rate of 5℃ / min and held for 4 h to complete the initial formation of the spinel phase. Next, the temperature was increased to 1780℃ at a rate of 3℃ / min and held for 12 h to complete the densification of the material and the purification of grain boundaries. Finally, the temperature was decreased to 1550℃ at a rate of 3℃ / min and held for 2 h to relieve stress. Then, the material was cooled to room temperature in the furnace to obtain a carbon-free composite spinel material.

[0029] Example 7: This example is basically the same as Example 2, except that the high-energy ball mill in S1 uses zirconia grinding balls, the ball mill is filled with high-purity nitrogen for protection, and the temperature is controlled at 20°C during the ball milling process; the specific surface area of ​​the composite powder is 5~10m². 2 / g, with a particle size distribution D50 of 0.5~0.8μm.

[0030] Example 8: This example is basically the same as Example 2, except that the high-energy ball mill in S1 uses zirconia grinding balls, the ball mill is filled with high-purity nitrogen for protection, and the temperature is controlled at 50°C during the ball milling process; the specific surface area of ​​the composite powder is 10~15m². 2 / g, with a particle size distribution D50 of 1.5~2μm.

[0031] Example 9: This example is basically the same as Example 2, except that the composite binder in S2 also contains 0.5% of the total mass of the powder as a plasticizer, which is glycerol; the material temperature is maintained at 40°C and the vacuum degree is maintained at -0.09MPa during the mixing process.

[0032] Example 10: This example is basically the same as Example 2, except that the composite binder in S2 also contains 1% of the total mass of the powder as a plasticizer, which is dibutyl phthalate; the material temperature is maintained at 60°C and the vacuum degree is maintained at -0.1MPa during the mixing process.

[0033] Example 11: This example is basically the same as Example 2, except that the isostatic pressing in S3 adopts a bidirectional pressurization method, first pre-pressing at 50MPa for 2 minutes, and then raising to the final pressure of 150MPa and holding for 5 minutes; during the drying process, the humidity gradually decreases from 90% to 30%, and the temperature gradually increases from 40℃ to 120℃.

[0034] Example 12: This example is basically the same as Example 2, except that the isostatic pressing in S3 adopts a bidirectional pressurization method, first pre-pressing at 100MPa for 5 min, and then raising to the final pressure of 250MPa and holding for 15 min; during the drying process, the humidity gradually decreases from 90% to 30%, and the temperature gradually increases from 40℃ to 120℃.

[0035] Example 13: This example is basically the same as Example 2, except that the sintering process described in S4 is carried out in a micro-oxidizing atmosphere with an oxygen partial pressure of 5 kPa, and the pressure inside the sintering furnace is kept 1 kPa higher than the outside pressure; during the 1700℃ holding stage, the oxygen flow rate is adjusted every 1 hour, and the flow rate varies within a range of 10 L / min.

[0036] Example 14: This example is basically the same as Example 2, except that the sintering process described in S4 is carried out in a micro-oxidizing atmosphere with an oxygen partial pressure of 15 kPa, and the pressure inside the sintering furnace is kept 5 kPa higher than the outside pressure; during the 1780℃ holding stage, the oxygen flow rate is adjusted every 2.5 h, and the flow rate varies from 50 L / min.

[0037] Example 15: This example is basically the same as Example 2, except that after S4, a heat treatment step is also included: the sintered carbon-free composite spinel material is annealed at 1400℃ for 4 h, argon gas is introduced for protection during the annealing process, and after annealing, it is cooled to 600℃ at a rate of 1℃ / min, and then cooled to room temperature in the furnace.

[0038] Example 16: This example is basically the same as Example 2, except that after S4, a heat treatment step is also included: the sintered carbon-free composite spinel material is annealed at 1500°C for 8 hours, argon gas is introduced for protection during the annealing process, and after annealing, it is cooled to 800°C at a rate of 2°C / min, and then cooled to room temperature in the furnace.

[0039] Example 17: This example is basically the same as Example 2, except that after S4, a heat treatment step is also included: the sintered carbon-free composite spinel material is annealed at 1450°C for 6 h, argon gas is introduced for protection during the annealing process, and after annealing, it is cooled to 700°C at a rate of 1.5°C / min, and then cooled to room temperature in the furnace.

[0040] Comparative Example 1: This comparative example is basically the same as Example 1, except that yttrium oxide stabilized zirconia micro powder was not added. Its 8% mass was made up by an equal amount of fused magnesia particles. The remaining components, proportions and preparation process parameters are completely consistent with those of Example 1.

[0041] Comparative Example 2: This comparative example is basically the same as Example 1, except that no rare earth oxide composite additive was added. Its 2% mass was made up by an equal amount of fused magnesia particles. The remaining components, proportions and preparation process parameters are completely consistent with those of Example 1.

[0042] Comparative Example 3: This comparative example is basically the same as Example 2, except that the sintering process of S4 is simplified: the dried green body is heated to 1750°C at 3°C / min, held at that temperature for 5 hours, and then cooled to room temperature in the furnace, omitting the key steps of segmented heating, long-term holding, and stress relief.

[0043] To investigate the properties of the carbon-free composite spinel materials in the above examples and control examples, the main materials were determined according to the experimental formulation, and samples were obtained for testing. Bulk density was determined using the Archimedes displacement method (GB / T 2997). High-temperature flexural strength was tested by a three-point bending test (GB / T 3002) on the samples at 1700°C in an inert atmosphere. Thermal shock resistance was tested according to the standard test method for thermal shock resistance of refractory materials (YB / T 376.3). The samples were held at 1100°C and then rapidly cooled to room temperature water, and this process was repeated until the samples fractured. The number of thermal cycles withstood was used as the evaluation index, and the results are shown in Table 1. Specific investigations are as follows: Table 1 Performance Test Table of Carbon-Free Composite Spinel Material Samples in Examples 2-17 and Comparative Examples 1-3

[0044] 1. Investigate the influence of ingredient parameters on the properties of carbon-free composite spinel materials: As shown in Table 1, the performance results of Example 2 were used as a benchmark to compare with the control examples lacking key components. The formulation and process combinations of Examples 1 and 2 exhibited the best overall performance, with leading levels of high bulk density, high-temperature strength, and thermal shock resistance. In contrast, Control Example 1, which completely omitted yttrium-stabilized zirconium oxide, performed the worst, with a sharp decrease in thermal shock resistance, indicating that the phase transformation toughening effect of zirconium oxide is indispensable for resisting thermal stress damage. Control Example 2, lacking rare earth additives, had the lowest high-temperature strength and significantly deteriorated bulk density, demonstrating that rare earth elements play a crucial role in promoting sintering densification and strengthening grain boundaries.

[0045] 2. Investigating the influence of key preparation process parameters on the properties of carbon-free composite spinel materials: As shown in Table 1, regarding the influence of composition, Example 3, with its lower content of activated alumina and rare earth elements, exhibited relatively poor performance across all aspects. Example 4, with its higher content, performed better than Example 3 but slightly worse than Example 2, which had a balanced composition, indicating the existence of an optimal composition range. Regarding the ball milling process, Example 5, using lower ball milling energy, showed poor performance, while Example 6, using higher ball milling energy, although showing better performance, still did not reach its optimal level. Example 2, with its moderate ball milling parameters, achieved optimal powder characteristics and final performance, demonstrating that the process has a clear optimal window.

[0046] Regarding molding pressure, Example 11, using lower pressure, exhibited relatively poor performance, while Example 12, using higher pressure, achieved the best bulk density and strength. Example 2's results fell in between, indicating that higher molding pressure is beneficial for material densification. In terms of sintering atmosphere control, Examples 13 and 14 showed similar but failed to surpass the optimized parameters used in Example 2, which achieved the best overall performance under precise oxygen partial pressure and dynamic flow rate regulation.

[0047] 3. Investigate the influence of key preparation processes on the properties of carbon-free composite spinel materials: As shown in Table 1, Comparative Example 3, which uses the conventional one-step sintering method, had the worst performance in all groups, fully demonstrating the necessity of the complex sintering process of this invention. After adding annealing treatment, the performance of Examples 15, 16, and 17 showed a clear increasing trend. Among them, Example 17, which used the optimized annealing process, performed best, with particularly outstanding thermal shock resistance. This indicates that controlling the annealing process parameters within the optimal range can effectively eliminate internal stress and stabilize the microstructure, thereby comprehensively improving the reliability and service life of the material.

Claims

1. A carbon-free composite spinel material for refining special steel for aircraft carriers, characterized in that, By mass percentage, it includes 20-30% activated alumina micro powder, 5-12% yttrium oxide stabilized zirconium oxide micro powder, 1-3% rare earth oxide composite additives, and the balance being fused magnesia particles; the rare earth oxide composite additives are powders composed of Y2O3 and La2O3 in a mass ratio of 2-3:

1.

2. The carbon-free composite spinel material for refining special steel for aircraft carriers according to claim 1, characterized in that, The fused magnesia particles contain more than 97.5% MgO, and their particle size distribution is as follows: 15-25% of the particles are 1-3mm, 10-20% of the particles are 0.5-1mm, 15-25% of the particles are 0.088-0.5mm, and the remainder is fine powder of 0.1μm to 0.088mm.

3. A method for preparing a carbon-free composite spinel material for refining special steel for aircraft carriers as described in any one of claims 1 or 2, characterized in that, Includes the following steps: S1. Raw material pretreatment and composite powder preparation According to the formula, fused magnesia particles, activated alumina micro powder, yttrium oxide stabilized zirconia micro powder, and rare earth oxide composite additives are placed together in a planetary ball mill. Anhydrous ethanol is used as the grinding medium, and high-energy ball milling is carried out for 4 to 10 hours at a ball-to-material ratio of 3 to 5:1 and a rotation speed of 280 to 400 r / min to obtain a uniformly distributed composite powder. S2, Vacuum mixing and aging treatment The composite powder described in S1 is placed in a vacuum plow, and a composite binder of 4-6% of the total powder mass is added. The mixture is then kneaded for 30-60 minutes under vacuum conditions of -0.08 to -0.1 MPa and temperature of 40-60℃ to obtain vacuum-degassed clay. The clay is then placed in a sealed container and aged at room temperature for 24-48 hours to obtain clay for use as a green body. The composite binder is composed of hydroxypropyl methylcellulose and polyethylene glycol in a mass ratio of 1:0.5-1. S3, Isostatic pressing and gradient drying The blank material described in S2 is loaded into a rubber mold and cold isostatically pressed at a pressure of 150~250MPa for 5~15 min. The molded blank is then placed in a humidity-controlled drying oven and pretreated at a temperature of 30~40℃ and a humidity of 80~90% for 12~24 h. The temperature is then increased to 110~120℃ at a rate of 0.5~1℃ / min and dried for 24~48 h to obtain a dried blank. S4, segmented controlled atmosphere sintering The dried green body described in S3 is placed in a high-temperature sintering furnace and sintered under a slightly positive pressure oxygen atmosphere. First, the temperature is increased to 600-800℃ at a rate of 1-2℃ / min and held for 2-4 hours to remove the organic binder. Then, the temperature is increased to 1200-1400℃ at a rate of 3-5℃ / min and held for 2-4 hours to complete the initial formation of the spinel phase. Next, the temperature is increased to 1700-1780℃ at a rate of 2-3℃ / min and held for 6-12 hours to complete the densification of the material and the purification of grain boundaries. Finally, the temperature is decreased to 1450-1550℃ at a rate of 2-3℃ / min and held for 1-2 hours to relieve stress. Then, the material is cooled to room temperature in the furnace to obtain a carbon-free composite spinel material.

4. The method for preparing a carbon-free composite spinel material for refining special steel for aircraft carriers according to claim 3, characterized in that, The high-energy ball mill described in S1 uses zirconia grinding balls, and the ball mill is filled with high-purity nitrogen for protection. The temperature is controlled at 20~50℃ during the ball milling process; the specific surface area of ​​the composite powder is 5~15m². 2 / g, with a particle size distribution D50 of 0.5~2μm.

5. The method for preparing a carbon-free composite spinel material for refining special steel for aircraft carriers according to claim 3, characterized in that, The composite binder described in S2 also includes 0.5-1% of a plasticizer by total powder mass, wherein the plasticizer is one of glycerol or dibutyl phthalate; during the mixing process, the material temperature is maintained at 40-60℃ and the vacuum degree is maintained at -0.09--0.1MPa.

6. The preparation method according to claim 3, characterized in that, The isostatic pressing process described in S3 adopts a bidirectional pressurization method, first pre-pressing at 50~100MPa for 2~5 min, and then raising to the final pressure of 150~250MPa and holding for 5~15 min; during the drying process, the humidity gradually decreases from 90% to 30%, and the temperature gradually increases from 40℃ to 120℃.

7. The preparation method according to claim 3, characterized in that, The sintering process described in S4 is carried out in a slightly oxidizing atmosphere with an oxygen partial pressure of 5~15 kPa, and the pressure inside the sintering furnace is maintained 1~5 kPa higher than the outside pressure. During the heat preservation stage at 1700~1780℃, the oxygen flow rate is adjusted every 1~2.5 h, and the flow rate varies from 10~50 L / min.

8. The preparation method according to claim 3, characterized in that, After S4 is completed, a heat treatment step is also included: the sintered carbon-free composite spinel material is annealed at 1400~1500℃ for 4~8 h, argon gas is introduced for protection during the annealing process, and after annealing, it is cooled to 600~800℃ at a rate of 1~2℃ / min, and then cooled to room temperature with the furnace.

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