Alumina-magnesia-aluminum metal composite refractory for RH refining furnace and preparation method thereof

Abstract

The application relates to the technical field of refractory materials, in particular to a metal aluminum-alumina-magnesia composite refractory material for RH refining furnaces and a preparation method thereof, and the preparation steps of the composite refractory material are as follows: step 1, metal aluminum powder, alumina powder and magnesia powder are dry-mixed first, a binder is added, and then the mixture is uniformly mixed, pressed into shape, and dried; step 2, the shaped and dried body is subjected to low-temperature nitriding treatment under nitrogen protection for 2-6 hours to obtain an embryo containing an Al@AIN core-shell structure; and step 3, the embryo containing the Al@AIN core-shell structure is subjected to high-temperature sintering by gradient heating to 1450-1650 DEG C, and then naturally cooled to obtain the composite refractory material. The prepared composite material has suitable bulk density, low porosity, compact structure, excellent mechanical properties, high strength and good thermal shock resistance at high temperatures, no obvious cracks and peeling after multiple thermal shock cycles, and excellent stability.

Description

Technical Field

[0001] This application relates to the field of refractory materials technology, and more specifically, to a metallic aluminum-alumina-magnesia composite refractory material suitable for RH refining furnaces and its preparation method. Background Technology

[0002] In the entire steel smelting process, the refining stage is a key step in improving the quality of steel. As an important piece of equipment for secondary refining, the RH refining furnace mainly undertakes the tasks of further purifying the primary steel, fine-tuning its composition, and removing impurities, so that the various performance indicators of the steel can meet the expected standards.

[0003] However, the service environment of RH refining furnaces is extremely harsh. The furnace lining refractory materials are subjected to prolonged high-temperature vacuum, scouring by molten steel, slag erosion, and cyclic thermal shock. Prolonged exposure to high temperatures can cause thermal expansion of the refractory materials, leading to cracks and even spalling. The molten steel slag contains various complex chemical components with strong chemical reactivity, reacting with the refractory materials and gradually dissolving and eroding their surface. Frequent temperature changes and repeated thermal shocks cause cracks to propagate and connect, ultimately causing the refractory materials to lose their protective and supportive functions. Traditional refractory materials for RH refining furnaces, such as magnesia-chromium and magnesia-carbon materials, have many problems. Magnesia-chromium materials produce harmful chromium-containing substances during use, posing a threat to the environment and human health. Magnesia-carbon materials cause carbonization of the molten steel, affecting steel quality. Furthermore, the traditional material preparation process is energy-intensive and does not meet the requirements of green and low-carbon development. Therefore, developing a high-performance, environmentally friendly refractory material for RH refining furnaces is of significant practical importance. Summary of the Invention

[0004] To address the technical problems mentioned in the background art, this application provides a metallic aluminum-alumina-magnesia composite refractory material for RH refining furnaces and its preparation method.

[0005] A composite refractory material of aluminum-alumina-magnesia for RH refining furnace adopts the following technical solution: A composite refractory material of aluminum-alumina-magnesium oxide for RH refining furnace comprises the following raw materials in the following mass fractions: 10-30 wt% aluminum powder, 40-60 wt% alumina powder, 10-30 wt% magnesium oxide powder, and 2-5 wt% binder.

[0006] Preferably, the aluminum powder has a particle size of 5-50 μm and a purity > 98%; the alumina powder has an Al2O3 purity > 99%; and the magnesium oxide powder is sintered magnesia with a purity > 92%.

[0007] A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps: Step 1: Add aluminum powder, alumina powder and magnesium oxide powder to a mixer and dry mix for 15-30 minutes. Then slowly add the binder while stirring, controlling the stirring speed at 100-200 rpm. Continue stirring for 1-2 hours. After mixing evenly, press into shape and dry. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 500-650℃ and subjected to low-temperature nitriding treatment for 2-6 hours to obtain a green body containing an Al@AIN core-shell structure. Step 3: The preform containing the Al@AIN core-shell structure is subjected to a gradient heating to 1450-1650℃ under a pressure of 0.01-0.05MPa, sintered at high temperature, and then naturally cooled to obtain the composite refractory material.

[0008] Preferably, the pressing pressure in step 1 is 150-300 MPa, the holding time is 2-5 min, and the drying temperature is 280-320℃ for 20-30 h.

[0009] Preferably, the heating rate in step 2, which raises the temperature to 500-650°C, is 2-5°C / min.

[0010] Preferably, the thickness of the AlN shell in the Al@AIN core-shell structure in step 3 is 1-3 μm.

[0011] Preferably, in step 3, the temperature is increased to 850-900℃ at a heating rate of 1-3℃ / min, held for 1-2 hours, and then increased to 1450-1650℃ at a heating rate of 2-4℃ / min, held for 6-10 hours.

[0012] In summary, this application has the following beneficial effects: This application achieves a completely carbon-free design by forming an Al2O3-MgO composite refractory material with an Al@AlN core-shell structure through low-temperature nitriding and high-temperature sintering. Under the high-temperature service environment of RH refining, no free carbon dissolves from the material, fundamentally avoiding the problem of carbon contamination in molten steel. Simultaneously, AlN exhibits excellent chemical compatibility with Al2O3 and MgO, significantly improving high-temperature stability and further ensuring the long service life of the material and the cleanliness of the molten steel.

[0013] This application utilizes low-temperature nitriding to in-situ generate an Al@AlN core-shell structure on the surface of metallic aluminum powder. The high-melting-point AlN shell spatially confines the internal Al, controlling the release temperature, morphology, and reaction pathway of the Al liquid. This allows metallic aluminum to exist in different morphologies (micro / nano-scale Al droplets, Al vapor, Al...) at different temperature ranges. x O yThe gradual release of the gas phase avoids the drawbacks of molten aluminum agglomeration hindering the reaction and blocking pores, resulting in poor uniformity of nitriding products. During the subsequent gradient heating sintering process, the Al core can release heat through oxidation reaction, promoting the synthesis of spinel phase (MgAlON); while the AlN shell can inhibit premature oxidation of metallic aluminum and at the same time fill the pores as a dispersed reinforcing phase, refining the microstructure, and finally forming a dense metallic aluminum-alumina-magnesium oxide composite multiphase composite refractory material, which significantly improves the material's thermal shock resistance and resistance to molten steel erosion.

[0014] This application employs a gradient heating sintering process to achieve multiphase synergistic strengthening. In the intermediate temperature stage, MgAlON spinel preferentially forms, and the accompanying volume expansion effectively seals pores. In the high temperature stage, Al2O3 and MgO undergo further solid-state reaction to generate a continuous network structure, while AlN acts as a second phase, pinning grain boundaries and inhibiting abnormal grain growth. The combined effect of these three factors gives the material high density, excellent resistance to alkaline slag erosion, and resistance to melting and seepage.

[0015] This application uses a composite of alkaline silica sol, aluminum borate, and water glass as a binder, which exhibits good compatibility with the system. It can partially transform into a silicate or aluminate transition phase during the low-temperature nitriding stage, enhancing the initial strength of the green body. Aluminum borate has high refractoriness; when combined with alkaline silica sol and water glass, it fills the material pores during high-temperature sintering, preventing heat transfer and slag penetration, thus improving overall refractoriness, refining the microstructure of the refractory material, and ensuring uniform stress distribution. Under rapid temperature changes, the uniform structure buffers thermal stress, reducing crack initiation and propagation, and improving thermal shock resistance. Simultaneously, it completely decomposes into SiO2 during high-temperature sintering, avoiding impurity residues, ensuring the material's high-temperature chemical stability and purity, and exhibiting strong process adaptability and excellent environmental friendliness. Detailed Implementation

[0016] The present application will be further described in detail below with reference to the embodiments.

[0017] The aluminum powder (particle size: 1250 mesh) used in the embodiments and comparative examples of this application was purchased from Lingshou County Yigao Mineral Products Processing Plant; the alumina powder was purchased from Gongyi Wanfang Refractory Materials Co., Ltd.; the sintered magnesia (purity: 96%) was purchased from Xinmi City Zhengyang Foundry Materials Factory; the alkaline silica sol was purchased from Jinan Feiyue Chemical Co., Ltd.; the aluminum borate was purchased from Hubei Dali Chemical Co., Ltd.; and the water glass was purchased from Jinan Zesheng Chemical Co., Ltd.

[0018] Examples 1-3 provide an antibacterial and abrasion-resistant nylon fiber and its preparation method.

[0019] Example 1 A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps; Step 1: Add 10wt% aluminum powder, 60wt% alumina powder, and 28wt% sintered magnesia to a mixer and dry mix for 150 min. Then slowly add 2wt% binder while stirring, controlling the stirring speed at 100 rpm. Continue stirring for 1 h. After mixing evenly, press and dry. The pressing pressure is 150 MPa, the holding time is 2 min, the drying temperature is 280℃, and the drying time is 20 h. The binder consists of alkaline silica sol, aluminum borate, and water glass in a mass ratio of 3:1:0.5. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 500℃ at a heating rate of 2℃ / min and subjected to low-temperature nitriding treatment for 2h to obtain a green body containing an Al@AIN core-shell structure with a thickness of 1μm. Step 3: The preform containing the Al@AIN core-shell structure is heated to 850°C at a rate of 1°C / min under a pressure of 0.01 MPa and held for 1 hour. Then, it is heated to 1450°C at a rate of 2°C / min and held for 6 hours. After gradient heating and high-temperature sintering, the composite refractory material is obtained after natural cooling.

[0020] Example 2 A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps; Step 1: Add 20wt% aluminum powder, 55wt% α-Al2O3 and 22wt% sintered magnesia to a mixer and dry mix for 20min. Then slowly add 3wt% binder while stirring, controlling the stirring speed at 150rpm. Continue stirring for 1.5h. After mixing evenly, press and dry. The pressing pressure is 200MPa, the holding time is 4min, the drying temperature is 300℃, and the drying time is 25h. The binder is composed of alkaline silica sol, aluminum borate and water glass in a mass ratio of 4:1.5:0.8. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 600℃ for 4 hours at a heating rate of 4℃ / min to obtain a green body containing an Al@AIN core-shell structure with a thickness of 2μm. Step 3: The preform containing the Al@AIN core-shell structure is heated to 880°C at a rate of 2°C / min under a pressure of 0.03MPa and held for 1.5h. Then, it is heated to 1550°C at a rate of 3°C / min and held for 8h. After gradient heating and high-temperature sintering, the composite refractory material is obtained after natural cooling.

[0021] Example 3 A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps; Step 1: Add 30wt% aluminum powder, 40wt% α-Al2O3 and 25wt% sintered magnesia to a mixer and dry mix for 30 minutes. Then slowly add 5wt% binder while stirring, controlling the stirring speed at 200 rpm. Continue stirring for 2 hours. After mixing evenly, press and dry. The pressing pressure is 300 MPa, the holding time is 5 minutes, the drying temperature is 320℃, and the drying time is 30 hours. The binder consists of alkaline silica sol, aluminum borate and water glass in a mass ratio of 5:2:1. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 650℃ at a heating rate of 5℃ / min and subjected to low-temperature nitriding treatment for 6h to obtain a green body containing Al@AIN core-shell structure with a thickness of 3μm. Step 3: The preform containing the Al@AIN core-shell structure is heated to 900℃ at a rate of 3℃ / min under a pressure of 0.05MPa and held for 2 hours. Then, it is heated to 1650℃ at a rate of 4℃ / min and held for 10 hours. After gradient heating and high-temperature sintering, the composite refractory material is obtained after natural cooling.

[0022] Comparative Example 1 A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps; Step 1: Add 10wt% aluminum powder, 60wt% alumina powder, and 28wt% sintered magnesia to a mixer and dry mix for 150 min. Then slowly add 2wt% binder while stirring, controlling the stirring speed at 100 rpm. Continue stirring for 1 h. After mixing evenly, press and dry. The pressing pressure is 150 MPa, the holding time is 2 min, the drying temperature is 280℃, and the drying time is 20 h. The binder consists of alkaline silica sol and water glass in a mass ratio of 3:0.5. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 500℃ at a heating rate of 2℃ / min and subjected to low-temperature nitriding treatment for 2h to obtain a green body containing an Al@AIN core-shell structure with a thickness of 1μm. Step 3: The preform containing the Al@AIN core-shell structure is heated to 850°C at a rate of 1°C / min under a pressure of 0.01 MPa and held for 1 hour. Then, it is heated to 1450°C at a rate of 2°C / min and held for 6 hours. After gradient heating and high-temperature sintering, the composite refractory material is obtained after natural cooling.

[0023] Comparative Example 2 A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps; Step 1: Add 10wt% aluminum powder, 60wt% alumina powder, and 28wt% sintered magnesia to a mixer and dry mix for 150 min. Then slowly add 2wt% binder while stirring, controlling the stirring speed at 100 rpm. Continue stirring for 1 h. After mixing evenly, press and dry. The pressing pressure is 150 MPa, the holding time is 2 min, the drying temperature is 280℃, and the drying time is 20 h. The binder consists of alkaline silica sol and aluminum borate in a mass ratio of 3:1. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 500℃ at a heating rate of 2℃ / min and subjected to low-temperature nitriding treatment for 2h to obtain a green body containing an Al@AIN core-shell structure with a thickness of 1μm. Step 3: The preform containing the Al@AIN core-shell structure is heated to 850°C at a rate of 1°C / min under a pressure of 0.01 MPa and held for 1 hour. Then, it is heated to 1450°C at a rate of 2°C / min and held for 6 hours. After gradient heating and high-temperature sintering, the composite refractory material is obtained after natural cooling.

[0024] Comparative Example 3 A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps; Step 1: Add 10wt% aluminum powder, 60wt% alumina powder, and 28wt% sintered magnesia to a mixer and dry mix for 150 min. Then slowly add 2wt% binder while stirring, controlling the stirring speed at 100 rpm. Continue stirring for 1 h. After mixing evenly, press and dry. The pressing pressure is 150 MPa, the holding time is 2 min, the drying temperature is 280℃, and the drying time is 20 h. The binder consists of alkaline silica sol, aluminum borate, and water glass in a mass ratio of 3:1:0.5. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 680℃ at a heating rate of 2℃ / min and subjected to low-temperature nitriding treatment for 2h to obtain a green body containing Al@AIN core-shell structure with a thickness of 1μm. Step 3: The preform containing the Al@AIN core-shell structure is heated to 850°C at a rate of 1°C / min under a pressure of 0.01 MPa and held for 1 hour. Then, it is heated to 1450°C at a rate of 2°C / min and held for 6 hours. After gradient heating and high-temperature sintering, the composite refractory material is obtained after natural cooling.

[0025] Comparative Example 4 A method for preparing a composite refractory material of metallic aluminum-alumina-magnesium oxide for RH refining furnace includes the following preparation steps; Step 1: Add 10wt% aluminum powder, 60wt% alumina powder, and 28wt% sintered magnesia to a mixer and dry mix for 150 min. Then slowly add 2wt% binder while stirring, controlling the stirring speed at 100 rpm. Continue stirring for 1 h. After mixing evenly, press and dry. The pressing pressure is 150 MPa, the holding time is 2 min, the drying temperature is 280℃, and the drying time is 20 h. The binder consists of alkaline silica sol, aluminum borate, and water glass in a mass ratio of 3:1:0.5. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 500℃ at a heating rate of 2℃ / min and subjected to low-temperature nitriding treatment for 2h to obtain a green body containing an Al@AIN core-shell structure with a thickness of 1μm. Step 3: The preform containing the Al@AIN core-shell structure is heated to 1450℃ at a pressure of 0.01MPa and a heating rate of 1℃ / min, held at that temperature for 7 hours, and then sintered at high temperature. After natural cooling, the composite refractory material is obtained.

[0026] Performance testing The comprehensive properties of the composite refractory materials prepared in Examples 1-3 and Comparative Examples 1-4 are as follows; Bulk density and apparent porosity: Tested in accordance with national standard GB / T 2997-2015 "Test methods for bulk density, apparent porosity and true porosity of dense shaped refractory products"; Room temperature compressive strength: Tested according to national standard GB / T 5072-2023 "Test method for room temperature compressive strength of dense shaped refractory products"; High-temperature flexural strength: Tested according to national standard GB / T 3002-2017 "Test Method for High-Temperature Flexural Strength of Refractory Materials"; Thermal shock resistance: Tested in accordance with national standard GB / T 30873-2014 "Test Method for Thermal Shock Resistance of Refractory Materials"; The test results are shown in Table 1.

[0027] Table 1 Performance parameters of the composite refractory materials in Examples 1-3 and Comparative Examples 1-4

[0028] As shown in Table 1, the composite refractory material prepared in this application exhibits suitable bulk density and low porosity, resulting in a dense structure that lays the foundation for its excellent mechanical properties. Its room-temperature compressive strength is >135 MPa, ensuring that the material can withstand certain pressure at room temperature without damage. In terms of thermal properties, its high-temperature flexural strength is greater than 18 MPa, maintaining high strength even at high temperatures. After multiple thermal shock cycles, the material shows no obvious cracks or spalling, demonstrating excellent stability.

[0029] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A composite refractory material of aluminum-alumina-magnesium oxide for RH refining furnaces, characterized in that, It is composed of the following raw materials in the following mass fractions: 10-30 wt% aluminum powder, 40-60 wt% alumina powder, 10-30 wt% magnesium oxide powder, and 2-5 wt% binder; the binder is composed of alkaline silica sol, aluminum borate, and water glass in a mass ratio of 3-5:1-2:0.5-1. The preparation method of the composite refractory material is as follows: Step 1: Add aluminum powder, alumina powder and magnesium oxide powder to a mixer and dry mix for 15-30 minutes. Then slowly add the binder while stirring, controlling the stirring speed at 100-200 rpm. Continue stirring for 1-2 hours. After mixing evenly, press into shape and dry. Step 2: Under nitrogen protection, the shaped and dried green body is heated to 500-650℃ and subjected to low-temperature nitriding treatment for 2-6 hours to obtain a green body containing Al@AlN core-shell structure; Step 3: The blank containing the Al@AlN core-shell structure is subjected to a gradient heating to 1450-1650℃ under a pressure of 0.01-0.05MPa, and after high-temperature sintering and natural cooling, the composite refractory material is obtained. In step 3, the temperature is increased to 850-900℃ at a rate of 1-3℃ / min and held for 1-2 hours. Then, the temperature is increased to 1450-1650℃ at a rate of 2-4℃ / min and held for 6-10 hours.

2. The composite refractory material according to claim 1, characterized in that, The aluminum powder has a particle size of 5-50 μm and a purity of >98%; the alumina powder has an Al2O3 purity of >99%; and the magnesium oxide powder is sintered magnesia with a purity of >92%.

3. The composite refractory material according to claim 1, characterized in that, The pressing pressure in step 1 is 150-300 MPa, and the holding time is 2-5 min; the drying temperature is 280-320℃, and the drying time is 20-30 h.

4. The composite refractory material according to claim 1, characterized in that, In step 2, the heating rate to 500-650℃ is 2-5℃ / min.

5. The composite refractory material according to claim 1, characterized in that, The thickness of the AlN shell in the Al@AlN core-shell structure in step 3 is 1-3 μm.

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