Metal yttrium directly bonded MgO-composite spinel brick and its preparation method and application

Abstract

The present invention discloses a metal yttrium directly bonded MgO-composite spinel brick, a preparation method thereof, and an application in a RH impregnation tube and RH lower tank under strong oxygen blowing conditions. The metal yttrium directly bonded MgO-composite spinel brick comprises raw materials and additives; the raw materials comprise the following components, by mass percentage: 25-50% fused magnesia aggregate, 20-45% Mg(Al,Cr)2O4 composite spinel aggregate, 10-20% Mg(Al,Cr)2O4 composite spinel fine powder, 8-12% light-burned magnesia, and 2-8% metal yttrium; the additives comprise 0.05-0.08% by weight of the raw materials, explosion-proof fiber, and 3-5% by weight of a binder; the binder is aluminum dihydrogen phosphate. The metal yttrium directly bonded MgO-composite spinel brick provided by the present invention has excellent corrosion resistance, oxidation resistance, and thermal shock resistance, and does not produce "overburning" under high-temperature strong oxygen blowing conditions, and can meet the harsh working conditions of the RH oxygen blowing process.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature refractory material preparation, and in particular to a metal yttrium directly bonded MgO-composite spinel brick, and a preparation method and application thereof. Background Art

[0002] RH refining, or vacuum degassing of molten steel, is an important secondary refining method for improving molten steel purity and is currently the most important refining method for ultra-low carbon, low oxygen content stainless steel. The RH oxygen blowing process is integrated into the vacuum degassing (RH) process to elevate the molten steel temperature and promote decarburization under negative pressure. However, the high-temperature, high-vacuum oxidizing environment created by this high oxygen blowing can significantly reduce the service life of the refractory lining in the RH dip tube. The lower trough of the RH is a typical gas-refractory-molten steel / slag three-phase interface. The Marangoni effect of the molten steel / slag causes rapid erosion of the refractory at the steel-slag interface. Furthermore, strong oxygen blowing can lead to strong oxidation and overburning of the refractory at the gas-solid-liquid interface. This localized overburning of the refractory can significantly deviate from the original refractory properties in the corresponding area, a major cause of cracking and spalling in the refractory lining under cyclic thermal shock conditions. The above process severely limits the processability and production efficiency of the RH oxygen blowing process. Therefore, it is necessary to specifically address the problem of rapid localized melting loss of the refractory materials lining the RH impregnation tube and RH lower tank under strong oxygen blowing conditions. New refractory materials with strong oxidation and erosion resistance, as well as strong sintering resistance under high-temperature strong oxygen blowing conditions, need to be developed to meet on-site use requirements and provide refractory support for the RH strong oxygen blowing process.

[0003] The literature "Suto M, Koyake T, Kawata Y. Wear of MgO-C Bricks Lining a RHLower Vessel [J]. Journal of the Technical Association of Refractories, 2004, 24 (3))" and "Chen Zhaoyou. Ways to improve the service life of refractory materials for off-furnace refining and their development trends [J]. Refractories, 2007, 41 (1): 1-12)" introduced that in the early days, in order to solve the problem of rapid melting loss of refractory materials in local areas of the RH immersion tube and RH lower tank lining, especially at the gas-solid-liquid interface, MgO-C or MgO-CaO-C masonry schemes were used. Although carbon composite refractory materials can effectively improve the corrosion resistance of materials, the problem of carbon composite refractory materials "adding carbon" to molten steel has always been a pain point in ultra-low carbon steel refining. At the same time, the oxidation of carbon composite refractory materials under strong oxygen blowing vacuum conditions and the reaction of MgO and C under high temperature vacuum will affect the stability of the carbon composite refractory lining. Therefore, MgO-C refractory materials cannot meet the process requirements of RH refining to produce ultra-low carbon and low oxygen steel under strong oxygen blowing conditions.

[0004] A patented technology for a composite refractory material for RH refining furnaces and its preparation method (CN202310585028.5) uses corundum, chromium-aluminum alloy powder and magnesia as the main raw materials, and forms a carbon-free MgAl2O4-MgCr2O4-MgAlON in-situ composite reinforced corundum composite refractory material at high temperature. Although it can avoid the problems of carbon increase and Mg vapor pollution of traditional RH lined magnesia carbon bricks to a certain extent; however, under the conditions of the RH oxygen blowing process, the nitride binding phase MgAlON will continue to oxidize, causing the binding phase to decompose and the refractory material structure to be destroyed. At the same time, the N element will dissolve into the molten steel after oxidation to form hard nitride inclusions, which brings new problems. Therefore, the above-mentioned materials still cannot meet the requirements of the RH oxygen blowing process. For the same reason, a patented technology for a preparation method of a magnesium-alon refractory material with coexisting morphologies for RH refining furnaces (CN202111527731.8) forms a MgAlON phase through high-temperature nitriding, which can meet the traditional RH refining process, but it is also unable to adapt to the stringent requirements of the RH oxygen blowing process.

[0005] The patented technology for the preparation of calcium-containing periclase-magnesium-aluminate spinel refractory materials for RH refining furnaces (CN202210012513.9) draws on the successful experience of using magnesia-calcium sand in VOD refining furnaces and introduces fine powder of fused magnesia-calcium-aluminate sand into the periclase-magnesium-aluminate spinel system. It is hoped that by leveraging the stable high-temperature vacuum structure and excellent alkaline slag resistance of CaO, the corrosion resistance of the overall material under high-temperature vacuum and the molten steel purification function of the free CaO coating will be improved. Traditional VOD linings do not have online repair and gunning, but the RH immersion pipe and RH lower trough need to be wet-gunned at high temperatures. CaO can easily hydrate and cause structural failure. Moreover, the CaO hydration problem is difficult to significantly improve, which limits the amount of CaO added, that is, the molten steel purification function and performance improvement of the CaO coating.

[0006] Therefore, it is urgent to develop a refractory material that can meet the stringent requirements of RH immersion tubes and RH lower troughs under strong oxygen blowing conditions, and has excellent thermal shock resistance and erosion resistance under high temperature and strong oxygen blowing conditions, and does not produce "overburning" under strong oxygen blowing conditions. Summary of the Invention

[0007] In order to solve the problems in the prior art of RH refining furnaces such as MgO-C / MgAlON combined with spinel and other composite refractory materials that have adverse effects on carbon and nitrogen addition in molten steel and rapid oxidation under strong oxygen blowing conditions leading to structural failure, as well as the problems of insufficient corrosion resistance of pure oxide refractory systems and structural spalling due to high-temperature overburning under the RH oxygen blowing process, the present invention provides a metal yttrium directly bonded MgO-composite spinel brick and a preparation method thereof, so as to further improve the performance of the refractory lining of the RH immersion tube and the RH lower tank under the RH oxygen blowing process, extend the service life without contaminating the molten steel, and provide refractory material support for ensuring the refining process of ultra-clean steel.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A metal yttrium directly bonded MgO-composite spinel brick comprises raw materials and additives; the raw materials comprise the following components by mass percentage: 25-50% fused magnesia aggregate, 20-45% Mg(Al,Cr)2O4 composite spinel aggregate, 10-20% Mg(Al,Cr)2O4 composite spinel fine powder, 8-12% light-burned magnesia, and 2-8% metal yttrium; the additives comprise explosion-proof fibers accounting for 0.05-0.08% by weight of the raw materials and a binder accounting for 3-5% by weight of the raw materials; the binder is aluminum dihydrogen phosphate.

[0010] Preferably, the Mg(Al, Cr)2O4 composite spinel raw material used for the Mg(Al, Cr)2O4 composite spinel aggregate and the Mg(Al, Cr)2O4 composite spinel fine powder has a Cr2O3 content of 10 to 35 wt%.

[0011] Preferably, the particle size of the metal yttrium is ≤20 μm, and the yttrium content in the metal yttrium is ≥99.6 wt%.

[0012] Preferably, the particle size of the light-burned magnesia is ≤45 μm, and the content of MgO in the light-burned magnesia is ≥99.0 wt%.

[0013] Preferably, the performance indicators of the metal yttrium directly combined with MgO-composite spinel brick are: apparent porosity 3.2-6.5%, bulk density 3.12-3.23 g / cm 3 The line change rate after high temperature 1700℃ is 1.01~1.80%, the line change rate after three re-firing at 1700℃ is 0.09~0.40%, the high temperature flexural strength under 1400℃×30min conditions is 15.6~23.5MPa, and the strength retention rate after three times of air cooling from 1100℃ to 20℃ is 64~75%.

[0014] A preparation method of a metal yttrium directly bonded MgO-composite spinel brick comprises the following steps: uniformly mixing the raw materials and additives, followed by mechanical pressing, baking, and carbon embedding and insulation treatment; wherein: the mechanical pressing pressure is 250-300 MPa, the baking temperature is 300-500°C for 5-10 hours, and the carbon embedding and insulation temperature is 1500-1550°C for 1-3 hours.

[0015] Preferably, the pressure of the machine compression molding is 250-280 MPa.

[0016] Preferably, the baking temperature is 400-500°C.

[0017] Preferably, the temperature of the carbon burial and heat preservation is 1500-1540°C.

[0018] The application of the above-mentioned metal yttrium directly combined with MgO-composite spinel bricks is used for RH impregnation pipes and RH lower tanks, and is particularly suitable for RH impregnation pipes and RH lower tanks under strong oxygen blowing conditions.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The matrix of the present invention uses elemental yttrium as the primary plastic metal bonding phase, and by introducing a high-melting-point metal phase (yttrium melting point 1522°C), the natural brittleness of the refractory material is addressed to a certain extent. Furthermore, under high-temperature, strong oxygen blowing conditions (RH), the elemental yttrium in the refractory surface matrix gradually oxidizes to form Y2O3. The in-situ formed Y2O3 exhibits comparable slag penetration resistance to non-oxide composite refractory systems, a point that has been fully demonstrated in Y2O3-containing refractory systems. Furthermore, it avoids the drawback of non-oxide systems, where carbides and nitrides are easily oxidized and contaminate the melt. More importantly, the in-situ formed Y2O3 phase does not produce intermediate compounds with MgO, the other main component of the matrix, at high temperatures. Therefore, the Y2O3 phase formed at high temperatures does not promote sintering of the matrix. Furthermore, the "pinning effect" of the in-situ formed Y2O3 phase in the matrix prevents secondary sintering of MgO grains in the matrix, thereby further preventing the matrix from over-burning under high-temperature, strong oxygen blowing conditions.

[0021] At the same time, in order to solve the enrichment phenomenon caused by the uneven distribution of introduced metallic yttrium in the matrix, which will cause the metallic yttrium to directly bond with the MgO-composite spinel brick during high-temperature oxidation service, resulting in uneven local oxidation expansion and structural failure, it is also necessary to strictly control the particle size and purity of the introduced elemental yttrium, and perform "infiltration" treatment on the entire material under a carbon-buried atmosphere protection environment, that is, without oxidizing the elemental yttrium, by raising the temperature to 1500℃-1550℃ to melt or semi-melt the metallic yttrium to realize the infiltration process in the matrix, thereby realizing the uniform distribution of the elemental yttrium, and finally realizing the bonding morphology of the metallic yttrium directly bonded to the MgO-composite spinel.

[0022] In addition, under the conditions of strong oxygen blowing, part of the Fe in the RH impregnation tube and the RH lower tank will be oxidized to form FeOt and dissolved in the slag, and the Fe2O3 content in the slag of the RH impregnation tube and the RH lower tank will increase. FeOt is an active corrosive medium in the slag. By utilizing the characteristics of the Al2O3-Cr2O3-Fe2O3 ternary infinite solid solution system and using Mg(Al,Cr)2O4 composite spinel as the main raw material (which has higher solid solution activity than traditional MgAl2O4 and MgCr2O4), the Fe2O3 in the slag can be effectively adsorbed or captured into the pores of the Mg(Al,Cr)2O4 composite spinel structure to form Mg(Al,Cr,Fe)2O4 composite spinel, thereby improving the overall material's resistance to slag erosion and penetration.

[0023] Based on the composite design of the raw material composition structure and the optimization of the firing process, the obtained metal yttrium directly combined with MgO-composite spinel brick has excellent corrosion resistance, oxidation resistance and thermal shock resistance, and does not produce "overburning" under high temperature and strong oxygen blowing conditions. It can meet the harsh working conditions requirements of the RH oxygen blowing process. DETAILED DESCRIPTION

[0024] In order to better explain the present invention, the main contents of the present invention are further illustrated below in conjunction with specific examples, but the contents of the present invention are not limited to the following examples.

[0025] The main contents of the present invention are further described below through Examples 1-4:

[0026] The requirements for some of the reagents used in Examples 1-4 are as follows:

[0027] Mg(Al,Cr)2O4 composite spinel raw material, wherein the content of Cr2O3 in its chemical composition is 10-35wt%;

[0028] The chemical composition of yttrium metal is Y ≥ 99.6 wt%, and the particle size is ≤ 20 μm;

[0029] The chemical composition of light-burned magnesia is MgO ≥ 99.0wt%, and the particle size is ≤ 45μm.

[0030] Example 1

[0031] The following raw materials, calculated by mass percentage, are used: 25% fused magnesia aggregate, 45% Mg(Al,Cr)2O4 composite spinel aggregate, 20% Mg(Al,Cr)2O4 composite spinel fine powder, 8% light-burned magnesia, and 2% yttrium metal. These raw materials, along with 0.05% explosion-proof fiber and 3% aluminum dihydrogen phosphate, are mixed uniformly and pressed into shape at 300 MPa. After baking at 500°C for 10 hours and then carbon-burying and holding at 1550°C for 3 hours, the resulting yttrium-bonded MgO-composite spinel brick is obtained.

[0032] The metal yttrium directly bonded MgO-composite spinel brick refractory material prepared in this embodiment was tested: the apparent porosity was 6.5%, the bulk density was 3.12 g / cm 3 The linear change rate after high-temperature 1700℃ firing is 1.01%, the linear change rate after three re-firing at 1700℃ is 0.09%, the high-temperature flexural strength (1400℃×30min) is 15.6MPa, and the strength retention rate after three times of air cooling from 1100℃ to 20℃ is 66%.

[0033] Example 2

[0034] The raw materials, calculated by mass percentage, are: 50% fused magnesia aggregate, 20% Mg(Al,Cr)2O4 composite spinel aggregate, 10% Mg(Al,Cr)2O4 composite spinel fine powder, 12% light-burned magnesia, and 8% yttrium metal. These raw materials, along with 0.08% explosion-proof fiber and 5% aluminum dihydrogen phosphate, are mixed uniformly and pressed into shape at 250 MPa. After baking at 300°C for 5 hours and then carbon-burying at 1500°C for 1 hour, yttrium metal-bonded MgO-composite spinel bricks are obtained.

[0035] The metal yttrium directly bonded MgO-composite spinel brick refractory prepared in this embodiment was tested: the apparent porosity was 3.2% and the bulk density was 3.23 g / cm 3 The linear change rate after high temperature 1700℃ firing is 1.80%, the linear change rate after three re-firing at 1700℃ is 0.40%, the high temperature flexural strength (1400℃×30min) is 23.5MPa, and the strength retention rate after three times of air cooling from 1100℃ to 20℃ is 64%.

[0036] Example 3

[0037] The raw materials, calculated by mass percentage, are: 38% fused magnesia aggregate, 32% Mg(Al,Cr)2O4 composite spinel aggregate, 15% Mg(Al,Cr)2O4 composite spinel fine powder, 9% light-burned magnesia, and 6% yttrium metal. These raw materials, along with 0.06% explosion-proof fiber and 4% aluminum dihydrogen phosphate, are mixed uniformly and pressed into shape at 280 MPa. After baking at 400°C for 10 hours and then carbon-burying and holding at 1540°C for 2 hours, the resulting yttrium-bonded MgO-composite spinel brick is obtained.

[0038] The metal yttrium directly bonded MgO-composite spinel brick refractory prepared in this embodiment was tested: the apparent porosity was 3.9%, the bulk density was 3.19 g / cm 3 The linear change rate after high-temperature 1700℃ firing is 1.55%, the linear change rate after three re-firing at 1700℃ is 0.35%, the high-temperature flexural strength (1400℃×30min) is 19.8MPa, and the strength retention rate after three times of air cooling from 1100℃ to 20℃ is 75%.

[0039] Example 4

[0040] The raw materials, calculated by mass percentage, are: 40% fused magnesia aggregate, 30% Mg(Al,Cr)2O4 composite spinel aggregate, 16% Mg(Al,Cr)2O4 composite spinel fine powder, 10% light-burned magnesia, and 4% yttrium. These raw materials, along with 0.07% explosion-proof fiber and 4% aluminum dihydrogen phosphate, are mixed uniformly and pressed into shape at 270 MPa. After baking at 400°C for 10 hours and then carbon-burying and holding at 1530°C for 2 hours, yttrium-bonded MgO-composite spinel bricks are obtained.

[0041] The metal yttrium directly bonded MgO-composite spinel brick refractory prepared in this embodiment was tested: the apparent porosity was 4.8%, the bulk density was 3.16 g / cm 3 The linear change rate after high-temperature firing at 1700℃ is 1.21%, the linear change rate after three re-firing at 1700℃ is 0.21%, the high-temperature flexural strength (1400℃×30min) is 17.4MPa, and the strength retention rate after three times of air cooling from 1100℃ to 20℃ is 69%.

[0042] Compared with traditional MgO-C / MgAlON combined with spinel and other composite refractory materials or pure oxide system refractory materials, the metal yttrium directly combined with MgO-composite spinel bricks prepared by the method of the present invention have excellent corrosion resistance, oxidation resistance and thermal shock resistance, and do not produce "overburning" phenomenon under high temperature and strong oxygen blowing conditions. In addition, the preparation process is simple and can meet the harsh working conditions requirements of the RH oxygen blowing process.

[0043] Other parts not described belong to the prior art.

Claims

1. A metal yttrium directly bonded MgO-composite spinel brick, characterized by: The invention comprises raw materials and additives; the raw materials comprise the following components in percentage by mass: 25-50% of fused magnesia aggregate, 20-45% of Mg(Al,Cr)2O4 composite spinel aggregate, 10-20% of Mg(Al,Cr)2O4 composite spinel fine powder, 8-12% of light-burned magnesia, and 2-8% of metallic yttrium; the additives comprise explosion-proof fibers accounting for 0.05-0.08% of the weight of the raw materials and a binder accounting for 3-5% of the weight of the raw materials; the binder is aluminum dihydrogen phosphate; the particle size of the metallic yttrium is ≤20 μm, and the yttrium content in the metallic yttrium is ≥99.6wt%; the particle size of the light-burned magnesia is ≤45 μm, and the MgO content in the light-burned magnesia is ≥99.0wt%.

2. The metal yttrium directly bonded MgO-composite spinel brick according to claim 1, characterized in that: The Mg(Al, Cr)2O4 composite spinel raw material used in the Mg(Al, Cr)2O4 composite spinel aggregate and the Mg(Al, Cr)2O4 composite spinel fine powder has a Cr2O3 content of 10-35wt%.

3. The metal yttrium directly bonded MgO-composite spinel brick according to any one of claims 1-2, characterized in that: The performance indicators of the metal yttrium directly combined with MgO-composite spinel brick are: apparent porosity 3.2~6.5%, bulk density 3.12~3.23g / cm 3 The linear change rate after high temperature 1700℃ sintering is 1.01~1.80%, the linear change rate after three re-sintering at 1700℃ is 0.09~0.40%, the high temperature flexural strength under 1400℃×30min conditions is 15.6~23.5MPa, and the strength retention rate after three times of air cooling from 1100℃ to 20℃ is 64~75%.

4. A method for preparing the metal yttrium directly bonded MgO-composite spinel brick according to claim 3, characterized in that: The method comprises the following steps: uniformly mixing the raw materials and additives, performing mechanical pressing, baking and carbon embedding and heat preservation treatment; wherein: the pressure of the mechanical pressing is 250-300 MPa, the temperature of the baking is 300-500°C and the time is 5-10 hours, and the temperature of the carbon embedding and heat preservation is 1500-1550°C and the time is 1-3 hours.

5. The method for preparing metal yttrium directly bonded MgO-composite spinel brick according to claim 4, characterized in that: The pressure of the machine pressing is 250-280 MPa.

6. The method for preparing a metal yttrium directly bonded MgO-composite spinel brick according to claim 4, characterized in that: The baking temperature is 400-500°C.

7. The method for preparing metal yttrium directly bonded MgO-composite spinel brick according to claim 4, characterized in that: The temperature of the carbon burial and heat preservation is 1500-1540°C.

8. An application of the metal yttrium directly bonded MgO-composite spinel brick according to claim 3, characterized in that: Used for RH dip tubes and RH lower tanks, especially for RH dip tubes and RH lower tanks under strong oxygen blowing conditions.