Production method for regulating and controlling internal stress of fused zirconia corundum brick

Abstract

The invention relates to the field of fused zirconia corundum bricks, and discloses a production method for regulating and controlling internal stress of fused zirconia corundum bricks, which comprises the following steps: preparing raw materials; melting in an electric furnace: putting the prepared raw materials into the electric furnace for melting; ventilating in stages in the melting process; preparing a mold for casting; after casting is completed, demolding and annealing are conducted; the raw materials comprise the following components in parts by weight: 50-65 parts of aluminum oxide; 25 to 35 parts of zirconium oxide; 8 to 12 parts of silicon dioxide; 0.5 to 2 parts of chromium sesquioxide; 0.5 to 1.5 parts of magnesium oxide; and 3-5 parts of scandium oxide. By adding scandium oxide and utilizing the characteristic that scandium oxide stabilizes a tetragonal phase, high-temperature phase change of zirconium oxide is effectively inhibited, and stress is reduced. Meanwhile, scandium oxide is used for refining grains, enhancing the grain boundary strength and reducing high-temperature stress concentration, so that the high-temperature stability of the fused zirconia corundum brick is improved, brittle fracture is avoided, and the thermal stability and durability are enhanced.

Description

Technical Field

[0001] The present invention relates to the field of electrofused zirconia corundum bricks, and specifically to a production method for regulating the internal stress of electrofused zirconia corundum bricks. Background Art

[0002] Electrofused zirconia corundum bricks are a kind of high-performance refractory materials, mainly prepared by electrofusion process from zirconia, alumina and a small amount of other stabilizers. They have excellent high-temperature strength, erosion resistance and thermal stability, and are widely used in extreme high-temperature environments such as glass furnaces, electric furnace linings, and metallurgical furnace linings. Due to the high refractoriness and corrosion resistance of zirconia, electrofused zirconia corundum bricks show excellent stability under working conditions of high temperature and high thermal shock, and are key materials indispensable in fields such as the glass industry, iron and steel smelting, and non-ferrous metal smelting.

[0003] Existing electrofused zirconia corundum bricks are prone to phase transformation of zirconia in high-temperature environments. When transforming from the tetragonal phase to the monoclinic phase, it is accompanied by volume change, resulting in the generation of stress inside the material, and then causing cracks or even brittle fracture. In addition, in traditional melting processes, the control of gas flow rate and type is not good, which easily leads to uneven oxidation reaction, reduction of melt purity, formation of structural defects, and weakening of the brick body performance. At the same time, during the cooling process, the temperature gradient is too large, resulting in heat stress concentration, increasing the risk of cracks and deformation, and affecting the service life of the brick body. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the present invention provides a production method for regulating the internal stress of electrofused zirconia corundum bricks, which solves the problems of stress concentration caused by zirconia phase transformation, purity reduction caused by unstable gas control during the melting process, and cracks and deformation caused by improper cooling rate.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A production method for regulating the internal stress of electrofused zirconia corundum bricks, comprising the following steps:

[0006] Prepare raw materials;

[0007] Electrofuse in an electric furnace, and put the prepared raw materials into the electric furnace for electrofusion;

[0008] Ventilate in stages during the electrofusion process;

[0009] Prepare a mold for casting;

[0010] Anneal after casting is completed.

[0011] Preferably, the raw materials include the following components in parts by weight:

[0012] Alumina: 50 - 65 parts;

[0013] Zirconia: 25 - 35 parts;

[0014] Silica: 8 - 12 parts;

[0015] Chromium(III) oxide: 0.5 - 2 parts;

[0016] Magnesium oxide: 0.5 - 1.5 parts;

[0017] Scandium oxide: 3 - 5 parts.

[0018] Among them, the composition of the raw materials directly affects the performance of the final fused zirconia corundum brick. Alumina and zirconia are the main components, providing the strength and high-temperature resistance of the material; silica, chromium(III) oxide, magnesium oxide, etc. are auxiliary components, which can improve the thermal stability, wear resistance of the material and regulate the expansion characteristics of the brick body. The addition of scandium oxide helps to improve the high-temperature stability of the zirconia corundum brick, reduce thermal shock resistance, and helps to improve its microstructure at high temperature, thereby reducing the generation of internal stress in the brick body. And scandium oxide has a stable tetragonal phase, so it can reduce the phase transformation stress of zirconia and refine the zirconia grains, improving the stability of the brick body in a high-temperature environment.

[0019] Preferably, in the preparation, the raw materials are poured into a planetary mixer and mixed for 15 - 30 min under the condition of a rotation speed of 30 - 80 rpm.

[0020] By using the mixer, the above raw materials can be stirred to improve the uniformity of the distribution among the raw materials.

[0021] Preferably, in the electric furnace melting, the uniformly mixed raw materials are added to the electric furnace, and then the raw materials are heated to 1900 - 2000 °C by the electric furnace.

[0022] The electrofusion process changes the crystal structure of the raw materials through high temperature to form a uniform fused zirconia corundum material. When heated to 1900 - 2000 °C, the melting degree of the raw materials is high enough to fully eliminate the tiny impurities or gases between the raw materials, ensuring the uniformity and proper chemical composition of the melt. In this way, it helps to reduce the internal stress caused by uneven composition or gas entrapment.

[0023] Preferably, the staged gas injection includes:

[0024] First stage: When the temperature of the raw materials is 1500 - 1600 °C, combustion-supporting gas is introduced into the electric furnace for oxidative refining, and the gas flow rate is 10 - 20 m 3 / h, and the duration is 5 - 10 min;

[0025] Second stage: When the temperature of the raw materials is 1900 - 2000 °C, inert gas is introduced into the electric furnace, and the gas flow rate is 10 - 20 m 3 / h, and the duration is 5 - 10 min;

[0026] Third stage: After the second stage, wait for 13 - 20 minutes, then introduce an inert gas into the electric furnace. The gas flow rate is 8 - 15 m 3 / h, and the duration is 3 - 5 minutes;

[0027] The purpose of staged gas injection is to remove excess oxygen and impurities during the melting process through precise gas flow rate and temperature control, and optimize the melting environment. In the first stage, metal impurities and gases are removed through oxidative refining, thereby reducing pores and other defects during the smelting process. In the second and third stages, introducing an inert gas helps prevent over-oxidation and provides a more stable melt for subsequent casting, reducing the generation of gas inclusions. Staged gas injection not only helps control the raw material composition, but also effectively regulates the physical properties and chemical stability of the melt, reducing the generation of internal stress.

[0028] The combustion-supporting gas includes oxygen, and the inert gas includes argon or helium.

[0029] Preferably, in the preparation of the mold, the mold temperature is preheated and maintained at 1500 - 1700 °C. After the third stage, the raw material temperature is reduced to 1500 - 1700 °C at a cooling rate of 1 - 3 °C / min and then casting is carried out, and the casting flow rate is 25 - 35 kg / s.

[0030] Preheating the mold temperature is to avoid too fast cooling, resulting in too low surface temperature of the material and forming cracks. Appropriate cooling rate and mold temperature can make the temperature gradient of the material more gentle, avoiding brick deformation or cracks caused by excessive local stress. Controlling the casting flow rate within the range of 25 - 35 kg / s helps ensure the uniform distribution of the melt in the mold, avoiding stress concentration caused by too fast cooling of the material, thereby reducing internal stress.

[0031] Preferably, after the casting is completed, first cool the mold and the raw material to 1200 - 1300 °C at a cooling rate of 1 - 3 °C / min, then cool the mold and the raw material to room temperature at a cooling rate of 5 - 10 °C / min, and finally demold.

[0032] A slow cooling rate can effectively slow down the internal stress caused by cooling. In the later stage of casting, temperature difference and rapid cooling may cause stress concentration inside the material, thus forming cracks. By first slowly cooling to 1200 - 1300 °C and then quickly cooling to room temperature, it helps the stress in the brick structure to be reasonably released, reducing the stress accumulation caused by temperature difference, and finally keeping the brick structure stable during the whole cooling process.

[0033] Preferably, in the annealing process, the demolded raw material is put into an annealing furnace, first heated to 800 - 1000 °C and kept warm for 120 - 180 min, and then cooled to room temperature at a cooling rate of ≤1 °C / min to obtain the electrofused zirconia corundum brick.

[0034] The purpose of the annealing process is to relieve the thermal stress inside the material during the long-time heating and slow cooling process. By keeping warm at 800 - 1000 °C, the microstructure in the material can reach a more stable state, eliminating the internal stress in the transition stage. In addition, the slow cooling after annealing enables the material to release the stress caused by the temperature difference during the process of gradually adapting to the temperature change, thereby reducing stress concentration and further improving the performance of the electrofused zirconia corundum brick.

[0035] The present invention provides a production method for regulating the internal stress of electrofused zirconia corundum bricks. It has the following beneficial effects:

[0036] 1. By utilizing the characteristic that scandium oxide can stabilize the tetragonal phase, the present invention can effectively inhibit the phase change of zirconia at high temperatures, reduce the stress caused thereby, and the addition of scandium oxide can effectively refine the grains of zirconia, improve the strength of the grain boundary, and reduce the stress concentration generated in a high-temperature environment, thus significantly improving the high-temperature stability of the electrofused zirconia corundum brick, effectively solving the stress problem caused by the phase change of zirconia in a high-temperature environment, avoiding the brittle fracture of the brick body at high temperatures, and enhancing its thermal stability and durability.

[0037] 2. By ventilating in stages during the melting process, the present invention can introduce combustion-supporting gases such as oxygen for oxidative refining according to the changes in different temperature conditions, remove the impurities generated during the smelting process, and promote the oxidation reaction; at the same time, inert gases can prevent over-oxidation or gas inclusions. By controlling the gas flow rate and gas type in stages, not only the problems of unstable gas flow rate and incomplete oxidation are effectively solved, but also the uniformity and purity of the melt are optimized, thereby further reducing the generation of internal stress.

[0038] 3. During the cooling process after casting, by first gradually cooling to 1200 - 1300 °C, then cooling to room temperature, and finally demolding, the present invention can avoid the excessive temperature difference between the inside and outside of the material caused by too rapid temperature change, thereby generating thermal stress and resulting in cracks or deformation of the brick body. By dividing the cooling process into two stages, first cooling to an appropriate temperature at a relatively slow cooling rate and then accelerating the cooling to room temperature, the stress accumulation caused by rapid cooling can be effectively slowed down, ensuring that the internal structure of the material is fully stabilized, avoiding the crack problem caused by excessive temperature difference, improving the mechanical strength and reliability of the electrofused zirconia corundum brick, and ensuring its excellent performance in practical applications. Description of the Drawings

[0039] Figure 1 Schematic flow chart of the production method of the present invention. Specific embodiments

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the specification of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0041] For a better understanding of the present invention, the above content will be described in detail below in conjunction with specific embodiments.

[0042] Please refer to the attached Figure 1 :

[0043] Example 1

[0044] Preparation steps:

[0045] Prepare raw materials: Add 60 parts of alumina, 30 parts of zirconia, 10 parts of silica, 1 part of chromium sesquioxide, 1 part of magnesia, and 4 parts of scandium oxide to a planetary mixer and mix at a speed of 50 rpm for 25 minutes;

[0046] Electric furnace melting:

[0047] Put the prepared raw materials into an electric furnace, and raise the temperature of the electric furnace to 1950 °C;

[0048] Stage-by-stage ventilation:

[0049] First stage: When the temperature of the raw materials reaches 1550 °C, introduce oxygen, and set the flow rate to 15 m 3 / h, and continue for 8 minutes;

[0050] Second stage: After the temperature rises to 1950 °C, introduce argon, and the gas flow rate is 15 m 3 / h, and continue for 8 minutes;

[0051] Third stage: After waiting for 15 minutes, introduce argon again, and adjust the gas flow rate to 10 m 3 / h, and continue for 4 minutes.

[0052] Casting:

[0053] Preheat the mold to 1600 °C, and start casting after cooling the raw materials to 1600 °C at a rate of 2 °C / min. The casting flow rate is 30 kg / s;

[0054] After casting is completed, first cool down to 1300 °C at a rate of 2 °C / min, then cool down to room temperature at a rate of 8 °C / min, and finally demold.

[0055] Annealing:

[0056] Put the demolded raw material into an annealing furnace, first heat it to 950 °C and hold for 150 minutes, and then cool it to room temperature at a cooling rate of 1 °C / min.

[0057] Example 2

[0058] Preparation steps:

[0059] Prepare raw materials:

[0060] Put 50 parts of alumina; 25 parts of zirconia; 8 parts of silica; 0.5 parts of chromium sesquioxide; 0.5 parts of magnesia; 3 parts of scandium oxide into a planetary mixer and mix at 30 rpm for 15 min;

[0061] Electric furnace melting:

[0062] Put the prepared raw material into an electric furnace, and raise the temperature of the electric furnace to 1900 °C;

[0063] Stage ventilation:

[0064] The first stage: When the temperature of the raw material reaches 1500 °C, introduce oxygen, and set the flow rate to 10 m 3 / h and continue for 5 minutes;

[0065] The second stage: After the temperature rises to 1900 °C, introduce argon, and the gas flow rate is 10 m 3 / h and continue for 5 minutes;

[0066] The third stage: After waiting for 13 minutes, introduce argon again, and adjust the gas flow rate to 8 m 3 / h and continue for 3 minutes.

[0067] Casting:

[0068] Preheat the mold to 1500 °C, start casting after the raw material is cooled to 1500 °C at 1 °C / min. The casting flow rate is 25 kg / s;

[0069] After casting is completed, first cool it to 1200 °C at a rate of 1 °C / min, then cool it to room temperature at a rate of 5 °C / min, and finally demold.

[0070] Annealing:

[0071] Put the demolded raw material into an annealing furnace, first heat it to 800 °C and hold for 120 minutes, and then cool it to room temperature at a cooling rate of 1 °C / min.

[0072] Example 3

[0073] Preparation steps:

[0074] Formulation raw materials:

[0075] Add 65 parts of alumina, 35 parts of zirconia, 12 parts of silica, 2 parts of chromium sesquioxide, 1.5 parts of magnesia, and 5 parts of scandium oxide to a planetary mixer and mix at 80 rpm for 30 min;

[0076] Electric furnace melting:

[0077] Put the prepared raw materials into an electric furnace and raise the temperature of the electric furnace to 2000 °C;

[0078] Staged ventilation:

[0079] First stage: When the temperature of the raw materials reaches 1600 °C, introduce oxygen with a flow rate set at 20 m 3 / h and continue for 10 minutes;

[0080] Second stage: After the temperature rises to 2000 °C, introduce argon with a gas flow rate of 20 m 3 / h and continue for 10 minutes;

[0081] Third stage: After waiting for 20 minutes, introduce argon again with the gas flow rate adjusted to 15 m 3 / h and continue for 5 minutes.

[0082] Casting:

[0083] Preheat the mold to 1700 °C, cool the raw materials to 1700 °C at a rate of 3 °C / min and then start casting. The casting flow rate is 35 kg / s;

[0084] After casting is completed, first cool to 1300 °C at a rate of 3 °C / min, then cool to room temperature at a rate of 10 °C / min, and finally demold.

[0085] Annealing:

[0086] Put the demolded raw materials into an annealing furnace, first heat to 1000 °C and hold for 180 minutes, and then cool to room temperature at a cooling rate of 1 °C / min.

[0087] Comparative Example 1

[0088] Comparative Example 1-1

[0089] Variable: Completely remove scandium oxide, and keep other parameters the same as in Example 1.

[0090] Formulation raw materials:

[0091] 60 parts of alumina, 30 parts of zirconia, 10 parts of silica, 1 part of chromium sesquioxide, 1 part of magnesia.

[0092] Without adding scandium oxide, the remaining preparation method is the same. Stir with a planetary mixer at a rotation speed of 50 rpm for 25 minutes.

[0093] Subsequent steps:

[0094] Electric furnace melting, staged ventilation, casting and cooling, and annealing are all the same as in Example 1.

[0095] Comparative Example 1-2

[0096] Variable: The addition amount of scandium oxide is higher than the range (6 parts), and other conditions remain unchanged.

[0097] Raw materials for preparation:

[0098] 58 parts of aluminum oxide, 28 parts of zirconium oxide, 10 parts of silicon dioxide, 1 part of chromium sesquioxide, 1 part of magnesium oxide, 6 parts of scandium oxide.

[0099] Other stirring parameters are the same as in Example 1.

[0100] Subsequent steps:

[0101] Electric furnace melting, staged ventilation, casting and cooling, and annealing are all the same as in Example 1.

[0102] Comparative Example 1-3

[0103] Variable: The addition amount of scandium oxide is lower than the range (2 parts), and other conditions remain unchanged.

[0104] Raw materials for preparation:

[0105] 61 parts of aluminum oxide, 29 parts of zirconium oxide, 10 parts of silicon dioxide, 1 part of chromium sesquioxide, 1 part of magnesium oxide, 2 parts of scandium oxide.

[0106] Other stirring parameters are the same as in Example 1.

[0107] Subsequent steps:

[0108] Electric furnace melting, staged ventilation, casting and cooling, and annealing are all the same as in Example 1.

[0109] Comparative Example 2

[0110] Comparative Example 2-1

[0111] Variable: Cancel staged ventilation and adopt single oxygen ventilation, and other conditions remain unchanged.

[0112] Raw materials for preparation:

[0113] The same as in Example 2.

[0114] Electric furnace melting:

[0115] Raise the temperature to 1900 °C and hold for 25 minutes.

[0116] Ventilation method (canceling stages):

[0117] Only oxygen is introduced, and no argon is introduced.

[0118] When the temperature reaches 1900 °C, oxygen is introduced, and the gas flow rate is 10 m 3 / h for 15 minutes.

[0119] Subsequent steps:

[0120] Casting, cooling, annealing are the same as in Example 2.

[0121] Comparative Example 2-2

[0122] Variables: Staged ventilation time, flow rate below the range.

[0123] Prepare raw materials:

[0124] The same as in Example 2.

[0125] Electric furnace melting:

[0126] The temperature is raised to 1850 °C.

[0127] Staged ventilation (adjusting parameters):

[0128] First stage: When the temperature is 1400 °C, oxygen is introduced, and the gas flow rate is 8 m 3 / h for 4 minutes.

[0129] Second stage: When the temperature is 1850 °C, argon is introduced, and the gas flow rate is 8 m 3 / h for 4 minutes.

[0130] Third stage: Wait for 12 minutes, then introduce argon at 7 m 3 / h for 2 minutes.

[0131] Subsequent steps:

[0132] Casting, cooling, annealing are the same as in Example 2.

[0133] Comparative Example 2-3

[0134] Variables: Staged ventilation time, flow rate above the range.

[0135] Prepare raw materials:

[0136] The same as in Example 2.

[0137] Electric furnace melting:

[0138] The temperature is raised to 2050 °C.

[0139] Staged ventilation (adjusting parameters):

[0140] The first stage: When the temperature is 1550 °C, oxygen is introduced, and the gas flow rate is 22 m 3 / h, lasting for 12 minutes.

[0141] The second stage: When the temperature is 2050 °C, argon is introduced, and the gas flow rate is 22 m 3 / h, lasting for 12 minutes.

[0142] The third stage: Wait for 21 minutes, then introduce argon at 6 m 3 / h, lasting for 6 minutes.

[0143] Subsequent steps:

[0144] Casting, cooling, annealing are the same as in Example 2.

[0145] Comparative Example 3-1

[0146] Variable: Cancel the staged cooling and directly cool down rapidly.

[0147] Prepare the raw materials:

[0148] The same as in Example 3.

[0149] Electric furnace melting, gas supply method:

[0150] The same as in Example 3.

[0151] Casting and cooling (canceling the stages):

[0152] Preheat the mold to 1700 °C, pour the melt after it cools down to 1700 °C, and the flow rate is 35 kg / s.

[0153] Directly cool down to room temperature at a rate of 15 °C / min.

[0154] Annealing:

[0155] The same as in Example 3.

[0156] Comparative Example 3-2

[0157] Variable: The cooling rate is higher than the range.

[0158] Prepare the raw materials:

[0159] The same as in Example 3.

[0160] Electric furnace melting, gas supply method:

[0161] The same as in Example 3.

[0162] Casting and cooling (adjusting the parameters):

[0163] Preheat the mold to 1700°C, cool the melt to 1700°C and then cast it, with a flow rate of 35 kg / s.

[0164] First, cool it at a rate of 5°C / min to 1300°C, and then cool it at a rate of 15°C / min to room temperature.

[0165] Annealing:

[0166] The same as in Example 3.

[0167] Comparative Example 3-3

[0168] Variable: The cooling rate is lower than the range.

[0169] Prepare raw materials:

[0170] The same as in Example 3.

[0171] Electric furnace melting, gas supply method:

[0172] The same as in Example 3.

[0173] Casting and cooling (adjust parameters):

[0174] Preheat the mold to 1700°C, cool the melt to 1700°C and then cast it, with a flow rate of 35 kg / s.

[0175] First, cool it at a rate of 1.5°C / min to 1300°C, and then cool it at a rate of 4.5°C / min to room temperature.

[0176] Annealing:

[0177] The same as in Example 3.

[0178] Experiment 1

[0179] Experiment purpose: To explore the influence of scandium oxide content on the material properties

[0180] Sample setting: Select Example 1 and Comparative Example 1 (Comparative Examples 1-1, 1-2, and 1-3) as samples for testing;

[0181] Testing steps:

[0182] Mechanical property testing

[0183] Vickers hardness: Use an HVS-1000 Vickers hardness tester, apply a 10 N load, hold the pressure for 10 s, test 5 different points for each sample, and take the average value.

[0184] Compressive strength: Use an electronic universal testing machine (Instron-3382), with a loading rate of 0.5 mm / min, measure each sample 3 times and take the average value.

[0185] Fracture toughness: The single-edge notch bending (SENB) method was used to measure the fracture toughness KIC, and the calculation method was based on the ASTM-E399-20 standard.

[0186] Thermal stability test

[0187] Coefficient of thermal expansion: Measured using a NETZSCH-DIL-402C thermomechanical dilatometer from 200 °C to 1600 °C with a heating rate of 5 °C / min.

[0188] Thermal shock test: The samples were quenched from 1200 °C to room temperature, and the crack situation was observed. Five groups of each sample were tested, and the failure rate was calculated.

[0189] Microstructural analysis

[0190] SEM observation: Using a Hitachi-S-4800 scanning electron microscope to observe the grain structure and porosity of the material, and analyze the effect of scandium oxide addition on the microstructure.

[0191] Density and porosity determination: The density of the material was measured using the Archimedes method, and the porosity was calculated according to the ASTM-C373-88 standard.

[0192] Experimental data

[0193] Table 1: Performance test data of fused zirconia corundum bricks with different scandium oxide contents

[0194]

[0195] Experimental summary

[0196] The addition of scandium oxide plays a crucial role in optimizing the comprehensive properties of fused zirconia corundum bricks. As can be seen from Table 1, when no scandium oxide is added (Control 1-1), the mechanical properties of the material all decrease significantly. The Vickers hardness decreases by 8.9%, the compressive strength decreases by 14.4%, and the fracture toughness decreases by 25.6%. This decrease may be related to grain boundary weakening. SEM observation shows that the grain size of the sample without scandium oxide addition is larger, and the grain boundary bonding is not tight, resulting in an increase in the overall brittleness of the material. In addition, the thermal shock failure rate is as high as 34.2%, indicating that the material is prone to cracking during the thermal cycle, which may be related to the internal stress concentration caused by uneven thermal expansion.

[0197] However, the higher the amount of scandium oxide added, the better. From the data, although the samples of Comparative Examples 1-2 are slightly better than (Comparative Examples 1-3) in terms of Vickers hardness, compressive strength, fracture toughness, etc., they do not exceed Example 1. Especially in terms of fracture toughness, the failure rate of heat shock resistance is slightly increased. The reason may be that after the excess of scandium oxide, more scandium-rich oxide phases are formed inside the material, and these phases may precipitate at the grain boundaries, resulting in uneven grain boundary energy, which ultimately affects the overall performance stability.

[0198] As for Comparative Examples 1-3 with lower scandium oxide content, although the hardness and strength are improved to a certain extent compared with the sample without scandium oxide, the fracture toughness is still 1.4 lower than that of Example 1, and the thermal shock resistance failure rate is also significantly higher than that of Example 1. This shows that the main role of scandium oxide is to refine the grains and improve the grain boundary bonding strength, and the content of Comparative Examples 1-3 may not be enough to fully exert these effects, so the performance improvement is limited.

[0199] From the microstructure point of view, scandium oxide mainly inhibits the growth of Al2O3 grains, improves crystal uniformity, and forms a strengthening phase at the grain boundary, thereby improving the toughness and thermal shock resistance of the material. However, if the content is too high, it may cause multiple phases to precipitate at the grain boundary, affecting the uniformity of the material. Therefore, in Example 1, various properties reach a better balance point, taking into account hardness, strength, and thermal shock resistance, and are suitable as an optimized formula for industrial applications.

[0200] Experiment 2

[0201] Experimental purpose: To verify the effect of phased ventilation process on the performance of fused zirconium corundum bricks

[0202] Sample setting: Example 2 and Comparative Example 2 (Comparative Example 2-1, 2-2 and 2-3) were selected as samples for testing;

[0203] Test steps:

[0204] Porosity and density determination

[0205] The porosity and density were determined by the Archimedes method according to ASTM-C373-88 standard.

[0206] Mechanical properties test

[0207] Vickers hardness (HV): HVS-1000 Vickers hardness tester, 10N load, holding pressure for 10s, 5 test points for each sample, and the average value.

[0208] Compressive strength (MPa): Instron-3382 electronic universal testing machine, loading rate 0.5 mm / min, each sample was measured 3 times and the average value was taken.

[0209] Microstructure analysis

[0210] SEM observation: Hitachi-S-4800 scanning electron microscope was used to analyze the grain boundary bonding condition and pore distribution.

[0211] Experimental data

[0212] Table 2: Influence of different gas ventilation processes on the properties of fused zirconia corundum bricks

[0213]

[0214] Experimental summary

[0215] When oxygen was introduced alone (Comparative Example 2-1), the porosity increased significantly, resulting in a 6.5% decrease in density, an 11.6% reduction in compressive strength, and a significant decrease in hardness. SEM observation showed that the pore distribution inside the material was uneven, and there was pore aggregation in some areas, which might lead to local stress concentration and ultimately weaken the overall strength of the material. When oxygen was supplied, the oxidation reaction of the raw materials was intense. Without argon protection, the oxides might grow excessively, affecting the grain boundary bonding. This explained the poor grain boundary integrity.

[0216] When the gas ventilation parameters were lower than the standard (Comparative Example 2-2), the properties of the material were between those of the standard process and the process without argon. Although the hardness and strength increased, they still did not reach the optimal level. The porosity was still 1.7% higher than that of Example 2 process, and the density decreased slightly. It was speculated that due to insufficient oxygen supply, the melt degassing was incomplete, and some gases could not be discharged in time, eventually forming residual pores. Although there was no serious damage to the grain boundaries, microscopic analysis showed that there were still some incompletely sintered and dense areas inside the material, which might affect the long-term service life.

[0217] For Comparative Example 2-3 with excessive gas ventilation, the hardness and compressive strength were slightly lower than those of Example 2, the density decreased by 0.75%, and the porosity increased. Although the overall structural integrity was still maintained well, excessive argon might cause obstruction to the internal fluidity of the material during melting, affecting the bubble removal effect. In addition, excessive oxygen introduction might lead to some peroxidation reactions, forming unexpected phase structures, which in turn affected the final mechanical properties. Generally speaking, the standard gas ventilation scheme was the best in controlling the porosity and optimizing the grain boundary bonding, ensuring the density and mechanical stability of the material.

[0218] Experiment 3

[0219] Experimental purpose: Influence of cooling rate on the properties of fused zirconia corundum bricks

[0220] Sample setting: Examples 3 and Comparative Examples 13 (Comparative Examples 3-1, 3-2, and 3-3) were selected as samples for testing; Experimental steps

[0221] Mechanical property test

[0222] Vickers hardness (HV): HVS-1000 Vickers hardness tester, 10N load, holding pressure for 10s, 5 test points for each sample, taking the average value.

[0223] Compressive strength (MPa): Instron 3382 electronic universal testing machine, loading rate 0.5mm / min, measuring 3 times for each sample and taking the average value.

[0224] Thermal stability test

[0225] Thermal shock test: Rapid cooling from 1200°C to room temperature, observing cracks, 5 samples in each group, calculating the failure rate.

[0226] Microstructure analysis

[0227] SEM observation: Hitachi-S-4800 scanning electron microscope, analyzing the grain morphology and crack distribution.

[0228] Residual stress determination: Stress analysis was carried out using XRD.

[0229] Experimental data

[0230] Table 3: Influence of different cooling rates on the properties of electrofused zirconia corundum bricks

[0231]

[0232] Experimental summary

[0233] For the samples with direct rapid cooling (Comparative Example 3-1), the overall performance deteriorated significantly. The compressive strength decreased by 18.9%, the Vickers hardness decreased by nearly 10%, and the thermal shock failure rate soared to 37.8%. SEM showed that the grain boundary cracks increased, and XRD tests indicated that the residual stress was as high as 126MPa, indicating that the internal stress was not released sufficiently. The rapid cooling led to a too large temperature gradient inside the material, causing the surface layer and the interior to shrink out of sync, thus forming a large number of microcracks. This uneven stress distribution ultimately reduced the thermal stability of the material, making it more prone to cracking in high-temperature environments.

[0234] For the samples with a cooling rate higher than that of Example 3 (Comparative Example 3-2), although the situation was slightly better than that of Comparative Example 3-1, it was still not ideal. The hardness and compressive strength decreased slightly, and the thermal shock failure rate was 16.8% higher than that of Example 3 during cooling. The crack rate increased to 5.3%, and more microcracks were shown at the grain boundaries. Analysis showed that a high cooling rate would still lead to the accumulation of thermal stress, resulting in local residual stress regions inside the material, which in turn affected the long-term service performance. In this case, although the overall structure of the material was relatively intact, sudden cracking might occur under repeated temperature changes.

[0235] In contrast, the sample with a lower cooling rate (Comparative Example 3-3) showed a performance closer to that of the cooling process in Example 3. The hardness and compressive strength still remained at a relatively high level, and the thermal shock failure rate was 14.9%, slightly higher than that in Example 3. SEM observations showed that the grain size was slightly larger, and the local densification phenomenon at the grain boundaries was not as good as that of the standard process. The low cooling rate can effectively reduce the accumulation of thermal stress, enabling the internal tissue stress to be evenly released. However, the problem of excessive grain growth still exists, resulting in a slight decrease in the density of the material. Although the impact of this scheme on the thermal shock performance is not serious, further reducing the cooling rate may affect the overall strength.

[0236] Overall, Example 3 provides the optimal balance point. The hardness, compressive strength, and thermal shock resistance all show the best performance, the residual stress is controlled within a reasonable range, and the crack rate is the lowest. This cooling scheme effectively controls grain growth while ensuring the uniform release of thermal stress, enabling the material to have good mechanical and thermal stability. Therefore, appropriate staged cooling is crucial for optimizing the microstructure of electrofused zircon corundum bricks, which can not only ensure the density but also reduce the internal residual stress and improve the thermal shock resistance.

[0237] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A production method for regulating the internal stress of fused zirconium corundum bricks, characterized in that: The following steps are involved: Prepare raw materials; Electric furnace melting: put the prepared raw materials into the electric furnace for melting; Ventilation in stages during the melting process; Prepare molds for casting; After casting, demoulding and annealing are carried out.

2. A production method for regulating the internal stress of fused zirconium corundum bricks according to claim 1, characterized in that: The raw materials include the following components in parts by weight: Alumina: 50-65 parts; Zirconia: 25-35 parts; Silicon dioxide: 8-12 parts; Chromium trioxide: 0.5-2 parts; Magnesium oxide: 0.5-1.5 parts; Scandium oxide: 3 to 5 parts.

3. A production method for regulating the internal stress of fused zirconium corundum bricks according to claim 2, characterized in that: In the preparation, the raw materials are poured into a planetary mixer and mixed at a rotation speed of 30 to 80 rpm for 15 to 30 minutes.

4. A production method for regulating the internal stress of fused zirconium corundum bricks according to claim 1, characterized in that: In the electric furnace melting, uniformly mixed raw materials are added into the electric furnace, and then the raw materials are heated to 1900-2000° C. by the electric furnace.

5. A production method for regulating the internal stress of fused zirconium corundum bricks according to claim 4, characterized in that: The staged ventilation includes: Stage 1: When the raw material temperature is 1500-1600℃, combustion-supporting gas is introduced into the electric furnace for oxidation refining, and the gas flow rate is 10-20m 3 / h, duration is 5 to 10 minutes; Stage 2: When the raw material temperature is 1900-2000℃, inert gas is introduced into the electric furnace with a gas flow rate of 10-20m 3 / h, duration is 5 to 10 minutes; Stage 3: After the end of stage 2, wait for 13 to 20 minutes and then introduce inert gas into the electric furnace with a gas flow rate of 8 to 15 m 3 / h, duration is 3 to 5 minutes; The combustion-supporting gas includes oxygen, and the inert gas includes argon or helium.

6. A production method for regulating the internal stress of fused zirconium corundum bricks according to claim 5, characterized in that: In the preparation of the mold, the mold temperature is preheated and maintained at 1500-1700° C., and after the three stages are completed, the raw material temperature is reduced to 1500-1700° C. at a cooling rate of 1-3° C. / min before casting, and the casting flow rate is 25-35 kg / s.

7. A production method for regulating the internal stress of fused zirconium corundum bricks according to claim 6, characterized in that: After the casting is completed, the mold and the raw material are first cooled to 1200-1300° C. at a cooling rate of 1-3° C. / min, then cooled to room temperature at a cooling rate of 5-10° C. / min, and finally demolded.

8. The production method for regulating the internal stress of fused zirconium corundum bricks according to claim 1, characterized in that: In the annealing, the demoulding raw material is placed in an annealing furnace, first heated to 800-1000° C. and kept warm for 120-180 min, and then cooled to room temperature at a cooling rate of ≤1° C. / min to obtain an electric fused zirconium corundum brick.

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