With the continuous development of iron and steel smelting technology, increasingly stringent performance requirements have been imposed on refractory lining materials used in high-temperature environments, such as hot metal ladles and torpedo ladles. Alumina-silicon carbide bricks, as a type of high-performance refractory material, have been widely used in critical areas of hot metal ladles and torpedo ladles due to their excellent corrosion resistance, spalling resistance, and high thermal shock stability.
Thermal shock resistance is an important indicator for evaluating the stability of refractory materials under conditions of rapid temperature fluctuations. It directly affects the service life of refractory linings and the safety of the smelting process. However, conventional alumina-silicon carbide bricks are prone to cracking and structural damage when exposed to extreme temperatures and rapid cooling, thereby limiting their further application. Therefore, improving the thermal shock resistance of alumina-silicon carbide bricks, particularly their stability under complex operating conditions involving high temperatures and rapid cooling, has become an important research topic in the field of refractory materials.
This study aims to investigate the effects of different raw material compositions and additives on the thermal shock resistance of alumina-silicon carbide bricks through experimental analysis, and to further elucidate the structural changes of the materials under high-temperature conditions and identify effective optimization approaches. Systematic thermal shock tests will be conducted on alumina-silicon carbide bricks of different specifications to provide theoretical insights and practical guidance for improving their thermal shock resistance, thereby offering technical support for the safe and stable operation of hot metal ladles and torpedo ladles in the iron and steel industry.
Basic Properties and Composition of Alumina-Silicon Carbide Bricks
Alumina-silicon carbide bricks are primarily composed of raw materials such as high-alumina bauxite, corundum, silicon carbide, and flake graphite. Appropriate amounts of additives are incorporated to improve their corrosion resistance, spalling resistance, and thermal shock stability. These raw materials impart excellent thermal stability and resistance to molten iron erosion, making alumina-silicon carbide bricks ideal lining materials for high-temperature applications, such as hot metal ladles and torpedo ladles.
The chemical composition of alumina-silicon carbide bricks varies depending on their manufacturing specifications and performance requirements. Common types include JH-ASCC55, JH-ASCC60, and JH-AMC-T. Among these, the Al₂O₃ contents are 52%, 60%, and 70%, respectively, while the combined SiC+C content is 15% for JH-ASCC55 and JH-ASCC60, compared with a relatively lower value of only 5% for JH-AMC-T. The appropriate combination of these components can effectively enhance the resistance of the bricks to high-temperature corrosion and improve their structural stability.
In terms of physical and chemical properties, the bulk density of alumina-silicon carbide bricks generally ranges from 2.75 to 2.90 g/cm³ after heat treatment at 200°C for 24 h. Following high-temperature treatment at 1450°C for 3 h, the bulk density remains between 2.70 and 2.85 g/cm³, indicating good stability at elevated temperatures. The compressive strength and flexural strength are also relatively high, generally exceeding 60 MPa and 15 MPa, respectively, ensuring reliable performance under high-temperature and heavy-load conditions. Furthermore, the permanent linear change typically remains within the range of 0 to +1%, further contributing to the dimensional and structural stability of the bricks.
Experimental Study on the Thermal Shock Resistance of Alumina-Silicon Carbide Bricks
Alumina-silicon carbide bricks are primarily composed of raw materials such as high-alumina bauxite, corundum, silicon carbide, and flake graphite. Appropriate amounts of additives are incorporated to improve their corrosion resistance, spalling resistance, and thermal shock stability. These raw materials impart excellent thermal stability and resistance to molten iron erosion, making alumina-silicon carbide bricks ideal lining materials for high-temperature applications, such as hot metal ladles and torpedo ladles.
The chemical composition of alumina-silicon carbide bricks varies depending on their manufacturing specifications and performance requirements. Common types include JH-ASCC55, JH-ASCC60, and JH-AMC-T. Among these, the Al₂O₃ contents are 52%, 60%, and 70%, respectively, while the SiC+C content is 15% for JH-ASCC55 and JH-ASCC60, compared with a relatively lower value of only 5% for JH-AMC-T. The appropriate combination of these components can effectively enhance the resistance of the bricks to high-temperature corrosion and improve their structural stability.
In terms of physical and chemical properties, the bulk density of alumina-silicon carbide bricks generally ranges from 2.75 to 2.90 g/cm³ after heat treatment at 200°C for 24 h. Following high-temperature treatment at 1450°C for 3 h, the bulk density remains between 2.70 and 2.85 g/cm³, indicating good stability at elevated temperatures. The compressive strength and flexural strength are also relatively high, generally exceeding 60 MPa and 15 MPa, respectively, ensuring reliable performance under high-temperature and heavy-load conditions. Furthermore, the permanent linear change typically remains within the range of 0 to +1%, further contributing to the dimensional and structural stability of the bricks.
Experimental Setup
1.Experimental Equipment and Instruments
The main equipment used in this experiment included a high-temperature furnace, thermal shock testing equipment, a digital electronic balance, a microscope, a compressive strength testing machine, and a flexural strength testing machine. The high-temperature furnace was used to simulate the thermal shock process experienced by alumina-silicon carbide bricks under high-temperature conditions, while the temperature control system ensured that temperature fluctuations remained within the predetermined range throughout the experiment. The compressive and flexural strength testing machines were used to evaluate the mechanical properties of alumina-silicon carbide bricks after high-temperature treatment. The microscope was employed to examine changes in the microstructure of the bricks after thermal shock, thereby providing further insight into their thermal shock resistance.
2. Preparation and Treatment of Experimental Samples
The experimental samples consisted of alumina-silicon carbide bricks of different specifications, including three grades: JH-ASCC55, JH-ASCC60, and JH-AMC-T. Samples of each grade were cut to standard dimensions to ensure consistency throughout the testing process. The sample surfaces were cleaned to remove impurities and dust, thereby minimizing potential interference with the experimental results. Before testing, all samples were allowed to stand at room temperature for 24 h to ensure their uniformity and stability.
3.Experimental Conditions and Parameter Settings
The experimental conditions and parameter settings are presented in Table 1.
| Item | Setting Parameters |
|---|---|
| Thermal shock test temperature range | 200~1450℃ |
| Thermal shock test cycle | 30 min heating, 5 min cooling |
| Temperature change rate | 5℃/min |
| Cooling method | Natural air cooling |
| Sample size | 150mm×150mm×50mm |
| Test times | At least 3 tests for each sample |
| Temperature accuracy of heating equipment | ±5℃ |
| Temperature for mechanical property test | Test after heating at 1450℃ for 3 h |
| Humidity control | Relative humidity: 50% |
| Linear change rate test | Measure after each heating cycle |
Table 1. Experimental Parameter Settings
During the experiment, the temperature was strictly controlled at a heating rate of 5°C/min to ensure stable temperature variations and minimize testing errors caused by improper temperature control. After testing, the mechanical properties of the samples were evaluated using compressive and flexural strength testing machines to ensure the reliability of the experimental data. Meanwhile, a microscope was used to examine the microstructural changes in the samples after thermal shock, thereby further analyzing the factors affecting their thermal shock resistance.
Experimental Procedure
1 .Thermal Shock Testing Procedure for Bricks
Thermal shock testing of the bricks was conducted using a high-temperature furnace to simulate actual operating conditions, enabling a comprehensive evaluation of the thermal shock resistance of alumina-silicon carbide bricks under rapid heating and cooling conditions. The specific testing procedure was as follows.
First, the alumina-silicon carbide brick samples were placed inside the furnace, with an initial temperature of 200°C, and preheated to the designated testing temperature. Subsequently, the heating rate was precisely controlled at 5°C/min until the target temperature of 1450°C was reached. The samples were then maintained at this temperature for 3 h to ensure sufficient exposure to the high-temperature environment, simulating the thermal conditions that may occur during actual industrial production.
Afterward, the cooling mode was activated, and the samples were removed from the furnace and allowed to cool naturally in ambient air for 5 h. Throughout the entire process, temperature variations and sample conditions were recorded periodically to ensure accurate control of the thermal cycle. Each sample underwent at least three thermal shock tests to ensure the reliability and reproducibility of the experimental results.
2.Control of Temperature Variations and Thermal Shock Cycles
(1) Control of Temperature Increase
At the beginning of the test, the furnace temperature was set to an initial value of 200°C and gradually increased at a predetermined heating rate of 5°C/min until the target temperature of 1450°C was reached. During the heating process, the temperature control system continuously monitored and adjusted the furnace temperature to ensure a stable and consistent heating rate, preventing uneven heating or excessive thermal stress caused by excessively rapid temperature increases. Temperature fluctuations throughout the heating process were maintained within ±5°C to ensure consistency of the experimental conditions.
(2) High-Temperature Holding Stage
After reaching the target temperature of 1450°C, the alumina-silicon carbide brick samples were maintained at this temperature for 3 h. During this period, the samples were exposed to a high-temperature environment to simulate the operating conditions that alumina-silicon carbide bricks may encounter during actual service. To minimize the influence of furnace temperature fluctuations on the experimental results, the temperature control system maintained a constant temperature within the specified range.
(3) Rapid Cooling Process Control
Immediately after the high-temperature holding stage, the samples underwent cooling treatment. Natural air cooling was adopted during this stage, with the samples placed in an ambient-temperature environment for a total cooling period of 5 h. This cooling procedure was intended to simulate rapid temperature reduction under thermal shock conditions. During this period, the temperature changes were monitored to ensure that the cooling process met the predetermined requirements and to minimize testing errors caused by excessively slow or rapid cooling.
(4) Repeated Testing of Thermal Shock Cycles
The thermal shock process was repeated at least three times for each sample to ensure the reliability and reproducibility of the experimental data. After each thermal shock cycle, changes in the external appearance of the samples, crack formation, and microstructural evolution were recorded. This ensured that temperature variations, sample conditions, and the effects of thermal shock on the physical properties of the bricks were accurately documented after each thermal cycle.
Analysis of Experimental Results
Comparison of Thermal Shock Resistance Among Alumina-Silicon Carbide Bricks of Different Specifications
Thermal shock tests were conducted on alumina-silicon carbide bricks of different specifications (JH-ASCC55, JH-ASCC60, and JH-AMC-T) to investigate the differences in their thermal shock resistance. The test results indicated that alumina-silicon carbide bricks of different specifications exhibited varying performance under high-temperature conditions, primarily in terms of thermal shock stability and mechanical properties after thermal shock exposure.
JH-ASCC55 and JH-ASCC60 exhibited relatively superior thermal shock resistance. In particular, after heating at 1450°C for 3 h, the samples showed no obvious cracks or structural damage. In contrast, JH-AMC-T bricks developed microcracks after undergoing the same high-temperature treatment, accompanied by reductions in both flexural and compressive strength, indicating relatively poor thermal shock resistance.
The experimental results showed that the compressive strengths of JH-ASCC55 and JH-ASCC60 were both 60 MPa, while their flexural strengths were 15 MPa, demonstrating good thermal shock stability. In comparison, JH-AMC-T exhibited a compressive strength of 50 MPa and a flexural strength of 12 MPa, both of which were relatively lower, indicating inferior performance after thermal shock exposure.
To provide a more intuitive comparison, the thermal shock resistance data for alumina-silicon carbide bricks of different specifications are presented in Table 2.
| Property Index | JH–ASCC55 | JH–ASCC60 | JH–AMC–T |
|---|---|---|---|
| Cold Crushing Strength / MPa | 60 | 60 | 50 |
| Modulus of Rupture / MPa | 15 | 15 | 12 |
| Bulk Density / g/cm³ | 2.70 | 2.85 | 2.85 |
| Cracks after thermal shock | None | None | Microcracks exist |
| Linear Change Rate / % | 0~+1 | 0~+1 | 0~+1 |
Table 2. Comparison of Thermal Shock Resistance of Alumina-Silicon Carbide Bricks with Different Specifications
A comprehensive analysis of the results indicates that JH-ASCC55 and JH-ASCC60 exhibit superior thermal shock resistance compared with JH-AMC-T, making them more suitable for demanding high-temperature operating environments. In contrast, JH-AMC-T is more susceptible to frequent thermal shock damage.
Effects of Thermal Shock on the Performance Changes of Alumina-Silicon Carbide Bricks
During thermal shock testing, significant temperature fluctuations had a considerable impact on the properties of alumina-silicon carbide bricks. The experimental results showed that their physical and mechanical properties gradually changed after undergoing several thermal shock cycles. Specifically, microcracks appeared on the brick surfaces, particularly during rapid cooling following high-temperature exposure, when crack formation became more pronounced.
As the number of thermal shock cycles increased, both the compressive and flexural strengths of the bricks gradually decreased, while the permanent linear change after thermal shock also increased. According to the experimental data, JH-ASCC55 and JH-ASCC60 maintained relatively high compressive and flexural strengths after thermal shock exposure, whereas JH-AMC-T exhibited a more pronounced reduction in strength.
In particular, after five thermal shock cycles, the compressive strength of JH-AMC-T decreased by 15%, while its flexural strength decreased by 20%. These results indicate that JH-AMC-T has relatively poor resistance to repeated thermal shock and is more susceptible to temperature fluctuations.
The specific effects of thermal shock on the performance changes of alumina-silicon carbide bricks are presented in Table 3.
| Property Index | Without thermal shock | 1 thermal shock cycle | 5 thermal shock cycles | 10 thermal shock cycles |
|---|---|---|---|---|
| Cold Crushing Strength / MPa | 60 | 58 | 55 | 50 |
| Modulus of Rupture / MPa | 15 | 14 | 13 | 12 |
| Linear Change Rate / % | 0 | 0.5 | 1.2 | 2 |
| Cracks | None | None | Microcracks | Obvious cracks |
Table 3. Specific Effects of Thermal Shock on the Performance Changes of Alumina-Silicon Carbide Bricks
As shown in Table 3, the mechanical properties of alumina-silicon carbide bricks gradually deteriorate with an increasing number of thermal shock cycles. In particular, after multiple thermal shock cycles, the formation of cracks further affects the overall performance of the bricks. Rapid heating and cooling during the thermal shock process induce changes in thermal stress within the brick structure, consequently affecting its mechanical properties, including compressive and flexural strength.
Effects of Different Additive Contents on Thermal Shock Resistance
The incorporation of additives into alumina-silicon carbide bricks can significantly improve their thermal shock resistance. In this experiment, different proportions of additives, such as graphite, zirconium, and calcium-based materials, were incorporated into the formulations to investigate their effects on thermal shock resistance.
The experimental results showed that appropriate amounts of additives can significantly enhance the thermal shock stability of alumina-silicon carbide bricks. The improvements were particularly evident in terms of structural stability under thermal shock conditions and resistance to erosion. The incorporation of graphite and zirconium effectively improved the microstructure of the bricks, making them more stable at high temperatures and less susceptible to crack formation.
The experimental data showed that when the additive content, particularly that of flake graphite, reached 3%, the thermal shock resistance of alumina-silicon carbide bricks improved significantly. The compressive strength increased from 50 MPa to 55 MPa, while the flexural strength increased from 12 MPa to 13 MPa. Meanwhile, the addition of additives helped maintain a relatively low permanent linear change and substantially reduced the probability of crack formation.
The effects of different additive contents on the thermal shock resistance of alumina-silicon carbide bricks are presented in Table 4.
| Type of Additive | Addition Amount / % | Cold Crushing Strength / MPa | Modulus of Rupture / MPa | Linear Change Rate / % | Crack Condition |
|---|---|---|---|---|---|
| No additive | 0 | 50 | 12 | 1.5 | Microcracks |
| Graphite | 1 | 52 | 13 | 1.2 | None |
| Graphite | 3 | 55 | 13 | 0.8 | None |
| Zirconium | 1 | 53 | 14 | 1.0 | None |
| Zirconium | 3 | 56 | 14 | 0.9 | None |
Table 4. Effects of Different Additive Contents on the Thermal Shock Resistance of Alumina-Silicon Carbide Bricks
Conclusion
In summary, this study systematically investigated the thermal shock resistance of alumina-silicon carbide bricks with different specifications and revealed the effects of different formulations and additives on their thermal shock stability. The experimental results showed that JH-ASCC55 and JH-ASCC60 exhibited superior thermal shock resistance under high-temperature conditions and maintained relatively high mechanical strength throughout repeated thermal shock cycles. In contrast, JH-AMC-T demonstrated relatively poor thermal shock resistance due to its lower high-temperature performance.
Furthermore, the incorporation of appropriate amounts of additives, such as graphite and zirconium, significantly improved the thermal shock resistance of alumina-silicon carbide bricks, reduced crack formation, and enhanced their structural stability. These findings provide an important theoretical basis and practical guidance for the application of alumina-silicon carbide bricks in high-temperature environments, such as hot metal ladles and torpedo ladles.
In the future, with further research into novel additives and continued optimization of manufacturing processes, the thermal shock resistance of alumina-silicon carbide bricks is expected to improve further, thereby promoting their wider application in the metallurgical industry and the field of high-temperature materials.