Carbon-containing refractories are widely used in off-site refining equipment, ladles, and continuous casting functional materials due to their excellent slag and thermal shock resistance.
Currently, commonly used shaped carbon-containing refractories include magnesia-carbon (MgO-C) bricks, alumina-magnesia-carbon (Al2O3-MgO-C) bricks, and alumina-carbon (Al2O3-C) bricks.
MgO-C bricks are primarily used in areas subject to severe corrosion, such as the slag line, and have a graphite content of 10%-15% by weight. Al2O3-MgO-C bricks are used in areas such as the ladle wall and bottom, and have a graphite content of 8%-10% by weight. Al2O3-C materials are primarily used in flow control functional components during continuous casting, and their graphite content is typically greater than 20% by weight.
In recent years, with the increasing demand for clean steel/specialty steels such as automotive sheet steel, high-end bearing steel, and nuclear power special steel, the graphite content in carbon-containing refractories must be reduced to minimize the impact of graphite dissolution on the quality of clean steel caused by carbon enrichment in molten steel. However, this further degrades the service performance of carbon-containing refractories.
On the other hand, advances in refining technology and continuous casting processes have placed higher demands on the service performance of carbon-containing refractories. Therefore, the development of low-carbon carbon-containing refractories while maintaining excellent service performance is an inevitable trend. To this end, this article reviews the coordinated control methods for reducing carbonization and enhancing the performance of carbon-containing refractories and points out the development trends of low-carbon refractories.
Optimization of carbon source
Carbon raw materials in carbon-containing refractory materials are mainly introduced in two forms: one is flake graphite as the matrix raw material, and the other is phenolic resin as the binder. Therefore, the optimization of carbon source usually has the following ways:
(1) Select different carbon sources: graphite (flake graphite, expanded graphite, microcrystalline graphite), two-dimensional nanocarbon materials (graphene, graphite oxide sheets), zero-dimensional or one-dimensional nanocarbon (zero-dimensional nanocarbon black, one-dimensional carbon nanotubes or carbon fibers);
(2) Modification catalysis of the binder: for example, using nickel nitrate to pyrolyze phenolic resin into carbon nanotubes.
Use of additives
Additives not only introduce multiple strengthening mechanisms through their own or in-situ ceramic phase formation, effectively improving the mechanical properties, thermal shock resistance, and erosion resistance of carbon-containing refractories, but also exert an antioxidant effect through oxygen consumption. Furthermore, numerous studies have shown that the combined use of multiple additives can more effectively improve the overall service performance of carbon-containing refractories due to the synergistic effects of multiple components and different morphological characteristics.
Introduction of pre-synthesized composite powders
Composite powders combine the advantages of single components and are more economical to produce than most pure powders. Numerous studies have demonstrated that modifying refractory matrices with composite powders is also an effective way to improve refractory performance. Therefore, the development of simple, cost-effective methods for producing high-performance composite powders has been a research hotspot in recent years.
Current development of low-carbon refractories focuses on two key areas.
First, continuously improving the service performance of refractories to achieve “longevity”;
Second, ensuring that carbon-containing refractories can meet the evolving requirements of smelting processes, particularly the stringent demands of clean steel production.
Nano-scaling is a key research direction for achieving longevity in carbon-containing refractories; low carbonization is a simpler and more efficient approach to meeting the requirements of clean steel production processes. However, the deterioration in thermal shock and slag resistance of carbon-containing refractories caused by low carbonization also requires nano-scaling to improve.
Thus, the coordinated development of “longevity,” “low carbonization,” and “nano-scaling” holds significant practical significance for the development and application of carbon-containing refractories.
The introduction of nanocarbon and nanoceramic phases can optimize the microstructure of low-carbon refractories, effectively improving their critical service properties, such as thermal shock resistance and erosion resistance. Composite additives offer greater advantages in improving refractory properties than single micro- and nano-components. Pre-synthesized composite powders, by eliminating the agglomeration of nano-components, can more effectively enhance the strengthening effect of low-carbon refractories.
Studying the strengthening mechanism of micro-nano additives in improving refractory performance provides a theoretical basis for improving the performance of low-carbon refractories and can better control the service performance of refractory materials through the use of micro-nano additives.
Using finite element simulations to determine the temperature and stress distribution of carbon-containing refractories during service, we can obtain the micromechanical parameters of refractory materials under different service conditions. We can analyze the interaction between micromechanical parameters and thermal shock resistance, and develop a thermal shock resistance prediction model based on micromechanical parameters. This is of great significance for the development of low-carbon refractories with long service life and high service stability.
