Performance of Clay Silicon Carbide Bricks and Their Application in Ladle Linings
2025-10-14 09:30:14
To extend the life of ladle linings, new materials must be specifically designed based on the challenges inherent in current ladle operations. These materials must possess excellent thermal shock resistance, resistance to desulfurizer erosion, and thermal insulation properties. Domestic and international research and development focuses on aluminum-carbon bricks, specifically designed for the hot metal environment. In recent years, aluminum-fired silicon carbide carbon bricks have been widely used in major steel mills due to their excellent thermal shock and erosion resistance. However, because they contain carbon materials such as graphite, exposed areas such as the slag line are susceptible to oxidation, becoming loose and susceptible to erosion, significantly reducing their erosion resistance. Furthermore, the presence of carbon increases thermal conductivity, leading to elevated furnace shell temperatures, significant heat loss, and the tendency for both lid and bottom buildup, making them difficult to handle and hindering production. The average temperature drop of molten iron ladles during transportation at a certain steel mill is approximately 190°C, slightly greater than that of other steel mills. Some steel mills have reduced this temperature drop by covering the ladles, but the problem of temperature drop and covering remains prominent in steel mills where the ladles operate openly and have long turnover routes. In response to this problem, clay silicon carbide bricks were developed that are well-suited to the ladle operation process and offer excellent performance. Their thermal shock resistance and thermal insulation properties surpass those of aluminum-chromium silicon carbide bricks and aluminum silicon carbide bricks.
1. The main raw materials for clay silicon carbide bricks are coke gemstone, andalusite, Guangxi white mud, silicon carbide, and alumina powder. The antioxidant is metallic silicon, and the binder is sulfite pulp wastewater. The main raw materials used are coke stones with a purity of ≥43.0% (Al?O?) and a particle size of 3μm to 0mm; andalusite with a purity of ≥69.0% (Al?O?) and a particle size of 3mm to 0mm; Guangxi clay with a purity of ≥30.0% (Al?O?) and a particle size of 200 mesh; silicon carbide (SiC) with a purity of ≥90.0% and a particle size of 200 mesh; and alumina powder with a purity of ≥99% (Al?O?) and a particle size of 3μm to 6μm.
2. To improve the service life of the ladle lining, the thermal shock resistance of the working layer bricks must be enhanced. To address the thermal stress generated by rapid alternating heating and cooling, a suitable lining structure should have an effective internal stress buffering and release mechanism to prevent the propagation of thermal shock microcracks and the resulting delamination of the lining. Under thermal shock, crack initiation, growth, and propagation in porous refractories like aluminum silicon carbide bricks are related to fracture surface energy. To improve the material's thermal shock resistance, it is important to ensure a high elastic modulus and low strength. Clay silicon carbide bricks have a lower compressive strength than aluminum silicon carbide bricks, which improves their thermal shock resistance. Furthermore, because their apparent porosity is higher than that of aluminum silicon carbide bricks, their evenly distributed pores effectively buffer and release thermal stress, significantly reducing the occurrence of lamellar cracking and spalling.
3. Under normal circumstances, due to the higher porosity of clay silicon carbide bricks compared to aluminum silicon carbide bricks, their looser structure reduces their corrosion resistance, making them more susceptible to desulfurization agents and slag. However, in actual use, due to their higher porosity, a layer of slag easily adheres to the surface. When the ladle cools down, the slag solidifies within the voids, partially filling the pores. The iron slag layer adhered to the surface blocks some pores and provides a protective and insulating effect, ensuring that the clay silicon carbide brick also possesses excellent slag resistance. Furthermore, the iron slag layer protects the brick lining from direct impact from high-temperature molten iron, providing a buffering effect and reducing damage to the brick lining caused by thermal shock stress.
4. The relatively high apparent porosity and low bulk density of clay silicon carbide bricks ensure their relatively good thermal insulation properties. Gas has the lowest thermal conductivity, and the evenly distributed pores of clay silicon carbide bricks reduce this thermal conductivity, minimizing the temperature drop caused by heat conduction at the bottom and opening of the ladle, helping to alleviate slagging and capping at the bottom and opening of the ladle.
Specific Applications: The original aluminum silicon carbide bricks were used in a 150-ton ladle, with a ladle lifespan of as little as 220 heats. During use, the ladle lining suffered severe spalling due to thermal shock, resulting in an uneven surface and dense, narrow, layered cracks on the exposed bricks. After clay silicon carbide bricks were put into use, the spalling phenomenon of the brick lining was greatly improved due to their excellent thermal shock resistance, and the brick lining surface was smooth and orderly. At the same time, due to their good thermal insulation, the bottom and cover phenomenon of the molten iron ladle was improved, the blasting machine packing phenomenon was reduced, and the mechanical stress damage of the lining was reduced. Once clay silicon carbide bricks were put into use in the 150-ton molten iron ladle, the average ladle life of the ladle reached 350 furnaces, and the service life was greatly improved. In addition, since the purchase price of clay silicon carbide bricks is cheaper than that of aluminum silicon carbide bricks, and because of their low body density, light weight, low weight per bag and long service life, the comprehensive use cost of the 150-ton molten iron ladle was greatly reduced after they were put into use. Due to the excellent use effect of clay silicon carbide bricks and significant cost reduction, they have completely replaced aluminum silicon carbide bricks in the 150-ton molten iron ladle system and are still in use today.
Summary
Based on the above analysis, the following conclusions are drawn: (1) Thermal shock is the main factor leading to damage to the molten iron ladle lining. The clay silicon carbide bricks developed have excellent thermal shock resistance and can significantly reduce the layered cracks and spalling caused by rapid heating and cooling during the transportation and iron-bearing process of the 150-ton molten iron ladle. (2) After being put into use, the clay silicon carbide bricks can ensure relatively good slag resistance and meet the requirements of the ladle lining for corrosion resistance to desulfurizers and molten iron slag. (3) The thermal insulation effect of clay silicon carbide bricks is better than that of aluminum silicon carbide bricks, which improves the phenomenon of the bottom and ladle opening of the 150-ton molten iron ladle being solidified.