As an indispensable equipment in steel smelting, the LF refining ladle has an extremely harsh working environment and is subjected to multiple tests such as high temperature, chemical erosion and mechanical scouring for a long time. Therefore, the selection of suitable refractory materials is crucial to extend the service life of the ladle and improve production efficiency. This article will conduct a detailed analysis from the aspects of refractory selection, performance requirements and application effects.
Ⅰ. Selection of refractory materials
1. Slag line area
The slag line area is the area where the ladle lining is most susceptible to erosion, mainly due to chemical erosion and high-temperature oxidation of high-basicity slag. Commonly used refractories include magnesia carbon bricks (MgO-C) and magnesia calcium bricks (MgO-CaO). Magnesia carbon bricks are widely used due to their high slag resistance and thermal conductivity of graphite, and the carbon content is usually between 10% and 14%. Magnesia calcium bricks react with high-basicity slag to generate high melting point phases (such as CaO·Al₂O₃), which are suitable for high-clean steel smelting.
2. Furnace wall and furnace bottom
The furnace wall and furnace bottom are mainly subjected to high temperature and mechanical scouring of molten steel. Magnesia carbon bricks are an ideal choice due to their excellent slag resistance and thermal shock resistance. In addition, alumina-magnesia carbon bricks (composite of Al₂O₃ and magnesia sand) are also commonly used in non-slag line areas. Their thermal shock resistance is better than that of pure magnesia carbon bricks and are suitable for areas with large temperature fluctuations.
3. Furnace cover
The furnace cover requires high-alumina bricks or magnesia-alumina spinel bricks with strong thermal shock resistance and thermal radiation. Amorphous refractory materials such as spray coatings and castables are also often used for local repairs to extend the service life of the furnace cover.
4. Breathable bricks (bottom blowing device)
Breathable bricks are used for argon stirring of molten steel and are required to have high wear resistance and thermal shock resistance. Alumina-magnesia spinel or high-alumina breathable bricks are common choices.
Ⅱ. Performance requirements of refractory materials
1. High temperature performance
Refractory materials need to be stable for a long time at 1600-1800℃ or even higher temperatures without melting or softening. High load softening temperature is also a key indicator, usually required to be 200℃ higher than the operating temperature to ensure sufficient strength when subjected to molten steel impact and furnace pressure.
2. Excellent thermal shock resistance
Due to the frequent rapid heating and cooling during the refining process, refractory materials should have a low thermal expansion coefficient and high thermal shock resistance to prevent cracking or spalling caused by sudden temperature changes.
3. Chemical corrosion resistance
The composition and alkalinity of slag vary greatly, and refractory materials need to be able to resist the erosion of acidic or alkaline slag while avoiding contamination of molten steel. Magnesia carbon bricks or magnesium dolomite carbon bricks are often selected because of their good slag resistance and molten steel purification functions.
4. Resistance to mechanical wear and impact
The stirring, gas blowing, and impact of slag and molten steel in the furnace require the refractory materials to have high mechanical strength and wear resistance to ensure that they are not easy to peel off or structurally damaged during long-term operation.
III. Application effect and optimization direction
1. Application effect
The application of magnesia carbon bricks in the slag line has achieved remarkable results. For example, after a steel plant used MgO-C bricks, the erosion rate was greatly reduced and the service life was significantly improved. Magnesium dolomite carbon bricks can absorb non-metallic inclusions in molten steel, have good slag resistance and purify molten steel, and are suitable for the production of clean steel.
2. Optimization direction
In order to improve the performance of refractory materials, antioxidants (such as Al and Si) can be added to delay carbon oxidation and improve high-temperature strength. In addition, the technology of in-situ generation of magnesia aluminum spinel is also used to enhance the thermal shock resistance and erosion resistance of materials.
In summary, the reasonable selection and maintenance of refractory materials can significantly extend the service life of LF refining ladle, reduce operating costs, and improve production efficiency. In the future, by further optimizing material formulation and construction technology, the performance of refractory materials will be further improved to better meet the needs of steel smelting.