Characterization of MgO-based Tundish Working Lining Materials: Microstructure and Properties

The tundish, a crucial component in the continuous casting process of steel, serves as a reservoir and distributor for molten metal before it is cast into molds. Its working lining materials are exposed to extreme conditions, including high temperatures, mechanical stresses, and chemical interactions with molten steel. The choice of tundish working lining material significantly affects the performance, service life, and efficiency of the casting process. Magnesium oxide (MgO)-based materials have emerged as one of the most widely used refractory materials for tundish working linings due to their superior thermal stability, resistance to slag, and overall durability. This article aims to provide an in-depth characterization of MgO-based tundish working lining materials, focusing on their microstructure, properties, and performance in continuous casting operations.

1. Composition of MgO-based Tundish Lining Materials

MgO-based tundish lining materials primarily consist of magnesium oxide (MgO), often combined with other compounds like alumina (Al₂O₃), silica (SiO₂), and chromia (Cr₂O₃). The exact composition varies depending on the specific needs of the casting process and the intended service conditions. The primary aim is to achieve a refractory material with high melting points, resistance to thermal shock, and low porosity.

- Pure MgO: High-purity MgO (≥95%) is typically used in the core structure of the lining due to its excellent stability at high temperatures and resistance to the chemical attack from molten steel and slag.

- Alumina (Al₂O₃): Alumina is often added to improve the material's strength at elevated temperatures and enhance resistance to slag infiltration.

- Silica (SiO₂): Silica helps improve the thermal shock resistance of the lining material.

- Chromia (Cr₂O₃): In some cases, chromia is added to improve the overall chemical stability and wear resistance of the material.

2. Microstructure of MgO-based Lining Materials

The microstructure of MgO-based tundish lining materials plays a pivotal role in their overall performance. The formation and distribution of different phases in the microstructure directly affect the material’s strength, thermal conductivity, and resistance to slag penetration.

- Grain Structure: MgO-based refractories typically exhibit a fine-grain structure, which ensures high thermal stability and uniform heat distribution. The grain size distribution is carefully controlled during manufacturing to optimize mechanical strength and resistance to thermal shock.

- Porosity: The porosity of MgO-based linings is a critical factor influencing their thermal conductivity and resistance to slag penetration. The porosity of these materials is typically low (below 10%) to reduce slag infiltration and prevent excessive wear. Additionally, low porosity enhances the refractory's ability to withstand thermal shock.

- Bonding Phase: MgO grains are often bonded with magnesium aluminate spinel (MgAl₂O₄) or periclase (MgO), which provide structural stability. The bonding phases influence the material's resistance to mechanical stress and slag corrosion. Periclase-magnesium aluminate spinel refractory castables are widely used for tundish linings in steel making due to their excellent thermal shock and slag resistance as well as due to their superior mechanical properties.

The formation of secondary phases, such as spinel or periclase, also improves the material’s ability to resist chemical attack from molten steel and slag. The presence of these phases in the microstructure enhances the material's durability and life span.

3. Properties of MgO-based Tundish Lining Materials

MgO-based tundish working linings offer a range of desirable properties that make them ideal for use in continuous casting operations.

- High Temperature Stability: One of the primary advantages of MgO-based materials is their ability to withstand extreme temperatures. MgO has a high melting point of around 2800°C, ensuring that the tundish lining remains stable even when subjected to molten steel temperatures, typically between 1400°C and 1600°C.

- Resistance to Slag: MgO-based materials exhibit excellent resistance to slag attack, which is essential for maintaining the structural integrity of the tundish lining. Slag infiltration can significantly reduce the lifespan of tundish linings, so resistance to this chemical attack is a key property.

- Thermal Shock Resistance: The ability of MgO-based materials to withstand rapid changes in temperature, such as those encountered during the heating and cooling cycles of the casting process, is a critical property. Fine-grained MgO refractories with low porosity offer superior thermal shock resistance compared to other refractory materials.

- Mechanical Strength: The mechanical strength of MgO-based materials is essential for withstanding the stresses experienced during casting operations. These materials are designed to be tough and durable, with the ability to resist deformation under high pressure or mechanical stress.

- Erosion Resistance: Continuous casting operations involve the constant flow of molten steel, which can erode the surface of tundish linings over time. MgO-based linings exhibit good erosion resistance, extending their useful life in the tundish.

4. Performance in Continuous Casting

MgO-based tundish linings are known for their long service life and cost-effectiveness. Their ability to withstand high temperatures, resist slag attack, and reduce thermal shock ensures that they remain effective throughout extended casting campaigns. The material's resistance to erosion and mechanical wear also plays a significant role in minimizing downtime for re-lining the tundish.

- Slag Line Protection: The interaction between molten steel and slag can lead to wear and tear on the tundish lining, particularly at the slag line. MgO-based linings provide exceptional protection at the slag line, where they resist chemical attack and erosion from the molten steel and slag.

- Reduced Maintenance Costs: Due to their durability and performance, MgO-based linings reduce the frequency of relining and maintenance, lowering operational costs and increasing productivity in steelmaking operations.

- Improved Casting Efficiency: By providing better thermal insulation and heat retention, MgO-based linings contribute to improved casting efficiency. The reduction in heat loss leads to a more stable casting process, reducing defects and improving overall product quality.

5. Conclusion

MgO-based tundish working linings are an excellent choice for industries involved in continuous casting due to their remarkable properties, including high temperature stability, slag resistance, and thermal shock resistance. The unique microstructure, which includes fine-grained MgO, spinel, and periclase bonding phases, ensures that these materials can withstand the harsh conditions present in tundish operations. As a result, MgO-based materials offer extended service life, reduced maintenance costs, and enhanced casting efficiency.

For industries seeking reliable and durable tundish linings, MgO-based refractories provide a proven solution. When choosing the right supplier for MgO-based tundish linings, it’s important to consider factors such as material composition, performance, and durability. Contact us for more information on how our high-quality MgO-based tundish working lining materials can enhance the performance of your continuous casting operations.