Liquid Slag Layer: Shielding and Reoxidation Prevention
The liquid slag film acts as a protective seal over the molten steel surface. It blocks atmospheric oxygen from contacting the liquid metal, thereby limiting secondary oxidation. At the same time, it isolates the carbon-rich layer from the steel, preventing surface carburization—especially important for low-carbon and ultra-low-carbon grades. This dual protective effect improves slab surface quality and minimizes metal losses during casting.
Solid Slag Layer: Thermal Retention and Meniscus Control
The solid slag blanket provides an insulating barrier that helps stabilize the temperature at the meniscus. By maintaining thermal equilibrium, it prevents premature solidification of the steel and reduces radiation heat loss into the surrounding environment. Stable meniscus conditions help minimize surface defects such as cracks and porosity, contributing to a cleaner and more uniform slab surface.
Liquid Slag Layer: Inclusion Assimilation and Steel Cleanliness
The liquid slag also functions as a refining agent. It dissolves and absorbs deoxidation products and eroded refractory particles suspended in the steel. By regulating slag viscosity, the absorption capacity remains consistent over time, preserving the metallurgical performance of the flux. This continuous cleaning action enhances steel purity and supports the production of high-quality surfaces.
Lubrication Control: Friction Reduction and Casting Speed
The slag film serves as a lubricating medium between the oscillating mold and the solidifying strand. Lower friction reduces mechanical wear on both the copper plates and the strand surface, allowing for higher casting speeds while maintaining process stability. Effective lubrication management directly influences operational reliability and overall productivity.
Heat Transfer Regulation: Uniform Cooling and Crack Prevention
A homogeneous slag film ensures even heat extraction across the mold face, preventing localized cooling variations. Such uniformity reduces thermal stress and lowers the risk of crack formation. This is particularly critical for peritectic steel grades, where excessive heat flux tends to aggravate surface cracking. Controlled heat transfer is therefore essential for achieving consistent slab quality.
Process Optimization Considerations
A well-designed mold flux must balance melting rate, viscosity, and crystallization behavior. Temperature control is equally important for preserving the correct layered structure of the slag pool. Chemical composition—particularly the Al₂O₃/SiO₂ ratio and the choice of fluxing agents—affects every functional property, making it a central factor in any optimization effort.
