Molten steel contains sulfur, oxygen, and non-metallic impurities. Separating these impurities determines the quality of the steel. Steelmaking refining slag plays the role of a “blood dialyzer” in the purification of molten steel.
I. What is Steelmaking Refining Slag? Refining slag is a metallurgical auxiliary material made from limestone, bauxite, etc., through sintering or pre-melting. It is added to the ladle during refining processes such as LF furnaces and RH furnaces. Commonly used slag systems include CaO-CaF₂ and CaO-Al₂O₃, characterized by low melting points and high basicity.
According to the production method, it is divided into three categories: mixed type (direct mixing, low cost but poor uniformity); sintered type (low-temperature sintering, more uniform composition but prone to gas absorption); and pre-melted type (complete melting, high purity, fast slag formation, but high cost).
II. Purification Mechanism of Refining Slag It relies on a dual mechanism of “chemical purification + physical isolation.”
Desulfurization and Deoxidation: CaO is the core component for desulfurization. After the formation of white slag (FeO < 1%), sulfur is converted into CaS, achieving deep desulfurization. The desulfurization rate can reach over 70% at a basicity of 3.4~4.2.
Adsorption of Inclusions: High-basicity, low-viscosity slag can effectively adsorb non-metallic inclusions such as Al₂O₃ and SiO₂.
Foamed Slag Protection: Covers the molten steel, isolates it from air to prevent secondary oxidation, protects the furnace lining, and maintains heat.
III. How to Scientifically Select Refining Slag
Consider steel grade, process, and environmental protection. A basicity of 2.5~3.0 can achieve good overall results. For plain carbon steel and construction steel, lower-cost sintered or mixed types can be selected; for high-quality steel grades such as automotive steel and electrical steel, high-basicity pre-melted types must be used.
IV. Green Transformation: A New Direction for Fluorine-Free Refining Slag
Traditional slag often adds fluorite (CaF₂) to reduce viscosity, but this generates highly toxic HF gas, which corrodes the furnace lining and pollutes water bodies. Wuhan Iron and Steel (WISCO) and other companies have developed fluorine-free refining slag, which does not corrode equipment, forms slag quickly, and achieves a balance between environmental protection and performance.
With the growing emphasis on green steelmaking, efficient, low-cost, and environmentally friendly new refining slags are becoming the industry mainstream, providing solid support for the production of high-end steel.
Kerui Refractory supplies various types of refining slags. Please contact us for any needs.