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The application of slag removal agent runs through the entire steelmaking process (converter, electric furnace, LF furnace, continuous casting, etc.), and the core functions revolve around the two major goals of 'purifying molten steel' and 'protecting molten steel':
Converter/Electric furnace steel discharge stage: Remove the initial slag and reduce inclusions When the converter or electric furnace smelting end point, a large amount of smelting slag (such as lime-iron oxide slag in the converter) will be generated in the molten steel. These slags contain high melting point oxides (such as FeO, MnO). If they enter the ladle with the molten steel, they will become the source of inclusions in the steel. At this time, add a slag removal agent (such as lime and fluorite composite agent), and the suspended small particles of inclusions can be condensed into large particles of slag through adsorption and polymerization, and float to the surface with the steel slag; at the same time, the viscous slag layer formed by the slag removal agent can prevent the slag from entering the ladle through the 'slag arrest' action (combined with the slag arrest ball/slag arrest plug), so that the thickness of the slag layer in the ladle can be reduced from 100-150mm to 30-50mm, and the inclusion content (TO, total oxygen) can be reduced by 20-30% (from 80-100ppm to 50-60ppm).
LF refining stage: deep purification, adjust the slag system
LF furnace (lap refining furnace) is the core link in the control of the purity of the molten steel. The function of the slag removal agent in this stage is:
Adsorption of inclusions: By reacting highly active ingredients (such as Al₂O₃, CaO) with fine inclusions in the molten steel (such as Al₂O₃, SiO₂), a low-melting point composite slag (melt from 1600℃ to 1300-1400℃), making it float up quickly;
Desulfurization/Deoxygenation: An alkaline slag removal agent (such as lime-based) can react with S in the molten steel to form CaS (enter the slag phase), and the desulfurization efficiency can reach 40-60% (reduce [S] from 0.02% to below 0.008%);
Insulation and insulation of air: The dense slag layer (thickness 50-80mm) formed by the slag removal agent can reduce heat dissipation of the molten steel (the cooling rate drops from 5-8℃/min to 2-3℃/min), and at the same time prevent O₂ and N₂ in the air from entering the molten steel (avoid [N] exceeding the standard, usually required ≤100ppm).
Continuous casting stage: prevent secondary oxidation of the crystallizer and improve the quality of the casting billet.
During continuous casting, when the steel enters the crystallizer from the tundra, it is easy to contact with the air and cause secondary oxidation (generating FeO, SiO₂ and other inclusions). Adding slag removal agent (such as perlite-based, composite carbonaceous agent) can:
Form a cover layer at the liquid level of the crystallizer to isolate the air (reduce the inclusions generated by secondary oxidation by 30-50%);
Absorb the fine inclusions flowing into the tundra to avoid subcutaneous inclusions or cracks in the casting billet (especially for steels with high cleanliness requirements such as low carbon steel and pipeline steel, the qualification rate of the casting billet can be increased by 5-10%).
