November 19, 2025
LF refining stands as one of the primary methods for secondary refining outside the furnace. The primary objectives of LF slagging are to facilitate desulfurization, deoxidation, enhance alloy yield, and eliminate inclusions. However, in the context of aluminum-killed steel slagging, there are inherent contradictions among desulfurization, silicon reversion, nitrogen pickup, and inclusion removal, necessitating a holistic consideration. The rapid and stable production of reducing white slag in LF, characterized by good fluidity and a certain degree of emulsification, is imperative for effective desulfurization, inclusion adsorption, and ensuring the quality of molten steel.
Taking the production of European standard S235JR controlled aluminum steel (a low-silicon steel) as an illustrative example, the production process encompasses the following steps: multi-blown converter → argon station → LF → continuous casting (CC). During converter steel production, stirring kinetic energy is harnessed to introduce an appropriate amount of lime for slag washing and pre-making reduction slag, ensuring basicity and preventing phosphorus and silicon reversion. The entire process involves gentle stirring of the steel to achieve uniform composition and temperature. Deoxidation of the liquid steel is accomplished using steel-core aluminum (or aluminum-manganese-magnesium). Based on the slag volume (typically around 5 kg/t), an appropriate amount of modifier is added promptly after steel production, with high-carbon manganese employed for alloying.
Through an in-depth analysis of the slag-making process, slag composition transformation, and comprehensive basicity changes of the slag, the following technological measures for rapid white slag formation are derived:
Pre-modification of Converter Slag:
Pre-modifying converter slag provides favorable conditions for rapid LF slag formation. Concurrently, strict control must be exercised over several critical aspects during converter steel production: blowing, slagging, bottom blowing, tapping, and deoxidation.
Early Rapid Slagging as a Prerequisite:
The key control points for early rapid slagging include rapid temperature increase, submerged arc operation, effective mixing, and the rational batch addition of slag-forming agents.
Intensive Stirring for Desulfurization (4.0–6.0 L/(min·t)):
Desulfurization should be conducted swiftly and within a short timeframe, ensuring effective desulfurization while minimizing secondary oxidation and nitrogen absorption by the liquid steel. Typically, this stage is completed within 10–20 minutes after the commencement of LF processing and represents the main refining stage.
Post-Desulfurization Tasks:
After desulfurization, the primary tasks of LF shift to temperature control, alloying, and inclusion removal. During this phase, it is crucial to maintain appropriate slag viscosity and control stirring intensity within the range of 0.5 L/(min·t) to 1.0 L/(min·t) (based on the principle of liquid level fluctuation without exposing the steel surface). The retention time should exceed 8 minutes.
In conclusion, a comprehensive understanding and precise control of the LF refining process, particularly in terms of slag formation and management, are essential for achieving high-quality molten steel and meeting stringent product specifications.
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