Based on industrial sampling, this study systematically investigates the effects of manganese alloying and calcium treatment on the evolution behavior of non‐metallic inclusions during LF refining of ST12 low‐carbon steel. By characterizing the morphology, composition, number density, and size of inclusions in steel samples taken at critical refining stages (enter station, post‐manganese alloying, post‐calcium treatment), and combining these with FactSage thermodynamic calculations, the study elucidates the mechanisms by which manganese alloying and calcium treatment influence inclusion evolution. The results indicate that the addition of the FeMn alloy significantly increased the number density of Al 2 O 3 inclusions in the steel (from 2.3 to 214.2 mm −2 ), concurrently enhancing their nucleation rate, which resulted in a reduction in the average inclusion size (from 2.7 to 0.44 μm). Subsequent calcium treatment effectively modified the high‐melting‐point solid Al 2 O 3 inclusions into low‐melting‐point liquid CaO‐Al 2 O 3 ‐CaS composite inclusions, increasing their number density from 3.9 to 326.1 mm −2 . Thermodynamic calculations revealed a “liquid window” (≈0.0022%−0.004%) for dissolved calcium in molten steel, within which inclusions can be fully liquefied. Further computational analysis indicated that the total oxygen content in steel is the most critical factor determining this window range and the effectiveness of calcium treatment.
Chen et al. (Wed,) studied this question.