Abstract: As a high-carbon emitting sector, the steel industry accounts for approximately 7% of global CO₂ emissions. Against the backdrop of the “dual carbon” goals, there is an urgent need to develop carbon reduction and CO₂ resource utilization technologies to promote the industry's green transformation. Refining, as a critical stage in the steelmaking process, currently has limited application of CO₂, particularly in studies of ultra-low-carbon Fe-C alloy systems under atmospheric pressure conditions. The reaction mechanism of CO₂ in ultra-low-carbon Fe-C alloy melt was systematically studied using FactSage thermodynamic calculations and high-temperature thermal experiments, with a focus on analyzing the effects of CO₂ injection flow rate, temperature, and injection duration on the evolution of carbon content in the melt. The results indicated that CO₂ injection caused carbon enrichment in the melt, with the enrichment rate significantly increasing with higher flow rates and temperatures. When the CO₂ flow rate increased from 40 mL/min to 80 mL/min, the enrichment rate rose from 0.001 81 %/min to 0.003 19 %/min, representing a 76% increase. After prolonged injection, the carbon mass fraction eventually stabilized at around 0.11% in the melt, reaching a dynamic equilibrium. This study provides theoretical basis and process parameter support for the industrial application of CO₂ in the refining of ultra-low-carbon steel.

Key words: steelmaking, refining, CO₂ resource utilization, decarbonization, thermodynamics