Thermodynamic analysis of elemental reactions in bottom-blown CO₂ process for SWRH72A cord steel

To systematically investigate the thermodynamic behavior of key elements in molten steel during the bottom-blown CO₂ process for refining SWRH72A cord steel, clarify the control mechanism of CO₂ injection on elemental content, and thereby optimize the refining process for precise composition control, this study takes Aosent Special Steel's SWRH72A steel as the test subject. Through a series of high-temperature hot tests, the reaction behavior of key elements under different CO₂ injection parameters was systematically compared. Experimental results indicate that pure CO₂ injection exhibits the most pronounced effect on carbon removal. Under continuous pure CO₂ injection for 120 min, the carbon mass fraction decreases from 0.57% to 0.30%. Mixed injection tests further demonstrate that a mixture ratio of 30%CO₂ (volume fraction) + 70%Ar (volume fraction) can stably control carbon content within the process internal control requirements. At a flow rate of 20 mL/min for 120 min, the Si mass fraction decreases from 0.105% to 0.042%. The oxidation rate of Si showed a positive correlation with CO₂ flow rate and its proportion in the mixed gas, with the greatest Si removal occurring under pure CO₂ conditions. Mn removal efficiency increases with higher CO₂ injection flow rates. Under pure CO₂ at 20 mL/min for 120 min, Mn mass fraction decreases from 0.37% to 0.19%. To meet stringent internal control requirements for Mn content in cord steel, an optimized process using a lower injection flow rate of 10 mL/min is recommended. Furthermore, the reaction between Al and CO₂ is extremely rapid. Due to its low initial content, Al is completely removed within 10 min after injection initiation, with its mass fraction dropping to 0. The 120 min injection test further confirmed that the Al mass fraction decreases to 0, achieving deep removal. Through systematic high-temperature hot-state experiments, this study elucidates the thermodynamic reaction mechanisms of bottom-blown CO₂ with four key elements(C, Si, Mn, and Al)during the refining process of SWRH72A cord steel. The findings provide theoretical support for applying CO₂ in precise control of molten steel composition during refining, offering significant reference value for enhancing the quality of high-end cord steel products and developing new green smelting technologies.