Transient Coupled Modeling of Multiphase Flow and Decarburization Kinetics in RH with Ladle Bottom-Blowing

The Rheinstahl–Heraeus with ladle bottom-blowing (LBB-RH) vacuum refining process has been developed to enhance circulation flow and decarburization efficiency for ultra-low carbon steel production. However, current numerical models rely on the steady-state assumption for Ar-molten steel flow, neglecting the transient evolution of CO bubbles generated by decarburization in LBB-RH. Thus, a transient coupled model integrating unsteady CO-Ar-molten steel flow with decarburization kinetics is established in this paper. The transient distributions of CO gas, flow velocity, circulation flow rate, and carbon mass concentration are systematically investigated. The results show that LBB-RH achieves higher velocity on the main longitudinal section but lower velocity at the vacuum chamber free surface. The circulation flow rate of LBB-RH reaches 1.58 times that of conventional RH at the 25th minute. Under identical argon flow rates, the carbon mass concentration in LBB-RH is less than that in conventional RH, but the difference diminishes to 4 × 10−6 at the 25th minute as the decarburization rate decays significantly. At the 4th minute, the average carbon mass concentration in LBB-RH is only 73.26% of that in conventional RH. The proposed transient coupled model quantitatively elucidates the transfer mechanism in LBB-RH, and offers a theoretical foundation for the industrial production of ultra-low carbon steel with enhanced overall performance.