Growth behavior of bubbles during carbon deoxidation and the deoxidation capacity in molten steel: A model coupled with a mass source term

Carbon deoxidation is a key clean technology, as its gaseous products can be easily removed from molten steel. Deoxidation efficiency heavily depends on the mass transfer and dynamic evolution of bottom-blown bubbles. To clarify the contribution of reaction-generated gases to secondary bubble expansion, this study establishes a kinetic model coupling liquid boundary layer mass transfer with dynamic bubble growth. By incorporating a dynamic CO mass source term, the model quantitatively describes the non-linear coupling mechanism between thermodynamic driving forces and bubble dynamics. To validate the model, a low-temperature bottom-blown physical analog was designed using the thermal decomposition of an ammonium bicarbonate (NH 4 HCO 3 ) solution at 80 °C, where the in situ generated gases successfully emulated the volumetric expansion of reactive bubbles. Simulations using the validated model indicate that initial oxygen content is the primary driving force for bubble growth. Under high-oxygen conditions (500 ppm), the vigorous carbon-oxygen reaction induces a bubble volume expansion of up to 12.39 times, significantly accelerating bubble ascent. Carbon variations between 0.2 and 1.0 wt% have negligible effects on bubble rise kinetics, showing it is not the rate-limiting step; instead, carbon primarily modulates the thermodynamic equilibrium. Regarding bubble size, although larger bubbles enhance single-bubble deoxidation capacity by lowering CO partial pressure, gas utilization efficiency decreases significantly. Specifically, doubling the initial bubble radius increases argon consumption eightfold for a mere 1.67-fold deoxidation gain. This work provides the mechanistic insights and a theoretical basis for carbon deoxidation in molten steel and the corresponding optimization strategy.