Thermodynamic Mechanism and Optimization of Dynamic Deoxidation and Alloying for Low‐Carbon Al‐Killed Steel Tapping Based on Instantaneous Yield

To address severe elemental yield fluctuations, high aluminum consumption, and low narrow‐window composition hit rates during BOF tapping, deoxidation, and alloying of hot‐rolled low‐carbon steels (SPHC and Q195L), this study evaluates the limitations of the traditional cumulative yield ( η ). As a state function, cumulative yield fails to characterize the dynamic response to varying alloy additions and cannot explain anomalous data where η falls outside the standard [0, 1] range. Therefore, a dynamic characterization method based on instantaneous yield ( η ′) is proposed. Industrial big data statistics combined with FactSage 8.4 multiphase thermodynamic simulations were employed to elucidate the elemental reaction evolution within the complex slag–metal system. The results reveal significant competition and inhibition among elements during multicomponent deoxidation and alloying. Reactions between various elements and dissolved oxygen exhibit distinct thermodynamic thresholds and staged characteristics with increasing alloy addition. Furthermore, η < 0 is attributed to steel–slag re‐equilibration driven by slag carryover, while η > 1 results from aluminothermic reduction of Si and Mn oxide phases. Based on these findings, the alloying processes for typical high‐production steel grades were optimized, successfully improving the narrow‐window composition control rate after BOF tapping.