Gas-flow-mediated pathway transition in hydrogen-enriched ironmaking

The utilization of hydrogen in ironmaking to achieve decarburization is a global consensus for industry. The successful implementation of hydrogen in a blast furnace requires not only high reduction efficiency but also efficient operation. The latter remains a significant challenge because of the limited understanding of the factors governing reduction continuity and slag compatibility within the cohesive zone. In this study, we employ in-situ high-temperature synchrotron X-ray diffraction and kinetic analysis to precisely track phase evolution and rate-limitation processes during hydrogen reduction by using the industrial sinter ores. Results demonstrate that hydrogen gas renewal, controlled by the imposed gas-flow condition, plays a critical role in governing high-temperature reaction pathway selection, which ultimately determines whether Fe (1-x) O is continuously reduced or incorporated into molten slag. A sufficient gas renewal maintains a liquid-involved slag environment compatible with continuous reduction of Fe (1-x) O to metallic Fe. Conversely, an insufficient gas renewal triggers α-C 2 S melting, subsequent interaction with Fe (1-x) O, and finally reduction stagnation of Fe (1−x) O. Within the critical cohesive zone of a blast furnace, this pathway shift and the resulting excessive liquefaction could hinder gas permeability. An inadequate hydrogen gas renewal therefore acts as a critically operational bottleneck for the efficient operation of a blast furnace. These findings provide a mechanistic framework for understanding and controlling reduction continuity, cohesive-zone stability, and ultimately blast furnace operation in hydrogen-enriched ironmaking.