Study on Reduction Melting Behavior of Iron-Bearing Burden Under Oxygen-Enriched Condition of Blast Furnace

The oxygen blast furnace (OBF) represents a key pathway toward deep decarbonization in ironmaking. The main difference between it and the traditional blast furnace is that the atmosphere in the furnace has high reduction potential and little nitrogen content. However, the burden metallurgical performance under CO-H2-rich, N2-lean atmospheres remains unclear. This study investigated the isothermal and non-isothermal reduction and softening–melting behavior of sinter and pellets. As CO increased from 59.2 to 79.2 vol%, the reduction degree rose from ~27% to ~90% within 180 min, with a rate index of 0.72–0.75%·min−1. The apparent activation energies of sinter and pellets were 113.0 kJ·mol−1 and 57.9 kJ·mol−1, respectively, indicating that the gas–solid interfacial chemical reaction is the rate-controlling step. Under non-isothermal conditions, the reduction start temperatures of both sinter and pellets decreased, and complete reduction was achieved at 1200 °C. Microstructural analysis revealed a four-stage structural evolution pathway. The softening–melting behavior indicated that oxygen-enriched conditions decrease the softening start temperature, whereas the melting start temperature increases due to the thickening of the metallic iron shell. The maximum pressure difference of the cohesive zone was reduced by 32.9%, and the air permeability was significantly improved. This study reveals the mechanism of charge reaction and structure evolution under OBF conditions and provides a theoretical basis for charge optimization and OBF operation control.