Microstructural Evolution and Its Effect on Reaction Rate During Reduction of High-Grade Hematite Ore Pellets With Hydrogen

Fossil-free ironmaking is crucial in mitigating CO2 emissions within the iron and steel industry. Among the various solutions being explored, hydrogen-based direct reduction stands out as one of the most promising approaches for sustainable ironmaking, offering significant potential for medium-term implementation. This study examines the use of pure hydrogen in the direct reduction of industrial iron ore pellets, focusing on the effects of temperature (700–1000 °C) on the reduction kinetics and microstructural evolution. Utilizing a custom-made thermogravimetric setup and microscopic analysis, the research characterizes the reduction process through continuous weight measurements and provides detailed insights into the microstructural and compositional changes across various pellet regions. Through detailed microscopic examination at various stages of reduction, the study emphasizes the heterogeneous nature of the process, particularly within the core of the pellets where complete metallization proves challenging at lower temperatures. The reduction rate was found to be highly dependent on both the temperature and the initial microstructure of the iron ore pellets, as well as its evolution during the reduction process.Graphical Abstract