Effect of carbonaceous material graphitization degree on carburization behavior in Fe-C mixture powder during rapid heating

Abstract

The transition to carbon-neutral steelmaking necessitates the development of alternative carburizing agents to replace fossil-derived carbon. This study investigates the effect of graphitization degree and ash content of biochar on the carburization behavior of Fe–C mixture powders during rapid heating. Carbonaceous materials with varying crystallinity and composition were prepared through heat treatment and acid leaching, and their structural disorder was evaluated using Raman spectroscopy (IV/IG ratio). Carburization behavior was examined using a laser microscope equipped with infrared image heating under controlled Ar–H2 atmosphere. Two experimental approaches were applied: compact Fe–C pellets to determine complete melting temperature, and iron plate–carbon contact samples to observe the initial melt formation. Results showed that ash content, rather than graphitization degree, was the dominant factor influencing carburization. Ash-rich samples exhibited delayed and localized melt formation, while ash-removed biochar showed earlier and more uniform melting. The IV/IG ratio had limited correlation with melting behavior. These findings suggest that removing ash from biochar significantly enhances its performance as a carbon-neutral carburizing agent in hydrogen-based steelmaking routes such as H-DRI–EAF, offering a practical strategy for decarbonization in ironmaking.