Toward Fossil‐Free Steelmaking: Overview of Physiochemical Properties of Hydrochar and Its Application in Blast Furnace and Electric Arc Furnace Processes

ABSTRACT The steel industry is among one of the largest CO 2 emitters in the world. To meet climate targets, replacing fossil‐based carbon with renewable biocarbon in metallurgical processes, particularly in blast furnaces (BFs) and electric arc furnaces (EAFs), has emerged as a viable short‐ to mid‐term solution. Hydrothermal carbonization is a promising technology that converts low‐grade, high‐moisture biomass into hydrochar, a carbon‐rich material with potential applications in ironmaking and steelmaking processes. This review examines the physicochemical and metallurgical properties of hydrochar—both in its pristine and pyrolyzed forms—derived from various biomass sources, and compares them with those of conventional carbonaceous materials such as fossil coal. This review also evaluates recent experimental and industrial studies demonstrating the application of hydrochar in BF injection and carbon composite agglomerates as well as its use for carburization and slag foaming in the EAF process. It demonstrates the potential of hydrochar as a partial substitute for fossil carbon, contributing to significant reductions in steel production‐related CO 2 emissions.