High performance ferro-coke from DRI: insights into microstructure, mechanical strength, and carbonisation behaviour

Ferro-coke has attracted attention as a low-carbon burden material for blast furnace ironmaking; however, its poor mechanical strength limits industrial application. This study reports a significant breakthrough in producing high strength ferro-coke by strategically integrating slightly caking coal, direct reduced iron (DRI), and a high-fluidity Australian coal (binder). More importantly, the relationship between iron-bearing material evolution, thermoplastic behaviour, and coke structure development during carbonisation is systematically studied. Our findings reveal a fundamental divergence in structural evolution in iron ore and DRI-based systems. Iron ore suppressed the formation of porous frameworks and anisotropic carbon structures, leading to weak bonding and loss of strength. Fe 2 O 3 reduction at 400–600 ℃ by H 2 and CO decreased the fluidity and shortened the plastic range of coal. In contrast, stable DRI enabled the development of a robust porous framework, improved microtexture, and stronger bonding, resulting in higher strength. Furthermore, the iron ore system experiences significant carbon depletion due to both iron oxide reduction and carbon gasification. This carbon consumption generated structural defects, lowering the strength of ore-based ferro-coke. Coal tar pitch (CTP) acted as an effective binder, approximately doubling the strength in both DRI and iron ore systems. In comparison, high-fluidity coal serves as an efficient binder only in the DRI-based systems. These findings provide new insights into the fundamental mechanism driving ferro-coke strength. From a practical perspective, CTP is essential for iron ore-based ferro-coke. The combination of DRI with high-fluidity coal offers a promising route for producing high-strength ferro-coke.