Ferro-coke 3D Microstructure Development and Impacts on Mechanical Strength

The addition of highly reactive ferro-coke in a blast furnace (BF) can lower the temperature of the thermal reserve zone (TRZ) and increase gas permeability through the ore layer, resulting in a decrease in fossil fuel rate and improved shaft efficiency. Ferro-coke should possess high reactivity and sufficient mechanical strength for handling, transport, and BF use. A better understanding of the relationship between microstructure and strength in ferro-coke is needed to optimise the blend composition and maximise strength. This study investigates the mechanism of ferro-coke microstructure formation using 3D micro-computed tomography (Micro-CT) image analysis, scanning electron microscopy (SEM), and von Mises stress distribution simulation. The impacts of iron feed (iron ore and reduced iron) and binder type (high fluidity coal and coal tar pitch (CTP)) on ferro-coke microstructure and strength were analysed. The results show that ferro-coke strength primarily depends on the bonding quality of inert components and ferrous particles to the coke matrix. The porosity of ferro-coke, a sign of the thermal plasticity of the blend, was closely correlated with strength. The addition of iron ore inhibited blend plasticity and the formation of a porous structure, resulting in poor bonding of inert components to the coke matrix. Results indicated that the iron ore and its reduction in carbonisation led to the loss of thermoplasticity, thus hindering microstructure development. CTP showed a strong binding ability in the presence of both iron ore and iron powder, while high fluidity coal showed limited binding ability when iron ore was used in ferro-coke.