Elucidating Pore Network Evolution in Laboratory- and Shaft-Furnace Hydrogen-Reduced Iron Pellets Using Nanotomographic Characterization

Direct reduced iron (DRI) is an increasingly important feedstock for modern steelmaking. Fundamental research into DRI properties is limited by the discrepancy between the behavior of industrially produced pellets and laboratory-produced pellets, leading to nongeneralizable conclusions from laboratory work. In this study, a detailed nano-computed tomographic characterization of ore pellets, hydrogen DRI reduced in a pilot-scale shaft furnace, and laboratory-reduced DRI is presented to better understand the microstructurally influenced property differences between the two. The shaft-furnace-reduced pellets show lower overall porosity but larger average pore volume thickness and solid volume thickness than the laboratory-reduced pellets. This effect is attributed to increased sintering behavior in the shaft furnace case. All pellet types show almost entirely connected pore volumes. The tortuosity of the pores is shown to increase with a degree of reduction, though the shaft furnace pellets show lower tortuosity than the laboratory-reduced pellets. Again, this difference is attributed to the larger pore volume thickness for shaft-furnace-reduced pellets.