Effect of Sintering and Porosity Development on Direct Reduction of Manganese Ore Pellets

High manganese steels with > 10% Mn offer a combination of high tensile strength and good ductility, two critical properties for automotive steels. Conventional routes to produce the Mn units used for steelmaking are energy- and capital-intensive. Therefore, a novel methane-based solid-state reduction process for manganese ore pellets is under investigation. It was found in preliminary tests that the reduction of ore pellets by methane was limited by gas transport to the pellet interior. To enhance the reducibility of Mn ore pellets, this study aimed at improving pellet porosity through adjustment of Mn ore powder particle size and the addition of limestone, which thermally decomposes to CaO and CO2. The change in compressive strength with an increase in pellet porosity was also studied. It was found that the increase in porosity as a result of limestone addition improves the reducibility of pellets and decreases the pellet strength. The effect of particle size on pellet reducibility was, however, more complicated because of the simultaneous change in the total surface area and sintering behavior of the particles.