Swelling Behavior of Iron Ore Pellets during Reduction in H2 and N2/H2 Atmospheres at Different Temperatures

The need to develop green steelmaking techniques has led to the replacement of reducing agents such as CO with H2. H2 and N2/H2 mixtures can be used for the carbothermal reduction of iron ore. Herein, the reduction swelling index (RSI) of iron ore pellets in a forming gas (N2/H2) atmosphere at temperatures of 700-1000 °C is investigated and it is compared with that in pure H2. It is showed in the experimental results that the RSI increases with increasing temperature for both the H2 and N2/H2 atmospheres. The maximum swelling is reached approximately 5 min into the H2 reduction process, while in the N2/H2 atmosphere, it is reached after 25-45 min of reduction, depending on the temperature. When the reduction temperature exceeds 900 °C, the RSI is greater than 20%. Scanning electron microscopy/energy-dispersive X-ray spectroscopy is performed to detect the changes in the microstructure and chemical composition of the samples. The nonreduced areas in the reduced pellets during the N2/H2 reduction process are analyzed using light optical microscopy.