Smelting of Iron Ore in Fe–Cr–C–Si Melts

Abstract

Direct smelting of the South African Sishen hematite ore in Fe–Cr–C–Si melts was studied, where the aim was to increase the Fe/Cr ratio of high carbon ferrochrome melts in order to approach stainless steel compositions. Experiments in the temperature range of 1600°C to 1750°C were conducted in an inductively heated rotating cylinder technique furnace; however, due to the very fast nature of the reactions, the sintered iron ore cylinders were not rotated. The molten alloy contained 50% Cr, 0.25 to 8% C, and 1.5 to 7% Si, balance being Fe. Relevant slag metal equilibrium in the system was determined from literature and Scanning Electron Microscope (SEM) examinations. In Fe–Cr–C melts, the rate increased with increasing temperature and was independent of the carbon concentration while it decreased with decreasing Cr content of the metal. At 1600°C, the formation of a carbide layer surrounding the iron oxide was observed to be a kinetic barrier for reduction. At 1650°C and higher temperatures, a mixed rate control was suggested. When the melt contained Si, the rate again increased with temperature and was independent of Si concentration. The rate limiting factor in Fe–Cr–Si melts was suggested as the diffusion of Si in the formed slag phase. In the presence of both carbon and silicon in the alloy phase the reduction rate was similar to the rates in Fe–Cr–Si melts.