Carbide formation and accumulation in SiMn furnaces

Recent excavations of Norwegian medium size SiMn furnaces have revealed spectacular amounts of carbide-rich materials accumulating on the sidewalls. In an excavated furnace from Eramet Kvinesdal, producing a 19%Si silicomanganese alloy prior shutdown, the sidewall materials contained silicon carbide in addition to SiMn alloy, slag and carbon. This contrasts with the large amounts of titanium carbides found in a furnace from Ferroglobe (Glencore then) which was producing 16%Si silicomanganese. The significant volume occupied by the carbides is likely to affect the flow of materials as well as furnace operation. It is therefore meaningful to understand how and when those carbides can form, especially concerning titanium carbide given the low content of titanium (about 0.3%) in the raw materials. The present study investigates the conditions under which TiC and SiC can appear in the furnace. Slag, alloy, and gas compositions were chosen to mimic industrial charges and were reacted between 1450 and 1650 °C. The reacted samples were further analysed by electron probe microanalysis with wavelength-dispersive X-ray spectroscopy (EPMA/WDS). Thermodynamic calculations were conducted using FactSage 8.0 and used for further reflection. The results indicate that TiC was formed by both precipitation and chemical reaction.