Cementite formation in CH4-H2-Ar gas mixture and cementite stability

Abstract

Iron ore reduction/cementation by CH4-H2-Ar gas (35vol% CH4, 55 vol% H2 and 10 vol% Ar) was examined in a fixed bed reactor in the temperature range of 600-925°C. Iron oxides were first reduced to metallic iron and then iron was carburised to cementite. The rate of iron ore reduction and iron cementation increased with increasing temperature. Iron carbide formed in the reduction/cementation process was unstable and decomposed to metallic iron and carbon. Cementite stability was studied in the temperature range of 500-850°C. At temperature below 600°C and above 750°C, the rate of cementite decomposition increased with the increase in temperature. However, in the range of 600-750°C the rate of cementite decomposition decreased with increasing temperature. Cementite was the most stable at 750°C and least stable at 600°C. At 750°C, iron ore was converted to cementite by gas containing 35 vol% CH4, 55 vol% H2 and 10 vol% Ar in 15 min.