A Study of Cementite Formation in the Reduction of Hematite by CO–CO₂ Gas Mixture Using High Temperature XRD

Formation of cementite in the reduction of hematite by CO–CO₂ gas was studied in situ using high temperature XRD (HT XRD) analysis. Reduction of hematite was examined in the temperature range 873–1173 K by CO–CO₂ gas mixture with high carbon activity. When carbon activity in the system was 1.5, cementite was formed only at 1023 K; it was not observed in experiments at 973, 1073 and 1123 K. Formation of cementite was observed at 923–1073 K when carbon activity increased to 3–5; and at 873 K when carbon activity was 10. Formation of cementite at 973–1073 K proceeded through metallic iron; however, in the reduction of hematite at 873 and 923 K, iron was not observed; cementite apparently was formed directly from wüstite. XRD spectra were used to estimate concentration of carbon in austenite in the process of cementite fromation.