Microstructure evolution of iron carbide during reaction with steam at elevated temperatures

摘要

Cross-sectional microscopy and X-ray diffractometry in combination with thermogravimetry were conducted to investigate the microstructure evolution of iron-ore derived iron carbide caused by the reaction with steam at elevated temperatures. During continuous heating from 393 to 1 373 K at l0Kmin~(-1), the microstructure of the iron carbide changed in the following sequence: (1) densification due to oxidation of Fe_3C, (2) coarsening by decomposition of Fe_3C and by reduction of iron oxides, and then (3) re-densification associated with oxidation of Fe. The microstructure evolution was found to correspond well to the volume change due to the phase transformations of the iron carbide. Graphite formed in the iron carbide as a result of decomposition of Fe_3C seems to have a highly crystallized lattice that contracts in its c-axis direction.