Free and Combined Carbon in Iron Using CH₄ as Carburizing Gas, in the Temperature Range from 900 °C to 1050 °C

Iron carbide is a metastable phase which can be produced after reduction and carburization of iron ores by gas-solid reactions. The total carbon concentration in Direct Reduced Iron (DRI) is present as free carbon and combined carbon in the form of iron carbides. Due to the thermodynamic instability of iron carbides, free carbon cannot be fully avoided during the carburizing process. The rate of production of iron carbides and free carbon depends on the carburizing gas, temperature and solid reactant properties. In previous investigations iron carbide has been produced with different mixtures containing H₂, CO and CH₄ usually at temperatures below 900 °C. In the present investigation the rate of formation and mechanisms of formation of iron carbide using pure methane in the temperature range from 900 °C to 1050 °C have been investigated. The results show that free carbon is present in most of the experimental conditions, however it was found an optimum temperature which can produce almost pure iron carbide. The reaction mechanism by chemical control proposed in previous studies was also confirmed.