Effect of Carbon Concentration and Carbon Bonding Type on the Melting Characteristics of Hydrogen-reduced Iron Ore Pellets

Decarbonization of the steel industry is one of the pathways towards a fossil-fuel-free environment. The steel industry is one of the top contributors to greenhouse gas emissions. Most of these emissions are directly linked to the use of a fossil-fuelbased reductant. Replacing the fossil-based reductant with green H2 enables the transition towards a fossil-free steel industry. The carbon-free iron produced will cause the refining and steelmaking operations to have a starting point far from today’s operations. In addition to carbon being an alloying element in steel production, carbon addition controls the melting characteristics of the reduced iron. In the present study, the effect of carbon content and form (cementite/graphite) in hydrogen-reduced iron ore pellets on their melting characteristics was examined by means of a differential thermal analyser and optical dilatometer. Carburized samples with a carbon content < 2 wt % did not show any initial melting at the eutectic temperature. At and above 2 wt %, the carburized samples showed an initial melting at the eutectic temperature irrespective of the carbon content. However, the absorbed heat varies with varied carbon content. The carbon form does not affect the initial melting temperature, but it affects the melting progression. Carburized samples melt homogenously, while melting of iron-graphite mixtures occurs locally at the interface between iron and carbon particles, and when the time is not long enough, melting might not occur to any significant extent. Therefore, at any given carbon content > 2 wt %, the molten fraction is higher in the case of carburized samples, which is indicated by the amount of absorbed melting heat.