Iron ore particles on the graphite powder were observed by laser microscope to study low temperature reduction and melting behavior. The iron ores were classified two types by the gangue behavior through the reduction process. One forms a gangue concentrated layer and the other does not. Melting start temperature of iron ores with the gangue concentrated layer was higher than that of without. In the case of the iron ores with gangue concentrated layer, the formed gangue layer prevents the reduced iron from contacting with graphite, and the melting start temperature was much higher than the eutectic temperature of the Fe-C binary system. The melting start temperature was lowered for the ore particle coated with CaCO₃ as the coated layer enhances melting of the gangue concentrated layer.
These results were confirmed by measurement of the softening and melt-down properties of the carbon composite iron ore briquette at a high temperature under-load test.
The direct contact of reduced iron with carbon is most important for the low temperature melting of iron ore. The selection of iron ore without gangue concentrated layer, flux addition to the iron ore with gangue concentrated layer will contribute to lowering the melt down temperature.