Carburized carbon content of reduced iron and direct carburization in carbon composite iron ore pellets heated at elevated temperature

Using coal char, coke and graphite, carbon composite iron ore pellets of 18 mm in diameter with the mixing ratio of [reducible oxygen mol(O)]/[fixed carbon mol(C)]=1 were prepared inside a rotating tire. The pellets were heated in nitrogen at 1 150-1 380degreesC until reactions just finished. The reacted pellet was separated into a shell part and a core part. The pulverized shell and core parts were repeatedly cleaned in ethanol under ultrasonic vibration to thoroughly remove attached carbon particles. The content of carbon dissolved in reduced iron was measured by analyzing them by the combustion method. The direct carburization through direct contact points is the major reaction and the gaseous carburization is the minor one. Coal char bearing pellets showed carbon contents much less than the others, less than 0.5 % in shell and increased with temperature at last exceeding soliclus line at 1 300degreesC in core. Increase in the mixing amount of char showed no change in the carbon content. But roughening the char significantly increased the content. Coke bearing pellets showed carbon contents near to soliclus line in shell and between solidus and liquidus lines in core. Graphite bearing pellets showed carbon content almost agreed with soliclus line in shell and above liquidus line in core. Free particles of coke and coal char were observed to drop from the void formed inside reacted pellets at 1 300degreesC or more. Free graphite particles were never observed from reacted pellets in any conditions. Recommended conditions for melting the reduced iron at low temperature were proposed.