Influence of Coke and Graphite on the Decomposition and Melting Behavior of a Mold Flux

The melting kinetics of mold fluxes used in steel continuous casting represents a fundamental factor to be considered in order to obtain a quality product without superficial defects and also to avoid production problems. This melting stage is controlled mainly by the type and amount of carbonaceous material added to the powder. In this work, structure, particle size and morphology of two carbonaceous materials: petroleum coke and synthetic graphite were analyzed. Both carbonaceous materials were separately added to a decarburized commercial mold flux. The melting behavior was monitored by HSM (hot stage microscopy) and a melting interval was identified using critical temperatures. A higher fusion rate, as inverse of melting interval, was observed in powder with coke addition. This fact was associated to a lower crystalline degree and a finer PSD (particle size distribution) presented by petroleum coke. Different values of the activation energy of decomposition were related to fusion rate of both mold fluxes. Higher rate of changes in activation energy during the progress of the reaction was observed in the sample with coke. This fact is associated to a faster change in the surface area of coke particles.