Effect of Graphite Nodule Number on Eutectic Solidification Time of Hypereutectic Ductile Iron Melt Based on Diffusion Theory

Abstract

  It was assumed that only primary graphite would grow in the eutectic stage and no other graphite would be nucleated in this stage, and that at the beginning of the eutectic stage, the graphite nodule would become enveloped by an austenite shell with subsequent growth occurring due to diffusion of carbon through the shell. An expression for the eutectic solidification time t_E is obtained as a function of the number of graphite nodules N_A, when the degree of super cooling ΔT is small.
    t_E=K_E/D_γ·ΔT·N_A
where K_E is a constant given by various carbon concentrations and D_γ is the diffusion coefficient of carbon in austenite. The numerical calculation indicates that the change in the composition of the melt has little effect on t_E, and that the melt having N_A more than 1,000 mm⁻² may complete eutectic solidification in a short period of time within 10 sec.