Interfacial Heat Transfer and Nucleation of Steel on Metallic Substrates

A modified levitated drop technique and an immersion technique were used to study the wetting and nucleation behavior of steel melts on a metallic substrate. Thermal histories of the solidifying shell and the substrate were recorded and used to elucidate the mechanisms of interfacial heat transfer and nucleation. The melt/substrate wetting behavior was shown to be contr olled by the melt surface tension. The interfacial heat transfer resistance was controlled by the degree of melt/substrate wetting consequently affecting the heat flux across the interface. According to the classical heterogeneous nucleation theory, improved wetting is expected to reduce the energy barrier for nucleation while increasing the cooling rate of the liquid. Because the overall nucl eation rate is controlled by both the rate of cluster formation and the rate of atom transfer to the nucleus, increasing the cooling rate above a critical level is expected to reduce the nucleation rate. The measured experimental data allowed the melt undercooling and the time for nucleation of the first solid phase to be determined and compared to the theoretical predictions. The implications of the mechanisms of nucleation on early shell growth are also considered.