Interfacial heat transfer and nucleation of steel on metallic substrates

Abstract

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 controlled 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 nucleation 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.

Interaction between Iron Droplets and H2S during Solidification: Effects on Heat Transfer, Surface Tension and Composition

“…1,4,6,10) Finally results available in the literature on the effect of melt surface tension have already been mentioned in the introduction. 2,4,5) In this work the final sulfur content in the iron samples cast in a gas atmosphere containing H 2 S was about 100 ppm; by using the expression for the liquidus temperature proposed by Turkdogan,11) T melting ϭ1 537Ϫ73. The sulfur pick-up would then lead to only a 2°C decrease in solidus temperature, i.e.…”

“…Examples of this are the results by Phinichka, 4) Strezov et al 2) and Evans et al 5) All of these authors found that, when casting steel in direct contact with a cooling substrate, the heat extraction rates increased with the increase of the concentration of the considered surface-active element (sulfur or tellurium). A higher content of surface active elements leads to a lower melt surface tension, which results in better wetting conditions between the mold and metal and thus better heat transfer conditions.…”

“…In previous studies [2][3][4][5][6]8) that focused on heat transfer in strip casting, heat fluxes determined during solidification experiments were considered only in the first 500 ms or less, paying attention especially to the very first milliseconds during which usually a high initial heat flux peak is observed. This approach makes sense when considering the order of magnitude of characteristic solidification times in strip casting, i.e.…”

Dynamic wetting and heat transfer at the initiation of aluminum solidification on copper substrates

“…However, the surface tension and contact angles values were taken from other publications and were not measured simultaneously with the heat transfer. Evans and Strezov [26] used a levitation apparatus to melt 0.7 g steel droplets and showed that an increase in the surface tension of steel droplets was associated with a decrease in the maximum heat fluxes.…”

“…There is indirect evidence that this may be the case through the work reported in references [23][24][25][26] but there is clearly a need for more experimental data. The experiments were carried out with aluminum droplets impinging on a copper substrate.…”