Formation of Deposited Oxide Film during the Sub-rapid Solidification of Silicon Steel Droplet and Its Effect on Interfacial Heat Transfer Behavior

The droplet solidification technique was used to investigate the formation of deposited film and the interfacial heat transfer for the sub-rapid solidification of silicon steels. The composition of deposited films consists of MnO, FeO and SiO₂ for both the low and high-silicon steels. The deposited film could improve the wetting condition between the steel droplet and substrate. And the wetting condition between the droplet and substrate improves with the increasing of ejection times from 1 to 9, and thus the final contact angles decrease gradually from 105.1 to 72.8 deg. The peak value of heat flux increases with the number of solidification tests, indicating that the heat transfer condition between the droplet and substrate improves with the deposition of film. The peak value of heat flux increases from 5.64 to 7.42 MW/m² for low-silicon steel after the 9th ejection, and it is from 6.03 to 9.06 MW/m² for high-silicon steel. This is because the interfacial thermal resistance between the droplet and substrate reduces gradually with the increasing of test times. A higher Mn content in the high-silicon steel leads to a higher deposited rate of the oxide film than the low-silicon steel. Compared with the low-silicon steel, the increment of MnO content in the film for the high-silicon steel is 6.60 wt pct, and there is no obvious increment of SiO₂ in the film, though the increment of Si in high-silicon steel is 6.06 wt pct, and for Mn is only 0.72 wt pct.