Formation of Naturally Deposited Film and Its Effect on Interfacial Heat Transfer during Strip Casting of Martensitic Steel

A strip-casting simulator has been successfully developed to simulate the initial contacting conditions between the twin roller and melt during the strip-casting process, in which the peak/average heat flux, secondary dendrite arm space and cooling rate of the martensitic strip cast are similar to those observed in the actual strip caster. During the casting experiments, a layer of dark deposited film can be found on the substrate, whose composition is 69.66Mn-15.36O-11.03Fe-3.95Si (wt.%). The deposited film starts to melt during the 5th immersion experiment and the melting area of the film increases with the repeat of the immersion test. The presence of solid deposited film first impairs the interfacial heat transfer; however, with the accumulation of the deposited film, melting of the film occurs that enhances the interfacial heat fluxes due to the improved melt/substrate interfacial contact, as the cavities or air pockets between the melt and the substrate are gradually filled with the increasing of the melting area of the deposited film. Compared with substrate roughness, the effect of the deposited film on heat transfer is more significant.