RECENT HIGH TEMPERATURE ADVENTURES IN THE CASTING OF METALS AND THEIR POTENTIAL IMPLICATIONS FOR THE NEAR NET SHAPE PRODUCTION OF STEEL SHEETS

The contacting of a liquid metal alloy with a freezing substrate during twin roll and belt casting operations commonly involves three phases: the contacting liquid metal, the colder substrate and/or superstrate being contacted and an intervening gas phase caught up and squeezed in between the two. Strip products can be cast in a satisfactory manner, or not, depending on interfacial chemical reactions, interfacial gas flows, meniscus behaviour, substrate topology and metal wetting/spreading characteristics. This paper describes a number of interesting experiments and mathematical models that have been devised to understand the nature and role of interfaces and how they bear on casting machine productivity, sheet surface quality and as-cast microstructures. It is shown that the thin layer of gas trapped between the substrate and the melt is an extremely effective source of thermal resistance, highly sensitive to belt surface topography and interfacial 'thickness'. Similarly, the way a liquid metal wets the substrate, either wetting or non-wetting or something in between, is very relevant to a sheet metal surface topography. For steel melts, this interfacial surface of contact is, in the main, non-wetting.