Recent High Temperature Adventures in the Casting of Metals and their Potential Implications for the Near Net Shape Production of Steel Sheets

Abstract

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.

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.

La mise en contact d'un alliage de métal liquide avec un substrat réfrigérant lors des opérations de coulée entre cylindres et de coulée entre bandes implique communément trois phases: le métal liquide qui entre en contact, le substrat et/ou la strate supérieure plus froid qui est contacté et une phase gazeuse intervenante retenue et comprimée entre les deux. On peut couler les produits de feuillard d'une manière satisfaisante, ou pas, dépendamment des réactions chimiques interfaciales, des écoulements interfaciaux de gaz, du comportement du ménisque, de la topologie du substrat et des caractéristiques de mouillage/étalement du métal. Cet article décrit un nombre d'expériences et de modèles mathématiques intéressants qui ont été conçus pour comprendre la nature et le rôle des interfaces et leur effet sur la productivité de l'équipement de coulée, sur la qualité de la surface de la tôle et sur la microstructure des bruts de coulée. On montre que la couche mince de gaz emprisonné entre le substrat et le métal liquide est une source extrêmement efficace de résistance thermique, très sensible à la topographie de la surface de la bande et à 'l'épaisseur' de l'interface. Pareillement, la façon dont un métal liquide mouille le substrat, soit mouillage, non-mouillage, ou quelque chose entre les deux, est très pertinent à la topographie de la surface d'une tôle de métal. Pour les bains d'acier, cette surface interfaciale de contact est, principalement, non-mouillante.