Mould lubrication and control of initial solidification associated with continuous casting of steel

Abstract

Synopsis : In continuous casting of steel, it is important to provide stable lubrication for a solidifying shell that is kept as uniform as possible in an oscillating mould, because this improves not only productivity of the process but also surface quality of cast slabs. In the first part of the present article, mould lubrication is reviewed with an emphasis on infiltration of mould flux in the channel between a solidifying shell and a mould. Theoretical understandings of the phenomenon are described in comparison with experimental and empirical knowledge in casting operation. Next, development of uneven solidifying shell is discussed from not only thermo-mechanical behavior of the shell but nucleation and growth during initial solidification at cast surface. This reveals importance of heat transfer control between the shell and mould. For this reason, the discussions are extended to crystallization of mould flux film that provides stable reduction in the heat transfer. Effect of the crystallization on conductive and radiative heat transfer through mould flux film is discussed as well as change in thermal resistance at interface between the flux film and mould wall. Then, recent studies on crystallization of cuspidine (3CaO · 2SiO2 · CaF2) are also referred. Finally, current knowledge of mould flux infiltration, control of initial solidification and heat transfer in continuous casting mould is briefly summarized.