Structure and Properties of Slags Used in the Continuous Casting of Steel: Part 1 Conventional Mould Powders

TLDR

Mould slag physical properties, such as viscosity, break temperature, fcryst, optical characteristics, and interfacial tension, are critical for continuous casting performance and are influenced by mould dimensions, casting conditions, and steel grade. This paper reviews the existing thermo‑physical data for conventional mould slags. It also surveys data for specialist powders, including F‑free and TRIP‑steel casting powders, to be detailed in Part 2. The review highlights the need to resolve large discrepancies in thermal conductivity above 1050 K between LP and THW methods, to obtain more accurate Cp, density, viscosity, and surface‑tension data, to standardise fcryst determination, to characterise slag‑film porosity, and notes that gaseous convection significantly contributes to heat transfer while glassy slag films are likely optically thin.

Abstract

The physical properties of mould slags are key to their performance in the continuous casting process. The magnitudes of key properties (viscosity, break temperature, fcryst and optical properties) are determined by the mould dimensions, casting conditions and the steel grade being cast. However, a range of other properties (e.g. interfacial tension, density) are needed to minimise defects and process problems. The extant data for thermo-physical properties of conventional mould slags are reviewed here and those for specialist powders (e.g. F-free or for casting TRIP steels) are reviewed in Part 2. It was concluded that there is a need for (i) resolution of the huge differences in thermal conductivity of mould slags for T>1050 K obtained with the LP and THW methods (ii) more data for some properties (e.g. Cp and density) and more accuracy for others (viscosity, surface tension) (iii) standardised procedures for the determination of fcryst and (iv) characterisation of the porosity in slag films. It was also concluded that (i) gaseous convection makes a significant contribution to the heat transfer in the powder bed and (ii) glassy slag films are probably optically-thin.