Interfacial Phenomena between Fluxes for Continuous Casting and Liquid Steel

摘要

Flow conditions due to disturbance of interfacial tension have been described theoretically and investigated experimentally. Furthermore relationships between convection flows in boundary liquid layers of continuous casting slags and mass transfer between metal and slag were examined. To this end samples were taken from the mould under operating conditions. The steels examined were CrNi and Cr steels. The results can be summarised as follows:rn1. A new dimensionless number, L_c σρη~(-2) = Ste (Steinmetz)-number, describing convection flows next to the interface in the liquid boundary layer due to disturbance of interfacial tension have been established and experimentally tested.rn2. With increasing values of the Ste-number the movement velocity of the volume elements near the interface increases.rn3. Phase boundary convection always occurs under continuous casting conditions regardless of the thickness of the liquid slag layer and regardless of the occurrence of free convection.rn4. A dimensionless empirical function describing the relation between convection flows in the boundary slag layer and mass transfer is developed and its coefficients for Ti-transfer into the flux layer have been determined.rnFor the conditions directly at the interface and their vicinity following conclusions can be derived:rn5. On both sides of the slag/metal interface high concentration gradients of all elements exist. The degree of gradients depends on the elements. The highest concentration gradients exist in the range up to approx. 150 nm on the metal side and up to approx. 400 nm on the slag side.rn6. The adsorption phase enriched with oxygen on the metal side of the interface contains mainly oxygen-, iron- and chromium ions which show the stoichiometric relations as FeO and CrO_n. A part of this phase contains Fe and Ni which are not associated with oxygen.rn7. The estimated average molar mass flow rate of oxygen through the slag/metal interface lays in the range of mass flow rate at which the interfacial tension is reduced to zero.