An Examination of Electrode-Change Practice in Electroslag Melting

Abstract

An examination of the unsteady-state heat balanced of an ESR furnace during a power interruption has been made. The results of this study show that the ingot heat balance during an electrode change may be characterized by a single term, the volume fraction of liquid solidified during the interruption. The application of this term to ESR and VAR practice is demonstrated. The structure and composition of ingot metal solidified during this change can be related to the local temperature gradients and solidification rate during the change. In turn, this may be related to the steady-state liquidus isotherm and the volume fraction solidified. The role of the local segregation coefficient in determining the maximum tolerable electrode change time is clearly demonstrated by the above parameters. The general relation of the above mechanisms to the electrode-change method is discussed for some practical cases. The engineering and economic problems associated with electrode-change practice are detailed. It is concluded that although there are many instances where a properly engineered electrode-change method may be used with no adverse effects in the ingot, the general applicability of the method is in doubt.