FEATURES OF THE FORMATION OF ENDOGENIC INOCULANTS IN THE METAL STREAM DURING THE CASTING OF LARGE INGOTS

Abstract

One promising method of controlling the structure of the metal in the production of ingots and large castings is the introduction of highly dispersed cooling particles - inoculants - into the melt. The iron powders used for this purpose are not always compatible with the chemical composition of the alloy which is being made. In addition, the outside surface of the inoc- ulants which are introduced may be oxidized. This diminishes the positive effect of the cooling additives on the crystallizati on of the ingot or casting. A more efficient approach would be to form drops inside the metal stream during the casting operation . The drops would solidify as they fall in the stream and act as cooling additives having the same chemical composition as the metal being cast. The possibility that an isolated drop will become separated from the stream is determined by many factors, particular- ly the ratio of the external forces acting on the melt and the interfacial forces. An analysis shows that there is little prob ability of a drop separating spontaneously from the melt, due to the strong surface tension of the liquid metal. Additional drops may be formed if individual drops falling about the periphery of the stream are purposedly broken up into smaller fractions. The p os- sibility of such fragmentation taking place is evaluated quantitatively on the basis of a criterion of the deformation of the d rops or Weber's criterion (1). This criterion is a ratio of parameters that are proportional to the aerodynamic flow reaching the drop and to the interfacial forces: