Prof Andreas Ludwig - Montanuniversität Leoben, Austria
Physical Classification of Macrosegregation
A. Ludwig1, M. Wu1,2, A. Kharicha1,2
1Department of Metallurgy, University of Leoben, Austria
2Christian Doppler Laboratory for Advanced Process Simulation of Solidification and Melting, University of Leoben, Austria
Solute composition inhomogeneities at a scale much larger than the microstructure are termed macrosegregation. They are typically classified according to their metallurgical appearance. In ingot castings they are known as ‘A’ and ‘V’ segregation, negative cone segregation, and positive secondary pipe segregation. There are ‘inverse’ segregation at casting surfaces and ‘centerline’ segregation in continuously cast slabs and blooms. Macrosegregation forms if a relative motion between the solute-enriched or -depleted melt and dendritic solid structures occurs. This might happen due to (i) solidification shrinkage, (ii) natural or forced convection, (iii) grain movement and/or (iv) deformation of the mushy solid. In recent years, the numerical description of the combination of these phenomena has become possible and so a tool has emerged which can be effectively used to get a deeper understanding into process details which are responsible for the formation of the above mentioned different types of macrosegregation. Based on extensive studies with this tool a physical classification of different types of macrosegregations is suggested.