Ghostlines form in large ingots and heavy steel castings due to segregation and density differences. Criteria like the Rayleigh criterion provide the prediction of ghost-lines, depending on the steel composition, cooling conditions, and permeability of the mushy zone. In collaboration with voestalpine Foundry, test castings with a weight of 2.5 tons are investigated by means of analytical investigations (OES, LECO, SEM-EDS) and metallographic methods (light microscopy). Structural parameters like primary and secondary dendrite spacings are measured. In parallel, the solidification of the ingots is simulated by means of MagmaSoft, providing information on solidification parameters and the Rayleigh number. Finally, the results will be used to adjust parameters in the simulations in order to meet the results of the analytical and metallographic investigations and to conclude on casting parameters and steel composition adjustments to better control the formation of ghost lines in heavy steel casting of creep resistant steels.