Influence of the Hot-Top Thermal Regime on the Severity and Extent of Macrosegregation in Large-Size Steel Ingots

The influence of hot-top designs with different heat capacities on the distribution of positive and negative macrosegregation was investigated on a 12 metric tonne (MT) cast ingot made using Cr-Mo low-alloy steel. The three-dimensional finite element modeling code THERCAST® was used to simulate the thermo-mechanical phenomena associated with the solidification process, running from filling the mold until complete solidification. The model was validated on an industrial-scale ingot and then utilized to evaluate the influence of the thermal history of the hot-top, a crucial component in the cast ingot setup. This assessment aimed to comprehend changes in solidification time, temperature, and heat flux—all of which contribute to the determination of macrosegregation severity. The results showed that preheating the hot-top had a minor effect on solidification time, while modifications of thermal conductivity in the hot-top region increased the solidification time by 31%, thereby significantly affecting the macrosegregation patterns. The results are discussed and interpreted in terms of the fundamental mechanisms governing the kinetics of solidification and macrosegregation phenomena.