Simulation and experimental validation of the effect of superheat on macrosegregation in large-size steel ingots

A 3D model was employed to study the effect of melt initial superheat on the macrosegregation formation using FE modeling and experimentation methods. The casting process of three ingots with the initial melt superheats of 75 °C, 65 °C, and 55 °C were simulated. The three cases represented three variables encountered in industry during casting of large size ingots. For the above three studied cases, all other casting conditions were kept the same. Results showed that the variation of initial melt superheat gave rise to changes in temperature pattern, liquid flow field, solidification speed, and thermomechanical contraction. Under the combined actions of all these changes, lower superheat tended to alleviate the segregation intensity in the upper part of the ingot body, in the hot-top, and in the solute-rich bands between the ingot centerline and periphery. The beneficial effect of lower superheat on alleviation of segregation severity was confirmed by experimental chemical measurement results. The results were analyzed in terms of heat and mass transfer theories and allow for a better understanding of the underlying mechanisms responsible for the occurrence of macrosegregation in ingot casting process. The findings should be helpful for the casting process design of a given ingot of high value-added steels or other alloys.