Simulation of the center-line segregation generated by the formation of bridging

The macrosegregation model that heat transfer, solidification, liquid flow and solute movement were considered was developed to simulate the generation of the center-line segregation in the casting of steel. The classical model which considers only the liquid flow caused by solidification shrinkage leads the negative segregation which contradicts the fact. In order to explain the contradiction, the bulging of the cast slab has been claimed to be important factor to form the positive segregation at the center of the cast. However, some experimental data show that the bulging has not been necessarily formed during the generation of center-line segregation. In this case, the bridging with the solidification shrinkage has been found to be formed instead of the bulging. In this paper, the macrosegregation model is developed considering, thus, three driving forces of fluid flow; solute concentration, thermal expansion and solidification shrinkage. This simulation results show that the primary driving force which results in the center-line segregation is the solidification shrinkage with the bridge. In addition to that, the mechanism of generating the center-line segregation is discussed based on the simulation results.