Evolution of Porosity Microsegregation in Continuous Casting Bloom During the Heating Process

The microsegregation of continuous casting bloom or slab could cause the banded structures in the rolled products, which would seriously reduce the anisotropy, plasticity, and toughness of steel. The previous research mostly focused on the dendrite microsegregation that is located between the dendrites. However, the microsegregation degree (MSD) of porosity segregation that is associated with and located around the center shrinkage cavity is much more serious than that of dendrite segregation. In this paper, a new evaluation method of microsegregation at the microscale that considered the proportion of segregated cells and microsegregation concentration ratio was developed based on the concept of degree centrality in “network science.” Combining this new microsegregation evaluation method and orthogonal experiment, the porosity microsegregation improvement of continuous casting bloom for heavy rail steel with different holding times and temperatures during the heating process was investigated by the diffusion kinetic model. The results show that the holding temperature has the greatest impact on element diffusion when compared to the shrinkage cavity size and holding time. When the size of the shrinkage cavity is greater than 400 μm, the optimal holding temperature is 1250 °C, and the optimal holding time is 90 min. The new diffusion kinetic model of porosity microsegregation has high accuracy with the optimal conditions of the heating process.