Distinct Mechanisms for Channel Segregation in Ultra-Heavy Advanced Steel Ingots via Numerical Simulation and Experimental Characterization

Channel segregation is one of the most common defects in solidifying steel, particularly in ultra-heavy advanced steel ingots, and it has a significant effect on the mechanical properties of the final products. However, the formation mechanism remains unclear. Here, based on numerical simulations and experimental characterization of 100-ton ultra-heavy 30Cr2Ni4MoV steel ingots used in nuclear power plants, it is strikingly found that channel segregations in the top riser and body are caused by two distinct mechanisms, natural convection and inclusion flotation, respectively. The flow instability and mush deformation in the riser originates from the complex geometry and heat transport. However, the onset of channel segregation in the ingot body stems from perturbation by inclusion flotation. Quantitatively, the initiation criterion of the modified Rayleigh number, including the inclusion effect and its critical value of 30, is proposed for the first time. In addition, it is proven that reducing the number of inclusions prevents channel segregation and improves the entire compositional homogeneity. This study highlights a novel idea by jointly controlling impurities and optimizing hot-top design to produce homogenized ultra-heavy steel ingots in key areas. Graphical Abstract