Abstract
Freckle defects were found in electro-slag remelting (ESR) ingots, which severely limit the development of the larger-diameter ingots. The macrostructure and the composition of the freckles in a low-alloy structure steel ESR ingot were investigated to clarify the freckle formation mechanism. The results shows that the freckles in the ingot were caused by the upward solute-rich liquid flow in the mushy zone, and the composition of the freckles corresponds to that of the liquid, with a liquid fraction of 0.36 to 0.43. The relative Rayleigh number (Ra), a freckle criterion considering the effect of a tilted solidification front, was adopted to evaluate the freckle formation tendency in the industrial-scale ESR ingots based on the results of the experiments, kinetic simulation and thermophysical property calculation. The calculated results of Ra are in good agreement with the actual distribution of the freckles in the ingot.
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