Modelling Macrosegregation in Electroslag Remelted Ingots
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Equations for predicting flow of interdendritic liquid and macrosegregation in ingots prepared by electroslag remelting (ESR) are derived, and computer predictions of macrosegregation based on these equations are compared with macrosegregation measured in experimental ingots.
Agreement between calculations and experimental results is excellent. Experiments have been on model ESR ingots (65–105 mm diameter) of Sn-Pb and Al-Cu alloys; in addition, results are discussed for a nickel-base alloy produced in a laboratory ESR ingot mold with a diameter of 200 mm. The influence of the important solidification parameters such as the shape and depth of the mushy zone and the local solidification time on the macrosegregation across the ESR ingots is quantitatively demonstrated. It is shown that macrosegregation theory predicts not only surface-to-center variations in compositions, but also predicts conditions under which a severe type of segregation, called “freckles”, forms in ESR ingots.
A method of minimizing macrosegregation is demonstrated whereby ingot rotation alters interdendritic flow behavior and therefore macrosegregation. Modest rotational speeds eliminate “freckles” and minimize surface-to-center type segregation, as well. It is also suggested that macrosegregation theory should be considered during the alloy design stage in that alloy constitution can possibly be adjusted to produce ESR ingots with no “freckles” and minimum segregation.
Recommendations to improve the “state of the art” in modelling macrosegregation are given. For example, the effect of convection of the liquid pool should be examined and possibly included in future models. In addition, the effect of the interdendritic liquid flow should be included in the energy equation when it is applied to the mushy zone of large ingots, and possibly, the electromagnetic force field should be included in the equation of motion in the mushy zone. The selections of values of permeability used for macro-segregation simulation are also discussed and compared to permeability measured by experiment.
KeywordsMushy Zone Versus Versus Versus Versus Versus Liquid Pool Interdendritic Liquid Ingot Surface
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