Squeezing Segregation–Investigation with Laboratory Experiments

Abstract

If a solidifying alloy is deformed the interdendritic liquid and the solid phase of the mushy zone may move relative to each other. Since their compositions differ macrosegregation will result. This phenomenon may occur in twin-roll casting of strip and in thin-slab casting when the thickness of the strip or of the strand, respectively, is reduced above the nip of the rolls or in a tong segment below the mold. Also soft reduction in conventional continuous casting makes concentration changes in the center plane according to the compression mechanism. We call this type of segregation “squeezing segregation” because the residual melt is squeezed out of the dendritic network to other parts of the body. In the present work the mechanism of the squeezing segregation has been investigated experimentally using a laboratory setup with which ingots of iron–carbon alloys were compressed during solidification with a rolling duo installed below the mold. Minima of carbon content down to about 50% of the initial carbon content were observed at the centerplane of the solidified ingot. The effect was also treated theoretically with a simple mathematical model.