Uneven composition on the scale of a whole ingot or cast slab. It forms when solute is carried over long distances by liquid flow or the settling of crystals, and heat treatment hardly removes it.
Japanese name: マクロ偏析
Macrosegregation appears in 1 practice question across 1 topic, including Solidification and cast structures.
Answer: C. Microsegregation varies over short distances and can be reduced by homogenization annealing, while macrosegregation results from solute carried over long distances by liquid flow and the like, and heat treatment hardly removes it
Microsegregation is the uneven concentration in which a solute with k < 1 is lean in the dendrite cores and rich between the dendrites, over a scale of the arm spacing, some tens of micrometers. Once the diffusion distance √(Dt) reaches about half of this, the concentration evens out, so homogenization annealing at high temperature can reduce it. Macrosegregation forms when enriched liquid moves distances of several centimeters to several meters, through suction of interdendritic liquid by solidification shrinkage, convection driven by density differences, settling of crystals and so on. Centerline segregation in continuously cast slabs is a typical example; the distances are far too large to be undone by diffusion, so it is countered during solidification, for example by soft reduction near the end of solidification or electromagnetic stirring. The options that swap the causes and the ease of removal by heat treatment, or treat the two as the same mechanism, are wrong.
Macrosegregation forms when enriched liquid moves distances of several centimeters to several meters, through suction of interdendritic liquid by solidification shrinkage, convection driven by density differences, settling of crystals and so on.
Segregation in castings and ingots includes microsegregatio…Dendrite Chvorinov's rule Constitutional supercooling Dendrite arm spacing Equilibrium partition coefficient Eutectic modification Scheil equation