Abstract
A recent asymptotic model for solidification shrinkage-induced macrosegregation in the continuous casting of binary alloys is extended for the purposes of understanding the link between solute segregation and centreline shrinkage porosity, a defect that commonly occurs in the continuous casting of steel. In particular, the analysis elucidates the relationship between microsegregation, mushy-zone permeability, heat transfer and centreline pressure, yielding an inequality that constitutes a criterion for whether or not centreline porosity will form. The possibilities for developing this approach to take account of gas porosity and the implementation of mechanical soft reduction to reduce macrosegregation and shrinkage porosity are also discussed.
Highlights
The formation of porosity in the casting of metals has been the subject of numerous solidification research studies since the 1960s
It is evident that the numerator and denominator of f (Z) in (4.64) vanish as the base of the mushy zone is reached, meaning that the actual forms of χ and κwill be critical in determining what happens:
If κ ∼ χ σ near χ = 0, with σ > 0, we are left considering χs1–σ ; from the point of view of avoiding centreline porosity, clearly if σ > 1, larger χs is preferable, whereas if 0 < σ < 1, smaller χs would be preferable
Summary
The formation of porosity in the casting of metals has been the subject of numerous solidification research studies since the 1960s. This under-researched topic is the focus of this paper. The porosity is believed to be caused by three main effects [8]:
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