Formation of columnar crystals with melt solidification in the direction of thermal flow
Most of the technical steels crystallize during solidification and form dendrites, i.e. the preferred crystallization of the corners of low-alloy mixed crystals. In this process, crystals with fir tree-like habitus (dendrites) are formed. With large wall thicknesses, the length of dendrites may be up to several centimeters and with fast cooling rates, the size of dendrites may be within submicroscopic scale. Increasing supercooling will cause less branching and thus smaller dendrites as schematically shown on fig. 1.Therefore, the boundary zone usually has fine dendrites and the core zone rough dendrites. The dendrites in the transcrystallization zone in-between are strictly oriented towards thermal flow.