1982 Volume 68 Issue 10 Pages 1613-1620
The extension of columnar or equiaxed zone in the as-cast structure of continuously cast slabs is primarily affected by the superheat temperature in the tundish, high temperatures promoting the form-ation of columnar grains and low temperatures that of equiaxed grains. At an intermediate temperature a sharp transition in the extent of each structure occurs. The formation of equiaxed crystals is enhanced by high freezing rates of the solid shell and by turbulent fluid flow. Under favourable conditions free crystals already exist in the mould. In bow type machines sedimentation of such suspended crystals is a geometrical phenomenon and depends on parameters such as machine radius, casting speed and heat extraction.
The experiment shows that in slabs of bow type machines the cast structure is asymmetric, the equiaxed zone extending further to the outer radius. At intermadiate superheat temperatures sedimenta-tion zone is entirely located within the lower strand section terminating distinctly below the centre line.Consequently the formation of free crystals may end before completion of strand solidification. Con-centration profiles of partly equiaxed solidified slabs are used to verify the sedimentation mechanism.Carbon is taken as an example to illustrate the decrease of concentration in equiaxed zone.