The geometrical characteristics of the octagonal billet lie between those of a square cross section and a round cross section, with the respective advantages of a square billet and a round billet, the billet leaving the mould has excellent structural rigidity and can significantly restrain the bulging deformation of the shell. Because of the low bulging deformation tendency of octagonal billet, the casting speed of octagonal billet can be higher than that of ordinary square billet.
As the side length of an octagonal shape is only 45% of that of a quadrilateral for an equal cross-sectional area, theoretically the drawing speed of an octagonal shape can be more than 2.2 times that of a quadrilateral shape for an equal cross-sectional area, for example, an octagonal billet with a cross-section equivalent to a 150 x 150 mm billet can be drawn at a speed of 9 m/min and an hourly single-strand output of 90 tonnes without the need to add a sector to the second cooling section. Based on this feature, conventional continuous casters without fan sections can compose a headless and semi-headless rolling lines with rolling mill train. As a result of the removal of the fan section, even in the event of a steel leak, production can be resumed quickly, unlike the caster with fan sections which take a long time.
The octagonal billet reduces the two-dimensional heat transfer from the corners of the square, making its surface temperature uniformity significantly improved, the measured surface temperature and corner difference of about 10 ℃, while the surface temperature of ordinary square billet and corner difference of more than 100 ℃, due to the increase in temperature uniformity, the internal quality of octagonal billet is inherently better than the square, but also can significantly improve the quality of rolled steel.
At the same time, the angle of the corners of octagonal billets is 135 degree can significantly reduce defects or cracks in the rolling process due to sharp corner; the square billet is 90 degree that will cause some folding defects or cracks. Due to this feature, the octagonal shape will be more advantageous to produce alloy steel which high internal quality is required.
