High speed continuous casting technique for hypo-peritectic medium thick slab was developed. For mild-cooling of solidified shell, the mold flux was designed to crystallize effectively by new method which gives accurate phase relation between mold flux composition and cuspidine (3CaO·2SiO2·CaF2).
The results were as follows;
(1) It was possible to increase casting speed to 5.0 m/min without surface longitudinal cracking on slabs by the developed mold flux of mild-cooling.
(2) The stability of phase equilibrium between mold flux composition and cuspidine was important to promote crystallization in flux film between mold and solidified shell. Then interaction between F- and Na+ was necessary to be considered for accurate prediction about phase relation between them.
(3) Because of crystallization in flux film, the top of solidified shell was cooled mildly to be uniform and that resulted in prevention of surface longitudinal crack of slabs.
