PRODUCTION OF ROUND CAST BILLET BY CONTINUOS CASTING

PROBLEM TO BE SOLVED: To prevent the development of internal crack, center segregation, axial core cracking and center porosity regardless of kinds of steels by performing the rolling reduction at high speed under a prescribed rolling reduction rate, when the center part has a solid phase ratio in a specific range. SOLUTION: Since the final solidified range of a round cast billet is the axial core part and the vol. ratio is lower in comparison with a cast slab having rectangular cross section, the solidification is acceleratedly progressed. On the other hand, since the fluidity of molten steel is necessary to reduce the center segregation, the unsolidified rolling reduction is executed under condition of =20mm/min. By this method, during rolling reduction, since the time applied with tension stress on the front surface of the solidified shell is reduced to quickly attain the compressive stress, the condensed molten steel is easily squeezed and the internal crack is eliminated.