Abstract: Main problems associated with square/round billet continuous casting include poor castability of molten steel,longitudinal surface cracks of round billet as well as internal strand defects which are difficult to eliminate during rolling due to low compression ratio.To increase castability of molten steel and improve strand surface and internal quality of the new 6-machine and 6-strand square/round billet caster,continuous casting processes of square/round billet and associated technologies were systematically studied.As a result,integrated technologies covering continuous casting processes and equipments for improving molten steel and strand quality were proposed.Large scale production application of the technologies shows that sequence casting heats in a single tundish can be increased from 4~5 heats to 7~8 heats;defect free rates of square and round billet surface can reach 98.91% and 97.81% respectively.The comprehensive rates of internal defects(such as center porosity,center segregation and center cracks)less than level 1.0 for the square and round billet are above 98.9%% and 98.5% respectively.Furthermore,carbon segregation index is in the range of 0.93~1.09.The results obtained provide significant technological supports for the operation of the new caster,improvement of billet quality,and development of new steel grades.