Abstract: In order to improve the macrostructure and center segregation of billet, heat transfer model of solidification of billet with 200 mm×200 mm section was established. The best position of F-EMS was analyzed considering both steel grade and casting speed. And finally, the F-EMS was moved to 9.85 m away from the mold level. After optimization on casting parameters and constant speed casting, the macro structure defects such as white band and central porosity were eliminated, and center segregation of low carbon steel and medium carbon steel was controlled about 1.05, center segregation of high carbon steel was controlled about 1.10. Moreover, experiment result shows that decreasing cooling water quantity of crystallizer from 130 m3/h to 110 m3/h can prevent the growth of columnar grains and increase the proportion of equiaxed grain.

Key words: billet, F-EMS, casting speed, mold cooling, center segregation