Nail-shooting technique is applied to measure shell thickness of 240 mm x 240 mm bloom of steel 35CrMoA

20CrMoA

GCrl5 and 60Si2MnA produced by the continuous caster. Length of the liquid core and solidification coefficient are calculated by using the solidification law. The electromagnetic stirring position of F-EMS at different drawing speeds is calculated by the solid phase ratio of 0. 70 and 0. 75 for the 240 mm x 240 mm bloom. The relationship between solidification coefficient of continuous casting machine and each process parameter is analyzed. The process optimization measures are： changing the electric stirring position

and modifying the F-EMS position to install according to high carbon steel GCrl5 and 60Si2MnA

and adjusting the casting speed value of four steel of 35CrMoA

20CrMoA

GCrl5 and 60Si2MnA to 0. 80

0. 81

0. 78 and 0. 80 m/min. The quality of billet is improved greatly after the process improvement

i. e. qualified ratio of center segregation rating ≤0.5 increases from original ≤40% to 100% and that of center porosity rating ≤1.5 increases from original ≤50% to ≥90%.