Effect of Electromagnetic Stirring on Solidification Structure and Central Porosity of Large-Sized Round Bloom in Continuous Casting

The effect of strand (S-) and final (F-) electromagnetic stirring (EMS) on solidification structure characteristic of a φ690 mm continuously cast round bloom has been investigated industrially and theoretically. The newly designed S1-EMS equipped just below the foot zone takes great effect on both equiaxed ratio and distribution alignment, as well as central porosity. Larger current S1-EMS leads to higher equiaxed ratio, more symmetrical equiaxed zone, and smaller diameter of central porosity, and the effect is much more obvious than conventional S2-EMS and F-EMS. It is also noticed that there should be a saturation effect of S1-EMS on the promotion of equiaxed dendrite nucleation. The S2-EMS is beneficial for the expanding of equiaxed zone and improving of central porosity. When S1-EMS is weak, strong S2-EMS results in more asymmetrical equiaxed zone. However, when S-EMS is strong, strong S2-EMS results in more symmetrical distribution of equiaxed zone. The F-EMS takes a little impact on the expanding of equiaxed zone in the large-sized round bloom, and almost no effect on the alignment. The central porosity, however, is improved by F-EMS with the help of decrease in temperature gradient and compensation of solidification contraction.