Solidification Structure and Segregation in Billet Continuous Casting Under High Casting Speed for Alloyed Steel

The solidification structure and segregation behavior in 20Mn2 alloyed steel from continuously cast billet with different casting speed (2.0, 2.4, 2.7 m/min) has been investigated, and the dendrite evolution and solute enrichment characteristics in the billet at high speed casting has been revealed. It is found that the deflection angle in the columnar dendrite induced by M-EMS decreases as withdraw speed increases, mainly due to the decrease in the average stay time in the stirring zone instead of the increase of steel flow rate, indicating the effect of M-EMS on the homogeneity of temperature and promotion of free nucleus formation reduces. The equiaxed ratio in the billet increases as casting speed increases from 2.4 to 2.7 m/min, attributed to the F-EMS acting as S-EMS to stimulate the formation of nucleus. The alignment of equiaxed zone in the case of 2.4 and 2.7 m/min is much better than that in 2.0 m/min, due to the weakening effect of M-EMS and strengthening effect of early F-EMS, together with the increase of superheat. The center segregation in the billet shows no obvious change as casting speed increases from 2.0 to 2.4 and 2.7 m/min, and low superheat, appropriate F-EMS and F-EMS working as S-EMS is the explanation for different trials respectively. The spot segregation in the billet deteriorates as casting speed increases, involving the increase in the size, number and solute content. The most severe solute enrichment is in the vicinity zone where fine dendrite and coarse dendrite contact. The countermeasures to improve the center quality of continuously cast billet at high speed is proposed. Medium superheat, strengthened M-EMS, intense secondary cooling, appropriate S-EMS and F-EMS are beneficial for most steels.