EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

A three-phase mixed columnar-equiaxed solidification model coupling mold electromagnetic stirring (M-EMS) was presented to study the initial solidification in the mold region of billet continuous casting (195 mm × 195 mm). This study focuses on the effect of M-EMS on the dissipation of superheat and its further impact on the formation of equiaxed zone. Heterogeneous nucleation and fragmentation of columnar dendrites are considered as the sources of the equiaxed crystals. Additionally, parameter studies were also performed by varying the superheat (10 ~ 30 K). Main findings were obtained:(1) The role of M-EMS is to speed up the superheat dissipation in the mold region, leaving the liquid core out of the mold region largely undercooled. This is beneficial for the heterogeneous nucleation of equiaxed crystals and survival of crystal fragments which are created by M-EMS-induced fragmentation of columnar dendrites. The equiaxed crystals or fragments will continue to grow and form an equiaxed zone in the strand center. The global heat transfer rate from the strand surface to the water-cooled copper mold is unlikely affected by the M-EMS. (2) The influence of M-EMS on the evolution of solid shell, which is defined by the volume fraction of solid (fs = 0.7), is not obvious, or not direct. The shell growth depends strongly on the degree of superheat. Finally, the superheat needs to be specially controlled when M-EMS is implemented, as it tends to result in a sub-surface negative segregation (white band).