Abstract
For the improvement of centerline segregation and center porosities in continuously cast blooms, the favorable conditions for electromagnetic stirring near the crator end have been determined by hot model experiments in which the influence of rotational stirring on V-shaped streaks formed at the zone with accelerated downward flow of residual melt caused by solidification shrinkage was investigated. It has been found that by rather weak electromagnetic stirring against the melt core kept in a range from 30 to 50mm in diameter, V-shaped segregations are quite improved together with control of solidification structure consisting mainly of non-columnar dendrites. It has been observed also that an excessively strong stirring in the core zone with non-columnar structure brings about rather detrimental influence on V-shaped streaks because of coagulation of a solute enriched residual melt in the slow movement of slurry consisting of equiaxed crystals and the residual melt.
The favorable conditions are discussed by taking a solidification sequence into account. They are the stability of non-columnar crystals, the movement of a mushy solid-liquid mixture by electromagnetic stirring, and a change in downward suction flow during solidification.
Based on these results obtained by the hot model experiments, test campaigns have been carried out by utilizing a newly designed electromagnetic stirring unit installed to bloom casters in Mizushima Works. Throughout the campaigns, favorable conditions for electromagnetic stirring at two locations, namely, in the spray cooling zone and near the crater end, have been established for the production of sound blooms with less centerline segregation and center porosities.
