Theoretical and experimental investigations on macrosegregation caused by mixing in the liquid bulk melt

An improved model describing the macrosegregation caused by mixing in the liquid bulk melt is presented. This model includes the mass transfer between the interdendritic liquid and the bulk melt which takes place additionally to the mass transfer via the boundary layer in front of the dendrite tips. Further, laboratory experiments on macrosegregation of iron-carbon alloys are described. The experiments were carried out in a unidirectional solidification device with 1,5 kg melts. During the solidification process the liquid melt was stirred by a ceramic blade stirrer with rotational speeds between 180 and 720 min^?1. The melts were supperheated above the liquidus temperature by amounts between 3 and 80 K. The solidification velocities were 2 to 6 mm/min. The experiments could satisfactorily be described by the model using an exchange factor α for the amount of additional mass transfer. The exchange factor increases with decreasing amounts of superheating and solidification velocity and with increasing stirring speed.