Abstract
In order to understand the formation mechanism of equiaxed grains due to forced convection, in-situ observation using succinonitrile, which is a transparent organic material, has been carried out. A new experimental technique, using a fiber scope, has been developed in this study to observe in a 3-D mold. Molten succinonitrile was poured into the mold and was unidirectionally solidified from a chill plate. During this experiment, molten succinonitrile was stirred by a rotor at various rotation rate. Phenomena in the mold were monitored by a fiber scope and recorded by video tape. Thermal field was also measured by some thermocouples.
Equiaxed grains formed in the presence of forced convection caused by the rotor, on the other hand, no equiaxed grain formed without forced convection, which agree with the industrial data. The number of equiaxed grain (Ne) as well as the diameter of equiaxed grain (De) increased with time (t). Ne and De are approximately proportional to t2.5 and t0.3 respectively. The rate of increase of Ne increases and the diameter of equiaxed grain decrease with increasng rotation rate. Furthermore, the temperature gradinet in the liquid was found to decrease with increasing rotation rate. Therefore, it can conclude that finer and more equiaxed grains form and they may continue to grow in the bulk liquid with higher rotation rate.
