1974 Volume 60 Issue 10 Pages 1454-1462
Unusual zones with columnar structure were observed near the bottom of the 100 t ingot. Metallographic examination of the unnsual zones has shown that the growth direction of one zone differs from those of other zones. This means that unusual zones originally solidify elsewhere and finally settle in the sedimental zone.
As it has previously been proposed that the top surface of the ingot is the place where the unusual zones originally solidify, the existence of the frozen top crust was checked at the hot top of a 120 t ingot. Some of the top crust could be picked up in the relatively early stage of solidification of the ingot and their structure was also columnar.
A small scale experiment using Al-0.2%Cu alloy proved that the top crust formed by putting a chill block on the top surface of the ingot sank to near the bottom of the ingot.
