Effect of linear rate of crystallization front advancement on extraoxis segregation formation in VAT ingots

In order to study the effect of the linear rate of crystallization front movement of the formation of extraaxial segregation, the 380 mm dia ingots of the KhN77TYUR alloy were produced by vacuum arc melting at melting rate of 2.3, 4.4, and 5.7 kg/min. The position of crystallization front at a given moment of time was registered by means of short-circuiting the electric arc. The experience in the production of steel and alloy ingots in vacuum arc furnaces shows that, to eliminate the extraaxial segregation, it is necessary to increase the temperature gradient before crystallization front while creating conditions for a directed solidification. The 380 mm dia ingots produced under conditions of melting rate of 2.3 to 2.9 kg/min have columnar or mixed structure with a negligible zone of equiaxial grain in the head part. In the solidification of the extraaxial segregation beams an additional redistribution on impurities occurs due to a selective crystallization. The segregation beam structure is characterized by the presence of fine weakly branched dendrites having in their intraaxial spaces carbide-, boride- and nitride phases. The distribution of chemical elements in the cross-section of the extraaxial segregation beam is presented