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TY  - THES
AU  - Chen, Zhiye
TI  - Quality of as cast ingots with extreme large shapes
PB  - Aachen, Techn. Hochsch.
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2015-01432
SP  - 158, A10 S. : Ill., graph. Darst.
PY  - 2015
N1  - Prüfungsjahr: 2014. - Publikationsjahr: 2015
N1  - Aachen, Techn. Hochsch., Diss., 2015
AB  - The quality of as-cast ingots and continuous cast products are controlled by solidification process mainly. Regarding to this, investigation on casting and solidification process of ingots and continuous cast products is considerable important in control of the quality of as-cast products especially for products with extremely heavy weight like several hundred tons. The present work focuses on the solidification process of large ingots. The complex solidification phenomena in large ingots have been investigated by means of three modelling methods, namely hot modelling, cold modelling and numerical modelling. In hot modelling, two series of ingot casting experiments has been performed for ingots with weight of 100 kg and 500 kg with various parameter combinations. The large ingots with weight of 500 kg solidify slowly in a specially designed isolating mould with the solidification time over several hours, and this slow solidification process simulates the solidification of industrial scale large ingots with weight between 3 to 6 t. Cooling curves have been measured by thermocouples during solidification, and as-cast structure and macrosegregation of solutes have been quantified. Based on this, solidification in large ingots has been investigated and three solidification regimes have been suggested and discussed. A-type Segregations could be produced in the laboratory for detailed studies.Meanwhile, water modelling (cold modelling) by using NH4Cl solution has been conducted with different cool conditions and initial solution temperature. A quasi 2-D water model has been built up with glass and aluminium, where hot saturated NH4Cl solution are poured in and crystallized subjected to cooling conditions. During precipitation of solid NH4Cl, phenomena such as dendritic growth and sedimentation of crystals are similar to those in ingots solidification, therefore NH4Cl solution is used as transparent analog to provide information of the solidification process in large ingots. Besides the experimental work, numerical modelling of ingot solidification has been performed as well. A two-phase solidification model based on volume-averaging-technique has been developed. This solidification model has been applied for the ingots with weight of 100 kg and 500 kg, and the simulation results have been compared with the experimental results regarding as-cast structure and macrosegregation. Furthermore, a channel-segregation model has been developed for the determination of the A-type segregation formation. The effects of carbon concentration and flow velocity of the solute enriched melt on the widening and closing of the potential channel have been investigated. Overall, solidification in large ingots has been investigated experimentally and numerically. The relationship among as-cast structure, local solidification driving force and solidification sequence in large ingots has been intensively studied, and the formation mechanism of A-segregation has also been explored.
LB  - PUB:(DE-HGF)11
UR  - https://publications.rwth-aachen.de/record/464637
ER  -