Abstract
Macrosegregation is the major defect in large steel ingots caused by solute partitioning and melt convection during casting. In this study, a three-phase (liquid, columnar dendrites, and equiaxed grains) model is proposed to simulate macrosegregation in a 36-t steel ingot. A supplementary set of conservation equations are employed in the model such that two types of equiaxed grains, either settling or adhering to the solid shell, are well simulated. The predicted concentration agrees quantitatively with the experimental value. A negative segregation cone was located at the bottom owing to the grain settlement and solute-enriched melt leaving from the mushy zone. The interdendritic liquid flow was carefully analyzed, and the formation of A-type segregations in the mid-height of the ingot is discussed. Negative segregation was observed near the riser neck due to the specific relationship between flow direction and temperature gradient. Additionally, the as-cast macrostructure of the ingot is presented, including the grain size distribution and columnar-equiaxed transition.
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Abbreviations
- g :
-
Volume fraction
- u :
-
Velocity, m·s−1
- ρ :
-
Density, kg·m−3
- Γ :
-
Phase transfer rate, kg·m−3·s−1
- μ :
-
Viscosity, kg·m−1·s−1
- p :
-
Pressure, Pa
- K :
-
Drag coefficient, kg-m−3·s−1
- C :
-
Species content, wt%
- R :
-
Grain radius, m
- k :
-
Thermal conductivity, W·m−1 ·k−1
- h :
-
Enthalpy, J·kg−1
- Ṅ :
-
Nucleation rate, m−3-s−1
- n :
-
Number density of equiaxed grains, m−3
- n max :
-
Maximum grain number density, m−3
- ΔTN :
-
Undercooling for maximum nucleation rate, K
- ΔTσ :
-
Gaussian distribution width of nucleation, K
- δ :
-
Factor of diffusion length
- β T :
-
Thermal expansion coefficient, K−1
- β C :
-
Concentration expansion coefficient
- β sl :
-
Density difference between liquid and solid.
- l:
-
Liquid phase
- c:
-
Columnar dendrite
- e:
-
Free-floating equiaxed grain
- es:
-
Stationary equiaxed grain
- ref:
-
Reference value
- *:
-
Equilibrium value at the interface
- b:
-
Buoyancy term
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Acknowledgements
This work was financially supported by the project to strengthen industrial development at the grassroots level of the Ministry of Industry and Information Technology (MUT), China (No. TC160A310/21). The cooperation of CITIC Heavy Industries Co., Ltd., Luoyang, China during the plant trials is gratefully acknowledged.
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Chen, Z., Shen, Hf. Simulation of macrosegregation in a 36-t steel ingot using a multiphase model. Int J Miner Metall Mater 27, 200–209 (2020). https://doi.org/10.1007/s12613-019-1875-9
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DOI: https://doi.org/10.1007/s12613-019-1875-9