Comparison of Transverse Uniform and Non-Uniform Secondary Cooling Strategies on Heat Transfer and Solidification Structure of Continuous-Casting Billet
Abstract
:1. Introduction
2. Brief Description of the Studied Continuous Caster
3. Spraying Nozzle Measurement of Water Flux Distribution
3.1. Experimental Apparatus
3.2. Water Flux Distribution Measurement
4. Numerical Modeling and Validation
4.1. Model Development
4.1.1. Heat Transfer Model
- The heat transfer in casting direction and meniscus was neglected.
- The convective heat transfer was equivalent to the conductive heat transfer by increasing the thermal conductivity of liquid and mushy zone.
- The heat transfer of radiation, contact with the supporting roller, and cooling water in the secondary cooling zone were included by an integrated heat transfer coefficient.
- The water flux distribution along the casting direction of each segment was uniform in the secondary cooling zone.
- The density, solid fraction, and thermal conductivity of the steel were temperature dependent.
- The dimensional change caused by solidification shrinkage was neglected on the analysis of temperature and solidification structure of the billet.
4.1.2. Nucleation Model
4.1.3. Dendritic Tip Growth Model
4.2. Material Properties
4.3. Model Validation
4.3.1. Casting Parameters
4.3.2. Heat Transfer Model Validation
4.3.3. CAFE Coupling Model Validation
5. Results and Discussion
5.1. Comparison of Surface Temperature
5.2. Comparison of Internal Temperature
5.3. Comparison of Solidification Structure
5.4. Summary
6. Conclusions
- For a single spraying nozzle, the transverse water flux distribution is non-uniform, and there is more water on the spraying center and less water on the spraying edge. However, a transverse uniform water flux distribution can be obtained in the effective range by adjusting the nozzle collocations.
- The transverse non-uniform secondary cooling water is able to improve the cooling uniformity along the transverse direction. The corner temperature is effectively increased and the transverse temperature difference is reduced. Nevertheless, the reheating rate of the surface center is increased when the billet enters into the air-cooling zone.
- Compared with the uniform cooling strategy, the cooling intensity of the non-uniform strategy on billet is enhanced. The shell thickness at the end of the secondary cooling zone is increased by 1.9 mm and the liquid pool length is decreased by 0.28 m.
- The non-uniform cooling strategy promotes the growth of columnar crystal. The compactness of central equiaxed crystal is increased and the equiaxed crystal ratio is decreased. These effects are equivalent to increasing the secondary cooling intensity.
- The non-uniform cooling strategy is beneficial to improving the surface quality, corner crack, and central segregation of billet, but may result in internal cracks. On the production of C80D steel, the non-uniform strategy is better than the uniform one.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Nozzle | Type number | Jet type | Pressure/MPa | Jet Distance/mm | Spraying Angle |
---|---|---|---|---|---|
Nozzle A | CONCAST 7565L | Full cone | 0.52 | 300 | 60.4° |
Nozzle B | CONCAST RE2-8-80/28 | Flat | 0.52 | 300 | 87.6°/26.4° |
Nozzle C | CONCAST RE1-4-80/28 | Flat | 0.52 | 300 | 82.4°/28.4° |
Nozzle D | ZY3/8PZ72667QZ1 | Full cone | 0.40 | 125 | 61.6° |
Nozzle E | 3665 | Full cone | 0.80 | 125 | 53.1° |
Nozzle F | 2265 | Full cone | 0.60 | 125 | 53.5° |
Zone | Water Flow Rate, m3/h | Boundary Condition | Calculated Formula |
---|---|---|---|
Mold | 113 | ||
Foot-roller zone | 8.06 | ||
Secondary cooling zone A | 12.96 | ||
Secondary cooling zone B | 5.76 | ||
Air-cooling zone | - |
Composition | C | Si | Mn | P | S |
---|---|---|---|---|---|
Mass fraction, % | 0.82 | 0.20 | 0.73 | 0.017 | 0.004 |
Partition coefficient, k0 | 0.35 | 0.52 | 0.75 | 0.06 | 0.025 |
Liquidus slope, m | −60 | −8 | −5 | −34 | −40 |
Diffusivity in liquid, D, m2/s | 2.0 × 10−8 | 2.4 × 10−9 | 2.0 × 10−8 | 4.7 × 10−9 | 4.5 × 10−9 |
Item | Value |
---|---|
Casting speed | 2.4 m/min |
Pouring temperature | 1485 °C |
Superheat | 15 °C |
Water flux of mold cooling | 113 m3/h |
Temperature difference between inlet and outlet of mold water | 7.9 °C |
Ambient temperature | 25 °C |
Cooling Strategy | Equiaxed Crystal Density | Equiaxed Crystal Ratio |
---|---|---|
Mode 1 | 0.83 /mm2 | 32.0% |
Mode 2 | 0.89 /mm2 | 28.4% |
Item | Uniform | Non-Uniform |
---|---|---|
Transverse temperature difference in the secondary cooling zone, °C | 356 | 174 |
Corner temperature at straightening point, °C | 760 | 792 |
Maximum reheating rate of surface center, °C/m | 95 | 138 |
Maximum reheating rate of billet corner, °C/m | 114 | 73 |
Liquid pool length, m | 10.60 | 10.32 |
Equiaxed crystal density, /mm2 | 0.83 | 0.89 |
Equiaxed crystal ratio, % | 32.0 | 28.4 |
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Han, Y.; Wang, X.; Zhang, J.; Zeng, F.; Chen, J.; Guan, M.; Liu, Q. Comparison of Transverse Uniform and Non-Uniform Secondary Cooling Strategies on Heat Transfer and Solidification Structure of Continuous-Casting Billet. Metals 2019, 9, 543. https://doi.org/10.3390/met9050543
Han Y, Wang X, Zhang J, Zeng F, Chen J, Guan M, Liu Q. Comparison of Transverse Uniform and Non-Uniform Secondary Cooling Strategies on Heat Transfer and Solidification Structure of Continuous-Casting Billet. Metals. 2019; 9(5):543. https://doi.org/10.3390/met9050543
Chicago/Turabian StyleHan, Yanshen, Xingyu Wang, Jiangshan Zhang, Fanzheng Zeng, Jun Chen, Min Guan, and Qing Liu. 2019. "Comparison of Transverse Uniform and Non-Uniform Secondary Cooling Strategies on Heat Transfer and Solidification Structure of Continuous-Casting Billet" Metals 9, no. 5: 543. https://doi.org/10.3390/met9050543