1
Thermal Analysis of Solidifying steel shell in Continuous Casting Process
Tran Hoang-Son, Castiaux Etienne,
Habraken Anne Marie
4th - 8th May, 2020
University of Liège
Recherche et Technologie en Wallonie DG06
2
Steel Continuous Casting
²
Real world: liquid and solid states –thermo-mechanical model should predict the steel shell behaviour
Current model: thermal approach (liquid steel is present however no fluid mechanic analysis), however temperature measurements within the mould validate the results
slag
3
Sticking Break-Out phenomenon (BO)
²
Effect of sticking event and appearance of tearing
oscilla
tion
Meniscus
Mould
Solidifiedshell
=shell
Break- Out or BO
Stickingpart
(Lee et al., 2009)
Coper mould
Mensicus
Liquid steel
solidified shell
Research objectives:
Analysis of the correlation between the mouldtp° field and the BO defect
Warn to the operator to adapt casting process features
EBDS product= tp° mould measurement by optical fibers= BO detection system called “Emerald”
http://www.ebds-engineering.com/en/Tensile force
4
Mould TP° measurement & Model challenges
²
• Multiple solid to liquid contact with the mould• Crack detection criterion crack propagation• Lagrangian code however liquid steel movement have to be implemented• Thermo-physical data and boundary conditions
Variation of temperature with time for some positions
2D Thermal Finite Element model
Broken shell in the top of the mould
CMAM Pascon, F., Habraken, A. (2007).
Tp°Data
Non calibrated tp° values just relative evolution
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2D FEM Thermal simulation
²
2D finite element model of the continuous casting
Cooling
system
Copper
plates
MeniscusLiquid
steel
Ferrostatic
pressure
Schematic representation of CC problem
Meniscus
Mouldall elementsalwaysactive
OFF Elementsin the slab
ON Elementsin the slab
Casting
Direction
In whiteliquidsteel
Convection and
Radiation
Element
In blacksolidsteel
6
Thermal simulation for steady state
²
6
Finite Element mesh - 2D
Mold
Liquid
Steel
Solid
+
Mushy
+
Liquid
Steel
tend
700mm
Thermal properties
of low carbon steel
fromPascon, F., Habraken, A. (2007). Finite element study of the effect of some local defects on the risk of transverse crackingin continuous casting of
steel slabs. Computer Methods in Applied Mechanics and Engineering, 196, 2285-5599.
18969 elements
18846 nodes
1800mm
Menicus
Initial stateFinal state.Predictions are stationary
Thermal simulation for steady state
²
7
Speed casting
(m/min)
Convection h
(mW/mm²K )
Thermal resistance of
Contacts R (mW/mm²K )
1.3 200 2.35
1520
1507
1497
1487
1477
1470
(°C)227
182
138
93
49
27
(°C)
P-2
P-3
P-1
The chosen parameters
steady state after 50s
10 20 30 40 50 60 70 80
50
100
150
200
250
Times (s)
Tem
pera
ture
(°C
)
Times-Temperature
P-1
P-2
P-3
8
Remeshing step
Old meshNew mesh
4164 elements
4051 nodes
Thermal field at the
end of steady
simulation at 83s
Finer mesh
near sticking
zone
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2D Model Methodology: start with an accurate thermal field
Mould
Sticking
Step 2 (crack in a refined mesh close to meniscus)
1st crack
Schematic approachThe thermal stationary field in a refined mesh (closed to meniscus)
= initial state where the user decide
1st sticking part location
1st crack position
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Model Methodology: add liquid elements within 1st crack
²
MouldMould
New
element
layers
Step 3
1st crack1stcrack
Temperature of liquid steel
Birth element technique to add liquid elements inside the crack
Sticking zone
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Links of craks and mould oscillations
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Rupture criteria for 2D FE thermal model= thinnest section of the shell
L
L< or = Vcasting× Tperiod of Oscillation
Negative Strip Time or NST:
The mold go down faster than the slab
high risk of cracks
Mould Oscillation to enhance slab displacement
Sticking Part
Descending part
NST =1
π𝑓arccos
𝑉0
2π𝑓𝐴
NST: Negative Strip Time (s)
𝐴 : Oscillation Amplitude
𝑉0 : Casting velocity
𝑓 : Oscillation Frequency
T : Oscillation Period
𝑵𝑺𝑻
𝑻=28%→35%
In practice
↑ higher oscillation Frequency ↓ NST (K. C. Mills et al. 1999)
Model constraints
Time for solidification < Negative Strip Time
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Model Methodoly: formation of a new solid shell
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MoldMould2nd crack
Solidification time = “negative strip time”(link with mould oscillation)
Step 5: 2nd crack eventStep 4: Liquid elements solidify
Crack: when high tension is applied due to relative mold-strand velocity (mould oscillation) and where the temperature is the hottest
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1st result of simulation
P-2
P-1
P-3
1st sticker
1st crack
3 measurement points
Thermal history computed by 2D FE thermal model
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Simulation results
0 10 20 30 40 50170
180
190
200
210
220
230
Times (s)
Tem
pera
ture
(°C
)
Times-Temperature
P-2P-1
Speed casting
(m/min)
Oscillation
Period (Hz)
Amplitude
(mm)
Solidification
Time -NST (s)
1.3 2 3.6 0.17
V 1→2= 46% Vcast V 2→3= 51% Vcast
Thermal peak velocity
Crack preview
Crack preview
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1st result of simulation
0 10 20 30 40 50170
180
190
200
210
220
230
Times (s)
Tem
pera
ture
(°C
)
Times-Temperature
P-3
Speed casting
(m/min)
Oscillation
Period (Hz)
Amplitude
(mm)
Solidification
Time -NST (s)
1.3 2 3.6 0.17
Crack preview
P-1
Crack velocity Vcrack= 62% Vcast
∆T= 5°C -20°C
Crack preview
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Influence of Casting speed
Speed
casting
(m/min)
Oscillation
Period (Hz)
Amplitude
(mm)
Solidification
Time -NST
(s)
NST/T Vcrack/VCast
0.7 2 2.0 0.173 34.6% 59.8%
1.0 2 2.9 0.174 34.8% 62,1%
1.3 2 3.6 0.170 34.2% 63.9%
10 20 30 40 50
170
180
190
200
210
220
Times (s)
Tem
pera
ture
(°C
)
Times-Temperature
10 20 30 40 50
170
180
190
200
210
220
Times (s)
Tem
pera
ture
(°C
)
Times-Temperature
10 20 30 40 50
170
180
190
200
210
220
Times (s)
Tem
pera
ture
(°C
)
Times-Temperature
Point 1
Point 2Point 3
Casting Speed = 0.7m/min
Casting Speed = 1.0m/min
Casting Speed = 1.3m/min
Convection h
(mW/mm²K )
Thermal resistance of
Contacts R (mW/mm²K )
200 2.35
Temperature Peak and Amplitude depends on Casting Speed
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Conclusions and Perspective
Perspective: local 3D thermo-mechanical study of the crack
2D thermal FE of the mould and the slab + calibration
Tp° field validated by optical fiber measurement
Sticking Break-Out phenomenon simulation
• Crack location is based on the thermal field
• Crack event is linked with the Negative Strip Time within oscillation cycle
• Birth element technique is used to fill the crack by liquid steel
Simulation results:
• Thermal peak velocities, peak shapes and amplitudes
• Fracture propagation velocity
(crack propagation = 62% of the casting speed)
• Sensitivity analysis confirms practice:
A Slower casting velocity decreases the crack propagation velocity
recover trends
observed by EBDS
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