15 Hyoung-Jun Lee Thermal Stress Cracking of Sliding Gate...
Transcript of 15 Hyoung-Jun Lee Thermal Stress Cracking of Sliding Gate...
Hyoung -Jun Lee, Seong -Mook Cho, Seon -Hyo Kim
Thermal Stress Cracking of Sliding Gate Plates
ANNUAL REPORT 2011UIUC, August 18, 2011
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 1
Hyoung -Jun Lee, Seong -Mook Cho, Seon -Hyo Kim
Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, South Korea
Brian G. Thomas
Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W.Green St., Urbana, IL, USA, 61801
Sang-Woo Han, Tae-In Jung, Joo Choi
POSCO Technical Research Laboratories, POSCO, Pohang, Kyungbuk 790-785, South Korea
- Evaluate possible mechanisms for crack formation
- Explore thermal and mechanical stress in a sliding gate plate during preheating and
Objectives
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 2
sliding gate plate during preheating and casting induced by thermal expansion and/or mechanical movement
- Predict crack formation
Research Background
UTNMetal Band
Plate
Ar Injection
Insulation
Bolt
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 3
Cassette
SEN
Insulation
Line Contact
� Why are cracks in sliding gate a concern?- Safety problem (Steel leakage)- Clogging (Air penetration)- Productivity Issue
Schematic of Sliding Nozzle System
Type of Cracks
Bottom view of used plate Photo of common
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 4
Bottom view of used plate
Cross section view of common crack
In Out
Photo of common through-thickness crack
Schematic of rare cracks locations
* Refractory component: 85% Alumina, 7% Zirconia, 8% Graphite
� Through-thickness cracks commonly form during the C.C. process
�If these cracks are serious, air penetration can oc cur: White area on the crack surface indicates that grap hite in
Understanding of cracking
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 5
sliding plate is oxidized�This suggests that steel is being oxidized
� Sometimes, different type of cracks can form, likely caused by abnormal non-uniform cassette pressure on middle of plate (not always through-thickness)
Possible Mechanisms of Common Crack Formation
� Thermal stress induced by temperature distribution of sliding plate with pre-heating and molten steel temperature
� High surface pressure from cassette bolted to the 3 sliding gate plates
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 6
3 sliding gate plates
� Friction force caused by mechanical movements for stabilizing the mold meniscus level
� Ferro-static pressure due to height difference between tundish free surface and sliding gate locat ion
Parameters Considered for Modeling
▽
h
Tundish
UTN
Tundish Free Surface
Schematic of sliding plate front view
Metal Band
Plate
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 7
Ferrostatic Pressure
Thermal Expansion
Comparing with thermal expansion pressure, ferrostatic pressure is negligible
MPa 540
C1000C 10367.8Pa 1065 169
−≈°×°×××−=
∆⋅⋅−=
−−
TEA
F α
MPa 124.0
m 8.1m/s 81.9kg/m 7020
23
≈××=
= ghh ργ UTN
SEN
� Pre-heatingSliding gate is heated from room temperature to pre-determined temperature
LNG (Liquefied Natural Gas) composition [1]
Internal Gas Temperature Prediction
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 8
- Methane(CH4): 88%- Ethane(C2H6): 5%- Propane(C3H8):5%- Butane(C4H6): 2%
Internal gas temp. is lower than flame temp. ���� 750 °°°°C is assumed
Singh VBA model [2] is used Flame Temperature: 1518.3 °°°°C
Free convection : Churchill and Chu equation[3] is used
2
278169
61
])Pr492.0(1[
387.0825.0
++= Ra
Nu ���� hhhho,preheato,preheato,preheato,preheat = = = = 7 W/m7 W/m7 W/m7 W/m2222·K·K·K·Kr
kNuh
2
⋅=
Heat Transfer Coefficient of Preheating
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 9
Forced convection : Petukhov, Kirillov and Popov equation[3] is used
)]1(Pr)8(7.1207.1[
Pr]Re)8[(3221 −+
=f
fNu D
r
kNuh
2
⋅=���� hhhhi,preheati,preheati,preheati,preheat = = = = 65 W/m65 W/m65 W/m65 W/m2222·K·K·K·K
�Molten steel
Molten steel flows through sliding plate bore (1550 ºC)
Sleicher and Rouse Equation[3] is used to calculate forced heat transfer coefficient
Forced Heat Transfer Coefficient of Molten Steel
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 10
forced heat transfer coefficient
�The forced heat transfer coefficient from molten st eel flow was calculated to be 28.7 x 103 W/mW/mW/mW/m2222·K·K·K·K
υur2
Re =αυ=Pr
Pr4
24.088.0
+−=a Pr)6.0(5.0
3
1 −+= Expb
baNu PrRe015.05 += r
kNuh
2
⋅=
200
300
400
Tem
pera
ture
(D
egre
e C
)
20 Elements-Internal Temp. 20 Elements-External Temp. 40 Elements-Internal Temp. 40 Elements-External Temp. Every 1 Sec.-Internal Temp.
Test Problem of Transient Heat ConductionAbaqus Model Validation with Singh VBA Model
ho = 20 W/m2KTo = 20 °C
t = 120 min.Tinitial = 20 °C
Schematic of test problem
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 11
0 20 40 60 80 100 1200
100
Tem
pera
ture
(D
egre
e C
)
Time (min.)
Every 1 Sec.-Internal Temp. Every 1 Sec.-External Temp. Every 100 Sec.-Internal Temp. Every 100 Sec.-External Temp. Singh VBA-Internal Temp. Singh VBA-External Temp.
k = 20 W/mKρ = 2460 kg/m3
Cp = 1500 J/kgK
hi = 70 W/m2KTi = 600 °C
*Other surfaces are insulated
- 20 and 40 elements results match- Time step of every 1 sec. and 100 sec. models matc h�The 100 sec. time step is used to tundish sliding ga te model- Abaqus model matchs Singh VBA model
Model Validation Problem – Ladle Plate Heating
①②③④①②③④①②③④①②③④
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 12
Schematic of casting equipment [4] Location of thermocouples in plate[5]
- Ladle plate temperature was measured during top teeming of molten steel into mold
- 4 Thermocouples were installed on upper plate- Plates were subjected to heat treatment at 170 °°°°C [5]
Heat Transfer Model Validation:Ladle-Plate Heating Problem
h i,preheat = 65 W/m2K, Ti,preheat = 25 ºC h i,steel = 29 x 103 W/m2K , Ti,steel = 1590 ºCε = 0
Insulatedh = 0ε = 0
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 13
Run transient 3-D heat conduction simulation of upp er ladle plate, to compare with measurements
ho,preheat = 7 W/m2K, To,preheat = 25 ºC ho,steel = 7 W/m2K, To,steel = 150 ºC ε = 0.92
Boundary conditionsFinite element mesh
Part Elements
Ladle Plate (Wedge) 92,378
Symbol Value Units
Initial Nozzle Temperature Tinitial 25 °°°°C
Preheating
Internal Gas Temperature Ti,preheat 750 °°°°C
Internal Convection Heat Transfer Coefficient (Forced) h i,preheat 65.24 W/m2·K
External Ambient Temperature To,preheat 25 °°°°C
External Convection Heat Transfer Coefficient (Free) ho,preheat 7 W/m2·K
Molten Steel Temperature Ti,steel 1590 °°°°C
Properties for Ladle Plate Model Validation Problem
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 14
Casting
Ti,steel 1590 C
Internal Convection Heat Transfer Coefficient (Forced) h i,steel 28719.63 W/m2·K
External Ambient Temperature To,steel 150 °°°°C
External Convection Heat Transfer Coefficient (Free) ho,steel 7 W/m2·K
Density [6] ρ 3200 kg/m 3
Thermal Conductivity [6] k 8.26 W/m·K
Specific Heat [6] Cp 1004.64 J/kg· °°°°C
Stefan-Boltzmann Const. σ 5.669 x 10-8 W/m2·K4
Emissivity [7] ε 0.92 -
Comparison of Measured and Predicted Temperature in Ladle Plate
600
800 Measured 1-a Measured 1-b Measured 2-a Measured 2-b
Tem
pera
ture
(D
egre
e C
)Temperature contour, 90 min
Temp ( °°°°C)
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 15
0 20 40 60 80 1000
200
400
600 Measured 2-b Measured 3 Measured 4-a Measured 4-b Predicted 1 Predicted 2-a Predicted 2-b Predicted 3 Predicted 4-a Predicted 4-bT
empe
ratu
re (
Deg
ree
C)
Time (min.)
Preheating Molten steel pouring
� Preheating is calculated until #1 T/C is reached to 150 °°°°C for 50 min.
� During 40 min. casting, experimental and predicted results are well-matched in heat transfer model of ladle plate
Model Validation Summary
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 16
transfer model of ladle plate
� Assumed internal gas temperature (750 °°°°C) is reasonable to be applied to tundish sliding gate nozzle model for preheating stage
� The heat transfer coefficients are used to tundish sliding gate nozzle model
½ Symmetric Model
Tundish Sliding Gate NozzleComponent & Finite Element Mesh
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 17
Part Elements
Upper Plate (Wedge) 15,133
Middle Plate (Wedge) 18,008
Lower Plate (Wedge) 18,782
Upper Band (Hex) 512
Middle Band (Hex) 512
Lower Band (Hex) 384
Total 52,871
Initial ConditionRoom Temp.
Pre-heating (750 °°°°C)Opening Ratio 100%
12600 sec
Mechanical Movement100% � 0%
Vel. : 25 mm/sec
Molten Steel Pouring (1550°°°°C) Mechanical Movement
Molten Steel Pouring (1550°°°°C)
Modeling Approach
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 18
(1550°°°°C)60%
12600 sec
Mechanical Movement0% � 60%
Vel. : 25 mm/sec
(1550°°°°C)0%
750 sec
Mechanical Movement60% � 0%
Vel. : 25 mm/sec
Preheating :3 hr 30 minC.C : 3 hr 30 min
Casting Finished
Casting Started
Symbol Value Units
Initial Nozzle Temperature Tinitial 25 °°°°C
Preheating
Internal Gas Temperature (Preheating) Ti,preheat 750 °°°°C
Internal Convection Heat Transfer Coefficient (Forced) h i,preheat 65.24 W/m2·K
External Ambient Temperature (Preheating) To,preheat 25 °°°°C
External Convection Heat Transfer Coefficient (Free) ho,preheat 7 W/m2·K
Molten Steel Temperature Ti,steel 1550 °°°°C
Internal Convection Heat Transfer Coefficient h 28719.63 W/m2·K
Properties for Tundish Sliding GateHeat Transfer Model
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 19
Casting
Internal Convection Heat Transfer Coefficient (Forced) h i,steel 28719.63 W/m2·K
External Ambient Temperature To,steel 150 °°°°C
External Convection Heat Transfer Coefficient (Free) ho,steel 7 W/m2·K
Refractory [6]
Density ρref 3200 kg/m 3
Thermal Conductivity kref 8.26 W/m·K
Specific Heat Cp,ref 1004.64 J/kg· °°°°C
Steel [6]
Density ρsteel 7860 kg/m 3
Thermal Conductivity ksteel 48.6 W/m·K
Specific Heat Cp,steel 418.6 J/kg· °°°°C
Stefan-Boltzmann Const. σ 5.669 x 10-8 W/m2·K4
Emissivity [7]εref 0.92 -
εsteel 0.75 -
Boundary Conditions of Preheating Step
Insulatedh = 0, ε = 0
h = 65 W/m2K Y Symmetry
Touching with nozzle
*Gap conductance= 7 W/m·K
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 20
h i = 65 W/m2KTi = 750 °°°°Cε = 0
ho = 7 W/m2KTo = 25 °°°°Cε = 0.92
h = 7 W/m2KT = 25 °°°°Cε = 0.75
[Schematics of heat transfer model] [Schematics of s tress model]
Y SymmetryUZ=0
Touching with cassetteUX = 0, UY = 0
nozzleUX = 0, UY = 0
*Gap conductance= 0 W/m·K
Boundary Conditions of Molten Steel Pouring Step
Insulatedh = 0, ε = 0
h = 29 x 103 W/m2K Y Symmetry
Touching with nozzleUX = 0, UY = 0
*Gap conductance= 7 W/m·K
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 21
h i = 29 x 103 W/m2KTi = 1550 °°°°Cε = 0
ho = 7 W/m2KTo = 150 °°°°Cε = 0.92
h = 7 W/m2KT = 150 °°°°Cε = 0.75
[Schematics of heat transfer model] [Schematics of stress model]
Y SymmetryUZ=0
Touching with cassetteUX = 0, UY = 0
*Gap conductance= 0 W/m·K
Boundary Conditions of Continuous Casting Step
Insulatedh = 0, ε = 0
h = 29 x 103 W/m2K Y Symmetry
Touching with nozzleUX = 0, UY = 0
*Gap conductance= 7 W/m·K
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 22
h i = 29 x 103 W/m2KTi = 1550 °°°°Cε = 0
ho = 7 W/m2KTo = 150 °°°°Cε = 0.92
h = 7 W/m2KT = 150 °°°°Cε = 0.75
[Schematics of heat transfer model]
Y SymmetryUZ=0
Touching with cassetteUX = 0, UY = 0
[Schematics of stress model]
*Gap conductance= 0 W/m·K
Thermo & Mechanical Behaviorof Preheating Step
Temperature ( °°°°C) Stress (Pa)
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 23
Thermo & Mechanical Behaviorof Molten Steel Pouring Step
Temperature ( °°°°C) Stress (Pa)
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 24
Thermo & Mechanical Behaviorof Continuous Casting Step
Temperature ( °°°°C) Stress (Pa)
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 25
Common Through-Thickness Crack Formation Mechanism – Tensile Stress
Middle section of middle plate, Pre-heating (750 °°°°C), 502 sec
Stress Distribution(Direction &Magnitude)
X
Y
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 26
Magnitude)
Photographof used plate Crack
Crack direction
Compressive strength ≈ 245 MpaTensileStrength≈ 12 Mpa
Middle section of middle plate, Pre-heating (750 °°°°C), 12600 sec
Stress Distribution(Direction &Magnitude)
Common Through-Thickness Crack Formation Mechanism – Compressive Stress
X
Y
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 27
Crack
Magnitude)
Photographof used plate
Compressive strength ≈ 245 MPa
Crack direction
Conclusion
� During preheating step, tensile and compressive stresses exceed tensile and compressive strength���� Crack location matches prediction
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 28
���� Crack location matches prediction
� If cracks are already formed in preheating step, different stress and temperature distributions will result
Future Work
� Creep and residual stress behavior is needed to better investigate cracks in sliding gate
� Thermal-stress simulation should extend after preheating
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 29
after preheating
� Cassette design is needed for exact deformation and pressure to plates
� UTN and SEN design is needed for knowing contact region
References
[1] Korea Gas Safety Corporation[2] Varun Kumar Singh, B.G. Thomas, CCC Annual report 2010, UIUC, August 12, 2010[3] Incropera, F.P., and Dewitte, P.D., 2002, Fundamentals of Heat and Mass Transfer, John Wiley and Sons, New York[4] “New Generation Ladle Slide Gate System for Performance
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 30
[4] “New Generation Ladle Slide Gate System for Performance Improvement”, J. Chaudhuri, 2007[5] “Thermal Loading of Periclase Plates in Sliding Gates of Steel-teeming Ladles”, K. V. Simonov, 1980[6] Chosun Refractories Co. Ltd. Research Center[7] Monarch Instrument, “Table of Total Emissivity”
Acknowledgements
• Continuous Casting Consortium Members(ABB, Arcelor-Mittal, Baosteel, Tata Steel, Magnesita Refractories, Nucor Steel, Nippon Steel, Postech, POSCO, SSAB, ANSYS-Fluent)
• National Center for Supercomputing Applications (NC SA)
Pohang University of Science and Technology Materials Science and Engineering Hyoung-Jun Lee 31
• National Center for Supercomputing Applications (NC SA) at UIUC – “Tungsten” cluster
• POSCO – Sung-Kwang Kim, Kwon-Myung Lee
• UIUC – Lance C. Hibbeler