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Heat resistant materials &
Creep behavior
20160502 2nd Seminar : General Topic
Min-Gu Jo
[CSSM]
Contents
• Thermal power station & Heat resistant materials
• Creep deformation
• HEA for Creep-resistant material
• ‘14 Korea 1st Energy supplement ratio• IEO Energy consumption prospect
• CCT (Clean Coal Technology) HELE coal technology (High Efficiency Low
Emission coal technology) CCS(CO2 Capture & Storage)
Energy consumption & Thermal power station
• Thermal power stationInternational Energy Outlook 2014
1/24
2015 Korea Energy Handbook
Coal thermal power station & Heat resistant materials
SC(Supercritical): 538℃↓USC(Ultra-supercritical): 566℃↑HSC(Advanced-USC): 704℃↑
• Current state of Korea- SC USC- 6000 ton CO2/MW- 30% efficiency (ave)
T ↑ Efficiency ↑ CO2 emission ↓
• Heat resistant materials
2/24
- Boiler (tube, pipe)
- Turbine- Welding part
- Bending part - Corrosion - Oxidation
• Coal thermal power station
TurbineBoiler Generator
3/24
• Definition: Phenomenon which materials gradual are changed(are deformed) under a constant applied load(stress)
Normally, under a constant applied load at an elevated temperature (T > 0.4 Tm) a time dependent dimensional changeJet engine (1% in 10,000 hrs), steam tube (1% in 100,000 hrs)
Creep
To determine the engineering creep curve of metal, a constant load is applied to a tensile specimenmaintained at constant temperature and the strain of the specimen is determined as a function of time
Tensile test: constant displacement determined stress
Creep test: constant stress determined strain and time
4/24
• Creep stages (3 steps)Primary creep (Transient): strain rate decreases with increasing time work hardeningSecondary creep (Steady-state): balance between work hardening and recoveryTertiary creep (Acceleration): strain rate increases due to creep damage (effective area decrease, metallurgical change)
5/24
• Creep mechanisms
- Dislocation glide (σ/G > 10-2)Involves dislocation moving along slip planes and overcoming barriers by thermal activationOccurs at high stress and low T
- Dislocation creep (climb, 10-1> σ/G >10-4)Involves dislocation movement to overcome barriers by thermally assisted mechanisms involving diffusion of vacancies or interstitials
- Diffusion creep (10-4 > σ/G)Involves the flow of vacancies and interstitials through a crystal under the influence of applied stressFavored at high T and low stressBulk diffusion (Nabarro-Herring creep), GB diffusion (Coble creep)
- Grain boundary slidingInvolves the sliding of grains past each other
6/24
7/24
C.M. Hu, Materials Characterization 61 (2010) 1043 – 1053
Josh Kacher, Acta Materialia 60 (2012) 6657–6672
Strengthening mechanism
Solid Solution HardeningSubstitutional solid solution (Mo, W, Co..)Interstitial solid solution (C, N, B)
Precipitation(Dispersion) Hardeningσ = 0.8MGb/λ
Work Hardening(Dislocation Hardening)σ0 = σi + αGbρ1/2
Grain Size Refinement Hardeningσy = σ0 + kD-1/2
Secondary Phase Hardeningσave = f1σ1 + f2σ2 f : volume fraction
Microstructural degradation heterogeneous failure
But, Creep is time-dependent deformationMicrostructure changes are effective
8/24
M23C6 ((Cr,Fe,Ni,Mo)23C6 )Crystal structure : FCC (a=10.57~10.68Å)Precipitation site : Grain boundary, Twin boundaryShape : Globular, PlateTypical Size : 200~500nm
Initial stage : Precipitation hardening Precipitate at grain boundary depletion zone Coarsening Decreasing strength
MX precipitates (MC, MN, M(CN), M1M2(CN))Alloy : Ti, Nb, V, Zr, Ta.. (strong carbide/nitride former)Crystal structure : FCC (a=4.40~4.47Å)Precipitation site : dislocation, stacking faults. Twin or grain boundaryShape : Cuboidal shape after sufficient aging
Providing good strengthening effect Stabilizing the alloy against intergranular corrosion
Carbo-Nitride
9/24
Z-Phase (CrNbN)Crystal structure: Tetragonal (a=3.037Å, C=7.391Å)Precipitation site : grain boundaries, twin boundary, dislocation Shape : Rodlike, CuboidalTypical Size : 20~50nm
Z phase forms Nb stabilised steel with N at low temperature than MX particles.Modified Z- phase : (Cr(Nb,V)N), CrVNMX precipitates Z-phase after long time annealing (stable phase below 1000oC)
M2N (Cr2N)Crystal structure: Hexagonal close packed (a=4.78Å c=4.44Å)Precipitation site : grain boundaries, twin boundary, dislocation Shape : Rodlike, CuboidalTypical Size : 20~50nm
10/24
Laves phase (Fe2Mo, Fe2Nb, Fe2W, Fe2Ta, Fe2Ti)Crystal structure : Hexagonal (a=4.73Å, C=7.72Å)Precipitation site : Grain boundary,Mo added steel : formation after a minimum of 1000h between 625~800oCNb stabilized steel : after long time aging, 5000~10000h between 625~800oC However, NbC and Z phase are more stable than Laves phase
σ-Phase (Fe,Ni)x(Cr,Mo)yCrystal structure : Tetragonal (a=8.80Å, C=4.54Å)Precipitation site : Grain boundary, Twin boundary, InclusionThe precipitates form after long term aging at high temperature (10,000~15,000h, 600oC)
G Phase (Ni16Nb6Si, Ni16Ti6Si7, (Ni,Fe,Cr)16(Nb,Ti)6Si7) (austenitic stainless steel)Crystal structure : FCC Phase (a=1.115~1.12Å)
Intermetallic compound
T. Sourmail, Precipitation in creep resistant austenitic stainless steels, Materials Science and Technology, 17 (2001) 1-14
11/24
10-1 100 101 102 103 104 105
0.050.100.150.200.250.300.350.400.450.50
80MPa 100MPa 120MPa 150MPa
Stra
in (m
m/m
m)
Time (h)10-1 100 101 102 103 104 105
0.05
0.10
0.15
0.20
0.25
0.30 150MPa 200MPa 250MPa 300MPa
Stra
in (m
m/m
m)
Time (h)
Typical creep curve
650oC 800oC
10-1 100 101 102 103 104 10510-810-710-610-510-410-310-210-1100
Cree
p ra
te (h
-1)
Time (h)
150MPa 200MPa 250MPa 300MPa
650oC
10-1 100 101 102 103 104 10510-7
10-6
10-5
10-4
10-3
10-2
10-1
100
80MPa 100MPa 120MPa 150MPa
Cree
p ra
te (h
-1)
Time (h)
800oC
12/24
D-B Park, PhD thesis, Korea univ (2013)
Stress dependences of minimum creep rates
100 200 300 40010-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
800°C 750°C 700°C 650°C
Min
imum
cre
ep ra
te (h
-1)
Stress (MPa)
33.8221088.5 σε −×= 59.6191098.1 σε −×=
02.6191095.1 σε −×=6.8271008.7 σε −×=
nm Aσε =
Dislocation creep
n=3~5: pure metal, simple alloy
n=3~12austenitic stainless steel
In this studyn=6~8.6
Norton law (Power law)
13/24
Dae-Bum Park, Materials Characterization 93 (2014) 52 – 61
Activation energy for dislocation creep
100 120 140 160 180 200 220 240 260280320340360380400420440460480500520540560
Activ
atio
n en
ergy
(kJ/
mol⋅K
)
Applied stress (MPa)0.92 0.94 0.96 0.98 1.00 1.02 1.04 1.06 1.08 1.10
10-8
10-7
10-6
10-5
10-4
10-3
10-2
120MPa 150MPa 200MPa 250MPa
Min
imum
cre
ep ra
te (h
-1)
1000/T (K-1)
−=
RTQA n expσε
γ-Fe self diffusion activation energy : 295kJ/mol14Cr-15Ni-Ti austenitic stainless : 460kJ/mol347H austenitic stainless steel : 441~461kJ/molTP347H austenitic stainless steel : 385~463kJ/mol
The similarly value of apparent activation energy (465~485kJ/mol)
14/24
Dae-Bum Park, Materials Characterization 93 (2014) 52 – 61
15/24
Fig. 4. (a) Creep rate versus time tested at 866 K and (b) creep-rupture plot of the Steel Aand Steel B acquired at various creep conditions.
Fig. 5. XRD profiles of the powders electrolytically extracted from the gauge part of creep specimens of (a) Steel A and (b) Steel B tested at 866 K.
Kyu-Ho Lee, Materials Characterization 102 (2015) 79–84
Fig. 7. Equilibrium phase fraction of high-Cr martensitic heat-resistant steels, (a) Steel A and (b) Steel B calculated by MatCalc.
Fig. 8. Development of phase fraction of the precipitates in (a) Steel A, (b) Steel B and (c) chemical composition ofM2N in Steel B during aging at 866 K calculated by thermo-kinetic simulation.
Kyu-Ho Lee, Materials Characterization 102 (2015) 79–84
Monkman-Grant relationship (predict the rupture time)
184.0006.1 =− rm tε
10-8 10-7 10-6 10-5 10-4 10-3 10-210-1
100
101
102
103
104
105
800°C 750°C 700°C 650°C
Tim
e to
rupt
ure
(h)
Minimum creep rate (h-1)
Ktrnm =ε
10-1 100 101 102 103 104 10510-810-710-610-510-410-310-210-1100
Cree
p ra
te (h
-1)
Time (h)
150MPa 200MPa 250MPa 300MPa
650oC
10-1 100 101 102 103 104 105
0.05
0.10
0.15
0.20
0.25
0.30 150MPa 200MPa 250MPa 300MPa
Stra
in (m
m/m
m)
Time (h)
650oC
16/24
Dae-Bum Park, Materials Characterization 93 (2014) 52 – 61
Larson-Miller plot (predict the rupture time)
23000 24000 25000 26000 27000 28000 29000 30000 31000
100
200
300
400500
304HV Super304H[1]
SUS 347H[2]
SUS 316[3]
Appl
ied
stre
ss (M
Pa)
LMP=(T)(logtr+25) (K,h)
KCtT r =+ )(log
[1] NRIM Creep data sheep No. 56[2] NRIM Creep data sheep No. 28B[3] NRIM Creep data sheep No. 6B
17/24
Dae-Bum Park, Materials Characterization 93 (2014) 52 – 61
High Entropy alloy(HEA) Introduction
1) Solid solution strengthening2) Distorted lattice structure3) Cocktail effect4) Sluggish effect
5) Nanoscale deformation twin (Cantor alloy)
Core effect
Daniel B. Miracle, “Exploration and Development of High Entropy Alloys for Structural Applications”, Entropy (2014), 16, 494-525
Definition: At least five major metallic element having an 5-35 at% B. Cantor, Materials Science and Engineering A 375–377 (2004) 213–218
FeCrMnNiCo
Yeh, Advanced Engineering Materials, 6, 5 (2004) 299-303 High-Entropy alloys (HEAs)
i
N
iiconf nnRS ln
1∑=
−=∆
18/24
30 40 50 60 70 80 90 100
0
5000
10000
15000
20000
25000
30000
35000
40000
Inte
nsity
Diffraction angle 2-Theta
Initial specimen information• EBSD IQ(Microstructure) • XRD
• Vickers hardness
161Hv±2.677
FCC singe phaseLattice parameter* : 3.58238 Å(*:Bragg’s law와 d-spacing으로얻은각각의면들의 lattice parameter의평균)
Element Wt% At%CrK 18.30 19.76
MnK 18.36 18.75FeK 19.95 20.80CoK 21.18 20.92NiK 19.94 19.78
Matrix Correction ZAF
• EDS
50.34㎛±19.89
19/24
Tensile results
0.0 0.1 0.2 0.3 0.4 0.5 0.60
200
400
600
RT 500 ℃ 600 ℃ 700 ℃
Eng
Stre
ss (M
Pa)
Eng Strain0.0 0.1 0.2 0.3 0.4
0
200
400
600
800
1000
RT 500 ℃ 600 ℃ 700 ℃
True
Stre
ss (M
Pa)
True Strain
0 100 200 300 400 500 600 700 800 9000
200
400
600
800
1000
1200
Cantor Ni-based super alloy (KIST) Austenite (NIMS) High Cr (NIMS) Low Cr (NIMS)
UTS
(MPa
)
Temperature ( ℃)10-4 10-3 10-2
200
250
300
350
400
450
500
550
600
UTS
(MPa
)
Strain rate (S-1)
27 ℃ 500 ℃ 600 ℃ 700 ℃
20/24
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
100
200
300
400
500
600
700
Cantor (This stduy) S304H (KEPCO)
Eng
Stre
ss (M
Pa)
Eng Strain
Tensile results compared with S304H
CantorStrain rate : 8.333x10-4 S304HStrain rate : 6.666x10-4
RT
RT
450℃
550℃
600℃650℃ 500℃
600℃
700℃
0 100 200 300 400 500 600 700 800
300
400
500
600
700
UTS
(MPa
)
Temperature ( ℃)
Cantor S304H
21/24
Creep results
10-3 10-2 10-1 100 101 102 10310-5
10-4
10-3
10-2
10-1
100MPa 200MPa
T=650 ℃
Stra
in
Time (hr)10-3 10-2 10-1 100 101 102 103
10-810-710-610-510-410-310-210-1100101102103
200MPa 100MPa
T=650 ℃
Cree
p ra
te (1
/h)
Time (hr)
100 101 102 103 104 1050
50
100
150
200
250
300
350
400 Cantor Ni-based super alloy (NIMS) Austenitre (NIMS) High Cr (NIMS) Low Cr (NIMS)
Stre
ss (M
Pa)
Rupture Time (hr)
22/24
XRD results after creep test
200MPa 100MPa Initial
40 50 60 70 80 90 100
Relat
ive In
tensit
y
Diffraction angle 2-theta
200MPa 100MPa Initial
45 48 51
Relat
ive In
tensit
y
Diffraction angle 2-theta
Specimen Initial 100MPa 200MPa
Crystalstructure FCC FCC FCC
Lattice parameter*(Å)
3.58238 3.58729 3.59578
(*:Bragg’s law와 d-spacing으로 얻은각각의면들의 lattice parameter의 평균)
23/24
Summary
24/24
• To improve efficiency of coal thermal power station, increase of operating temperature is required. Therefore, research on heat-resistant material should be preceded.
• Materials with high heat-resistance, oxidation-resistance, corrosion-resistance, weldability and especially creep-resistance are required as the structural materials for the thermal power station application.
• Creep phenomenon is a time-dependent deformation behavior and microstructural change is dominant effect on the failure of materials.
• Through the creep test condition under high temperature and constant load compare to the real operating condition, we expect to predict the lifetime of structural materials for the thermal power station.
Thank you for your attention
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