Post on 14-Dec-2015
Strength of Energy Engineering Materials
Abdel-Fatah M HASHEM
Professor of materials scienceSouth Valley University, EGYPT
April 2009, Japan
Collaborative Research Centre SFB 651 at the AU and SVU
%65
%58
TurbinesFluid dynamicsPhys. chemistryMetal physicsMaterialsCastingCoatingWeldingMetal formingLaser techn.
12 years15 Professors and their co- workers20 Million € =150 Million Egypt. pounds
Inlet Temperature of Gas turbines: from 1230 °C to 1320 °C
Inlet Temperature of Steam Turbines: from 600 °C to
700 °C
Steam turbine (Siemens)
<1990 560 °C 12% Cr, 1% Mo (X20CrMoV12-1)>1990 600 °C 9% Cr-Steels P91 +0% W
E911 +1% W P92: +2% W>2000 625 °C NF12: 12% Cr, 3% W, 3% Co Goal 700 °C Nickel-Base-Alloys
E9110.40
0.42
0.44
0.46
0.48
150 200 250 300
650 °C
700 °C
450°C
500 °C
550 °C
600 °C
Pressure, bar
The
rmal
Effi
cie
ncy
T
h
Steam Turbine: Increase of efficiency
X20CrMoV12-1 12C1Mo-VP91: 9Cr-1Mo-VNbE911 X12CrMoWVNbN10-1-1P92 (NF616) 9Cr-0,5Mo-1.8W-V-NbNF12: 12Cr-2.6W-2.5Co-0.5Ni-V-Nb
Steam Turbine: Cooling system
Laboratory experimentsReality: Multi-axial stress state with stress components varying with timeData available: Uni-axial experiments with simple time functionsTherefore, Modelling is essential
Strain
Str
ess
Low cycle fatigue test
= const.T = const.
Time
Cre
ep
Str
ain
Creep test
= const.T = const.
Time
Str
ess
Relaxation test
= const.T = const.
Strain rate
Str
ess
Tensile Test
d/dt = const.T = const.
Influence of Temperature on the Stress strain Curve
200 °C - 700 °C Intercrystalline damage
< 700° C Dynamic recrystallisation
0
100
200
300
400
500
600
700
0 10 20 30
b)
AA7075-T7351
250 °C
200 °C
150 °C
100 °C
20 °C
300 °C
Engineering Strain , %
Eng
inee
ring
Str
ess
, M
Pa
0
200
400
600
800
1000
0 20 40 60
a)
- 50
/ °C =
X6CrNi18-11
1000900
- 100- 150
400
800
700650
500600
200100
23
Engineering Strain , %
Eng
inee
ring
Str
ess
, M
Pa
23 °C – 150 °C Dynamic recovery
200 °C - 300 °C Intercrystalline damage
Flow curve: Description and Influence of strain rate
4321
2
21
/exp(1:
MagdEl)1(/
KocksMecking/
CCCCaGb
kckdd
kkdd
?10nKK
0
200
400
600
800
1000
0 0.1 0.2 0.3
293 K373 K473 K573 K873 K923 K773 K973 K1073 K1173 K
X6CrNi18-11
True Strain
Tru
e S
tre
ss,
M
Pa
0
100
200
300
400
500
0 0.1 0.2 0.3
1.7 10-5
1.7 10-6
1.7 10-4
1.7 10-3
d/dt / s-1
=
True StrainT
rue
Sre
ss ,
MP
a
Power law ?
Creep curves and creep rate curves
)]/(exp[),(min RTQSf
10-4
10-3
10-2
10-1
100
10-2
100
102
104
106
200190180160140130120110100 90 70
X6CrNi18-11: 700 °C
/MPa=
Time , h
Cre
ep
Str
ain
10-5
10-4
10-3
10-2
10-1
100
10-2
100
102
104
106
200190180160140130120110100 90 70
b)
/MPa=
Time , h
Cre
ep
Ra
te ,
h
-1
Minimum creep rate as stress function and creep fracture curve
10-5
10-4
10-3
10-2
10-1
100
100 200 300
C [sinh(/*)]N
C exp( )
C ( /*)N
X6CrNi18-11 = 700 °C
Creep Stress, MPa
Min
imum
Cre
ep
Rat
e ,
h-1
50
100
150
200
250
0.1 10 1000
X6CrNi18-11 = 700 °C
Fracture time , h S
tres
s ,
MP
a
Garofallo*
sinh
)exp(
BailyNorton
min
min
min
N
N
Soderberg
Up to 10000 h University laboratoryUp to 200000 h Industry, Standards
Proof stress and creep strength as Loading limitsDesign limits: with a factor of safety of 1.5
1 .Low Temperatures: 0,2% Proof Stress
2 .High Temperatures: Creep Strength= Stress for a fracture time of 100000 h
0
200
400
600
200 400 600 800 1000
Ni-Base Alloyaustenitic Steel12% Cr-SteelLA 2.25%Cr-SteelLA 1%Cr-SteelLA Mo-SteelLA Mn-Steelunalloyed Steel
Rp0,2
Rm 100000 h
Temperature oC
Rp
0,2
,
Rm
10
00
00
h ,
M
Pa
0
50
100
150
200
500 550 600 650 700
NF 616(9Cr-0.5Mo-1.8W-VNb)
X20CrMoV12-1(12Cr-1Mo-V)
E 911(10Cr-1Mo -1W-VNb)
T 91(9Cr-1Mo-VNb)
Temperature , °C
Cre
ep
Ste
ng
th
Rm
10
0 0
00
,
MP
a
Maximum service temperature: Creep strength for 100000 h = 100 MPa
Increase of creep strength1. Reducing grain boundary area per unit volume
Coarce grains Directional Single solidification crystals
10-8
10-7
10-6
10-5
10-4
10 20 50 100 200
Ilschner
= 704 oC
65
85
105130
0 / MPa =
austenitic Steel
Grain Size , µm M
inim
um
Cre
ep
Ra
te
, 1
/s
Increase of creep strength2. Precipitation hardening Barriers for the dislocation
10-7
10-5
10-3
10-1
10-1
101
103
105
/ MPa =
100110
130140
Alloy 800HT, solution annealed
=700°C
Time , h
Min
imu
m C
ree
p R
ate
, 1
/h
Influence of nitrides0.05 m% N
[Abe, F.: Sol.State.Phys. 8(2004)305 ]
Increase of creep strength3. Reinforcement by continuous fibres
10-7
10-6
10-5
10-4
10-3
10-2
100
101
102
103
FibreComposite
0
10.660.450.24
Vf=
Stress, MPa
Min
imu
m C
ree
p R
ate
, 1
/h
Not for cyclic compression !
Creep under stresses and temperatures
varying with time The Creep rate depends on the effective stress i.e. on the difference between Applied stress and internal back stress
niC )(
0
50
100
0 2 4 6 8
X6CrNi18-11690 °C
i
Time , h
App
lied
and
Bac
k S
tess
, M
Pa
0
50
100
0 2 4 6 8
X6CrNi18-11690 °C
i
Time , h
Concept of the internal back stress
i
niC
0
)(
10-5
10-4
10-3
10-2
10-1
5 10 20 50 100
/ °C =
800710
650
X6CrNi18-11
Effective Stress ( - is) , MPa
Min
imum
Cre
ep R
ate
,
h-1
-0.0002
-0.0001
0
0.0001
0.0002
0.0003
0 200 400 600 800 1000
X22CrMoV12-1T = 700 °C
30
50
60
80
90
95R / MPa =
0 = 100 MPa
Time , s
Cre
ep
Str
ain
aft
er
Str
ess
dro
p
Internal back stress
)/(exp1 11
1
1
C
C
d
d
is
i
iisi
/1
/1 ississis )/exp()( 0 TkTiss
0
100
200
800 900 1000 1100 1200
X8CrNi18-11X22CrMoV12-1X8CrNiMoNb16-16
iss
=k0exp(/T)
Temperature, K
Sat
urat
ion
Bac
k S
ress
is
s , M
Pa
0
100
200
0 100 200 300 400
700 °C
650 °C
710 °C
650 °CX22CrMoV12-1
X6CrNi18-11
Applied Stress , MPa
Inte
rna
l Bac
k st
ress
is ,
MP
a0
0.25
0.50
0.75
1.00
0 0.2 0.4 0.6 0.8 1.0
Pure AluminiumX8CrNiMoNb16-16X6CrNi18-11X22CrNiMoV 12 1
Relative Creep Strain / 1
Rel
ativ
e In
tern
al B
ack
Str
ess
i /
is
Cyclic creep: Life assessment
L= 0.6 under pulsating stressL= 0.8 under pulsating Temperature
10-5
10-4
10-3
10-2
10-1
0 200 400 600
= 150 MPa changing periodically
X6CrNi18-11
650 °C
635 °C
time , h
10-5
10-4
10-3
10-2
10-1
0 200 400 600
changing periodically650 °C
X6CrNi18-11
150 MPa
125 MPa
Time , h
Cre
ep
Ra
te,
h-1
Lt
t
f
Stress Relaxation: Basic equation
tt0
L0
elL
0
cL
0
el 0 L
0
),,(0
)()(
)()(
.00
tTE
tE
t
tt
const
cr
cr
crel
el
• Creep strain increases with time• Total strain remains constant• The elastic strain decreases• Stress decreases with time
Stress relaxation curves
Nickel-base alloy :Crystalline order changes around 550°C increases the specific volume And hence reduces relaxation
0
100
200
300
400
0 1000 2000 3000
X22CrMoV12-1
550 °C
600 °C
500 °C
Time , h
Str
ess
, M
Pa
0
100
200
300
0 10 20 30 40
0 / MPa =T = 650 °C
X6CrNi18-11
100150200250
300
Str
ess
,
MP
a
0
100
200
0 20 40 60 80
650 °C
600 °C
700 °C
X6 CrNi 18 11
0 = 200 MPa
0
100
200
300
400
500
0 1000 2000 3000
NiCr20TiAl
750 °C
650 °C
600 °C550 °C
500 °C
Time , h
Low Cycle Fatigue: Modelling
-400
0
400
-0.008 0 0.008
6
5
43
2
1
Total Strain tot
Str
ess
, M
Pa
-2000
-1000
0
1000
2000
-0.02 -0.01 0 0.01 0.02
1 tot
Tool Steel = 20 °CN=1
Re
Re
/
Total Strain
Str
ess
, M
Pa
-300
-150
0
150
300
-0.008 -0.004 0 0.004 0.008
50 20 10 9 8 7 6 5 4 3 2 1
N=X8CrNi18-10650 °C
Total Strain
Str
ess
, M
Pa
-1x105
0
1x105
2x105
3x105
-300 -150 0 150 300
6
5 4
3
21
2F
i
Stress , MPa
d/d to
t , M
Pa
Low Cycle Fatigue: Life assessment
0.002
0.005
0.01
0.02
0.05
101
102
103
104
105
106
t=0.18 N
- 0.6 + 0.026 N
- 0.14
pl=0.18 N
- 0.6 el=0.026 N
- 0.14
Schwingspielzahl N
Sch
win
gb
reite
de
r D
ehn
un
g
-2000
0
2000
-0.02 0 0.02
-2000
0
2000
-0.02 0 0.02
-2000
0
2000
-0.02 0 0.02
-2000
0
2000
-0.02 0 0.02
,
M
Pa
0
0
el/2
pl
el/2
t
Total strain
Str
ess
,
MP
a
Number of cycles at fracture
Voids: Growth by diffusion and by creep deformation
Void growth by Diffusion
Void growth by creep deformation of the surrounding materials
Wedge type micro-cracks
0.001
0.01
0.1
1
0 1 2 3 4 5 6 7 8
X8CrNiMoNb16-16
X6CrNi18-11
T = 700 °C = 80 MPa
Crack length classF
ract
ion
of
Cra
ck le
ng
th c
lass
X
n
61000 Cracks in X6CrNiMoNb16-1650000 Cracks in X6CrNi18-11
Material: Ni-based superalloy
Thank you for your attention