Creep-Resistant Steels
Z-phase, inaccurate data
Thermodynamics
Cannot win, can only break even
Can only break even at absolute zero
Cannot reach absolute zero
Goal
Increase as far as is possible, the
maximum temperature in the cycle
i.e. better materials & engineering
Taylor & Thornton, ALSTOM Power, Rugby
0.5 µm
b
a
time = t
time = t+∆t
2.25Cr1Mo 600°C
Yamasaki & Bhadeshia, 2003
concentration
b
C
b
a
C0
a
C
x
interface
distance
concentration
b
C
b
a
flux
a
C
interface
distance
C0
Coarsening
diffusion
flux
r
concentration
1
q
r
2
a
aq
cr
1
q
aq
cr
2
distance
Mean radius / m
10
-6
10
-7
10
-8
10
-9
1/3
1/2
10
2
10
3
10
4
10
5
10
6
10
7
10
8
10
9
10
10
10
8
10
9
10
10
Fujita & Bhadeshia,
2000
18
m
-3
4
2
10
Number density
Time / s
0 2
10
10
3
10
4
10
5
10
6
10
Time / s
7
10
1
Data from Abe,
1999
M_23C_6 size / µm
0W 1W 2W 4W
10
0
10
-1
10
-2
10
Fe-9Cr-W alloys
1
10
2
10
3
Time at 600 °C / h
10
4
Mole fraction of phase
0.03
M_23 C_6
0.02
0.01
0.00
Laves phase
0
1
2
3
Tungsten / wt%
4
5
Multicomponent
coarsening
Venugopalan & Kirkaldy, 1978
Effective diffusivity / m s 2
-1
Coarsening accelerated by tungsten
1.8e-19
chromium alone
1.7e-19
1.6e-19
multicomponent
1.5e-19
0
1
2
3
4
Tungsten / wt%
5
concentration
in ferrite
Multiphase
coarsening ?
Laves
q
q
distance
650 oC
Cole &
Bhadeshia, 2002