Creep-Resistant Steels

Z-phase, inaccurate data

Thermodynamics Cannot win, can only break even Can only break even at absolute zero Self evident truth, statement which commands general belief, an unverifiable although widely accepted fact Cannot reach absolute zero

Goal Increase as far as is possible, the maximum temperature in the cycle i.e. better materials & engineering Self evident truth, statement which commands general belief, an unverifiable although widely accepted fact

Taylor & Thornton, ALSTOM Power, Rugby

0.5 µm

b a time = t+∆t time = t

2.25Cr1Mo 600°C

Yamasaki & Bhadeshia, 2003

x

Coarsening diffusion r r flux concentration q a q aq c r aq c r 1 2 flux q a q concentration aq c r 1 aq c r 2 distance

Mean radius / m Time / s Number density Time / s 10 -9 -8 -7 -6 1/3 Mean radius / m 1/2 10 9 8 7 6 5 4 3 2 Time / s 2 4 -3 Number density 18 10 m 10 9 8 7 6 5 4 3 2 Time / s Fujita & Bhadeshia, 2000

Data from Abe, 1999 Fe-9Cr-W alloys M_23C_6 size / µm 10 -2 -1 1 Data from Abe, 1999 Fe-9Cr-W alloys 0W 1W 2W 4W M_23C_6 size / µm 10 4 3 2 1 Time at 600 °C / h

Mole fraction of phase 0.00 0.01 0.02 0.03 M_23 C_6 Laves phase 5 4 3 Tungsten / wt%

Multicomponent coarsening Venugopalan & Kirkaldy, 1978

Coarsening accelerated by tungsten -1 2 chromium alone Effective diffusivity / m s multicomponent 5 4 3 2 1 Tungsten / wt%

Multiphase coarsening ? Laves concentration in ferrite q q distance

650 oC Cole & Bhadeshia, 2002