1. Microstructural Stability of Strong 9-12Cr Steels www.msm.cam.ac.uk/phase-trans 650°C

2. Tempered martensite Tempered bainite Nam (1999)

3. Kimura et al., 2001

4. Thermodynamic stability 650°C Extrapolation of short-term data Fe-0.2C-1.5Mn wt% Stability: stored energy

5. martensite

8. Long term stability requires precipitates which are close to equilibrium Laves, intermetallics, MX Metastable phases not appropriate Interfacial energy?

9. diffusion flux distance concentration c  r c r 1 2 r 1 r 2    Coarsening

11. 1CrMoV 2.25CrMo 3.5NiCrMoV 9Cr1Mo 9CrMoWV 12CrMoVW 0.00 0.01 0.02 0.03 0.04 0.05 0.06 M23C6 M2XLaves Fraction 565 °C

12. 0.25CrMoV 1CrMoV 2.25Cr1Mo Mod. 2.25Cr1Mo 3Cr1.5Mo 3.5NiCrMoV 9Cr1Mo Mod. 9Cr1Mo9Cr0.5MoWV 12CrMoV 12CrMoVW 12CrMoVNb 0.0 0.2 0.4 0.6 0.8 Cr Mo Mole fraction 565 °C

13. 0.25CrMoV 1CrMoV 2.25Cr1Mo Mod. 2.25Cr1Mo 3Cr1.5Mo 3.5NiCrMoV 9Cr1Mo Mod. 9Cr1Mo 9Cr0.5MoWV 12CrMoV 12CrMoVW 12CrMoVNb 0.00 0.02 0.04 0.06 0.08 0.10 0.12 Mole fraction Cr Cr concentration in ferrite 565 °C

14. c  Concentration Distance c  c r  = c   2 c   V  1 - c  kT r c    c  Coarsening reduced if last term small

15. 0.25CrMoV 1CrMoV 2.25Cr1Mo Mod. 2.25Cr1Mo 3Cr1.5Mo 3.5NiCrMoV 9Cr1Mo Mod. 9Cr1Mo 9Cr0.5MoWV 12CrMoV 12CrMoVW 12CrMoVNb 0.00 0.05 0.10 0.15 0.20 Stability parameter c   1 - c   c    c  Stability parameter =

16. Comparison 0.15C-0.25Si-0.50Mn-2.3Cr-1Mo- 0.10Ni 0.10C-0.60Si-0.40Mn-9.0Cr-1Mo- 0.00Ni 1056 °C for 12 h, 740 °C for 13 h

17. 23456 0 50 100 150 200 log(time/ h) 9Cr1Mo 2.25Cr1Mo Creep rupture stress/ MPa

18. Equilibrium precipitates Small interfacial energy (?) Small volume fraction Which precipitates are effective? Short term --> Long term data?

21. non-linear functions

26. Brun, Robson, Narayan, MacKay & Bhadeshia, 1998

27. precipitates solid solution iron + microstructure 550 °C 600 °C Murugananth & Bhadeshia, 2001 10 5 h Creep Strength, 2.25Cr1Mo

28. Murugananth & Bhadeshia, 2001 elements in solution

29. Kimura et al., 2001

30. Muneki, Obuko, Abe (2005) Paper 42, this conference Fe-12Ni-9Co-10W-5Cr-B

31. Sourmail & Bhadeshia, 2004

32. Data from Abe, Masuyama, Sawaragi and Kimura, 2004

36. Difficult to achieve long-term stability using fine or metastable precipitates. Way forward is to avoid microstructure (Kimura, Abe) Extrapolation is optimal with neural networks