Carbide Precipitation in Steel Weld Metals www.msm.cam.ac.uk/phase-trans

Self evident truth, statement which commands general belief, an unverifiable although widely accepted fact

CASE 1: Sensitisation Shimada et al., 2002

Sourmail, Too, Bhadeshia, 2003

Sourmail, Too, Bhadeshia, 2003

CASE 2: elimination of carbides Carbon supersaturated plate Carbon diffusion into Carbon diffusion into austenite austenite and carbide precipitation in ferrite Carbide precipitation from austenite UPPER BAINITE LOWER BAINITE (High Temperature) (Low Temperature) CASE 2: elimination of carbides

Fe-1Mn-C wt % manual metal arc welds 0.2 0.4 0.6 0.8 1.0 Allotriomorphic Volume fraction Widmanstatten Acicular 0.11 0.09 0.07 0.05 0.03 Carbon / wt %

wt%

CASE 3: carbide strengthening

0.5 µm

a time = t+∆t time = t

b a time = t+∆t time = t

2.25Cr1Mo 600 °C M3C M2X M23C6 Time / h 1000 h

3Cr1.5Mo 600 °C M23C6 Time / h

Components of Creep Strength, 2.25Cr1Mo iron + microstructure 550 °C solid solution 600 °C precipitates Murugananth & Bhadeshia, 2001

elements in solution Murugananth & Bhadeshia, 2001

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

Fujita and Bhadeshia, 2002

Fujita and Bhadeshia, 2002

Fujita and Bhadeshia, 2002

Summary Significant advances in theory Can model diffusion-controlled growth, coarsening Elimination of cementite Long-term microstructural stability can be estimated

Conclusions