Carbide Precipitation in Steel Weld Metals

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Carbide Precipitation in Steel Weld Metals
www.msm.cam.ac.uk/phase-trans
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CASE 1 Sensitisation
Shimada et al., 2002
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Sourmail, Too, Bhadeshia, 2003
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Sourmail, Too, Bhadeshia, 2003
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Carbon supersaturated plate
Carbon diffusion into
Carbon diffusion into
austenite and carbide
austenite
precipitation in ferrite
Carbide precipitation
from austenite
LOWER BAINITE
UPPER BAINITE
(Low Temperature)
(High Temperature)
CASE 2 elimination of carbides
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Fe-1Mn-C wt manual metal arc welds
Allotriomorphic
Volume fraction
Widmanstatten
Acicular
Carbon / wt
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wt
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CASE 3 carbide strengthening
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0.5 µm
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a
time t?t
time t
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b
a
time t?t
time t
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2.25Cr1Mo 600 C
M3C
M2X
M23C6
Time / h
1000 h
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3Cr1.5Mo 600 C
M23C6
Time / h
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Components of Creep Strength, 2.25Cr1Mo
iron microstructure
550 C
solid solution
600 C
precipitates
Murugananth Bhadeshia, 2001
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elements in solution
Murugananth Bhadeshia, 2001
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Coarsening
diffusion
r
r
2
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flux
a
q
q
concentration
aq
c
r
aq
1
c
r
2
distance
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Fujita and Bhadeshia, 2002
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Fujita and Bhadeshia, 2002
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Fujita and Bhadeshia, 2002
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Summary

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

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Conclusions