the university of adelaide, adelaide, south australia 5005 cold cracking and segregation in...
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The University of Adelaide, Adelaide, South Australia 5005
Cold Cracking and Segregation in Multi-Pass Welds of a
Quenched and Tempered Steel
GLF Powell, IH Brown, VM Linton; University of Adelaide
JL Davidson; Defence Science and Technology Organisation
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The University of Adelaide, Adelaide, South Australia 5005
Hydrogen Assisted Cold Cracking of Welds
• Contributing factors– Hydrogen– Stress: applied or residual– Susceptible microstructure
• Susceptibility expressed in terms of carbon equivalent calculated from nominal weld metal composition
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
Segregation in Welds
• Macrosegregation– Solute banding– Normal to solidification growth direction
• Microsegretation– Intercellular-dendritic– Parallel to the solidification growth direction
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The University of Adelaide, Adelaide, South Australia 5005
LIQUID
SOLID
Micro segregation of Ni, Mn, Mo, Cr
START
FINISH
Macro segregation
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
Micro hardness
0
100
200
300
400
500
2kJFCAW 3kJFCAW 4kJFCAW GMAW2kJ GMAW3kJ GMAW4kJ
Welding Parameters
Micr
ohar
dnes
s
interCellular-dendriticboundary
cellular dendrite
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The University of Adelaide, Adelaide, South Australia 5005
50x
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The University of Adelaide, Adelaide, South Australia 5005
250x
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The University of Adelaide, Adelaide, South Australia 5005
Line Scan ahead of Crack
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106
113
120
127
134
141
Distance mm
Wt%
W%(Mn) W%(Ni) W%(Mo)
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The University of Adelaide, Adelaide, South Australia 5005
Summary
• Micro-segregation appears to occur on the cellular dendritic boundaries
• Micro-segregation of all elements appears to be in the same ratio of 1.4:1
• The micro-segregated region is harder than the matrix by the order of 100Hv
• The crack path is through the intercellular dendritic micro-segregated harder regions
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The University of Adelaide, Adelaide, South Australia 5005
Experimental Welds
• Quenched and tempered steel
• Multipass submerged arc welds
Element %Wt Element %Wt
Carbon 0.076 Chromium 0.34
Manganese 1.37 Molybdenum 0.5
Silicon 0.38 Phosphorus 0.013
Nickel 2.43 Sulphur 0.005
Weld Metal Composition
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The University of Adelaide, Adelaide, South Australia 5005
Welding Conditions
• Carbon equivalent Ceq = 0.63
• Heat input = 1.3kJ/mm
• Preheat 40oC
• Radiography revealed short cracks, later identified as fish eyes
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
From Davidson 1996
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
Line Scan Ahead of Crack
0
0.5
1
1.5
2
2.5
3
3.5
0 20 40 60 80 100 120 140 160
Distance (mm)
We
igh
t %
Wt% Cr
Wt% Mn
Wt% Ni
Wt% Mo
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
Summary - Microsegregation• There appears to be a hydrogen bubble associated
with the initiation point of each “fish-eye”
• Micro-segregation of all elements appears to be in the same ratio of 1.4:1
• The crack path is through the intercellular dendritic micro-segregated harder regions
• The value of the carbon equivalent as calculated by usual methods should be increased by a factor of 1.4 to take account of the micro-segregation
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
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The University of Adelaide, Adelaide, South Australia 5005
Line Scan through Banding
0
0.5
1
1.5
2
2.5
3
3.5
0 10 20 30 40 50
Distance (mm)
We
igh
t % Wt% Cr
Wt% Mo
Wt % Mn
Wt % Ni
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The University of Adelaide, Adelaide, South Australia 5005
Mn
Cr
Ni
Mo
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The University of Adelaide, Adelaide, South Australia 5005
Summary - Macro-segregation • Only manganese was found segregated in a banded
region • The manganese concentration in the band was double
that of the material nominal composition • Cracks were found in this macro-segregated band• The band appeared to be associated with either the top
or the bottom of a weld pass• The shape of the concentration profile as revealed by X-
ray analysis is the same as that predicted for a perturbation in the solidification rate
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The University of Adelaide, Adelaide, South Australia 5005
After Davies and Garland
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The University of Adelaide, Adelaide, South Australia 5005
Conclusions
• Segregation, both micro and macro appears to influence the susceptibility of a weld metal to hydrogen cracking
• Segregation factors could be included when using ‘rule of thumb’ measures to determine weld metal susceptibility and welding parameters