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
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
The University of Adelaide, Adelaide, South Australia 5005
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
The University of Adelaide, Adelaide, South Australia 5005
LIQUID
SOLID
Micro segregation of Ni, Mn, Mo, Cr
START
FINISH
Macro segregation
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
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
The University of Adelaide, Adelaide, South Australia 5005
50x
The University of Adelaide, Adelaide, South Australia 5005
250x
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)
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
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
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
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
From Davidson 1996
The University of Adelaide, Adelaide, South Australia 5005
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
The University of Adelaide, Adelaide, South Australia 5005
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
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
The University of Adelaide, Adelaide, South Australia 5005
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
The University of Adelaide, Adelaide, South Australia 5005
Mn
Cr
Ni
Mo
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
The University of Adelaide, Adelaide, South Australia 5005
After Davies and Garland
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