Cooperative Research Centre for Welded Structures CRC-WS HACC • For cracking to occur requires the simultaneous presence of: – Hydrogen – Applied stress – A susceptible microstructure
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Cooperative Research Centre for Welded Structures
CRC-WS
HACC
• For cracking to occur requires the simultaneous presence of:– Hydrogen– Applied stress– A susceptible microstructure
Cooperative Research Centre for Welded Structures
CRC-WS
Susceptible Microstructure
• Weld metal microstructure is not uniform:– Microscopic segregation– Macroscopic segregation
lead to local variations in chemistry and potentially microstructure
Cooperative Research Centre for Welded Structures
CRC-WS
Crack in SMAW HSLA steel
Cooperative Research Centre for Welded Structures
CRC-WS
Crack in FCAW in HSLA steel, etched in Nital
Cooperative Research Centre for Welded Structures
CRC-WS
Crack in FCAW in HSLA steel, etched in Le Pera’s reagent
Cooperative Research Centre for Welded Structures
CRC-WS
X-ray map of Mn distribution in FCAW. White areas indicate highest concentrations.
Cooperative Research Centre for Welded Structures
CRC-WS
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)
Cooperative Research Centre for Welded Structures
CRC-WS
Micro hardness
0
100
200
300
400
500
2kJFCAW 3kJFCAW 4kJFCAW GMAW2kJ GMAW3kJ GMAW4kJ
Welding Parameters
Micr
ohar
dnes
s
interCellular-dendriticboundary
cellular dendrite
Cooperative Research Centre for Welded Structures
CRC-WS
Crack in SAW in Q&T steel
Cooperative Research Centre for Welded Structures
CRC-WS
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
Cooperative Research Centre for Welded Structures
CRC-WS
Cooperative Research Centre for Welded Structures
CRC-WS
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
Cooperative Research Centre for Welded Structures
CRC-WS
Proposed UoA Work
• Quantify the role of segregation on weld metal susceptibility to HACC
• Expand hydrogen diffusion model to consider hydrogen segregation
• Investigate the parameters that determine whether a HACC microcrack propagates to be significant
• Contribute segregation and hydrogen diffusion strands to the overall model of weld metal HACC
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