the university of adelaide, adelaide, south australia 5005 cold cracking and segregation in...

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