MetFab - Air Products Welder's Handbook - Flipbook - Page 36
Solidification cracks
Causes:
The liquid weld pool contracts as
it solidifies to form a weld bead.
Solidification starts from the outside
of the weld pool and progresses
towards the centerline. Solidification
cracking occurs during the final stage of
solidification when the liquid weld pool
has insufficient strength to withstand
the contraction stresses generated as the
weld pool solidifies and contracts.
Prevention methods:
• Weld pool composition –
impurities that encourage the
formation of low melting point films
such as sulphur and phosphorus should
be minimised. Increased levels of
manganese, silicon and nickel can help
to reduce this risk.
• Weld bead shape –
- use welding conditions which
produce a depth to width ratio in
the range of 0.5 - 0.8.
- aim for a slightly convex weld cap.
- avoid excessively wide root gaps.
- use high performance weld
process gas mixtures containing
helium.
• Welding speed –
excessive welding speeds which
produce long weld pools, which may
increase the risk of cracking.
32
