Page 107 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews

Fracture Modes and Welding Defects

Figure 7.1 Solidification cracking
apart along the weakened centre of the weld bead (see Fig.
7.1).
Solidification cracking can be avoided by the following
methods:
Adding manganese (to form manganese sulphide). The
manganese combines with the liquid sulphur to form
manganese sulphide (MnS), which has a melting point
similar to steel. The manganese sulphide structure is spherical
and forms between the solidifying weld metal grains without
forming a liquid film. This maintains the cohesion between
the grains and prevents a crack occurring.
Keep sulphur levels low:
. Specify low sulphur content material with a content
<0.03% S.
. Keep surfaces clean of contaminants such as oils, paints
and grease.
. Use welding processes that have a low dilution level of
parent plate to weld metal (to reduce the levels of sulphur
being introduced into the weld metal from the parent
plate).
. Ensure temperature indicating crayons used close to welds
do not contain sulphur.

91

Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200907QG Welding chap7.3d Page 91 of 107