Page 84 - SSAB Welding Handbook Edition 2

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14.0 Avoidance of discontinuities in the joint Welding handbook

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Fig. 14.4: Lack fusion between the weld passes. Fig. 14.5: Lack fusion between the weld metal and the parent metal.
(Reproduced by permission, TWI Ltd.) (Reproduced by permission, TWI Ltd.)

4 In many cases, a lower welding speed will reduce
the risk for lack of fusion because it promotes a
14.2 Lack of fusion wider and larger weld penetration. However, a
welding speed that is too low can lead to a build
Description of lack of fusion up of molten weld metal in front of the arc
Lack of fusion occurs when there is insufficient causing insufficient penetration.
penetration between at least one weld pass and the 4 The angle and the position of the torch, if placed
sidewall of the joint or between different weld passes, improperly in relation to the joint, could cause
according to fig. 14.4 - fig. 14.5. Lack of fusion is lack of fusion. Adjusting these two parameters
similar to lack of root penetration and there are may improve the penetration profile of the weld
certain preventative actions that counteract both of metal, thus counteracting lack of fusion.
these discontinuities.
For MAG welding:
Frequent causes of lack of fusion and remedies to
prevent this discontinuity: 4 An increased fraction of CO in Ar/CO mixtures
2
2
increases the size and roundness of the weld pool.
4 Avoid a joint that is too narrow. An appropriate
joint configuration will facilitate a sufficient These aspects can promote an enhanced resistance
weld fusion. It is, therefore, beneficial to take the to lack of fusion.
measures that were presented for lack of root 4 Welding with flux and metal cored wires
penetration, see fig. 14.3. promotes an increased width of the weld metal
and provides a higher resistance to lack of fusion
4 Plan the weld passes so that they are situated in
locations that are suitable to one another in order than welding with solid wires.
to avoid lack of fusion.
4 For multi-pass welds, the shape of the cap of the Acceptance criteria according to
weld metal should not be too convex since that EN ISO 5817
can counteract a complete fusion for the next Lack of fusions that are surface breaking are
weld pass to come. At the same it, it should not normally not permitted in any quality level. Internal
be too concave because that can cause types can be present at certain sizes in quality level
solidification cracks. D but not at any time in level C and B.

84 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.