Page 21 - SSAB Welding Handbook Edition 2

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Welding handbook 4.0 Hydrogen cracks

that this is because the methods based on carbon Sources of hydrogen are related to:
equivalents are more generally adapted in order to 4 The characteristics of the consumable, and how it
©SSAB
suit a wide range of steels. The minimum required is handled.
preheat recommendations from SSAB are derived 4 Welding environment issues.
from evaluations with TEKKEN tests. The basis for
this methodology is well recognized within welding 4 The hydrogen content in the steel itself and in its
technology. shop primer, when applied.

Hydrogen pickup is feasible because the heated,
4.3 The influence of alloy elements molten weld metal largely dissolves the hydrogen.
in unalloyed and low-alloyed The solubility of the hydrogen decreases as the
consumables temperature drops when the weld metal is in a solid
state. The dissolved hydrogen diffuses, via the HAZ,
The objective of adding alloys to the consumables is to both the unaffected parent metal and the
to attain favorable properties in the weld metal and surrounding air. If just a fraction too much of the
to achieve beneficial properties during welding. diffusible hydrogen remains in the HAZ or the weld
metal, there will be a risk for hydrogen cracks in
The resistance towards hydrogen cracks in the weld these locations.
metal can be expressed by the carbon equivalent
according to the CET method, see formula 3.2 A crucial issue is, therefore, to keep the hydrogen
chapter 3. The CEV method is not applicable for level in the joint sufficiently low. Requested maximum
consumables. levels of hydrogen at these locations can be obtained
by following the recommendations put forth by SSAB.
When the carbon equivalent of the welded steels has
a CET value that is equal or greater than the CET
value for the consumable +0.03, the minimum preheat Hydrogen levels in unalloyed and
temperature is only set by the requirements for the low-alloyed consumables
steels. Unalloyed and low-alloyed consumables with The hydrogen in the weld metal that diffuses to its
a yield strength of less than 700 MPa in the all weld surroundings is called the diffusible hydrogen
metal normally have a carbon equivalent that fulfils content. The part of the hydrogen that is dissolved by
this criterion.
the weld metal is called the residual hydrogen content.
Consumables for the Hardox and Strenx grades are
The Strenx grades can be welded with high strength recommended to have a diffusible hydrogen level that
consumables that have a yield strength of 700 MPa corresponds to ≤ 5ml H / 100 g of weld metal.
and above. When the carbon equivalent of the welded 2
steels has a CET value that is lower than the CET The implicit meaning of hydrogen content refers
value of the consumable with a 0.03 unit increase, to the diffusible amount of hydrogen for the given
the preheat temperature is adapted to fulfill the consumable. Further information regarding hydrogen
requirements for the steels as well as for the content in different types of consumables is described
consumable being used.
in chapter 6.

4.4 Hydrogen content in the joint The storage and handling of the consumables should
be in accordance to the manufacturer in order to
During arc welding, the joint is always exposed to avoid excessive hydrogen pickup. The most stringent
some level of hydrogen and the weld metal receives a requirements regarding the handling of consumables
larger amount of hydrogen in comparison to the normally apply to consumables for MMA welding
surrounding parent metal. and for the flux used in SAW.

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. 21
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.