Submerged Arc Welding Technical Handbook - Esab

How to choose the right flux-wire
combination
Stainless steel
When joining stainless steel the wire shall be of the same
chemical composition as the base material or over-alloyed. For
similar wires a low-C variant should be chosen over a
Nb-stabilized as long as it is permitted by the customer contract.
OK Flux 10.93 is often the correct flux, but alternative fluxes are
chosen if the ferrite content needs to be changed slightly or if the
risk of hot cracking needs to be reduced.
Ni-alloys and 9% Ni-steels
Ni-alloys are welded with OK Flux 10.90. The wire shall be of the
same chemical composition as the base material. 9% Ni-steels
are also welded with OK Flux 10.90 and various welding wires
e.g. OK Autrod 19.81, 19.82, or 19.83.
Non and low alloyed steels
Fluxes can be chosen for particular applications, such as low
impurity levels in creep resistant steels, pipemills, welding on rust
or mill scale, narrow gap welding or low temperature toughness.
The correct flux for these applications can be chosen with the
flux characteristics selection chart on page 9. For some low
alloyed steels, e.g. creep resistant steels, the chemistry of the filler
wire shall match the chemistry of the base material. The
corresponding fluxes are selected with the table on page 13. For
other applications, the best flux-wire-combination is identified by
criteria such as running characteristics, specified toughness and
strength or joint preparation.
Flux basicity
Basicity is calculated from a flux’s chemical components,
independently of the wire. Higher basicity gives better impact
values, but reduces features such as welding speed, parameter
envelope or fine rippling of the weld bead. It is therefore beneficial
to choose the lowest possible flux basicity at the specified
toughness. From the various basicity formulas the following is the
most generally accepted one:
The formula shows that low basicity fluxes contain more
multiple oxides. A certain amount of atomically bonded oxygen
is favourable for the weld microstructure. In all weld metal,
however, this favourable level is already exceeded, even with
high basic fluxes. Typical oxygen levels are:
Low basicity flux
> 750 ppm
High basic flux
< 300 ppm
In highly diluted welds with low oxygen parent material,
however, the oxygen level can fall below the favourable level.
The different basicity and oxygen levels lead to large differences
in all weld metal toughness with the same wire, Autrod 12.22:
Low basicity flux OK Flux 10.81 >47J/ +20°C
Neutral basicity flux OK Flux 10.78 >47J/ -20°C
Basic flux OK Flux 10.71 >47J/ -40°C
High basic flux OK Flux 10.62 >47J/ -50°C
Strength
The strength of non-alloyed weld metal is mainly achieved with
C, Mn and Si. A number of wires are available for various
strength levels, using the same flux. Generally, the weld
strength should match the base metal. The flux also influences
the strength level, because each flux alloys different amounts of
Mn and Si to the weld metal.
Welding joint
Dilution also affects the Mn and Si content, making mechanical
properties of actual joints differ largely from all weld metal. A
multi-run V-joint consists of approximately 90% weld metal with
mechanical properties similar to all weld metal. In a square butt
joint, however, only 20% is weld metal resulting in mechanical
properties that are largely influenced by the parent material
chemistry (see page 65 - 67).
Based on this formula fluxes are divided into the following groups:
B < 0.9 low basicity flux
B > 2.0 high basic flux
Approvals
Approval society requirements are taken into account when
specifying a flux/wire combination. Alternative combinations
may be used, if the preferred one does not have the required
approval (e.g.: CE-marking, marine societies, federal approvals,
TÜV, DB). Please contact ESAB, if no combination fulfils the
customer approval requirements.
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