Page 69 - SSAB Welding Handbook Edition 2

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Welding handbook 12.0 The use of shielding gas

12.0 The use of shielding gas
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The main function of the shielding gas is to protect is also possible. However, the use of this kind of arc
the melt from the nitrogen and the oxygen in the air when welding high strength steels such as Strenx and
during welding, thus promoting beneficial mechanical Hardox is comparatively unusual.
properties in the weld metal. Additionally, the
shielding gas aids in:
4 Facilitating a stabilized arc during welding Arc types for MAG welding
4 Achieving high welding productivity Each arc type is confined to certain intervals of the
4 Providing an appropriate weld penetration profile current and voltage that are applied during the
welding operation. A schematic diagram for the
The chemical composition of the shielding gas is emergence of short arc and spray arc is illustrated in
dependent on the specific welding situation. In fig. 12.1. Improper settings of the current and voltage
this context, proposals of suitable shielding gas can result in the formation of a globular arc that is
compositions and flow rates are described for the very unstable and, therefore, undesirable.
different MAG processes as well as for the TIG
process. The selection and application of the
shielding gas for Hardox and Strenx steels is the
same as for unalloyed and low-alloyed steels in
general.

12.1 MAG welding Globular Spray

MAG welding is performed with different kinds of Short circuiting
consumables including solid wires, flux cored wires Voltage
and metal cored wires. A typical shielding gas for
MAG welding with these types of consumables is
a mixture of argon (Ar) and carbon dioxide (CO ).
2
Another alternative is a shielding gas consisting of
100% CO , which can be an alternative in certain
2
situations for MAG welding with flux cored wires. Current
The proportions of argon and carbon dioxide in Ar/
CO mixtures are related to the type of arc that is Fig. 12.1: The short arc and spray arc appearance for different levels
2
applied. Some mixtures are optimized for welding of current and voltage settings during MAG welding with an Ar/CO
2
shielding gas mixture. Welding is typically performed with D.C.
with a specific arc. Others can attain favorable results
when welding with more than one arc type.

The two principal arc types that are feasible during
MAG welding are short arc and spray arc. A pulsed
arc, which can be considered as a kind of spray arc,

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. 69
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.