manufacture, processing and use of stainless steel - International ...

Arc voltage or arc length
Arc voltage and arc length are directly related; they depend on the electrode type, the
welding process and the power supply. In general, increasing arc voltage, and thus
arc length, results in increased fume generation.
Type of metal transfer
In GMAW using a solid wire electrode, the type of metal transfer during welding
depends on the current and the voltage. At low current and voltage, short circuiting
transfer occurs (i.e. metal droplets are deposited during short circuits between the
electrode and the weld pool). At high currents, spray transfer occurs when fine metal
droplets are propelled across the arc. Spray transfer of metal is associated with
greater generation of welding fume than short circuiting transfer.
For other welding processes, the type of metal transfer does not change substantially
with current or voltage.
Methods for welding of stainless steel
Gas tungsten arc welding (GTAW)
The GTAW process involves the use of a tungsten electrode that carries the current
between the electrode and the workpiece. In this welding process the electrode is not
consumed. Filler metal may be added either manually, using 900mm lengths of bare
rod, or it may be automatically fed from spools of wire. Gases (argon, helium, and/or
hydrogen) are used to prevent oxidation of the electrode and to shield the welding
zones.
Gas metal arc welding (GMAW)
GMAW is an arc welding process that involves automatic feeding of a continuous,
consumable electrode. An externally supplied gas provides shielding. GMAW
involves two main types of metal transfer – short circuiting and spray transfer
(described in the earlier part of this section).
Shielded metal arc welding (SMAW)
SMAW employs a covered (coated) electrode. The weld is produced by fusion of
metal from the electrode core with edges of the joint. The coating of the electrode
provides a molten mineral substance, called slag, which forms over the fused weld,
protecting the weld during solidification and controlling the contour of the weld bead.
The electrode coating also provides shielding gases, and metallic ingredients, some of
which act as supplementary alloying ingredients for the weld metal. The composition
of the electrode coating is complex, containing many different substances. A typical
electrode coating would contain the following substances:
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