Lincoln Electric Welder - Manual (Page 23)

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the fastest deposition rates with the
GMAW process but wire feeding
equipment, power supplies and the
requirement for inert gas shielding
add to the cost of using these fillers.
However, there is little need to
remove slag between passes. Solid
and metal cored wire can be used in
shortcircuiting, globular and spray
modes of arc operation which gives
a wide range of deposition rates and
heat input levels. Solid and metal
cored wire can therefore be used for
welding a wide range of thicknesses.
Gas metal arc welding with spray
transfer is used to join sections
thicker than about 0.25 inch
because deposition rates are higher
than with other transfer modes.
Welding pro ce dures are simular for
conventional austenitic and PH
stainless steels.
The shielding gas is generally argon
with 1 to 2 percent oxygen added for
arc stability. Mixtures of argon and
helium are employed if a hotter arc is
desired. A small oxygen addition
can be added to provide a stable
arc, but some aluminum or titanium
can be lost from certain PH filler
metals during transfer across the arc
as a result of oxidation. Response of
the weld metal to heat treatment
might be less because of this action.
For flat position welding, spray
transfer is usually preferred. For
other welding positions,
shortcircuiting transfer is often used
with helium-rich gas such as 90%
He 7.5% A -2.5% CO
2
or pulsed
spray transfer can be employed
using argon or an argon-helium
mixture with a small addition of
oxygen or carbon dioxide.
9.4
FLUX CORED
ARC WELDING
Flux cored wire uses basically the
same wire feed equipment and
power supply as solid and metal
core wire. Wires can be designed
for use with gas shielding (AWS
Classes EXXXTX-1 or EXXXTX-4) or
without gas shielding (AWS Classes
EXXXTO-3). The “-1” indicates CO
2
shielding gas, while the “-4”
indicates 75% Argon - 25% CO
2
shielding gas. Although carbon
dioxide gas shield ing is not
recommended for gas metal arc
welding, it is com mon ly used with
flux cored arc welding because the
slag protects the metal from carbon
pickup. Use of EXXXTO-3 with gas
will result in high ferrite. Use of
EXXXTX-1 or EXXXTX-4 without gas
will result in little or no ferrite and
possibly porosity. Solid wire, metal
core and flux core wire have an
advantage over coated electrodes by
their continuous nature in that it is
not necessary to stop welding to
change electrodes.
Electrode Size Recommended Current (Amp)
mm. inch. E3XX-15 Electrodes E3XX-16 Electrodes E3XX-17 Electrodes
2.4 3/32 30 - 70 30 - 65 40 - 80
3.2 1/8 45 - 95 55 - 95 80 - 115
4.0 5/32 75 - 130 80 - 135 100 - 150
4.8 3/16 95 - 165 120 - 185 130 - 200
6.4 1/4 150 - 225 200 - 275 Consult Manufacturer
Optimum current for flat position is
about 10% below maximum;
optimum for vertical-up welding,
about 20% below maximum;
optimum for vertical-down welding,
about maximum.
Optimum current for flat position is
about 10% below maximum; AC
range is about 10% higher.
Optimum current for flat position is
about 10% below maximum.
TABLE XVI — Recommended Current Ranges For Austenitic Stainless Steel Electrodes (DCEP)
9.5
GAS TUNGSTEN
ARC WELDING
Manual and automatic gas tungsten
arc welding (GTAW) processes are
frequently used for joining con ven -
tional and PH stainless steels,
particularly in thicknesses up to
about 0.25 inch.
Normally direct current, electrode
negative is used with a power supply
having drooping volt-amperage
characteristic. However, alternating
current is sometimes used to weld
those steels containing aluminum to
take advantage of the arc cleaning
action.
10.0
PROCEDURES
FOR WELDING
STAINLESS
STEELS
Once a joint design has been
established and a welding process
and filler material have been
selected, a welding procedure may
be developed. For any process, it is
important that joint edges and filler
material be clean and free of any
oxide, organic material or other con -
tam ination. Thermal cut edges must
be cleaned to remove oxide film.