Lincoln Electric Welder - Manual (Page 34)

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welds and will result in a neater weld.
Forehand welding should be used for
butt welds. Outside corner welds
may be made with a straight motion.
A slight backward and forward
motion along the axis of the joint
should be used. Figure 16 summa -
rizes the welding procedures
normally used for the shortcircuiting
transfer welding of stainless steel.
Shortcircuiting transfer welds on
stainless steel made with a shielding
gas of 90% He, 7-1/2% A, 2-1/2%
CO
2
show good corrosion resistance
and coalescence. Butt, lap and
single fillet welds in material ranging
from .060 inch to .125 inch in 304,
310, 316, 321, 347, 410 and similar
stainless steels can be made
successfully.
The pulsed arc process, as normally
used, is a spray transfer process
wherein one small drop of molten
metal is transferred across the arc for
each high current pulse of weld
current. The high current pulse must
be of sufficient magnitude and dur -
ation to cause at least one small drop
of molten metal to form and be
propelled by the pinch effect from the
end of the wire to the weld puddle.
During the low current portion of the
weld cycle, the arc is maintained and
the wire is heated, but the heat
developed is not adequate to transfer
any metal. For this reason, the time
duration at the low current value
must be limited otherwise metal
would be transferred in the globular
mode.
Wire diameters of 0.045 and 0.035
inch are most commonly used with
this process. Gases for pulsed arc
welding, such as argon plus 1%
oxygen are popular, the same as
used for spray arc welding. These
and other wire sizes can be welded
in the spray transfer mode at a lower
average current with pulsed current
than with continuous weld current.
The advantage of this is that thin
material can be welded in the spray
transfer mode which produces a
smooth weld with less spatter than
the shortcircuiting transfer mode.
Another advantage is that for a given
average current, spray transfer can
be obtained with a larger diameter
wire than could be obtained with
con tinuous currents. Larger diam eter
wires are less costly than smaller
sizes, and the lower ratio of surface
to volume reduces the amount of
deposit contamination.
The electrode diameters for gas
metal arc welding are generally
between 0.030 and 3/32 inch. For
each electrode diameter, there is a
certain minimum welding current that
must be exceeded to achieve spray
transfer. For example, when welding
stainless steel in an argon-oxygen
atmosphere with 0.045 inch diameter
stainless steel electrode, spray
transfer will be obtained at a welding
current of about 220 amp DCRP. It
must be kept in mind that, along with
the minimum current, a minimum arc
voltage must also be obtained. This
is generally between 22 and 30 volts.
Electrodes come on spools varying in
weight between 2 and 60 lb. Also
available are electrodes for welding
the straight chromium stainless steels
and austenitic electrodes that contain
more than the usual amount of
silicon. The latter have particularly
good wetting characteristics when
used with the shortcircuiting transfer
process.
Some stainless steel weld metals
during welding have a tendency to -
ward hot shortness or tearing when
they contain little or no ferrite – Type
347, for example. When welding
these, more welding passes than
indicated in the procedures may be
needed. Stringer bead techniques
are also recommended rather than
weaving or oscillating from side to
side. Hot cracking may be elimi -
nated by stringer bead techniques
since there is a reduction in con -
traction stresses, hence cooling is
more rapid through the hot short
temperature range. A procedure that
tends to produce a more convex
bead than normal can be very
helpful, and care should be taken to
fill craters.
Weld metal hot cracking may be
reduced by shortcircuiting transfer
welding, because of the lower
dilution from the base metal.
Excessive dilution may produce a
completely austenitic weld metal
having strong cracking
characteristics.
When welding magnetic stainless
steels (ferritic and martensitic types)
to the relatively nonmagnetic types
(austenitic types), it is desirable to:
1. Use a single bevel joint to obtain
minimum joint reinforcement.
2. Use low heat input shortcircuiting
transfer to minimize the arc de flec -
tion encountered when welding
magnetic to nonmagnetic steels.
3. For uniform fusion, be sure the
Wire Size: 1.2mm (0.045 in.)
Shielding Gas: 75% He, 25% A
Electrode: 4.0-4.8mm (5/32-3/16 in.) 2% Th
Arc Arc Travel Speed Wire Speed Feed Deposition Rate
Current Voltage
Amps Volts mm/Sec In/Min. mm/Sec In/Min. Kg/Hr Lbs/Hr
300 10 - 12 1.7 - 4.2 4 - 10 46 - 157 110 - 370 1.4 - 4.5 3 - 10
400 11 - 13 2.5 - 5.9 6 - 14 78 - 188 185 - 445 2.3 - 5.4 5 - 12
500 12 - 15 3.4 - 8.5 8 - 20 125 - 282 295 - 665 3.6 - 8.2 8 - 18
TABLE XVII — Typical Travel Speeds and Deposition Rates with GTAW-Hot Wire