Lincoln Electric Welder - Manual (Page 24)

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Rough machined surfaces on joint
edge preparation should be avoid ed to
prevent entrapment of contaminants.
Heat input for arc welding stainless
steels should be minimized to
minimize distortion and to minimize
the possibility of sensitization of the
heat affected zone. This is partic -
ularly important for standard,
nonstabilized austenitic stainless
steels.
10.1
WELDING WITH THE
SHIELDED METAL ARC
PROCESS
All stainless steel shielded metal arc
electrode coverings must be pro -
tected from moisture pickup.
Normally, electrodes packaged in
hermetically sealed containers can
be stored for several years without
deteriorating. However, after the
container is opened, the coating
begins to absorb moisture and,
depending on the ambient air con di -
tion, may need to be reconditioned
after only four hours of exposure,
otherwise porosity may result,
especially at arc starts.
Usually, redrying at 500 to 600°F
(260 to 316°C) for 1 hour restores
the electrode to its original condition,
and storing in a holding oven at
300°F (149°C) is satisfactory. Due to
differences in materials and
processing, the supplier should be
consulted if large amounts of
electrodes are involved.
DC electrodes (EXXX-15) operate on
DC only, have good penetration,
produce fillets with a slightly convex
profile, and are recommended for:
• Vertical and overhead welding and
all position applications such as
pipe. The slag has a fast freeze
characteristic.
• Root passes on heavy plate. The
larger throat section of the convex
bead helps prevent cracking.
• Austenitic stainless welds that
cannot contain any ferrite.
AC-DC electrodes (EXXX-16 and
EXXX-17) are always used on DC
when this type of power is available.
The fillet profile is flat (EXXX-16) to
slightly concave (EXXX-17), the weld
surface is smoother and the penetra -
tion is less than with EXXX-15 (DC
only) electrodes. The larger amount
of slag requires more care to avoid
slag inclusions. These electrodes are
recommended for horizontal fillets
and for all flat position welding.
EXXX-16 electrodes are also used in
all positions by skilled welders.
EXXX-17 electrodes can also be used
in all positions, but a wider weave is
generally necessary in the vertical-up
position than is necessary for EXXX-
16 electrodes.
Cleaning: For high quality welds,
joints must be clean and dry. The
choice of power brushing,
degreasing, pickling, grinding or
merely wiping depends upon the
kind and amount of dirt. Some
specific recommendations are:
1. Remove moisture by heating or by
blowing with dry air (beware of
moisture in the air line). Moisture
can collect on a weldment over -
night in high humidity conditions.
2. Eliminate organic contaminants
such as paints, antispatter com -
pounds, grease pencil marks,
cutting compounds, adhesive
from protective paper and soap
used for leak testing.
3. Flame beveling and machining
may leave contaminants or oxide
films that must be removed.
4. Avoid zinc contamination from
brushes or tools that have been
used on galvanized steel. Zinc
contamination causes cracking.
Use only stainless steel wire
brushes that have been used only
on stainless steel.
5. Avoid copper contamination from
rubbing stainless over copper
hold-down fixtures, etc. Copper
contamination causes cracking.
Welding Techniques: Welding with
stainless steel electrodes requires
techniques similar to those used for
mild steel low hydrogen electrodes.
Use a short arc, but keep the coating
from touching the puddle. Certain
electrodes are designed to be
dragged on the base metal in down -
hand and horizontal welding. Flat
beads with good wash-in promote
easy slag removal in deep grooves.
Fill each crater before breaking the
arc to avoid crater cracks. Clean the
slag thoroughly from the finish of the
bead before starting another elec -
trode, and clean the complete weld
before started the next pass. On
deep groove butt joints, the root pass
should penetrate only enough to fuse
to both plates and seal the opening.
More penetration may cause cracks.
For vertical and overhead positions
never use an electrode larger than
5/32". The DC electrodes (EXXX-15)
are preferred, but the AC-DC
electrodes (EXXX-16) can be used for
welding vertical up (using DC). On
thick plate, use the triangular weave
or inverted Vee technique, welding
vertical up. On thin plate, use small
beads, vertical down.
The EXXX-17 AC-DC electrodes are
more difficult to use vertical up than
the EXXX-16 electrodes. A wider
weave is generally necessary.
Welding techniques can help control
distortion. Weld with low current con -
sistent with sufficient penetration to
reduce the heat input to the work
(Table XVI). Use stringer beads at a
higher speed rather than wide beads
at a slower speed. If weave beads
must be made, limit the weave to
2-1/2 times the electrode diameter.
Other means to control distortion are:
• Use rigid fixtures to hold parts in
alignment.
• Use chill bars near the weld and
backing bars under the weld.
Rapid cooling of austenitic
stainless steels is beneficial rather
than harmful. If copper is used as
the chill bar material, care must be
exercised to prevent copper grain
boundary penetration where the