Lincoln Electric Welder - Manual (Page 25)

23
heat affected zone temperature
exceeds the melting temperature
of copper. This can be prevented
by applying a thin nickel plate to
the copper.
• Plan the sequence of welding,
using the same techniques as with
mild steel such as skip welding
and back step welding.
Joining Stainless and Other
Steels: In some applications,
stainless steel weld metal is applied
to mild steel: for example, lining mild
steel vessels or containers with
stainless steel. For such
applications, stainless electrodes
with higher alloy content are used so
the admixture of the mild steel into
the stainless weld deposit does not
form an unsatisfactory alloy.
When stainless steel is joined to mild
steel, the mild steel is often
“buttered” with stainless steel. This
technique consists of depositing a
layer of stainless on the surface of
the mild steel, then completing the
joint with stainless electrode, as
illustrated in Figure 5. The electrode
commonly used for buttering is
E309. This technique is also used
for joining hard-to-weld or high car -
bon steels that cannot be preheated.
E308 electrode is used for joining
austenitic manganese steel to carbon
steel or to manganese steel. How -
ever, for the components that must
be replaced periodically, such as
dipper teeth, a manganese steel
electrode is recommended because
the stainless weld is more difficult to
torch cut.
Power Sources: The open circuit
voltage of light duty AC transformer
welders may not be high enough for
larger diameters of EXXX-16
electrodes; otherwise, the same
power sources used with steel
electrodes are satisfactory for
stainless electrodes.
Parameters and procedures for
welding stainless steel in thicknesses
from 18 gauge to 1/2 inch are given
in Figures 6, 7, 8, 9 and 10. These
show joint designs and backup bars
for butt, tee, lap and 90 degree edge
joints.
10.2
WELDING WITH
THE SUBMERGED
ARC PROCESS
The submerged arc process is
applicable to the welding of stainless
steels where the higher heat input
and slower solidification are tolerable.
With submerged arc welding,
depend ing upon the flux chosen, the
silicon content may be much higher
than with other processes, a factor
that may promote hot shortness or
fis sur ing when ferrite is less than
4FN.
The submerged arc process is not
recommended where a weld deposit
is needed that is fully austenitic or is
controlled to a low ferrite content
(below 4FN). However, high quality
welds may be produced for appli ca -
tions in which more than 4FN in weld
deposits is allowable. Figure 11
shows the type of butt joint designs
that can be used for submerged arc
welding.
Good quality single pass welds up to
5/16 inch thick can be made using
the square groove butt joint, Figure
11 (a), without root opening and with
suitable backing. Two pass welds
up to 5/8 inch thick are also made
without root opening. It is essential
on two pass welds, however, that the
edges be closely butted since weld
backing is not used. The advantage
of this joint design is that it requires a
minimum of edge preparation, yet
produces welds of good quality
having adequate penetration.
Single V-groove welds with a root
face, Figure 11 (b), are used with
nonfusible backing for single pass
butt welds of 5/16 inch thickness or
greater. For most industrial
applications, the maximum thickness
is of the order of 1-1/4 to 1-1/2 inch.
Root face dimensions are 1/8 to 3/16
inch. This joint is also used for two
pass welds without backing where
plate thickness exceeds 5/8 inch.
The first pass is made in the V of the
joint, Figure 11 (b). The work is
then turned over and the first pass
becomes the backing pass. In this
position, the finishing pass is made
on the flat side of the joint penetrat -
ing into the root of the first pass. The
root face is approximately 3/8 inch for
two pass welds.
The double V-groove butt, Figure 11
(d), is the basic joint design for
submerged arc welding. A large
root face is generally used with this
design. Figure 12 shows a typical
double V-groove weld in 3/4 inch
304 plate and describes the welding
sequence.
A single U-groove butt joint design,
Figure 11 (f), is also commonly
used. A small manually produced
backing weld is often made from the
reverse side of the joint. It is usually
desirable to fill the U-groove with 2
passes per layer as soon as possible
after the root pass. Slag removal
from a submerged arc weld pass
tieing in to both sides of the groove
can be very difficult.
For stainless steel welding, DC
power is mostly used on thin
sections. Either AC or DC may be
used on heavier pieces but DC is
preferred. Currents used are about
80% of those used for carbon steel.
Single pass techniques usually result
in dilution levels of 40% to 60%.
This may be decreased by using
FIGURE 5 —
Buttering technique for joining
mild steel to stainless steel.