7
STAINLESS STEEL
Short arc welding should be used for
welding thin materials in the flat position, bridging large gaps and all
welding out of position. The best shielding
gas to use for short arc welding of stainless steel is A-1025 (90%
Helium, 7.5% Argon and 2.5% CO2).
This mixture provides good penetration, arc stability, and weld
properties (particularly corrosion resistance)
in single or multi-pass weldments. C-25 (75% Ar - 25% CO2
can be used, but only for single pass
welds where corrosion resistance of the weld metal is not essential to
the end use. CO2
shielding can never be used. Spray
arc should be used in the flat position for single or multi- pass welding of thicker
material. For spray arc
welding, an Ar-1% 02 gas mixture will yield
the best results, particularly from the standpoint of bead
appearance. If, for a certain application,
wetting of the weld bead has proven difficult, an Ar-2% 02
shielding gas
mixture will help. However, the chrome oxide build-up will cause the weld bead
to be slightly discolored. As
for the welding techniques that can be used, the same considerations are true
with stainless steel as for low
carbon mild steel. However, the forehand technique is sometimes preferred, as
a flatter weld can be made,
although the surface will be more oxidized. Welding
conditions for stainless steel are shown in Table
8-3 (at back of book).
Figure 8-3 shows accurate burn-off
characteristics for various size stainless steel wires and Figure 8-4 shows the
deposition rates for these
wire-feed speeds.
