General Welding Considerations
The ferritic stainless steels are generally less
weldable than the austenitic stainless steel and
produce welded joints having lower toughness
because of grain coarsening that occurs at the
high welding temperatures. Group I alloys
(Table 1) exhibit the poorest weldability. These
alloys require both preheating and postweld heat
treatments (PWHTs). Group II alloys (Table 2)
are more easily welded, but still require preheating
and post heating. The Group III superferritics
contain much lower carbon than do the other ferritic
grades and exhibit improved weldability.
The superferritics do not require preheating or
PWHTs (more detailed information on the weldability
of ferritic stainless steels can be found in
the following section).
Welds in ferritic stainless steel base metals
can be produced in several ways: (a) autogenously
(i.e., without the addition of filler
metal), (b) with a matching filler metal, (c) with
an austenitic stainless steel filler metal, or (d)
using a high-nickel filler alloy. Table 5 lists
some base metal-filler metal combinations for
selected ferritic stainless steels.
The most commonly used welding processes
to join ferritic stainless are the arc welding
processes—namely gas-tungsten arc welding
(GTAW), gas-metal arc welding (GMAW),
shielded-metal arc welding, and plasma arc
welding. Other welding processes occasionally