| Duplex
Stainless Steel
Duplex stainless steels have a two-phase structure of
almost equal proportions of austenite and ferrite. The
composition of the most common duplex steels lies within
the range 22-26% Cr, 4-7% Ni, and 0-3% Mo, normally
with a small amount of nitrogen (0.1-0.3%) to stabilize
the austenite. Modern duplex steels are readily weldable,
but the procedure, especially maintaining the heat input
range, must be strictly followed to obtain the correct
weld metal structure.
Avoiding weld imperfections –
Although most welding processes can be used, low heat
input welding procedures are usually avoided. Preheat
is not normally required, and the maximum interpass
temperature must be controlled. Choice of filler is
important as it is designed to produce a weld metal
structure with a ferrite-austenite balance to match
the parent metal. To compensate for nitrogen loss, the
filler may be overalloyed with nitrogen or the shielding
gas itself may contain a small amount of nitrogen.
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