| Austenitic
Stainless Steel
Austenitic stainless steels typically have 16 –
26% chromium (Cr) and 8 – 22% nickel (Ni). Alloy
304, which contains approximately 18% Cr and 10% Ni,
is a commonly used alloy for welded fabrications, and
these alloys can be readily welded using any of the
arc welding processes (TIG, MIG, MMA, and SA). They
exhibit good toughness because they are non-hardenable
on cooling, and there is no need for pre- or post-weld
heat treatment.
Avoiding weld imperfections –
Austenitic stainless steel is readily welded, but weld
metal and HAZ cracking can occur. Weld metal solidification
cracking is more likely to occur in fully austenitic
structures, which are more crack sensitive than those
containing a small amount of ferrite as ferrite has
the capacity to dissolve harmful impurities which would
otherwise form low melting point segregates and interdendritic
cracks. The presence of 5 - 10% ferrite in the microstructure
is extremely beneficial so the choice of filler material
composition is crucial in suppressing the risk of cracking.
An indication of the ferrite-austenite balance for different
compositions is provided by the Schaeffler diagram.
For example, when welding Alloy 304 stainless steel,
an Alloy 308 filler material, which has a slightly different
alloy content, is used. |
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