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Duplex
These are stainless steels containing relatively high
chromium levels (between 18% and 28%) and moderate amounts
of nickel (between 4.5% and 8%). The high corrosion
resistance and the excellent mechanical properties of
duplex stainless steels can be explained by their chemical
composition and balanced ("duplex") microstructure
of approximately equivalent volume fractions of ferrite
and austenite. Alloys 2304 and 2205 are the most common
grades.
"Super" duplex grades have enhanced
pitting and crevice corrosion resistance compared with
the ordinary austenitic or duplex types. This is due
to the further additions of chromium, molybdenum, and
nitrogen to these grades. Alloy 2507 is the most common
grade.
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