Duplex stainless steels have a ‘duplex’ two-phase micro-structure consisting of both austenitic and ferritic grains that gives them a combination of attractive properties. Duplex alloys were developed around a 22% Chromium addition level, which largely defines them from subsequent super duplex alloys which were developed around a 25% Chromium addition level for higher corrosion resistance still.

In general, they are twice as strong as either austenitic or ferritic stainless steels. They achieve good toughness and ductility, somewhere between the two. Their corrosion resistance is also very good, assuming comparable levels of Chromium, Molybdenum and Nitrogen in selected compositions. One important advantage over austenitic stainless steels is their resistance to stress corrosion cracking. Yet they are significantly more cost effective, and less prone to price variability, due to their lower nickel content.

AlloyCommon NameRelated SpecificationsTensile StrengthProof TestElongation
BritishEuropeanUnited StatesN/mm2 (ksi)N/mm2 (ksi)(%)
Alloy 2205 UNS S32205 Duplex F60 (UNS31803 Duplex F51) 1.4462
ASTM A479/A182
UNS S32205 Duplex F60
UNS S31803 Duplex F51
655 (95) 450 (65) 25

Alloy 2205:

Alloy 2205 is a 22% Cr duplex stainless steel, supplied in the solution annealed condition. As a duplex stainless steel, it combines the desirable aspect of properties of both austenitic and ferritic grades. The high chromium, molybdenum and nitrogen contents results in a Pitting Resistance Equivalent number (PREN) of 33-34, providing pitting and crevice corrosion resistance superior to Alloy 316L or Alloy 317L austenitic stainless steels in almost all corrosive media. Due to its excellent corrosion properties, Duplex 2205 is well suited to environments containing chlorides and hydrogen sulphide, for use in oil and gas extraction from sour wells, in refineries and in process solutions contaminated with chlorides.