Duplex stainless steels have a mixed microstructure of roughly equal parts austenite and ferrite. This gives about twice the yield strength of the standard austenitic grades together with very good resistance to chloride-induced pitting, crevice and stress corrosion, which makes them established materials for seawater, offshore and chemical process equipment.
Grades in this family
| Grade | Type | UNS | Standard | Tensile strength Rm, min. (MPa) | Yield strength Rp0.2, min. (MPa) |
|---|---|---|---|---|---|
| CD3MN (4A) | 22Cr-5Ni-Mo-N duplex stainless steel | J92205 | ASTM A890/A890M, A995/A995M Gr. 4A | 620 | 415 |
| CE3MN (5A) | 25Cr-7Ni-Mo-N super duplex stainless steel | J93404 | ASTM A890/A890M, A995/A995M Gr. 5A | 690 | 515 |
Minimum values (or ranges) for separately cast test bars as specified in
Casting and processing considerations
The phase balance and freedom from intermetallic phases such as sigma depend on a correct solution anneal followed by rapid quenching; slow cooling of heavy sections is the main risk. Ferrite content, impact toughness and corrosion testing are frequently specified as acceptance tests and should be defined at the enquiry stage.
Reference data compiled from the cited standards for orientation. Always work from the current edition of the governing specification; values are not a guaranteed LOSTWAX delivery specification.