Duplex stainless steels have a mixed microstructure of roughly equal parts austenite and ferrite. That combination gives them around twice the yield strength of 304 or 316 together with much better resistance to chloride pitting and stress corrosion cracking. Super duplex pushes those properties further.
The grades
| Duplex 2205 | Super Duplex 2507 | |
| UNS | S31803 / S32205 | S32750 (also S32760) |
| ASTM A182 forgings | F51 / F60 | F53 (F55 for S32760) |
| Typical chemistry | 22% Cr, 5% Ni, 3% Mo, 0.15% N | 25% Cr, 7% Ni, 4% Mo, 0.27% N |
| PREN | about 34–36 | 40 minimum |
| Min. yield strength | 450 MPa | 550 MPa |
For comparison, annealed 316L has a minimum yield strength of around 170 MPa, which is why duplex grades often allow thinner, lighter components.
Where they are used
- Duplex 2205: chemical processing, pulp and paper, desalination, heat exchangers, and oil and gas lines where 316 is not enough.
- Super duplex 2507: seawater systems, offshore platforms, fire-water and ballast lines, and sour or highly chloride-rich process streams.
Limits to keep in mind
Duplex grades are generally not used above roughly 250–300 °C, because prolonged exposure at higher temperature causes embrittlement. They also need controlled welding procedures and heat input to keep the right ferrite–austenite balance, so ferrite checks and PMI testing are part of good practice.
Choosing between them
If 316L is pitting or cracking, 2205 is usually the next step. If you are dealing with warm seawater or very high chlorides, move to 2507. Pioneer Forge India manufactures flanges and fittings in both duplex and super duplex — share your service conditions and we will recommend a grade.
Need materials for your project?
Send your specification and get a competitive quotation.