Duplex Stainless Steel
Duplex stainless combines the strength of ferritic with the corrosion resistance of austenitic steel. Learn when to choose 2205 or 2507 over standard 316.
What Is Duplex Stainless?
Duplex stainless steel has a microstructure that is approximately 50% austenite and 50% ferrite — hence 'duplex'. This dual structure gives it properties that neither austenitic (304, 316) nor ferritic grades achieve alone: higher strength and better chloride stress corrosion cracking resistance than 316.
The most common duplex grade is 2205 (UNS S31803/S32205). Super duplex grades like 2507 (UNS S32750) offer even higher alloy content for the most aggressive environments.
Properties Comparison
| Property | 316L | 2205 (Duplex) | 2507 (Super Duplex) |
|---|---|---|---|
| Yield strength (MPa) | 220 | 450 | 550 |
| Tensile strength (MPa) | 520 | 620 | 795 |
| Chloride pitting res. (PREN) | 24 | 35 | 43 |
| Stress corrosion cracking | Poor above 60°C | Good | Excellent |
| Density (kg/m³) | 8000 | 7850 | 7850 |
| Max service temp (°C) | 870 | 300 | 300 |
When to Choose Duplex
- Chloride stress corrosion cracking risk: In hot (>60°C) chloride environments where 316 will crack, duplex is the upgrade.
- High strength needed: Duplex has 2× the yield strength of 316 — allows thinner wall, lighter weight, lower cost for the same pressure.
- Seawater applications: Super duplex 2507 is one of the few materials that resists seawater pitting long-term.
- Oil and gas: Resistant to H₂S and CO₂ corrosion in sour service environments.
Limitations
- Temperature limit: Duplex embrittles above 300°C (475°C embrittlement) — not suitable for high-temperature service.
- Welding complexity: Requires controlled heat input and nitrogen backing gas to maintain the 50/50 phase balance.
- Not for cryogenic: Ferritic phase becomes brittle at low temperatures — use austenitic 316L for cryogenic service.
How CHI can help
Ask CHI about duplex stainless steel and to determine when it offers advantages over 316 for your application. The CHI assistant can recommend the right material for your specific application, explain chemical compatibility, and flag when a material is unsuitable for your operating temperature or environment.