UNS S32205 Duplex Stainless Steel: Twice the Strength of 316L vs UNS N08904 (904L) Super Austenitic Stainless Steel
Side-by-side engineering comparison of UNS S32205 Duplex Stainless Steel: Twice the Strength of 316L (ASTM A240/A789) and UNS N08904 (904L) Super Austenitic Stainless Steel (ASTM A240/B625). Compare mechanical properties, chemical composition, density, yield strength, international equivalents, and typical applications to select the right material for your project.
Quick Verdict
If strength per millimetre and chloride SCC immunity are the drivers — offshore structures, desalination, tanks under pressure — choose 2205 duplex: 450 MPa yield is 2.6× the austenitics, achieved with lower nickel cost. If uniform corrosion in hot acid is the driver — sulfuric acid handling, heat exchanger plates, vessel internals that need maximum resistance to general attack — choose 904L, which outperforms 2205 in uniform corrosion but is softer and more expensive....
Double the yield strength with excellent chloride scc resistance
Superior uniform corrosion resistance and formability
Quick Comparison
| Property | UNS S32205 Duplex Stainle | UNS N08904 (904L) Super A |
|---|---|---|
| Standard | ASTM A240/A789 | ASTM A240/B625 |
| Category | Stainless Steel | Stainless Steel |
| Density | 7.80 g/cm³ | 8.00 g/cm³ |
| Yield Strength | 450 MPa (65 ksi) | 220 MPa (32 ksi) |
| Tensile Strength | 655 MPa (95 ksi) | 490 MPa (71 ksi) |
| Key Applications | UNS S32205 (2205) is a duplex stainless steel with a balanced ferrite-austenite microstructure (~50/50), combining the b... | UNS N08904 (904L) is a high-alloy austenitic stainless steel with elevated nickel (23-28%), chromium (19-23%), molybdenu... |
International Equivalents
| UNS S32205 Duplex St Equivalents | UNS N08904 (904L) Su Equivalents |
|---|---|
| EN 1.4462 | EN 1.4539 |
| X2CrNiMoN22-5-3 | X1NiCrMoCu25-20-5 |
| SUS329J3L | SUS890L |
| 022Cr22Ni5Mo3N | 00Cr20Ni25Mo4.5Cu |
| 2205 | 904L |
How to Choose
| Choose UNS S32205 Duplex Stainle when... | 2205 duplex stainless provides 450 MPa yield (2.6× 316L's 170 MPa) and immunity to chloride stress corrosion cracking with lower nickel content, making it the cost-effective structural choice for offshore, desalination, and chemical tanks. |
| Choose UNS N08904 (904L) Super A when... | 904L super-austenitic offers better general (uniform) corrosion resistance — especially in sulfuric acid — and superior formability, but has only 220 MPa yield at higher cost. |
Decision Checklist: Which Is Right for You?
| Criterion | UNS S32205 Duplex St | UNS N08904 (904L) Su |
|---|---|---|
| Double The Yield Strength With Excellent Chloride Scc Resistance | ✓ | |
| Superior Uniform Corrosion Resistance And Formability | ✓ | |
| Higher yield strength | ✓ | |
| Strength — 2205 (450 MPa yield) vs 904L (220 MPa); choose 2205 for pre... | ✓ | |
| Uniform corrosion — 904L excels in hot sulfuric acid and aggressive un... | ✓ | |
| Cost — 2205 is generally cheaper than 904L due to lower nickel; for st... | ✓ |
Selection Guide
If strength per millimetre and chloride SCC immunity are the drivers — offshore structures, desalination, tanks under pressure — choose 2205 duplex: 450 MPa yield is 2.6× the austenitics, achieved with lower nickel cost. If uniform corrosion in hot acid is the driver — sulfuric acid handling, heat exchanger plates, vessel internals that need maximum resistance to general attack — choose 904L, which outperforms 2205 in uniform corrosion but is softer and more expensive. In brief: 2205 for strength, weight, and SCC; 904L for aggressive uniform corrosion.
Key Decision Factors
- Strength — 2205 (450 MPa yield) vs 904L (220 MPa); choose 2205 for pressure and weight savings
- Uniform corrosion — 904L excels in hot sulfuric acid and aggressive uniform attack; 2205 is superior for localized (pitting/SCC) attack
- Cost — 2205 is generally cheaper than 904L due to lower nickel; for strength-dominated design 2205 delivers cost leverage
- Formability — 904L's austenite is easier to form and weld than 2205's duplex (which needs controlled heat input)
When to Use Each
Use UNS S32205 Duplex St for:
2205's 450 MPa yield and immunity to chloride stress corrosion cracking make it standard for offshore platforms, subsea manifolds, and topside piping where both strength and chloride resistance are required.
2205 resists chloride pitting, crevice corrosion, and SCC in high-chloride feedwater, reducing wall thickness and weight for membranes and pressure vessels.
The duplex structure provides two-phase strength and corrosion margin — 2205 is widely specified for chloride-bearing storage tanks and process equipment.
Use UNS N08904 (904L) Su for:
904L's copper and high nickel provide superior resistance to hot sulfuric acid — the preferred material for acid coolers, digesters, and acid recovery systems where 2205 is inadequate.
904L is used for plate heat exchangers in aggressive process streams where uniform corrosion resistance and formability matter more than strength.
904L's austenitic structure offers better cold formability and weldability for complex vessel internals and equipment fabricated into aggressive streams.
Frequently Asked Questions
What is the main difference between UNS S32205 Duplex Stainless St and UNS N08904 (904L) Super Austen?
UNS S32205 Duplex Stainless Steel: Twice the Strength of 316L (ASTM A240/A789) provides 450 MPa (65 ksi) yield strength at 7.80 g/cm³ density, while UNS N08904 (904L) Super Austenitic Stainless Steel (ASTM A240/B625) delivers 220 MPa (32 ksi) at 8.00 g/cm³. The choice depends on whether your application prioritizes double the yield strength with excellent chloride SCC resistance or superior uniform corrosion resistance and formability.
Can UNS S32205 Duplex Stainless St be substituted for UNS N08904 (904L) Super Austen?
In many applications, these materials can be cross-referenced, but direct substitution should always be verified against specific project specifications, especially for double the yield strength with excellent chloride SCC resistance, superior uniform corrosion resistance and formability, and operating environment. Consult your engineer of record.
Which is more expensive, 2205 or 904L?
Generally 2205 is the cheaper option per tonne because it uses less nickel (3.5-5.5%) than 904L (23-25%). However, because 2205 is roughly twice the strength, you often need far less of it for a load-bearing design, compounding the cost advantage. Data includes material price, fabrication cost, and typically a lower wall-thickness requirement — making 2205 the clear cost winner for strength-critical chemical and offshore service.
Can 904L replace 2205?
Only if strength is not a factor and uniform corrosion is the concern — then yes for acid service. For pressure vessels and offshore structures that exploit 2205's 450 MPa yield, 904L would require roughly double the wall thickness, negating any material advantage. And 904L, being austenitic, is more susceptible to chloride SCC at high temperatures than 2205. The two are complementary — 2205 for strength-localized-corrosion, 904L for uniform acid corrosion, not true substitutes.
Which has better weldability?
904L has simpler weldability — austenitic stainless welds with conventional procedures and tolerates higher heat input. 2205 duplex requires controlled heat input and interpass temperature to maintain the balanced 50/50 austenite-ferrite structure and avoid secondary phases; it welds fine but demands more skill and procedure control. For large complex fabrications, 904L is easier; for structural integrity at minimum weight, 2205 wins.