2205 Duplex Stainless vs 904L Stainless
2205 and 904L are both premium stainless grades for aggressive corrosion service, but they take different metallurgical routes. 2205 is a high-strength duplex austenite-ferrite alloy, while 904L is a high-nickel super-austenitic grade alloyed with copper. Engineers weigh them when chlorides or acids exceed 316's limits, choosing between 2205's high strength and stress-corrosion-cracking resistance or 904L's superior reducing-acid resistance.
The verdict
Choose 2205 when you need both corrosion resistance and high strength — its duplex structure gives ~450 MPa yield (double 904L's 220 MPa) plus strong resistance to chloride stress-corrosion cracking. Choose 904L for severe reducing-acid service, especially sulfuric and phosphoric acid, where its high nickel and copper outperform duplex, accepting lower strength and higher cost.
Side-by-side data
| Property | 2205 Duplex Stainless | 904L Stainless |
|---|---|---|
| Category | Stainless Steel | Stainless Steel |
| Density (g/cm³) | 7.8 | 8 |
| Tensile strength (MPa) | 655 | 520 |
| Yield strength (MPa) | 450 | 220 |
| Elongation (%) | 25 | 35 |
| Hardness | 31 HRC | 70 HRB |
| Max service temp (°C) | 300 | 400 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 19 | 12 |
| Typically used for | High-strength chloride-rich service | Sulfuric acid & severe corrosion |
Which should you choose?
Choose 2205 Duplex Stainless when…
- You need high strength plus corrosion resistance (450 MPa yield lets you thin sections)
- Chloride stress-corrosion cracking is a primary risk (duplex strongly resists it)
- High-pressure tanks, piping or vessels where strength saves weight
- Seawater, brine and high-chloride process media are the main threat
- You want better pitting/crevice resistance than 316 at lower cost than 904L
- Service stays below ~300°C (duplex embrittles above that)
Choose 904L Stainless when…
- The medium is concentrated sulfuric or phosphoric acid (copper addition excels here)
- Reducing-acid resistance matters more than mechanical strength
- The part is formed or welded and benefits from austenitic ductility (35% elongation)
- Crevice corrosion from high nickel/chromium/molybdenum/copper is the goal
- Maximum resistance to chloride SCC via very high nickel content
- A fully austenitic, non-magnetic structure is preferred
Key differences that matter
- 2205 is duplex (austenite-ferrite); 904L is fully austenitic — different microstructures
- 2205 is far stronger: ~450 MPa yield vs 904L's ~220 MPa, allowing thinner sections
- 904L's high nickel and copper give superior resistance to sulfuric/phosphoric (reducing) acids
- Both resist chloride stress-corrosion cracking well — duplex via structure, 904L via high nickel
- 904L is more ductile (35% vs 25% elongation) and fully non-magnetic; 2205 is partly magnetic
- Both machine slowly; both are costly, with 904L typically the pricier per kilogram
- Both limited to ~300-400°C service in this data; not for high-temperature use
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Open the Material SelectorGet a Quote →Frequently asked questions
Is 2205 stronger than 904L?
Yes, by roughly double. 2205's duplex structure delivers about 450 MPa yield and 655 MPa tensile, while 904L sits near 220 MPa yield and 520 MPa tensile. That strength lets 2205 use thinner walls in pressure vessels and piping, often offsetting material cost — whereas 904L is chosen for chemistry, not strength.
Which resists acids better, 2205 or 904L?
904L for reducing acids. Its high nickel and deliberate copper addition make it excel in sulfuric and phosphoric acid, environments where duplex 2205 is less suited. 2205 is excellent against chlorides and pitting, but for concentrated reducing acids 904L is the specialized grade.
Do both resist stress-corrosion cracking?
Yes, both far better than 316. Duplex 2205 resists chloride stress-corrosion cracking through its ferrite-containing microstructure, while 904L resists it through very high nickel content. Both are good choices where hot chlorides would crack standard austenitic grades, with 2205 adding a large strength advantage.
Which is easier to machine or form?
Both machine slowly, but 904L is more formable thanks to its fully austenitic ductility (35% elongation) and non-magnetic behavior. 2205 is harder (around 31 HRC) and work-hardens aggressively, making it tougher to machine, though both demand rigid setups and sharp tooling.
Is 904L more expensive than 2205?
Generally yes. 904L's very high nickel plus copper and molybdenum make it one of the most expensive standard stainless grades, typically above duplex 2205. 2205 partly offsets its cost through high strength that reduces material volume, so for strength-driven chloride service it is often the more economical pick.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.