Duplex stainless steels are a class of stainless steels with a dual-phase microstructure of austenite and ferrite, combining high strength with excellent corrosion resistance. Compared with conventional austenitic grades (such as 304 and 316L), duplex steels perform significantly better in petrochemical, offshore, and desalination industries.
Among them, 2205 (UNS S32205) is the most widely used standard duplex stainless steel, while 2507 (UNS S32750), as a súper dúplex, demonstrates superior performance in extreme environments.
Comparison: Duplex 2205 vs. Super Duplex 2507
2.1 Chemical Composition (wt%)
| Calificación | Cr | Ni | Mes | norte | Otros |
| 2205 | 21–23% | 4.5–6.5% | 2.5–3.5% | 0.14–0.20% | Mn ≤2% |
| 2507 | 24–26% | 6–8% | 3–5% | 0.24–0.32% | Cu ≤0.5% |
Diferencia clave: 2507 has higher Cr, Mo, Ni, and N → better corrosion resistance and strength compared to 2205.
2.2 PREN (Número equivalente de resistencia a las picaduras)
- 2205: ~35–37
- 2507: ~40–45
Conclusión: 2507 is a “super duplex” grade, offering greater reliability in seawater and chloride-rich environments.
2.3 Mechanical Properties
| Propiedad | 2205 | 2507 |
| Fuerza de fluencia | ≥450 MPa | ≥550 MPa |
| Resistencia a la tracción | ≥620 MPa | ≥800 MPa |
| Alargamiento | 25–30% | 15–25% |
Conclusión: 2507 offers higher strength, but slightly lower ductility.
2.4 Corrosion Resistance
- 2205: Good resistance to pitting and crevice corrosion, suitable for medium-to-high chloride environments.
- 2507: Can withstand long-term service in natural seawater (Cl⁻ ~19,000 ppm) with minimal risk of pitting or stress corrosion cracking (SCC).
2.5 Applications
- 2205: Petrochemical equipment, heat exchangers, desalination (freshwater side), chemical tanks, auxiliary piping on offshore platforms, pulp and paper bleaching equipment.
- 2507: Subsea pipelines and wellhead equipment, desalination brine/reject systems, marine heat exchangers and condensers, high-pressure seawater injection systems.
2.6 Cost & Fabrication
- 2205: Lower cost, better workability and weldability.
- 2507: Higher cost, more difficult to fabricate and weld; requires strict heat input control and matching filler metals.
2.7 Overall Comparison
- Fortaleza: 2507 > 2205
- Resistencia a la corrosión: 2507 > 2205 (especially in seawater/high chloride environments)
- Toughness/Ductility: 2205 > 2507
- Cost & Fabrication: 2205 is more economical and easier to process
- Typical Use:
2205 → Medium-to-high corrosion environments (refining, pulp & paper, desalination
Why Develop 2507 (Super Duplex)?
Limitations of 2205:
- PREN ~35–37 → still at risk of pitting in long-term exposure to natural seawater.
- Increased risk of SCC in high-chloride environments at >50 °C.
Advantages of 2507:
- PREN ~40–45 → reliable in natural seawater and high-temperature, high-chloride service.
- Higher strength (yield ≥550 MPa) → suitable for subsea manifolds and high-pressure injection systems.
In other words: 2205 is the general-purpose grade, while 2507 is the safeguard grade for extreme conditions.
The Evolution of the Duplex Stainless Steel Family
Driven by diverse application needs, duplex stainless steels have expanded into different categories:
| Categoría | Representative Grades | PREN | Características | Aplicaciones |
| Lean Duplex | 2304 (UNS S32304) | 22–25 | Low-cost, stronger than 304/316, moderate corrosion resistance | Architecture, freshwater, mild environments |
| Standard Duplex | 2205 (UNS S32205) | 35–37 | Balanced strength & corrosion resistance; most widely used | Chemicals, petrochemicals, desalination freshwater side |
| Super Duplex | 2507 (UNS S32750), Zeron 100 | 40–45 | Excellent seawater resistance, higher strength | Offshore oil & gas, seawater heat exchangers, brine systems |
| Hyper Duplex | S32707, S33207 | 48–52 | Extreme corrosion resistance + ultra-high strength, higher cost | Deepwater (>2000 m) oil & gas, harshest conditions |
Conclusión
- 2205: General-purpose, suitable for most applications requiring both strength and corrosion resistance.
- 2507 / Zeron 100: Preferred choice for extreme seawater and chloride environments.
- 2304: Low-cost option, suitable for mild corrosion.
- Hyper Duplex: Next-generation materials, designed for ultra-harsh deepwater and high-chloride service.
In one sentence: 2205 is the “workhorse duplex,” 2507 is the “super duplex for extreme environments,” and the continuous evolution of the duplex family ensures full coverage from mild to ultra-severe service conditions.
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