Comprehensive Analysis of Super Duplex Stainless Steel 2507
Preferred material for harsh environments
As a representative of super duplex stainless steel, 2507 (UNS S32750) has become the preferred material for harsh environments such as petroleum, chemical, and marine engineering due to its perfect balance of high strength and corrosion resistance.
This article will conduct in-depth analysis from the dimensions of chemical composition, physical properties, corrosion resistance, processing technology, application fields, and future development.
Chemical composition of super duplex 2507
The chemical composition of super duplex stainless steel 2507 has been carefully designed, and its core elements include:
Chromium (Cr): 24-26% – forms a passivation film to resist oxidative media.
Molybdenum (Mo): 3-5% – enhances resistance to pitting and crevice corrosion.
Nickel (Ni): 6-8% – stabilizes austenite phase and enhances toughness.
Nitrogen (N): 0.24-0.32% – inhibits intermetallic phase precipitation, improves strength, and replaces some nickel to reduce costs.
Low carbon (C): ≤ 0.03% – reduces the precipitation of carbides at grain boundaries and avoids the risk of intergranular corrosion.
Characteristics of biphasic structure:
By solution annealing at 1050-1120 ℃ and water quenching treatment, a phase ratio of approximately 50/50 between ferrite (α) and austenite (γ) was obtained.
This structure combines:
Advantages of ferrite – high yield strength, resistance to chloride stress corrosion cracking (SCC).
Advantages of austenite – good toughness and work hardening ability.
Physical and mechanical properties of super duplex 2507
| Properties | Value | Comparative advantage |
|---|---|---|
| Tensile strength（σb） | ≥730-800 MPa | Improved by over 80% compared to 316L |
| Yield strength（σ0.2） | ≥550 MPa | 1.2 times that of 2205 duplex steel |
| Elongation rate（δ） | ≥20% | Maintain high plasticity |
| Hardness（HB） | ≤310 | For heavy-duty components |
| Density | 7.8 g/cm³ | Near carbon steel, convenient for mixed structure design |
Chemical resistance and heat resistance of super duplex 2507
Corrosion resistance
Chloride environment:
The equivalent resistance to pitting corrosion (PREN=% Cr+3.3 ×% Mo+16 ×% N) is ≥ 42, markedly far exceeding 316L (PREN ≈ 26) and 2205 (PREN ≈ 35).
Critical pitting temperature (1M NaCl): ≥ 70 ℃, 15 ℃ higher than 904L.
Critical crevice corrosion temperature (10% FeCl ∝): ≥ 45 ℃.
Acidic medium:
In dilute sulfuric acid containing 2000ppm Cl ⁻, the corrosion rate is ≤ 0.1 mm/year.
Tolerate ≤ 10% dilute hydrochloric acid, while 316L will corrode severely in this environment
Stress Corrosion Cracking (SCC):
Dual phase structure blocks crack propagation, especially suitable for high-pressure chlorine containing environments (such as subsea pipelines).
Intergranular corrosion:
Low carbon design+nitrogen control technology to avoid chromium carbide precipitation during heat treatment
Heat resistance
The long-term use temperature should not exceed 300 ℃ (570 ° F), otherwise the precipitation of intermetallic phases (σ, χ phases) above this temperature can lead to embrittlement.
Economy and processing performance of super duplex 2507
Procurement Cost
Initial cost:
about 50% higher than 316L, but with low lifecycle cost – due to reducing wall thickness (such as reducing tank wall thickness by 30-50%) and lowering maintenance frequency
Processability
Hot processing and cold forming
Hot processing temperature: 1027-1232 ℃ (1875-2250 ° F), followed by solution annealing and water quenching.
Cold forming restriction: Annealing is required when the deformation exceeds 10% to avoid cracking (due to high yield strength and low ductility).
Key points of welding process
Filling material: Special welding material ER2594/E2594, basically matched with dual phase structure.
Parameter control: Heat input: 5-20 kJ/cm (lower limit for thin parts, upper limit for thick parts).
Interlayer temperature: ≤ 100 ℃ (to prevent imbalance of gamma → alpha phase transition).
Protective gas: argon or a mixture of 90% N ₂ and 10% H ₂ in order to enhance root corrosion resistance.
Main application industries
| Industries | Typical Applications | Performance |
|---|---|---|
| Oil and Gas | Subsea pipelines, platform heat exchangers | Resistant to high pressure and seawater corrosion |
| Chemical Industry | Reactor, acid washing equipment | Resistant to sulfuric acid/hydrochloric acid mixed medium |
| Seawater Desalination | High pressure reverse osmosis membrane shell, seawater pump | 3 times longer lifespan against chloride ion erosion |
| Environment Protection | Flue gas desulfurization (FGD) absorption tower | Corrosion resistance to sulfides |
| Ship Engineering | Propeller shaft, seawater valve | High strength+anti biological attachment |
Future Development and Challenges
High temperature performance optimization:
Microaloying (adding copper and tungsten) is used to suppress the precipitation of the σ phase, in order to achieve the goal of increasing the long-term operating temperature to 350 ℃.
Sustainable Manufacturing:
Develop low nickel high nitrogen formulas (such as reducing Ni to 5%) to reduce dependence on strategic metals.
Additive Manufacturing Applications:
Laser Powder Bed Melting (LPBF) technology is used to form complex components in order to solve the problem of springback in traditional processing
Conclusion
The super duplex stainless steel 2507 achieved performance breakthroughs in extreme corrosion and high load environments through the precise composition design of 25Cr-7Ni-4Mo-0.27N and the synergistic effect of the duplex structure.
Despite its strict processing requirements (such as welding heat input control), its irreplaceability has been verified in fields such as oil platforms and seawater desalination.
In conclusion, with the optimization of composition and innovation in manufacturing technology, super duplex stainless steel 2507 will continue to expand its application boundaries in new energy equipment and deep-sea engineering, becoming a strategic choice in the field of high-performance materials consequently.
More info please check :SAF 2207 – Wikipedia
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