2507 Super Duplex Stainless Steel: Properties and Uses
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What Is 2507 Stainless Steel?
2507 is a super duplex stainless steel with a two-phase microstructure of approximately 50% ferrite and 50% austenite. It is designated UNS S32750 under ASTM A240 / ASME SA-240 and EN 1.4410 / X2CrNiMoN25-7-4 under the EN 10088 system. The duplex structure gives it the best of both families: the high strength of ferritic steel and the toughness plus corrosion resistance of austenitic steel, with far better resistance to chloride stress corrosion cracking than either alone.
Chemical Composition
| Element | Range (wt %) |
|---|---|
| Carbon (C) | ≤ 0.03 |
| Silicon (Si) | ≤ 0.80 |
| Manganese (Mn) | ≤ 1.20 |
| Phosphorus (P) | ≤ 0.035 |
| Sulfur (S) | ≤ 0.020 |
| Chromium (Cr) | 24.0 – 26.0 |
| Nickel (Ni) | 6.0 – 8.0 |
| Molybdenum (Mo) | 3.0 – 5.0 |
| Nitrogen (N) | 0.24 – 0.32 |
The pitting resistance equivalent number, PREN = Cr + 3.3Mo + 16N, is typically above 40 for 2507, compared with roughly 25 for 316L. That margin decides service life in chloride-rich process streams.
Mechanical Properties (ASTM A240 Minimums)
| Property | Minimum Value |
|---|---|
| Tensile strength | ≥ 800 MPa |
| Yield strength Rp0.2 | ≥ 550 MPa |
| Elongation (in 50 mm) | ≥ 15% |
| Hardness | ≤ 32 HRC / 310 HB |
Yield strength is roughly double that of austenitic 316L, allowing thinner wall sections and lighter structures under the same design pressure. The low coefficient of thermal expansion and high thermal conductivity also improve performance in heat-exchanger service.
Corrosion Resistance
Pitting and crevice corrosion: the high chromium, molybdenum and nitrogen content gives excellent resistance in chloride media, including seawater.
Stress corrosion cracking: the duplex microstructure is highly resistant to chloride SCC, a common failure mode of austenitic grades in hot chloride service.
Acid attack: 2507 performs well in dilute sulfuric acid containing chlorides and in dilute hydrochloric acid, with iso-corrosion rates near 0.1 mm/year at moderate temperatures, where 316L would suffer local or general corrosion.
Intergranular corrosion: the low carbon content minimizes carbide precipitation during heat treatment and welding.
Applications
2507 is specified for oil and gas production and flowlines, offshore platform heat exchangers, seawater systems and fire-water networks, desalination plants, flue-gas desulfurization and waste-gas purification equipment, chemical tanker piping, pulp and paper digesters, and structural or mechanical components that need both high strength and high corrosion resistance. Recommended matching welding consumables are ER2594 wire and E2594 electrodes, with interpass temperature controlled to limit secondary-phase precipitation.
Selection and Service Notes
Service temperature is normally limited to below about 250–300°C; prolonged exposure above 300°C (570°F) can embrittle the duplex structure and reduce toughness.
Welding requires controlled heat input, filler metal of matching composition, and often solution annealing after severe forming.
Confirm the required product form standard (plate to ASTM A240, seamless pipe to ASTM A790 / A789) when ordering.
Frequently Asked Questions
What does the name 2507 mean?
It is the trade designation reflecting the nominal 25% chromium, 7% nickel composition; the formal designations are UNS S32750 and EN 1.4410 (X2CrNiMoN25-7-4).
How does 2507 compare with 2205 duplex?
2507 contains more chromium, molybdenum and nitrogen, giving higher strength and better pitting resistance (PREN > 40 vs ≈ 35 for 2205). 2205 is adequate for many seawater applications; 2507 is chosen for the most aggressive chloride and acid service.
Is 2507 better than 316L in seawater?
Yes, significantly. 316L is prone to pitting and crevice corrosion in warm seawater; 2507 is designed for permanent seawater exposure.
Can 2507 replace 904L?
In chloride-bearing sulfuric acid, 2507 often outperforms 904L and offers higher strength at lower cost. In hot, pure concentrated sulfuric acid, the fully austenitic 904L remains the conventional choice.
Is 2507 magnetic?
Partially. The ferrite phase makes it magnetic, unlike fully austenitic grades.
What welding consumables are recommended?
Matching super duplex consumables ER2594 (wire) and E2594 (electrode), with interpass temperature limited to about 150°C to avoid sigma-phase formation.
