2507 Stainless Steel (UNS S32750)
Super-duplex (austenitic-ferritic) · ASTM A240/A240M, A789/A790 · Density 7.8 g/cm³
2507 (UNS S32750) is a super-duplex stainless steel with 25% chromium, 7% nickel, 4% molybdenum and 0.28% nitrogen. With PREN above 40 and minimum yield strength of 550 MPa, it withstands hot seawater, brines and sour service that defeat 316L and standard duplex 2205, and is a staple of offshore oil & gas and desalination plants.
Chemical Composition (wt%)
| C | Mn | Si | Cr | Ni | Mo | N | P | S |
|---|---|---|---|---|---|---|---|---|
| ≤0.030 | ≤1.20 | ≤0.80 | 24.0–26.0 | 6.0–8.0 | 3.0–5.0 | 0.24–0.32 | ≤0.035 | ≤0.020 |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A240/A240M, A789/A790.
Mechanical Properties
| Tensile strength | ≥795 MPa (116 ksi) |
|---|---|
| Yield strength (0.2%) | ≥550 MPa (80 ksi) |
| Elongation (50 mm) | ≥15% |
| Hardness | ≤310 HBW |
| PREN | ≥40 |
Room-temperature minimum values are summarized for annealed flat product under ASTM A240/A240M, A789/A790 unless a condition is named in the property label; product form and thickness can change the requirement.
Physical Properties & Structure
| Density | 7.8 g/cm³ |
|---|---|
| Magnetic response | Magnetic because the microstructure contains a substantial ferrite fraction. |
| Microstructure | Super-duplex (austenitic-ferritic) |
Corrosion Resistance & Limits
- The mixed austenitic-ferritic structure provides high strength and improved resistance to chloride pitting and stress-corrosion cracking relative to 304/316-type grades.
- PREN is only a screening index. Temperature, crevices, weld phase balance, heat tint, deposits and actual solution chemistry still govern suitability.
Fabrication & Heat Treatment
| Welding | Use a qualified duplex procedure with controlled heat input, interpass temperature and filler to maintain phase balance, toughness and corrosion resistance. |
|---|---|
| Forming | Higher yield strength increases forming load and springback. Severe cold work may require solution annealing under a qualified route. |
| Machining | Use rigid equipment, positive feeds and lower cutting speed than common austenitic grades because high strength and work hardening raise cutting load. |
| Heat treatment | Solution anneal and rapid cooling are used to restore the specified duplex structure. Local stress relief can form harmful intermetallic phases and is not a generic remedy. |
Equivalent Grades
The closest international equivalents of 2507 Stainless Steel are 1.4410 (X2CrNiMoN25-7-4) in the EN system, 022Cr25Ni7Mo4N in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | S32750 |
| EN | 1.4410 (X2CrNiMoN25-7-4) |
| GB | 022Cr25Ni7Mo4N |
Reference Product Forms & Dimensional Ranges
Common reference product forms for 2507 stainless steel: Sheet / Plate, Pipe / Tube, Bar.
| Finishes | No.1, 2B |
|---|---|
| Plate thickness | 3–50 mm |
| Bar diameter | 10–200 mm |
Common surface and delivery options: No.1, 2B, BA or mechanically polished finish when supported by the product route; Annealed and pickled, descaled or polished tube finish as specified; Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance.
These published ranges are engineering references, not a live-stock or production-capability promise. Confirm the required product form, dimensions, condition, finish and supply route in the quotation.
Typical Applications
- Offshore oil and gas flowlines and manifolds
- Seawater lift and firewater systems
- Desalination high-pressure sections
- Scrubbers and chemical tankers
- Heat exchangers in hot brines
Frequently Asked Questions
What is the difference between 2507 and 2205 duplex?
2507 raises chromium, molybdenum and nitrogen to push PREN above 40 (2205 sits around 34–38) and lifts the stated minimum yield strength. It provides more chloride margin than 2205 but has a narrower fabrication window; compare the service conditions and current delivered quotation rather than assuming a fixed premium.
What does PREN over 40 mean?
PREN (Pitting Resistance Equivalent Number = %Cr + 3.3×%Mo + 16×%N) estimates resistance to chloride pitting. Alloys above 40 are classed as seawater-resistant 'super' grades, suitable for hot chloride brines and crevice-prone joints. 2507's typical PREN is 41–43.
What is the service temperature range of 2507?
Design codes generally allow −50 °C to about +250 °C. Extended exposure above ~300 °C precipitates embrittling sigma phase in the ferrite, so super-duplex is never used for furnace or high-temperature duty despite its strength.
2507 Compared With Other Grades
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.
Other stainless steel grades:
304304L316316L201321310S4104302205202301309S316Ti347904L409L420439441444303317L254 SMO440C17-4 PH2304
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