2507 Duplex Stainless Steel: Uses and Applications
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What Is 2507 Super Duplex Stainless Steel?
2507 (UNS S32750, EN 1.4410) is a super duplex stainless steel with a two-phase microstructure of roughly 50% austenite and 50% ferrite. The duplex structure combines the high strength of ferritic steel with the toughness and corrosion resistance of austenitic steel. The high chromium, molybdenum, and nitrogen content gives it a PREN above 40, so it resists pitting, crevice corrosion, and stress corrosion cracking in chloride-rich seawater and process media where 316L and even 2205 duplex fail.
Composition and Key Properties
| Item | Value |
|---|---|
| Chromium | 24.0-26.0% |
| Nickel | 6.0-8.0% |
| Molybdenum | 3.0-5.0% |
| Nitrogen | 0.24-0.32% |
| Yield strength, min (MPa) | 550 |
| Tensile strength, min (MPa) | 795 |
| Elongation, min (%) | 15 (plate, per A240) |
| PREN (Cr + 3.3Mo + 16N) | above 40 |
Because nitrogen is a strong austenite former, the 0.27% nitrogen level is essential: it stabilizes the phase balance, raises yield strength, and improves pitting resistance. Grade coverage includes ASTM A240 (plate), A789/A790 (tube and pipe), A182 (forgings), and A276 (bar).
Industry Applications
Oil and gas: subsea manifolds, flowlines, process piping, and wellhead equipment exposed to produced water with chlorides and CO2/H2S.
Offshore platforms: heat exchanger tubes, seawater cooling and fire-fighting systems, sprinkler and water stabilization lines.
Petrochemical: reactors, columns, and piping in chloride-bearing process streams.
Desalination: high-pressure piping, seawater intake lines, and evaporator components in reverse osmosis and thermal plants.
Flue gas desulfurization (FGD): absorber vessels and ducting where acidic chloride condensate forms.
Mechanical and structural: shafts, impellers, and fasteners that need both high strength and corrosion resistance.
Fabrication and Service Limits
2507 is welded with matching over-alloyed duplex consumables, and the interpass temperature must be controlled below about 150 °C to avoid sigma phase and nitrogen loss in the heat-affected zone. The material is normally used in the solution-annealed condition, and post-weld heat treatment is generally not required. Continuous service above 250-300 °C is avoided because the ferrite phase embrittles; conversely, below about -50 °C the toughness drops, so impact testing per the governing code should be confirmed for low-temperature service.
Common Misconceptions
'2507 is just a stronger 316L.' It is a different alloy family: duplex microstructure, PREN above 40, and roughly double the yield strength, at a higher price and with stricter welding control.
'2507 resists everything, including reducing acids.' It is excellent in chloride-oxidizing media but is attacked by strong reducing acids such as hydrochloric acid; grade selection must match the full environment.
'2205 and 2507 are interchangeable.' 2205 (S32205) has PREN about 35 and yield strength about 450 MPa; 2507 is the higher-alloy super duplex for more aggressive seawater and sour service.
Frequently Asked Questions
What does 2507 stainless steel contain?
Nominally 25% chromium, 7% nickel, 4% molybdenum, and 0.27% nitrogen, with the balance iron; per ASTM A240 the limits are Cr 24-26%, Ni 6-8%, Mo 3-5%, N 0.24-0.32%.
What is the difference between 2507 and 2205 duplex?
2205 (UNS S32205) has about 22% Cr, 5% Ni, 3% Mo, and 0.17% N with a PREN near 35; 2507 has about 25% Cr, 7% Ni, 4% Mo, 0.27% N and a PREN above 40, plus roughly 20% higher yield strength.
Is 2507 magnetic?
Partly. The ferrite phase is magnetic, so 2507 shows a strong magnetic response, unlike fully austenitic 316L. This is normal and does not indicate a defect.
Why is 2507 used in seawater?
Its PREN above 40 resists pitting and crevice corrosion in chlorides, and the duplex structure resists chloride stress corrosion cracking, which are the two failure modes that eliminate 304 and 316 in seawater.
Can 2507 be welded without post-weld heat treatment?
Yes. With matching duplex filler, controlled heat input, and interpass temperature below about 150 °C, the as-welded joint meets the required properties and PWHT is not normally performed.
What standards cover 2507?
ASTM A240 (plate, sheet, strip), A789 and A790 (seamless and welded tube and pipe), A182 (forgings and flanges), and A276 (bar); EN 1.4410 in EN 10088; JIS SUS329J4L is the closest 2507-type designation in the Japanese system.
