1.2507 Super Duplex Steel — Grades F53 & S32750
Introducing 1.2507 Super Duplex Steel
1.2507 is the European Werkstoff number for a premium super duplex stainless steel, better known in North America under its equivalent designations UNS S32750 and ASTM/ASME F53. Part of the super duplex family, this alloy pairs a balanced austenitic-ferritic microstructure with high chromium, molybdenum, and nitrogen content to deliver a rare combination of mechanical strength and resistance to localized corrosion. At Acier Alloys, 1.2507 / S32750 / F53 ranks among our most in-demand grades for offshore, marine, and process industry projects where failure is simply not an option.
Metallurgy and Chemical Composition
The strength of this grade lies in its dual-phase structure: roughly equal proportions of austenite and ferrite give it toughness and ductility from the austenite phase, combined with strength and stress-corrosion resistance from the ferrite phase. The table below sets out the standard chemical composition ranges.
Element | Composition (%) |
Chromium (Cr) | 24.0 – 26.0 |
Nickel (Ni) | 6.0 – 8.0 |
Molybdenum (Mo) | 3.0 – 5.0 |
Nitrogen (N) | 0.24 – 0.32 |
Carbon (C) | 0.03 max |
PREN | ≥ 40 |
Mechanical Properties
Property | Typical Value |
Tensile Strength | 800 MPa min |
Yield Strength (0.2% offset) | 550 MPa min |
Elongation | 15% min |
Hardness | ≤ 32 HRC |
Impact Toughness (-46°C) | Excellent, Charpy V-notch qualified |
Key Advantages
◆ Superior Corrosion Resistance — a PREN rating above 40 gives strong resistance to chloride pitting and crevice attack
◆ High Mechanical Strength — close to double the yield strength of common austenitic grades, allowing lighter, thinner sections
◆ Reliable Weldability — a balanced phase structure supports predictable results with standard duplex welding procedures
◆ Extended Service Life — well matched to components exposed to seawater, sour gas, and aggressive process media
Manufacturing Process & Quality Control
Every batch of 1.2507 / S32750 / F53 supplied by Acier Alloys is melted, hot worked, and solution annealed to achieve the correct balance of austenite and ferrite phases, followed by rapid quenching to lock in that microstructure and prevent the formation of embrittling intermetallic phases. Material is verified through chemical analysis, mechanical testing, and where required, ferrite content measurement and corrosion testing such as ASTM G48 pitting resistance evaluation. Each shipment is accompanied by full mill test certification (EN 10204 3.1/3.2), with third-party inspection and positive material identification (PMI) available on request for critical projects.
Common Applications
◆ Offshore oil & gas platforms and subsea equipment
◆ Seawater cooling systems and desalination plants
◆ Chemical and petrochemical processing equipment
◆ Pulp and paper industry components
◆ High-pressure pipe fittings, flanges, and valves (F53)
Available Product Forms
Acier Alloys supplies 1.2507 / S32750 / F53 super duplex steel in round bars, plates, sheets, pipes, tubes, fittings, and forged flanges, cut and finished to specification with complete documentation.
Frequently Asked Questions
Is 1.2507 the same as S32750?
Yes. 1.2507 is the European Werkstoff designation and S32750 is the equivalent UNS number for the same super duplex chemistry; F53 refers to the ASTM/ASME forging and fitting specification for this alloy.
What makes super duplex better than standard duplex for offshore use?
Super duplex grades carry higher chromium, molybdenum, and nitrogen content, giving a PREN above 40 compared with around 35 for standard duplex, which translates into markedly better resistance to pitting and crevice corrosion in high-chloride seawater service.
Can 1.2507 be welded on site?
Yes, with correct procedure. Controlled heat input and matching super duplex filler metal are essential to preserve the phase balance and corrosion performance; our technical team can advise on qualified welding procedures for your project.
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