Super duplex 2507: UNS S32750 and EN 1.4410

2507 is one of the best-known super duplex stainless steels used in highly corrosive chloride-containing service.

The common designation map is:

• UNS S32750;
• EN 1.4410;
• X2CrNiMoN25-7-4;
• commercial shorthand 2507.

Major producers list these designations together for the same grade family, but—as with any cross-standard comparison—the product standard and form still matter.

Why is it called super duplex?

2507 retains the mixed austenitic-ferritic structure of duplex stainless steel but uses a higher alloy content than standard 2205.

Typical nominal chemistry is around:

• 25% chromium;
• 7% nickel;
• 4% molybdenum;
• about 0.3% nitrogen.

That combination gives high mechanical strength together with excellent resistance to pitting, crevice corrosion and chloride stress-corrosion cracking.

Alleima describes SAF 2507 as a high-alloy super-duplex grade for highly corrosive conditions, while Outokumpu positions 1.4410/S32750 above 2205 in both corrosion resistance and strength.

1.4410 and S32750: common cross-designation, not a shortcut

For many commercial products, 1.4410 and S32750 are the normal EN/UNS designations for the same 2507 family.

But a PO should still identify the governing product standard and product form. Plate, bar, seamless pipe, welded pipe, forgings and fittings can sit under different standards even when the base alloy designation is the same.

So the correct procurement question is not only:

Is 1.4410 equivalent to S32750?

It is:

Does this specific product, in this form and condition, comply with the standard and supplementary requirements in the purchase specification?

PREN is one reason 2507 is used in chloride service

Using typical producer chemistry, 2507 has a PRE value in the low-40s. Outokumpu publishes a typical PRE of about 43 for its 2507 grade.

This is substantially above standard 316L and above 2205.

But PREN is only a composition-based screening tool. It does not replace actual corrosion testing or service-specific material selection.

See PREN explained.

Typical applications

Producer literature commonly identifies applications such as:

• seawater and desalination equipment;
• oil and gas tubulars, valves, fittings and flanges;
• chemical-process equipment;
• scrubbers;
• deep-sea/offshore systems.

Actual suitability still depends on temperature, chloride level, pressure, H2S/CO2 exposure, fabrication and design.

Heat treatment and phase balance are critical

The “super” alloy content does not protect a poorly processed component from metallurgical damage.

Duplex and super-duplex stainless steels are sensitive to detrimental phase precipitation when exposed to unsuitable temperature/time cycles. Correct solution annealing and rapid cooling are therefore central to the final properties.

See Solution annealing of stainless and duplex steel.

Welding requires discipline

2507 is weldable, but the welding procedure has to control heat input and cooling so that the weld and heat-affected zone retain acceptable phase balance and corrosion properties.

Project specifications may also impose:

• ferrite measurement;
• corrosion testing;
• impact testing;
• PMI;
• hardness limits;
• additional NDT;
• qualification to NORSOK or other offshore requirements.

Do not assume those requirements from the grade name alone.

Sour-service acceptance is separate

Alleima lists S32750/1.4410 products that can comply with ISO 15156/NACE MR0175 under defined product and service conditions.

That is not the same as saying every 2507 heat is universally “NACE compliant.”

See NACE MR0175 / ISO 15156 applicability.

2507 vs 2205

Compared with standard 2205, 2507 generally offers:

• higher localized-corrosion resistance;
• higher alloy content;
• high strength;
• higher material cost;
• tighter fabrication/welding control in demanding applications.

That does not make 2507 a routine substitute for 2205. Design, welding, availability and code requirements all need checking.

See Duplex 2205.

MetalMate takeaway

2507 / S32750 / 1.4410 is a high-alloy super-duplex family for demanding chloride service, but the grade name alone is not a complete specification. Product standard, heat treatment, phase balance, welding, corrosion tests, sour-service limits and project requirements still control acceptance.

Related Knowledge

• Duplex 2205
• PREN explained
• Solution annealing
• NACE MR0175 / ISO 15156 applicability

References

• Alleima, SAF 2507 — UNS S32750, EN 1.4410: https://www.alleima.com/en/technical-center/material-datasheets/tube-and-pipe-seamless/saf-2507/
• Alleima, SAF 2507 bar — product standards and material designations: https://www.alleima.com/en/technical-center/material-datasheets/bar-and-hollow-bar/bar/saf-2507/
• Outokumpu, Forta duplex datasheet — 2507 designation and typical PRE: https://www.outokumpu.com/de-de/industries/-/media/files/products/forta/outokumpu-forta-range-datasheet.pdf