2507 Super Duplex Stainless Steel: UNS S32750 Properties and Uses

What Is 2507 Super Duplex Stainless Steel?

2507 is a super duplex stainless steel whose microstructure contains both ferrite and austenite, normally in roughly equal proportions and typically 40-60% ferrite by volume. The grade was developed for chloride environments that are too severe for standard duplex stainless steel, and its higher chromium, molybdenum and nitrogen content places it in the super duplex family.

It is specified as UNS S32750 in ASTM A240/A240M for plate, sheet and strip, ASTM A276/A276M and A479/A479M for bar, ASTM A789/A790 for welded and seamless tube, and ASTM A182 for forged flanges, fittings and valves. The European designation is EN 1.4410 (X2CrNiMoN25-7-4) in EN 10088-2, and the same chemistry is adopted in ASME SA-240, SA-182 and SA-789/SA-790. Grade identification for project documentation is best made by the UNS number S32750 or the EN number 1.4410 rather than by trade names.

Chemical Composition of 2507 (UNS S32750)

Element	UNS S32750 (ASTM A240/A240M)
Carbon (C)	0.030% max
Silicon (Si)	0.80% max
Manganese (Mn)	1.20% max
Phosphorus (P)	0.035% max
Sulfur (S)	0.020% max
Chromium (Cr)	24.0-26.0%
Nickel (Ni)	6.0-8.0%
Molybdenum (Mo)	3.0-5.0%
Nitrogen (N)	0.24-0.32%
Copper (Cu)	0.50% max

The high chromium and molybdenum levels build a very stable passive film, while the nitrogen addition strengthens the austenite and further raises pitting resistance. Calculated as Cr + 3.3Mo + 16N, a nominal 2507 heat returns a pitting resistance equivalent number of about 42, and compliant production material generally sits above 40; a standard duplex grade such as 2205 sits in the 34-38 band and 316L in the 24-26 band.

Mechanical Properties and Corrosion Performance

Property	2507 super duplex (S32750)	2205 duplex (S32205)
0.2% proof stress, min	550 MPa	450 MPa
Tensile strength, min	800 MPa	620 MPa
Elongation, min	15%	25%
Pitting resistance equivalent number	Above 40	34-38
Structure	Ferrite plus austenite	Ferrite plus austenite

2507 resists pitting, crevice corrosion and general corrosion in chloride-bearing water far beyond the capability of 2205, and it is highly resistant to chloride stress corrosion cracking because of its two-phase structure. Seawater at elevated temperature, chlorinated cooling water, bleaching liquors and dilute reducing acids are all within its normal working range. Like all duplex grades it is not intended for strongly reducing acids or for service where the passive film cannot be established, and crevice geometry, deposits and poor weld cleaning remain the common causes of field failures.

Typical Applications of 2507 Super Duplex Steel

Desalination: reverse osmosis high-pressure pumps, membranes, brine discharge lines and pretreatment equipment

Subsea and offshore: manifolds, flowlines, jumpers, seawater injection and lift piping, FPSO process systems

Oil and gas: wells and surface equipment covered by NACE MR0175 / ISO 15156, subject to the hardness and temperature limits set in those documents

Chemical and petrochemical process equipment, including reactors, columns and pipework handling chlorides

Heat exchangers, condensers and cooling-water systems in coastal power stations

Flue-gas desulfurisation scrubbers, pulp and paper bleach plants, and firefighting water systems

Fabrication, Welding and Casting Equivalents

Welding is performed by TIG, gas metal arc or submerged arc with matching super duplex filler such as ER2594, under a procedure qualified to ASME IX or EN ISO 15614.

Heat input is normally held to roughly 0.5-1.5 kJ/mm with interpass temperature below about 150 degrees C, so that the weld and heat-affected zone keep a balanced ferrite-austenite structure.

Nitrogen-bearing shielding and backing gas help the weld metal restore austenite; post-weld heat treatment is not required, and solution annealing at about 1020-1100 degrees C with rapid cooling is used only when the specification demands it.

Machining is more demanding than for austenitic grades: the material is stronger, work hardens readily and generates high cutting forces, so rigid set-ups, sharp tooling and generous coolant are needed.

Cast equivalents are covered by ASTM A890/A995 Grade 5A, with UNS number J93404, and by ASME SA-890/SA-995 for pressure-retaining castings. Note that ASME SA-351 applies to austenitic castings and is not the correct specification for super duplex castings.

Continuous service is generally limited to about 250 degrees C, above which sigma-phase precipitation progressively reduces toughness and corrosion resistance.

Frequently Asked Questions About 2507 Super Duplex Steel

Q: Is 2507 super duplex stainless steel magnetic?
Yes. The ferrite phase is ferromagnetic, so 2507 is clearly attracted by a magnet. This is expected for a duplex grade and is not a sign of incorrect material; chemistry and phase balance should be confirmed on the mill certificate.

Q: What is the difference between 2205 and 2507?
2507 contains more chromium, molybdenum and nitrogen, giving a pitting resistance equivalent number above 40 against 34-38 for 2205, and a minimum proof stress of 550 MPa against 450 MPa. 2507 therefore handles hotter, more concentrated chlorides, but it costs more, so 2205 remains the cost-effective choice in milder duty.

Q: What is the equivalent of 2507 stainless steel?
UNS S32750, EN 1.4410 (X2CrNiMoN25-7-4), ASTM A182 F53 for forgings, ASTM A789/A790 for tube and ASTM A890/A995 Grade 5A (UNS J93404) for castings. Castings and forgings must always be ordered to the matching product specification.

Q: Is 2507 suitable for seawater service?
Yes, and it is one of the standard materials for desalination and offshore seawater systems. Performance still depends on good design: avoid stagnant crevices, keep surfaces clean, and respect the temperature limits for the chloride concentration involved.

Q: What welding consumable is used for 2507?
Matching super duplex filler such as ER2594 is used for the root and fill passes, with nitrogen-bearing shielding and backing gas. Consumable selection and heat input limits are set out in the qualified welding procedure.

Q: Does 2507 stainless steel rust?
Under its design conditions it does not rust, and it resists pitting and crevice attack far better than 2205 or 316L. Corrosion can still occur where chlorides concentrate under deposits, in tight crevices or at uncleaned weld heat tint, so pickling and passivation of welds is standard practice.