1.4410 (X2CrNiMoN25-7-4) Material Equivalent: Super Duplex 2507
What EN 1.4410 Is
EN 1.4410, designated X2CrNiMoN25-7-4, is a super duplex stainless steel defined in the EN 10088 series. It carries about 25 % chromium, 7 % nickel, 4 % molybdenum and a substantial nitrogen addition, and it is known internationally by its UNS number S32750 and the trade name 2507. The grade combines very high mechanical strength with a pitting resistance equivalent number of 40 or more, which is why it is specified for offshore, desalination and aggressive chemical duty.
It should not be confused with the standard duplex grade 2205. The extra chromium, molybdenum and nitrogen raise both the corrosion resistance and the price, and they also narrow the processing window during welding and hot forming.
Cross-Standard Equivalents
| System | Designation |
|---|---|
| EN 10088-2 and EN 10088-3 | X2CrNiMoN25-7-4 (1.4410) |
| UNS (United States) | S32750 |
| ASTM product standards | A240 (plate, sheet, strip), A276 and A479 (bar), A790 and A928 (pipe), A182 F53 (forgings and flanges) |
| Common trade name | 2507 super duplex |
| China | 022Cr25Ni7Mo4N, historically written 00Cr25Ni7Mo4N (GB/T 20878) |
| Offshore material data sheets | NORSOK M-630 data sheet D57 class |
Ordering by trade name alone is risky because the same name is applied to bar, plate and pipe produced to different product standards with different acceptance tests. The purchase order should name the UNS number, the product standard and the required test schedule.
Chemical Composition
| Element, % | Requirement | Function |
|---|---|---|
| C | 0.030 max | Keeps chromium in solution and limits carbide precipitation |
| Cr | 24.0-26.0 | Passive film stability and pitting resistance |
| Ni | 6.0-8.0 | Balances the austenite to ferrite ratio |
| Mo | 3.0-5.0 | Resistance to pitting and crevice corrosion |
| N | 0.24-0.32 | Strength and localised corrosion resistance |
| Mn | 1.20 max | Deoxidising, kept low to protect the ferrite balance |
| PREN | 40 minimum | Computed as Cr + 3.3 Mo + 16 N |
The nitrogen range is the element most often misunderstood. It must be high enough to restore austenite after rapid cooling and to raise pitting resistance, but not so high that porosity appears in weld metal. Consumables for this grade are therefore nitrogen-enriched and matched to the base metal rather than taken from a generic duplex stock.
Mechanical Properties by Product Form
| Product form | 0.2 % proof strength | Tensile strength | Elongation |
|---|---|---|---|
| Bar | 550 MPa minimum | 795 MPa minimum (ASTM A276 / A479) | 15 % minimum |
| Plate and sheet | 550 MPa minimum | 795 MPa minimum (ASTM A240) | 15 % minimum |
| EN 10088-3, bar and plate | 550 MPa minimum | 750-1000 MPa depending on form | 25 % minimum |
The two systems do not ask for the same thing, which is a common source of dispute. The ASTM route sets a higher minimum tensile strength with a lower elongation floor, while the EN route accepts a wider tensile band with a higher elongation requirement. When a project calls for both, the specification should state which certificate governs. Hardness is normally capped around 310 HBW, and Charpy-V impact testing at minus 46 degrees C is routinely specified for offshore and cold-climate applications, with the energy level set by the project specification rather than by the grade standard.
Density is about 7.8 g/cm3 and the elastic modulus is close to 200 GPa, similar enough to carbon steel that mixed-material assemblies behave predictably. The high proof strength allows wall thickness reductions of 40 to 50 % against an austenitic Type 316L design, which frequently decides the material selection on its own.
Corrosion and Service Limits
A pitting resistance equivalent number of 40 or above places the grade well beyond 2205 and far beyond 316L. In practice it resists pitting, crevice corrosion and chloride stress corrosion cracking in sea water, brine, and chloride-bearing process streams, and it is widely used for heat exchangers, seawater piping, pumps and valves, subsea manifolds and desalination plant equipment.
Service limits nonetheless apply. Continuous service temperature is normally held below about 250 degrees C for long-term exposure because intermetallic phases form at higher temperature and reduce toughness. The grade is also susceptible to hydrogen-induced cracking in sour service unless hardness, chemistry and heat treatment are controlled to the requirements of the applicable sour service standard, and it is not intended for use in strong reducing acids.
Welding and Fabrication
Super duplex welding is a controlled process rather than a routine one. Heat input is limited, interpass temperature is capped, typically at 150 degrees C, and the weld metal ferrite content is measured and controlled so that the balance of austenite and ferrite stays within the qualified range. A slight nitrogen addition to the shielding gas is common practice on the root to help austenite re-form after the fast cooling of a thin-wall joint.
Fabrication also demands clean, dedicated tooling. A super duplex surface contaminated with carbon steel dust or chloride-bearing marking fluid will pit within weeks even though the base metal is sound. Pickling and passivation after fabrication, followed by a documented rinse and a ferroxyl or similar free-iron check on critical items, is normal good practice.
Frequently Asked Questions
Q: What is the ASTM equivalent of 1.4410?
A: UNS S32750, covered by ASTM A240 for plate, A276 and A479 for bar, A790 and A928 for pipe and A182 F53 for forgings and flanges.
Q: Is 2507 the same as 1.4410?
A: Yes, 2507 is the trade name for the grade whose EN designation is X2CrNiMoN25-7-4, or 1.4410, and whose UNS number is S32750.
Q: How does 1.4410 differ from 2205 duplex?
A: Higher chromium, molybdenum and nitrogen push the pitting resistance equivalent above 40 instead of about 35, and the proof strength is roughly 550 MPa against 450 MPa. The processing window is narrower and the price is higher.
Q: Why is the ferrite content of a weld checked?
A: The corrosion resistance and toughness of a duplex weld depend on keeping the austenite to ferrite balance close to 50-50. Too much ferrite, caused by excessive heat input or slow cooling, embrittles the weld and lowers its resistance to chloride attack.
Q: Can the grade be machined and formed normally?
A: It machines at about twice the resistance of 316L and work hardens quickly, so low surface speeds, rigid tooling and generous coolant are needed. Cold forming is possible but the high proof strength makes springback significant.
Q: What certification should be requested?
A: An EN 10204 3.1 or 3.2 inspection certificate giving heat number, chemical analysis including nitrogen, mechanical results per product form, hardness and, where specified, ferrite content and impact results.
