Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Super Duplex 2507 Chemical Composition (UNS S32750)
Super Duplex 2507 chemistry is defined by the UNS S32750 window, registered in parallel as EN 10088-3 grade 1.4410 (X2CrNiMoN25-7-4). Nominal composition is 25 Cr, 7 Ni, 3.5 to 4 Mo, 0.24 to 0.32 N, with copper restricted to 0.50 percent maximum as a residual, not an intentional addition, and no intentional tungsten. PREN, calculated as Cr + 3.3 times Mo + 16 times N, sits at 41 or higher, qualifying the alloy as super duplex per NORSOK M-630. The chemistry below is harmonised across ASTM A479 (bar and shapes), ASTM A182 grade F53 (forgings and flanges), ASTM A789 (tube), ASTM A790 (pipe), ASTM A815 (fittings, designation WP-S32750), ASTM A1082 (high-strength bolting), and EN 10088-3 (1.4410).
ASTM A479 / A182 F53 Chemistry Window (UNS S32750)
The ASTM A479 chemistry window is the master reference for super duplex 2507 bar and shapes; ASTM A182 F53 mirrors it for forgings and flanges. Heat analysis is performed by the steel mill on each cast and reported on the EN 10204 type 3.1 mill test certificate.
| Element | Min, % | Max, % | Typical Mill Heat, % |
|---|---|---|---|
| Carbon (C) | (no min) | 0.030 | 0.020 |
| Manganese (Mn) | (no min) | 1.20 | 0.80 |
| Phosphorus (P) | (no min) | 0.035 | 0.025 |
| Sulfur (S) | (no min) | 0.020 | 0.001 |
| Silicon (Si) | (no min) | 0.80 | 0.40 |
| Chromium (Cr) | 24.0 | 26.0 | 25.0 |
| Nickel (Ni) | 6.0 | 8.0 | 7.0 |
| Molybdenum (Mo) | 3.0 | 5.0 | 3.8 |
| Nitrogen (N) | 0.24 | 0.32 | 0.28 |
| Copper (Cu) | (no min) | 0.50 max, residual, not intentional | 0.20 |
| Tungsten (W) | No intentional addition (key distinguisher from UNS S32760 Zeron 100) | ||
EN 10088-3 Grade 1.4410 (X2CrNiMoN25-7-4) Chemistry Window
European EN 10088-3 lists the same chemistry under Werkstoff 1.4410, name X2CrNiMoN25-7-4. The numeric ranges are essentially identical to ASTM A479. A few elements (sulfur, silicon) are slightly tighter in EN; mill certificates issued in Europe routinely cite both UNS S32750 and 1.4410 designations.
| Element | EN 10088-3 Min, % | EN 10088-3 Max, % |
|---|---|---|
| Carbon (C) | (no min) | 0.030 |
| Manganese (Mn) | (no min) | 1.20 |
| Phosphorus (P) | (no min) | 0.035 |
| Sulfur (S) | (no min) | 0.015 |
| Silicon (Si) | (no min) | 1.00 |
| Chromium (Cr) | 24.0 | 26.0 |
| Nickel (Ni) | 6.0 | 8.0 |
| Molybdenum (Mo) | 3.0 | 5.0 |
| Nitrogen (N) | 0.24 | 0.35 |
| Copper (Cu) | (no min) | 0.50 |
PREN Calculation for Super Duplex 2507
PREN (Pitting Resistance Equivalent Number) ranks alloys by their predicted resistance to chloride-induced pitting. The standard formula is given below; super duplex 2507 typically lands in the 41 to 43 band, comfortably above the NORSOK M-630 threshold of 40 for super duplex classification. A dedicated explainer with worked examples is on the PREN page.
PREN = %Cr + 3.3 x %Mo + 16 x %N
| Heat | Cr, % | Mo, % | N, % | PREN |
|---|---|---|---|---|
| Minimum spec point | 24.0 | 3.0 | 0.24 | 37.7 |
| Typical mill heat | 25.0 | 3.8 | 0.28 | 42.0 |
| Maximum spec point | 26.0 | 5.0 | 0.32 | 47.6 |
The minimum-spec PREN of 37.7 is below the 40 threshold, which is why mills target the centre of the chemistry window rather than the corners. Industry practice is to size chromium, molybdenum, and nitrogen so that PREN is at least 41 on every heat, regardless of where each individual element falls within its allowed range.
Why No Intentional Copper or Tungsten
The defining metallurgical signature of UNS S32750 is the absence of intentional copper and tungsten. Both elements are deliberate additions in sister super duplex grades, and confusion between the alloys is the single most common engineering error in this family.
- Zeron 100 (UNS S32760) contains nominal 0.5 to 1.0 percent copper and 0.5 to 1.0 percent tungsten. Both elements raise pitting resistance and slightly improve resistance to dilute reducing acids. Forging spec is ASTM A182 F55, not F53.
- Ferralium 255 (UNS S32550) contains 1.5 to 2.5 percent copper for resistance to sulfuric acid service. Forging spec is ASTM A182 F61.
- Super Duplex 2507 (UNS S32750) contains neither. The PREN target is met through chromium, molybdenum, and nitrogen alone. Forging spec is ASTM A182 F53.
Project specifications routinely call out the alloy by UNS number. Substituting S32760 or S32550 where the spec says S32750 is non-compliant, even if the substitute alloy has equal or higher PREN.
ASTM A1082 Bolting Chemistry (UNS S32750)
For high-strength bolting per ASTM A1082, the UNS S32750 chemistry row matches the bar specification. The standard groups duplex grades together with chemistry, solution-treatment temperature, and mechanical-property requirements in dedicated tables. This page summarises the bolting-relevant differences.
| Parameter | ASTM A1082 Requirement |
|---|---|
| Solution treatment, deg C | 1025 to 1125 |
| Tensile strength, min | 800 MPa (116 ksi) |
| Yield strength, min | 550 MPa (80 ksi) |
| Elongation, min | 15 percent |
| Hardness, max | 33 HRC (lower of 28 HRC applies for NACE MR0175 sour service) |
Related Super Duplex 2507 References
- UNS S32750 reference page
- Super Duplex 2507 mechanical properties
- Super Duplex 2507 heat treatment
- Ferrite content (NORSOK M-630)
- ASTM A479 super duplex 2507
- ASTM A182 F53 forgings
- NORSOK M-630 super duplex MDS
- Super duplex 2507 fasteners and pipe
Super Duplex 2507 Chemistry FAQ
What is the chemical composition of Super Duplex 2507?
Nominal composition is 25 percent chromium, 7 percent nickel, 3.5 to 4 percent molybdenum, and 0.24 to 0.32 percent nitrogen. Carbon is restricted to 0.030 percent maximum to suppress carbide precipitation. Copper sits at 0.50 percent maximum as a residual, not an intentional addition. Tungsten is not intentionally added. Full element-by-element windows for ASTM A479 and EN 10088-3 are tabled above.
What is the PREN of UNS S32750?
PREN of a typical mill heat is 41 to 43, calculated as Cr + 3.3 times Mo + 16 times N. NORSOK M-630 requires PREN of 40 or above for super duplex classification. Mills target chemistry at the centre of the window rather than at the spec corners so that PREN is comfortably above 40 on every cast.
Does Super Duplex 2507 contain copper?
Copper is restricted to 0.50 percent maximum as a residual, not as an intentional addition. Typical mill heats run at 0.20 percent or below. By contrast, Zeron 100 (S32760) intentionally adds 0.5 to 1.0 percent copper, and Ferralium 255 (S32550) adds 1.5 to 2.5 percent. The presence of intentional copper changes the alloy and the applicable forging specification.
Is UNS S32750 the same chemistry as 1.4410?
Yes within negligible tolerance. UNS S32750 (American) and EN 10088-3 grade 1.4410 / X2CrNiMoN25-7-4 (European) refer to the same super duplex stainless steel. EN 10088-3 lists slightly tighter sulfur (0.015 max vs 0.020 max) and slightly wider silicon (1.00 max vs 0.80 max), but the principal alloying elements (Cr, Ni, Mo, N) are identical.
Why is the carbon content held below 0.030 percent?
Low carbon (0.030 percent maximum) suppresses chromium-carbide precipitation at grain boundaries during slow cooling through the sensitisation range. Carbide precipitation depletes chromium locally and creates intergranular corrosion sites. The L (low-carbon) chemistry of UNS S32750 is the default; there is no high-carbon variant.
Is the chemistry the same in bar, plate, pipe, and forgings?
Yes. The UNS S32750 chemistry window is identical across ASTM A479 (bar), A789 (tube), A790 (pipe), A815 (fittings), A276 (shapes), A182 F53 (forgings, flanges), and A1082 (bolting). Mechanical-property requirements vary slightly between product forms, but chemistry does not.
What is the difference between UNS S32750 and UNS S32760 chemistry?
Both are super duplex stainless steels with PREN above 40. The chemistry difference is copper and tungsten: UNS S32760 (Zeron 100) intentionally adds 0.5 to 1.0 percent of each, UNS S32750 (Super Duplex 2507) adds neither. Forging specs differ accordingly: ASTM A182 F53 for S32750, F55 for S32760.
Which standards govern Super Duplex 2507 chemistry?
The principal references are ASTM A479 (bar), ASTM A182 grade F53 (forgings), ASTM A1082 (bolting), EN 10088-3 grade 1.4410, and NORSOK M-630 (which incorporates the ASTM A479 window into the Norwegian Continental Shelf material data sheets D55, D57). Mill heat analysis is reported on EN 10204 type 3.1 certificates as standard, with type 3.2 third-party-witnessed certificates available on request.
Satisfaction Survey
