Zeron 100 / F55 super duplex stainless steel: standards, composition and properties
UNS S32760, 1.4501
F55 is the ASTM A182 forging of super duplex UNS S32760, known by the trade name Zeron 100: austenitic-ferritic stainless with 24–26 % Cr, 3–4 % Mo, 0.20–0.30 % N and additions of copper and tungsten (0.5–1.0 % each), with PREN ≥ 40 required by purchase specifications (NORSOK M-630, manufacturer) and a yield strength of 550 MPa. In EN it is 1.4501; as a casting, grade 6A (CD3MWCuN). F53 (S32750, 2507) is another super duplex, without Cu and W, and has its own page.
One composition, several standards
The name changes with the product form. When specifying, cite the standard, grade and class.
| Form | ASTM/ASME | Grade/class | EN | ABNT/others |
|---|---|---|---|---|
| Forging and flange (B16.5) | A182 / SA-182 | F55 (S32760) | EN 10250-4 / EN 10222-5: 1.4501* | NORSOK M-630 MDS D54* |
| Bar | A479 / SA-479; A276 | S32760 | EN 10088-3 / EN 10272: 1.4501 | NORSOK MDS D57* |
| Plate, coil, strip | A240 / SA-240 | S32760 | EN 10088-2 / EN 10028-7: 1.4501 | NORSOK MDS D55* |
| Seamless pipe (line) | A790 / SA-790 | S32760 | EN 10216-5: 1.4501 | NORSOK MDS D51* |
| Heat exchanger tube | A789 / SA-789 | S32760 | EN 10216-5 | NORSOK MDS D58* |
| Welded pipe | A790 (welded); A928 (fusion welded, classes 1–5) | S32760 | EN 10217-7: 1.4501* | NORSOK MDS D52* |
| Fittings (butt-weld) | A815 / SA-815 | WPS32760 (classes WP-S, WP-W, WP-WX, CR)* | EN 10253-4* | NORSOK MDS D53* |
| Casting | A890 / A995 (pressure) | 6A = CD3MWCuN (J93380) | — | NORSOK MDS D56* |
| Welding consumable | AWS A5.9 / A5.4 / A5.22 | ER2594, E2594, E2594T; Zeron 100X type | EN ISO 14343: 25 9 4 N L | Zeron 100X (with W) matches S32760 |
| Washer/bolt, sour service | A182 / A479 / A276 + NACE | S32760 | — | NACE MR0175/ISO 15156-3; NACE MR0103; API 6A* |
NBR 5601 has no super duplex grade (not confirmed*); specify by UNS + ASTM/EN product standard. The NORSOK MDS numbers come from an old revision list and may have changed in current editions of M-630*.
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7222.30.00* | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Seamless pipe | 7304.41.90 | 7304.41 | 7304.41.6045 | 7304 41 00 |
| Welded pipe | 7306.40.00 | 7306.40 | 7306.40.5085 | 7306 40 80 |
| Flange and fitting | 7307.21.00 | 7307.21 | 7307.21.5000 | 7307 21 00 |
Class in Dustre's NCM table (INF 004): stainless steel.
*: US and EU codes are for reference; confirm with your customs broker. NCM codes with * were checked by Dustre against the current NCM, outside the INF 004 table. HS = first 6 digits of the NCM.
Chemical composition by standard (%)
The ranges of each standard side by side, to see where they differ.
| Standard / grade | C max | Mn max | P max | S max | Si max | Cr | Ni | Mo | N | Others |
|---|---|---|---|---|---|---|---|---|---|---|
| A240/A182 F55 (S32760) | 0.030 | 1.00 | 0.030 | 0.010 | 1.00 | 24.0–26.0 | 6.0–8.0 | 3.0–4.0 | 0.20–0.30 | Cu 0.50–1.00; W 0.50–1.00*; PREN ≥ 40 |
| A890/A995 6A (CD3MWCuN) | 0.03 | 1.00 | 0.030 | 0.025 | 1.00 | 24.0–26.0 | 6.5–8.5 | 3.0–4.0 | 0.20–0.30 | Cu 0.5–1.0; W 0.5–1.0 |
Mechanical properties by standard
Minimum values at room temperature, in the stated delivery condition.
| Standard and condition | YS min | UTS | Elong. | RA | Hardness |
|---|---|---|---|---|---|
| FORGINGS | |||||
| A182 F55, solution annealed | 550 MPa (80 ksi) | 750–895 MPa (109–130 ksi) | 25 % | 45 % | not specified* |
| ROLLED | |||||
| A240 S32760, plate | 550 MPa | 750–895 MPa | 25 % | — | 270 HBW max* (sources differ) |
| A479 / A276 bar S32760 | 550 MPa | 750–895 MPa* | 25 %* | * | 310 HBW max (Langley) |
| PIPE, FITTINGS AND CASTINGS | |||||
| A790 / A789 S32760 | 550 MPa | 750–895 MPa | 25 % | — | 310 HBW / 32 HRC max* |
| A815 WPS32760 | per starting material* | 750 MPa min* | 25 %* | — | * |
| A890 / A995 6A (CD3MWCuN) | 450 MPa (65 ksi) | 690 MPa min (100 ksi) | 25 % | — | — |
F55 (S32760) vs. F53 (S32750): Zeron 100 vs. 2507
Both alloys share the same 25Cr-7Ni base and the same 550 MPa YS. S32750 (2507) uses more Mo (up to 5 %) and N (0.24–0.32 %) and has no W; it has a higher minimum UTS (800 MPa) and lower elongation (15 %). S32760 (Zeron 100) adds Cu and W (0.5–1.0 % each), has Mo max 4 % and carries PREN ≥ 40 as a requirement in the composition itself; UTS sits at 750–895 MPa with 25 % elongation. In practice they are interchangeable in many MDS (NORSOK lists both on the same data sheet), but they are not the same grade: check which UNS the specification requires, and use a compatible consumable (ER2594 or Zeron 100X type).
Heat treatments required by the standards
| Standard | Delivery condition | Temperature |
|---|---|---|
| A182 F55 / A240 S32760 | Solution annealed and liquid cooled | 1100–1140 °C (2010–2085 °F) |
| A790 S32760 | Solution annealed and rapidly cooled | 1070–1140 °C (1960–2085 °F) (Total Materia)* |
| A890 / A995 6A | Solution annealed and water quenched | 1100 °C min* |
Variants in the family
| Variant | Standards | Difference | YS / UTS |
|---|---|---|---|
| S32750 (2507, SAF 2507, 1.4410) | A182 F53, A240, A479, A790, A789, A815, A928 | Mo 3–5 %, N 0.24–0.32 %, no W/Cu | 550 / 800 MPa |
| S32760 (Zeron 100, 1.4501) | A182 F55, A240, A276, A479, A790, A789, A815, A928 | Cu 0.5–1 % and W 0.5–1 %; PREN ≥ 40 required | 550 / 750–895 MPa |
| S32550 (Ferralium 255, 1.4507) | A182 F61, A240, A479, A276, A790 | Cu 1.5–2.5 %, lower Ni and N; minimum PREN may be < 40 | 550 / 750–760 MPa |
| S32520 (UR 52N+, Ferralium 255-SD50, 1.4507) | A182 F59, A240, A789, A790, A928 | Cu 0.5–3 %*, N up to 0.35 %; PREN > 40 | 550 / 770 MPa |
| CE3MN (5A, J93404) | A890 / A995 5A | Casting equivalent to 2507; Mo 4–5 % | 515 / 690 MPa |
| CD3MWCuN (6A, J93380) | A890 / A995 6A | Casting equivalent to Zeron 100 (Cu + W) | 450 / 690 MPa |
Corrosion, PREN and temperature
- PREN: Cr + 3.3 (Mo + 0.5 W) + 16 N. For S32760, NORSOK M-630, NACE MR0175 and the manufacturer specification (Zeron 100) require PREN ≥ 40; with the ASTM minimum contents the calculation gives ≈ 38, which is why the PREN is checked on the heat.
- Pitting and crevice corrosion: the usual test is ASTM G48 method A at 50 °C for 24 h, no pitting (22Cr: 40 °C). Typical CPT well above that of 22Cr duplex and 316L.
- Intermetallic phases (sigma, chi): precipitate quickly between ~600 and 1000 °C; the critical formation range goes from ~320 to 955 °C (A923). Slow cooling after solution annealing or welding with high heat input collapses toughness and pitting resistance.
- 475 °C embrittlement: the ferrite hardens with long exposure between ~300 and 525 °C, which limits continuous use to about 250 °C (ASME usually accepts up to ~315 °C)*.
- Low temperature: toughness proven by Charpy at −46 °C (NORSOK: 45 J average / 35 J individual) or −40 °C (A923 method B).
- NACE MR0175/ISO 15156-3: solution-annealed super duplex is accepted with pH2S, chloride and temperature limits that depend on the PREN range (40–45); NACE MR0103 limits super duplex to 32 HRC; NORSOK purchases usually require 28 HRC / 270 HB*.
Tests required for super duplex (ASTM A923, G48, NORSOK)
- ASTM A923: detects intermetallic phases: method A (NaOH etch, acceptance only), method B (Charpy) and method C (ferric chloride).
- A923 method C: S32750, S32550 and S32520 tested at 40 °C, maximum loss 10 mdd. S32760 did not appear in the 2008 edition; confirm in the current edition*.
- A923 method B: S32750 at −40 °C with energy agreed between purchaser and supplier; casting J93404 (5A) at −46 °C, 54 J min.
- ASTM G48 A at 50 °C / 24 h: no pitting and mass loss ≤ 4 g/m² is the usual NORSOK M-630/M-650 criterion*.
- Ferrite (ASTM E562): 35–55 % in base metal; in the weld, 30–70 % (NORSOK M-601)*.
- NORSOK M-650: manufacturer qualification (forge, foundry, mill) for 25Cr; requires a qualification piece with the tests above.
Welding
| Item | Usual practice |
|---|---|
| Consumable | ER2594 (AWS A5.9), E2594 (A5.4) or a Zeron 100X type consumable (with W); EN ISO 14343 25 9 4 N L |
| Gas | Ar + 2 % N2 (shielding) and Ar or Ar + N2 for purging, to avoid nitrogen loss at the root |
| Preheat | Not used |
| Interpass | Max 100–150 °C (100 °C common for 25Cr)* |
| Heat input | Low and controlled, ~0.5–1.5 kJ/mm, to balance ferrite without precipitating sigma* |
| PWHT | No stress relief is done; if needed, only full solution annealing with water quenching |
| Control | Ferrite and hardness in qualification (350 HV10 max usual), G48 and Charpy per NORSOK M-601/M-650* |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
International equivalents
| System | Designation |
|---|---|
| UNS | S32760; equivalent casting J93380 (6A) |
| ASTM forging | F55 (S32760) |
| EN / W.Nr. | 1.4501 X2CrNiMoCuWN25-7-4 |
| Trade names | Zeron 100 (Rolled Alloys) |
| JIS | No direct JIS equivalent* |
| GB | No direct GB equivalent* |
| ABNT / SAE / AISI | No AISI/SAE designation; NBR 5601 has no corresponding grade* |
Equivalence is by approximate composition; minimum properties, tests and heat treatment change from standard to standard.
Typical applications
| Form or industry | Where it is used |
|---|---|
| Offshore oil and gas | Seawater lines, injection, manifolds, umbilicals and firewater systems (NORSOK) |
| Subsea | Connectors, F55 flanges, hubs and valves in contact with seawater |
| Desalination (SWRO) | High-pressure pipes and vessels with brine |
| Chemicals and pulp | Exchangers, pumps and equipment with chlorides and acids |
| Pumps and valves | Cast 6A bodies, shafts and internals in A479 bar |
| Fastening | Super duplex studs and nuts for chloride and H2S service |
Frequently asked questions
Are F53 and F55 the same thing?
No. F53 is S32750 (2507) and F55 is S32760 (Zeron 100, with Cu and W). They have the same 550 MPa YS and 25Cr base, but composition, UTS and heat treatment differ.
What is the minimum PREN of F55?
PREN ≥ 40, required by purchase specifications (NORSOK M-630, NACE MR0175 and the manufacturer) and checked on the heat analysis: Cr + 3.3 (Mo + 0.5 W) + 16 N. With the ASTM minimum contents alone the calculation would give ≈ 38.
What is the difference between duplex and super duplex?
22Cr duplex (S31803/S32205, F51/F60) has PREN ~34 and YS 450 MPa. 25Cr super duplex has PREN ≥ 40 and YS 550 MPa, for seawater and more aggressive chlorides.
Which casting corresponds to Zeron 100?
ASTM A890/A995 grade 6A (CD3MWCuN, J93380), with Cu and W like S32760.
