- Same corrosion class: 1.4501 (S32760) and 2507 (S32750) are both super duplex, PREN typically 41–43 — effectively equal in chloride and seawater pitting.
- 1.4501 adds tungsten + copper: copper improves resistance in sulfuric and phosphoric (reducing) acids; tungsten holds strength above ~250 °C.
- 2507 adds value on strength & price: marginally higher guaranteed strength, wider availability and lower cost.
- Decision rule: reducing-acid or high-temperature duty → 1.4501; chloride / seawater on a budget → 2507; otherwise let cost and lead time decide.
- Naming: 1.4501 = S32760 = X2CrNiMoCuWN25-7-4 = Zeron 100; 2507 = S32750 = EN 1.4410 = X2CrNiMoN25-7-4.
Same corrosion class, different specialty
1.4501 (S32760) and 2507 (S32750) are both super duplex stainless steels with a 25Cr–7Ni–4Mo backbone and near-identical chloride pitting resistance. Treating them as interchangeable in seawater is defensible.
They diverge on two deliberate additions in 1.4501: tungsten and copper. Copper buys real corrosion margin in sulfuric and phosphoric acid; tungsten holds strength above 250 °C. 2507 answers with slightly higher typical strength, wider availability, and lower price.
Rule of thumb: reducing-acid or high-temperature duty → 1.4501. Chloride and seawater duty on a budget → 2507. Everything in between → either will serve, so let cost and lead time decide.
Meet the two grades
Both alloys sit in the super duplex family — a roughly 50/50 mix of austenite and ferrite, with enough chromium, molybdenum and nitrogen to push the pitting index past the super-duplex threshold. The confusing part is the naming, so let us clear it first.
2507 is a commercial name. Its formal identity is UNS S32750, EN number 1.4410, chemical designation X2CrNiMoN25-7-4. It carries no intentional tungsten and only residual copper.
1.4501 is the EN number for UNS S32760 — chemical designation X2CrNiMoCuWN25-7-4, also supplied under the registered trade name Zeron® 100 (a trademark of Rolled Alloys, Inc., used here for identification only). The extra letters Cu and W in that designation are the whole story: copper and tungsten, added on purpose.
So the two grades share a skeleton and differ by two elements. Everything below flows from that.
Chemistry, element by element
Line up the two composition envelopes and most elements overlap almost completely. The meaningful differences are in the last three rows.
| Element (wt%) | 1.4501 / S32760 | 2507 / S32750 | What it changes |
|---|---|---|---|
| Chromium | 24.0–26.0 | 24.0–26.0 | Passive film former — equal |
| Nickel | 6.0–8.0 | 6.0–8.0 | Austenite stabiliser — equal |
| Molybdenum | 3.0–4.0 | 3.0–5.0 | 2507 has more headroom |
| Nitrogen | 0.20–0.30 | 0.24–0.32 | 2507 slightly richer |
| Carbon (max) | 0.030 | 0.030 | Ultra-low — equal |
| Tungsten | 0.50–1.00 | — | 1.4501 only high-temp strength |
| Copper | 0.50–1.00 | ≤0.50 | 1.4501 acid resistance |
Why copper is the headline
Copper does something molybdenum and chromium cannot: it stabilises the passive film in reducing acids, where oxygen is scarce and ordinary stainless passivity struggles. In dilute-to-intermediate sulfuric acid — the exact window where standard duplex actively corrodes — a copper-enriched surface layer slows the dissolution reaction. That is the single clearest reason to reach for 1.4501 over 2507, and it is baked into the chemistry, not the marketing.
What tungsten adds
Tungsten behaves like a heavier cousin of molybdenum. It contributes to pitting resistance (at roughly half molybdenum's weighting) and, more usefully, props up the ferrite phase's strength at elevated temperature. Where a component runs continuously above about 250 °C, the tungsten in 1.4501 keeps a measurable strength edge that 2507 gives up.
PREN and pitting: closer than the sales sheets suggest
PREN — the Pitting Resistance Equivalent Number — is the usual first number engineers compare. For tungsten-bearing grades the correct form is:
PREN = %Cr + 3.3 × (%Mo + 0.5×%W) + 16 × %N
Run both grades at nominal chemistry and they land within a point or two of each other, typically in the 41–43 band. 1.4501 earns its PREN partly through tungsten; 2507 earns a comparable number through its higher molybdenum and nitrogen ceiling. Both are guaranteed to clear PREN ≥ 40, the super-duplex line.
The honest engineering takeaway: in chloride and seawater pitting, the two grades are effectively equivalent. Any datasheet that presents a one-point PREN gap as a decisive advantage is over-reading a number that varies more with heat chemistry and processing than with the grade name. What actually decides pitting performance in the field is a clean, homogenised microstructure — which is a forging-and-heat-treatment question, not a grade question.
A number that misleads
PREN is a bulk-chemistry calculation. In a poorly processed part, local molybdenum-depleted zones can sit 5–8 points below the calculated value. A correctly forged and solution-annealed S32750 will out-corrode a segregated, badly quenched S32760 every time. Grade choice sets the ceiling; processing decides whether you reach it.
Mechanical properties
Both grades roughly double the yield strength of 316L austenitic stainless, which is the reason super duplex lets designers thin down walls and shed weight. Between the two, 2507 usually shows a slight edge in minimum guaranteed strength thanks to its higher nitrogen ceiling; the practical gap is small.
| Property (solution annealed) | 1.4501 / S32760 | 2507 / S32750 | Edge |
|---|---|---|---|
| Yield strength Rp0.2 | ≥530 MPa | ≥550 MPa | 2507 |
| Tensile strength Rm | 730–930 MPa | 800–1000 MPa | 2507 |
| Elongation A | ≥25% | ≥25% | equal |
| Impact KV (−20 °C) | ≥45 J | ≥45 J | equal |
| Hardness | ≤290 HB | ≤290 HB | equal |
| Strength >250 °C | maintained by W | falls off sooner | 1.4501 |
For ambient-temperature pressure design, treat the two as structurally interchangeable and let the corrosion environment drive the decision. The one place strength genuinely tips toward a grade is elevated temperature, where 1.4501's tungsten earns its keep.
Corrosion behaviour, by environment
This is where the grades stop being interchangeable. Match the environment to the alloy rather than chasing a single headline number.
Chloride & seawater — a genuine tie
In warm seawater, produced water, and other chloride-dominated service, the two grades perform in the same class. Critical pitting temperatures sit above roughly 50 °C for both, and both are fundamentally immune to the chloride stress-corrosion cracking that destroys austenitic 316L. If chloride is your only concern, pick on price and availability — which usually points to 2507.
Reducing acids — 1.4501 pulls ahead
Introduce sulfuric or phosphoric acid and copper starts to matter. In intermediate-concentration hot sulfuric acid — the aggressive middle band where duplex steels can corrode measurably — 1.4501's copper film suppresses active dissolution, and its corrosion rate can run several times lower than 2507 in the same bath. For fertiliser plants, sulfuric acid coolers, and mixed-acid process streams, this is the reason the grade exists. If your medium carries any reducing acid, favour 1.4501 super duplex forgings.
High-temperature service — tungsten's turn
Above about 250 °C, tungsten's stabilising effect on the ferrite phase gives 1.4501 a strength and softening-resistance advantage. Neither grade is a true high-temperature alloy — both must respect the sigma-phase embrittlement window — but within their working range, 1.4501 holds up better when the metal runs hot.
Both share one hazard: sigma phase
Whichever grade you pick, the manufacturing risk is identical. Sigma phase — a brittle Cr-Mo intermetallic — nucleates within minutes in the 700–1000 °C range and can slash impact toughness by more than half. That is why the fabrication route, not the grade, most often determines whether a super duplex component survives its design life.
Cost, supply and standards
2507 is the more established commodity of the two. Its lean chemistry — no deliberate tungsten, minimal copper — makes it cheaper per kilogram and more widely stocked as bar, plate and billet. For a chloride application with no acid component, paying the 1.4501 premium buys little.
1.4501 costs more because tungsten and copper cost more, and because fewer mills carry it in inventory, which can lengthen raw-material lead time on large heats. You pay that premium to solve a specific problem — acid service or high-temperature strength — not for a general upgrade.
On paper both grades sit within the same specification families for forgings: EN 10088-3 and EN 10222-5 for European practice, ASTM A182 for the equivalent forged grades (F55 for S32760, F53 for S32750). Both are also listed within NACE MR0175 / ISO 15156-3 for sour service, provided the finished part meets the standard's hardness limits — a material-property requirement we can supply against on request. Forgings can be delivered with an EN 10204 3.1 material test certificate as standard, or a 3.2 certificate countersigned by a client-nominated independent third-party inspector.
How to choose — a clean decision rule
Skip the spec-sheet duel and answer three questions about your service: is there acid, does it run hot, and how tight is the budget? That resolves almost every case.
Specify 1.4501 when
- The medium contains sulfuric, phosphoric or other reducing acids — even in trace amounts
- You run mixed-acid or chlorinated chemical-plant service
- Operating temperature stays above ~250 °C
- Your PREN target sits at the very top of the super-duplex band
- Total cost of ownership matters more than purchase price in a corrosion-critical duty
Specify 2507 when
- Service is chloride- or seawater-dominated with no reducing acid
- You need the marginally higher guaranteed strength
- Budget and lead time are real constraints
- The grade is already stocked or approved on your project
- Offshore, marine and general super-duplex duty within PREN 40+
When the answer is genuinely "either" — moderate chloride, ambient temperature, no acid — the two grades are close enough that supply and price should settle it. If you are unsure how your environment maps to a grade, our metallurgists will run a corrosion assessment against your chloride level, temperature, pH and acid species before you commit. For the alternative grade, see our companion 2507 / 1.4410 super duplex forgings page.
Why the forging route matters more than the grade
Here is the point most grade comparisons bury: for either alloy, how the part is made outweighs which of the two you picked. A cast super duplex component — of either grade — carries dendritic segregation that leaves molybdenum-depleted pockets with local PREN near standard-duplex levels, exactly where pitting starts. Forging mechanically breaks up that structure; solution annealing homogenises it; the result is uniform corrosion resistance across the whole section.
Forging also closes internal porosity and aligns grain flow with the loading direction, which cast structures cannot match. For wellhead bodies, pressure-vessel components, pump casings and rolled rings, a forged part of the correct grade — properly heat-treated and phase-balance verified — is the specification that actually survives — which is exactly what a correctly forged, solution-annealed and phase-balance-verified 1.4501 (X2CrNiMoCuWN25-7-4) forging part delivers.
Frequently asked questions
Is 1.4501 stronger than 2507?
Not usually. In solution-annealed condition 2507 (S32750) carries a marginally higher minimum yield and tensile strength, driven by its higher nitrogen ceiling. The difference is small and both exceed 530 MPa yield, so for most designs they are structurally interchangeable. The exception is service above ~250 °C, where the tungsten in 1.4501 holds strength better.
Which has the higher PREN, 1.4501 or 2507?
Both are guaranteed PREN ≥ 40 and typically land between 41 and 43. 1.4501 reaches it partly through tungsten; 2507 through slightly higher molybdenum and nitrogen. Their chloride pitting resistance is effectively equivalent, so PREN alone should not decide the grade.
What is the difference between S32760 and S32750?
S32760 (1.4501) adds tungsten (0.5–1.0%) and copper (0.5–1.0%) to the same 25Cr-7Ni-4Mo base as S32750 (2507). Tungsten lifts high-temperature strength and adds to PREN; copper improves resistance in reducing acids such as sulfuric and phosphoric acid. S32750 leans on slightly higher molybdenum and nitrogen instead. In chloride and seawater the two are effectively equal — the differences appear in acid and high-temperature duty.
Is Zeron 100 the same as 1.4501?
Yes. Zeron 100 is a trade name for the super duplex grade standardised as UNS S32760 and EN 1.4501 (X2CrNiMoCuWN25-7-4). Zeron 100, S32760 and 1.4501 all refer to the same tungsten-and-copper enhanced super duplex alloy.
Are 1.4410 and 2507 the same thing?
Yes. 1.4410 is the EN number for 2507 (UNS S32750, X2CrNiMoN25-7-4). 1.4501 is a separate grade — UNS S32760, X2CrNiMoCuWN25-7-4, trade name Zeron 100 — that adds tungsten and copper on top of the same 25-7-4 base.
Which grade is better for seawater service?
For plain warm seawater and chloride service, 1.4501 and 2507 perform in the same class — both are super duplex with PREN typically 41–43 and critical pitting temperatures above ~50 °C. Neither has a decisive edge, so 2507 is often selected for seawater on cost and availability. 1.4501 becomes the better pick only when the seawater also carries reducing acids or the component runs hot.
When is the extra cost of 1.4501 justified?
When the service medium contains sulfuric, phosphoric or other reducing acids, in mixed-acid chemical duty, or where temperature runs above ~250 °C. In those cases copper and tungsten deliver corrosion or strength margin that 2507 cannot. In plain chloride or seawater service, the premium buys little and 2507 is the economical choice.
What does "25-7-4" mean in super duplex steel?
The numbers are the nominal alloy content: about 25% chromium, 7% nickel and 4% molybdenum. Both 1.4501 and 2507 share this 25-7-4 backbone, which places them in the super duplex class with a roughly 50% austenite / 50% ferrite microstructure.
Can you supply both grades as forgings?
Both grades are routinely produced as forgings — bars, shafts, seamless rolled rings, hollow forgings, discs and valve bodies — supplied with an EN 10204 3.1 material test certificate as standard, or 3.2 with a client-nominated third-party inspector. The harder question is usually which grade to specify, which is what this comparison is designed to answer.
Governing standards & references
The grade definitions, chemistry limits and processing requirements in this comparison follow the published standards below. Always verify against the current edition applicable to your project and country.
- EN 10088-3 — Stainless steels: technical delivery conditions for semi-finished products, bars and rods (defines 1.4501 and 1.4410 chemistry).
- ASTM A182 / A182M — Forged or rolled alloy and stainless steel pipe flanges, forged fittings and valves (grade F55 = S32760, F53 = S32750).
- EN 10222-5 — Steel forgings for pressure purposes: martensitic, austenitic and austenitic-ferritic (duplex) stainless steels.
- NACE MR0175 / ISO 15156-3 — Materials for use in H₂S-containing (sour) environments — hardness limits for duplex and super duplex.
- ASTM A923 & ASTM A1084 — Test methods for detecting detrimental intermetallic (sigma) phase in duplex and super duplex stainless steels.
Not sure which grade your project needs?
Send us your service conditions — chloride level, temperature, pH, acid species — and our metallurgists will recommend 1.4501 or 2507 with the data behind it, then quote the forging. Response within 24 working hours.