Super Duplex S32750 vs S32760: Tungsten vs Higher-Chromium Approach to PREN Optimization

QUICK ANSWER

S32750 (2507) and S32760 (Zeron 100) are both super duplex stainless steels with a certified minimum PREN of 40, but they get there differently: S32750 leans on a higher molybdenum and nitrogen ceiling within the Cr-Mo-N system, while S32760 caps molybdenum lower and adds tungsten plus copper.
Per ASTM A240, standard (unmodified) PREN = %Cr + 3.3(%Mo) + 16(%N); tungsten is not part of that formula, so S32760's real-world pitting resistance in mixed-halide and reducing-acid service is often understated by the plain PREN number.
For most chloride and offshore service, the two grades are functionally interchangeable and are typically selected on cost, availability, and mill lead time rather than metallurgy alone.
S32760 has a documented edge in hot seawater and mixed-acid/reducing environments (copper effect); S32750 is generally the lower-cost, more widely stocked option.

Super Duplex S32750 vs S32760

S32750 and S32760 are both certified super duplex stainless steels in the same performance tier (PREN ≥ 40, 50:50 austenite-ferrite microstructure), but they reach that tier through two distinct alloying philosophies - one built around maximizing chromium, molybdenum, and nitrogen, the other built around a lower-molybdenum matrix supplemented with tungsten and copper.

Super duplex stainless steels are grades whose Pitting Resistance Equivalent Number (PREN) exceeds roughly 40, placing them above standard duplex grades such as S32205 (2205, PREN 29–33) and closer to super austenitic performance, while retaining the higher strength and stress-corrosion-cracking resistance of a duplex microstructure.

UNS S32750, commercially known as 2507 or SAF 2507, was developed by Sandvik in the 1980s. UNS S32760, commercially known as Zeron 100, was developed in the UK (originally by Mather & Platt, now supplied by Rolled Alloys and other licensed producers) in the 1970s.

Source: Langley Alloys, "What Is the Difference Between S32750 and S32760?"; Rolled Alloys ZERON 100 technical literature.

Both grades are governed by ASTM A240 (plate/sheet/strip), A182 (forgings/fittings, F53 and F55 respectively), A789/A790 (tube and pipe), and A276/A479 (bar), and both are candidates for the same class of offshore, desalination, and chemical-processing equipment. Because they are frequently substituted for one another in procurement specifications, the practical question for a buyer or engineer is not "which is stronger" - both meet essentially the same minimum mechanical property class - but which alloying route better fits the specific corrosive environment, welding process, and supply chain at hand.

The two grades share an identical 24.0–26.0% chromium band under ASTM A240, so the real differentiation is not chromium itself but how each grade fills out the rest of the pitting-resistant elements: S32750 is allowed up to 5.0% molybdenum and 0.32% nitrogen with no tungsten, while S32760 caps molybdenum at 4.0% and adds 0.50–1.00% tungsten and 0.50–1.00% copper.

The table below lists the ASTM A240 heat-analysis composition limits for both grades.

Element (wt.%)	S32750 (2507 / F53)	S32760 (Zeron 100 / F55)
Carbon, max	0.030	0.030
Manganese, max	1.20	1.00
Silicon, max	0.80	1.00
Phosphorus, max	0.035	0.035
Sulfur, max	0.020	0.010
Chromium	24.0–26.0	24.0–26.0
Nickel	6.0–8.0	6.0–8.0
Molybdenum	3.0–5.0	3.0–4.0
Nitrogen	0.24–0.32	0.20–0.30
Copper, max	0.50	0.50–1.00
Tungsten	not specified	0.50–1.00
Certified minimum PREN	≥ 40–41*	≥ 40.0

Source: ASTM A240/A240M composition tables for UNS S32750 and UNS S32760; Rolled Alloys ZERON 100 datasheet; Smith Metal / Smiths Advanced Metals UNS S32760 datasheets.

*Reported minimum PREN requirements vary slightly by mill specification (commonly ≥ 40 or ≥ 41 for S32750); always confirm against the governing purchase specification and MTR.

Reading the numbers: S32750's wider molybdenum window (up to 5.0% versus 4.0% for S32760) and higher nitrogen ceiling (0.32% versus 0.30%) let mills push the classic chromium-molybdenum-nitrogen system harder to guarantee a high PREN without adding new elements. S32760 instead holds molybdenum to a narrower, lower band and brings in tungsten and copper - elements that do not exist in S32750's specification at all - to reach a comparable pitting-resistance class through a different mechanism, discussed in the next section.

The standard PREN formula (%Cr + 3.3×%Mo + 16×%N) does not include tungsten, so it slightly understates S32760's pitting resistance; engineers who want an apples-to-apples comparison use the tungsten-adjusted PREN-W formula instead.

Standard PREN: PREN = %Cr + 3.3(%Mo) + 16(%N). This is the formula cited on both grades' ASTM datasheets and is the version used to certify the ASTM minimum (≥ 40–41).

Tungsten-adjusted PREN-W: PREN-W = %Cr + 3.3(%Mo + 0.5×%W) + 16(%N). Because tungsten behaves metallurgically like a weaker version of molybdenum in resisting chloride pitting, it is credited at roughly half the coefficient of molybdenum. This modified formula is the one used in NORSOK and most super duplex design literature specifically to make W-bearing grades like S32760 comparable to Mo-only grades like S32750.

Source: NORSOK M-630 material data sheets; Rolled Alloys and Zeron 100 technical literature on PREN-W.

Using nominal mid-range chemistries as an illustration (not a specification requirement):

Grade	Nominal Cr / Mo / N (/ W)	Standard PREN	PREN-W (tungsten-adjusted)
S32750	25% / 4.0% / 0.28%	≈ 42.7	n/a (no W term)
S32760	25% / 3.6% / 0.25% / 0.7% W	≈ 40.9	≈ 42.0

Illustrative calculation from nominal mid-range values; actual heat chemistry and certified PREN will vary by mill and must be confirmed against the mill test report (MTR).

The practical takeaway: on the unmodified formula that both mills print on their certificates, S32750 typically calculates a marginally higher PREN because of its higher nitrogen allowance. Once tungsten is credited, S32760's effective pitting resistance closes most of that gap - and, as the next section shows, its measured performance in some environments exceeds what either PREN number alone would predict.

Tungsten stabilizes the passive film against chloride attack in a similar way to molybdenum but somewhat less efficiently on a per-atom basis, which is why it is only half-credited in PREN-W; the copper addition alongside it, however, gives S32760 a real, PREN-independent advantage in non-oxidizing and mixed acid environments that S32750 does not share.

Does Tungsten Deliver the Same Corrosion Benefit as Molybdenum

Molybdenum works primarily by stabilizing the chromium-rich passive oxide film and inhibiting the anodic dissolution reaction inside an active pit, which is why it carries the largest coefficient (3.3) in the PREN formula. Tungsten occupies a similar lattice position in the passive film and provides a related, but weaker, stabilizing effect - the basis for the 0.5 coefficient it receives in PREN-W.

Copper is not part of any PREN formula at all, because it does not meaningfully affect chloride pitting. Its benefit is different: copper improves resistance to general corrosion in non-oxidizing, reducing acids such as dilute sulfuric and hydrochloric acid - the same reason copper-bearing grades like 904L are specified for sulfuric acid service. S32760's copper content therefore gives it a corrosion advantage in mixed acid/chloride streams that a PREN comparison alone will never capture, regardless of which formula is used.

Measured Critical Pitting Temperature (ASTM G48, 6% Ferric Chloride)

Condition	S32750 (2507)	S32760 (Zeron 100)
Wrought, solution-annealed - CPT	≈ 78°C (reported)	70–80°C
Wrought - CCT (crevice)	≈ 37°C (reported)	typically lower than CPT, grade-dependent
As-welded (matching/overmatching filler) - CPT	≈ 50–60°C (literature range)	35–60°C with Zeron 100X filler

Source: pipingpipeline.com Alloy 2507 technical page; NACE/ForceTechnology weld-CPT literature review; zeron100.com (Rolled Alloys) ZERON 100 corrosion data.

Two things stand out. First, both grades lose a substantial fraction of their pitting resistance after welding - a reminder that the base-metal PREN is a starting point, not a guarantee, and that filler-metal selection and weld heat input govern real joint performance. Second, the wrought CPT ranges genuinely overlap: for straightforward chloride service at ambient-to-moderate temperature, the two grades perform similarly, and the choice comes down to the specific service chemistry and the points covered below.

Both grades share the same minimum 0.2% yield strength of 550 MPa (80 ksi) under ASTM A240, but S32750 is specified to a higher minimum tensile strength with lower minimum elongation, while S32760 allows more elongation - a reflection of its slightly leaner molybdenum matrix.
Property (ASTM A240, room temperature)	S32750	S32760
0.2% Offset Yield Strength, min	550 MPa (80 ksi)	550 MPa (80 ksi)
Ultimate Tensile Strength, min	795 MPa (116 ksi)	750 MPa (109 ksi)
Elongation, min	15%	25%
Brinell Hardness, typical max	≈ 310 HB	270–310 HB (spec-dependent)
Microstructure	≈ 50% ferrite / 50% austenite	≈ 50% ferrite / 50% austenite
Max recommended service temperature	general duplex limit ≈ 300–315°C	≈ 300°C (572°F); prolonged higher-temperature exposure reduces toughness

Source: ASTM A240/A240M mechanical property tables; Rolled Alloys ZERON 100 datasheet; gravitycastindia.com ASTM A240 UNS S32750/S32760 reference sheets. Confirm against the current edition of the governing standard and the applicable MTR before design use.

For sour service governed by NACE MR0175/ISO 15156, both grades are subject to a hardness ceiling (commonly cited around 28–32 HRC depending on the specific service category), so hardness must be verified on the MTR rather than assumed from nominal typical values - the same caution that applies to any precipitation-hardened or high-strength corrosion-resistant alloy in sour environments.

Both grades are weldable with standard GTAW, GMAW, SMAW, and SAW processes and share the same ASME Section IX P-Number group, but S32760 requires a dedicated overmatching filler (Zeron 100X) to preserve its copper-tungsten chemistry in the weld metal, while S32750 is more commonly welded with the widely stocked ER2594/E2594 super duplex filler family.

Both grades fall under ASME Section IX P-Number 10H, Group 1, meaning a welder or procedure qualified on one super duplex grade is broadly qualified across the family, subject to the specific WPS/PQR requirements. ER2594 (AWS A5.9) and its covered-electrode counterpart E2595/E2594 (AWS A5.4) are commonly used across S32750, S32760, and related super duplex grades including S32550 and S31260.

Source: Rolled Alloys ZERON 100 FAQ; Washington Alloy ER2594 product literature.

However, because tungsten and copper are not present in a generic ER2594 deposit at S32760's levels, welding S32760 to itself with a standard super duplex filler will not fully replicate the base metal's tungsten/copper chemistry in the fusion zone. Rolled Alloys and other Zeron 100 licensees instead supply a dedicated overmatched filler (marketed as Zeron 100X, or a matching Zeron 100M filler when a post-weld solution anneal is planned) specifically to preserve that chemistry and the associated corrosion performance across the joint.

Mixed joints between S32750 and S32760 are routinely made with a standard 25% Cr super duplex filler such as ER2594, since the filler need only match the leaner of the two base metals for corrosion and mechanical qualification - subject to project-specific WPS/PQR requirements.

Both grades are covered by a parallel set of ASTM/ASME product-form standards and the same offshore and sour-service qualification frameworks, so specification compliance is rarely the deciding factor between them - mill certification to the correct product-form standard is what matters.
Product form	S32750	S32760
Plate / sheet / strip	ASTM A240 / ASME SA-240	ASTM A240 / ASME SA-240
Forgings / fittings	ASTM A182 Grade F53	ASTM A182 Grade F55
Seamless & welded tube	ASTM A789	ASTM A789
Seamless & welded pipe	ASTM A790	ASTM A790
Bar	ASTM A276 / A479	ASTM A276 / A479
Castings	ASTM A890 Grade 5A	ASTM A890 (grade per casting spec)
Sour-service qualification	NACE MR0175 / ISO 15156-3	NACE MR0175 / ISO 15156-3
Offshore material data sheets	NORSOK M-630	NORSOK M-630 (Zeron 100 has dedicated Rolled Alloys MDS D51–D58)

Source: ASTM A182, A240, A276, A479, A789, A790, A890 designation lists per grade; Smiths Advanced Metals UNS S32760 datasheet; Rolled Alloys ZERON 100 datasheet.

S32750 is generally the lower-cost, more widely multi-sourced option because it is produced to a generic UNS/ASTM specification by numerous mills worldwide, while S32760/Zeron 100 carries a modest premium tied to its tungsten and copper additions and, in some product forms, closer association with a smaller group of licensed producers.

Which Grade Costs Less and Is Easier to Source

Because S32750 is a straightforward Cr-Mo-N system with no proprietary trace elements, it is produced by a broad base of international mills and is typically the more readily available, lower-premium option in standard product forms such as pipe, plate, and fittings. S32760's tungsten and copper additions add a modest raw-material cost, and while UNS S32760 itself is an open specification that any qualified mill can produce, the Zeron 100 trade name and its dedicated welding consumables (Zeron 100X/100M) are most closely associated with Rolled Alloys and its licensed supply chain, which can narrow sourcing options for buyers who specify the trade name rather than the UNS designation. Buyers should specify by UNS number and governing ASTM standard, not trade name, unless a specific mill's tightened internal chemistry is a genuine project requirement.

For most offshore, subsea, and general chloride-bearing chemical service, S32750 and S32760 are interchangeable and selected on cost and availability; S32760 is the stronger choice specifically for hot seawater and for streams that combine chlorides with reducing or mixed acids, where its copper content adds real value beyond PREN.
Application	Better fit	Why
Subsea pipelines, risers, manifolds (ambient/moderate temp. chlorides)	Either grade	Overlapping CPT/CCT ranges and identical yield-strength class; select on cost and mill availability
Hot seawater / MSF desalination (>40°C)	S32760	Documented field performance history and slight edge from tungsten/copper in hot chloride service
Mixed chloride + reducing acid streams (e.g., dilute H2SO4/HCl with chlorides)	S32760	Copper addition improves reducing-acid resistance independent of PREN; S32750 has no copper specification
General chemical processing, pulp & paper, FGD scrubbers	Either grade	Both widely qualified; local mill stock usually decides
High-strength structural components (fasteners, shafts) needing max tensile	S32750	Higher minimum tensile strength (795 vs. 750 MPa) at the same yield class
Applications needing higher minimum elongation/ductility margin	S32760	Higher minimum elongation (25% vs. 15%)

Source: Kalpataru Piping Solutions, "S32750 vs S32760 (Zeron 100): When to Use Each"; Rolled Alloys ZERON 100 application literature.

Default to S32750 for cost-driven, standard chloride service; move to S32760 when the environment includes hot seawater or reducing/mixed acids, or when a project specification calls for Zeron 100 by name.

Confirm chloride concentration, temperature, and whether the stream includes reducing or mixed acids - the presence of reducing acid conditions favors S32760's copper content.

Check whether the project specification calls out UNS S32750/S32760 generically or the Zeron 100 trade name specifically, since the latter narrows the qualified supplier list.

Verify the certified PREN and full heat chemistry on the MTR rather than relying on nominal or mid-range published values.

For welded assemblies, confirm the qualified WPS/PQR and filler metal (ER2594/E2594 for S32750; Zeron 100X or 100M for S32760) and re-verify CPT on representative weld coupons - base-metal CPT does not carry over to the weld.

For sour service, verify hardness against the applicable NACE MR0175/ISO 15156 category rather than the general mill maximum.

Compare current mill lead times and premiums for both UNS numbers in the required product form before finalizing specification, since availability can shift year to year.

Q: Is S32760 always better than S32750 because it has more alloying elements?

A: No. More elements do not automatically mean better performance for a given service. S32760's tungsten and copper give it a real advantage in hot seawater and reducing/mixed acid service, but S32750's higher minimum tensile strength and typically lower cost make it the better choice for many standard chloride applications.

Q: Can S32750 and S32760 be welded to each other?

A: Yes. A 25% chromium super duplex filler such as ER2594 is commonly used to join S32750 to S32760, subject to project-specific WPS/PQR qualification, since the filler needs to satisfy the requirements of the leaner of the two base metals.

Q: Does a higher PREN number always mean better corrosion resistance in service?

A: Not entirely. PREN is a useful screening index based on chromium, molybdenum, and nitrogen, but it does not capture the copper effect in reducing acids, does not account for tungsten unless the PREN-W formula is used, and does not reflect the CPT reduction that occurs after welding. It should be treated as a starting point, verified against actual test data for the specific environment.

Q: Is Zeron 100 the same thing as S32760?

A: Zeron 100 is the trade name for material produced to the UNS S32760 specification, most closely associated with Rolled Alloys and its licensed supply chain. The terms are commonly used interchangeably, but a project specification calling out "Zeron 100" by name may narrow the acceptable supplier list compared with one that simply calls out "UNS S32760."

Q: Which grade is more commonly stocked for general oil and gas piping?

A: S32750 is generally more widely available across a broader base of international mills because it is a straightforward Cr-Mo-N system with no proprietary elements; actual regional stock levels should be confirmed with EETA or another qualified supplier for the specific product form and size required.