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Super Duplex S32750 (UNS S32750, F53, 1.4410) is the workhorse 'super duplex' grade: a two-phase austenitic-ferritic stainless steel built for aggressive chloride environments where 316L and even Duplex 2205 run out of pitting or strength margin. This guide explains what it is, why it performs, and how it fits the wider Super Duplex S32750 hub.
Super Duplex S32750 (UNS S32750, forge grade F53, W.Nr 1.4410) is a high-alloy duplex stainless steel whose roughly 25% chromium, 7% nickel and 4% molybdenum chemistry - plus about 0.25% nitrogen - gives it a pitting-resistance equivalent number (PREN) above 40, the threshold that defines the 'super duplex' class.
Like all duplex stainless steels, S32750 is a roughly 50/50 mixture of austenite and ferrite. The two phases are what make it special: the ferrite supplies chromium and molybdenum for corrosion resistance and high strength, while the austenite supplies nickel and nitrogen for toughness and resistance to chloride stress-corrosion cracking. The result is a single alloy that is both stronger and more corrosion-resistant than conventional austenitic grades such as 316L stainless steel.
It is the most widely used 'super duplex' grade and is the reference point for the whole family. Our Super Duplex S32750 hub page collects the full set of supporting articles, from mechanical and corrosion properties to welding and heat treatment.
UNS S32750 is the Unified Numbering System code for this alloy; 'S' marks a stainless steel, and the number uniquely identifies the 25-7-4 chemistry. In forged or flanged product it is also sold as F53, and in Europe as W.Nr 1.4410.
The UNS system lets buyers and mills refer to the exact alloy by a single code instead of a long chemical description. 'S32750' therefore means one specific composition (see the table below), not a family. The same number appears on mill certificates, purchase orders and standards, which is why it is the safest way to specify the material. Forged and cast components use the 'F53' designation under ASTM A182, while the European material number is 1.4410.
If you work across standards, our page on the duplex stainless steel numbering system explains how UNS, ASTM and EN codes map to each other.
Annealed S32750 contains 24-26% chromium, 6-8% nickel, 3-5% molybdenum and 0.24-0.32% nitrogen, with carbon held at or below 0.030% - the balance being iron.
The composition below is the ASTM A789/A790/A240 specification range. These are the numbers that determine both strength and corrosion resistance; the nitrogen in particular is what lifts the PREN above 40 without adding more expensive molybdenum.
Typical UNS S32750 composition (ASTM A789/A790/A240, wt%)
Element | S32750 range (min-max) | Role |
Chromium (Cr) | 24.0 - 26.0 | Pitting and crevice corrosion resistance |
Nickel (Ni) | 6.0 - 8.0 | Austenite balance, toughness, SCC resistance |
Molybdenum (Mo) | 3.0 - 5.0 | Localized corrosion resistance |
Nitrogen (N) | 0.24 - 0.32 | Strength, PREN, phase balance |
Carbon (C) | 0.030 max | Low to avoid sensitisation |
Manganese (Mn) | 1.20 max | Minor |
Silicon (Si) | 0.80 max | Minor |
Phosphorus (P) | 0.035 max | Impurity |
Sulfur (S) | 0.020 max | Impurity |
Copper (Cu) | 0.50 max | Minor, some resistance to sulfuric acid |
It earns the 'super' label because its PREN exceeds 40, the informal boundary between standard duplex grades (PREN around 35) and the higher-alloyed 'super duplex' group.
Duplex stainless steels are themselves split into 'lean duplex' (PREN ~25-30), standard duplex such as Duplex 2205 (PREN ~35), and super duplex (PREN 40+). S32750 sits firmly in the top band, which is what lets it survive seawater, brackish and many process streams that corrode 2205. The short comparison below shows where the boundary falls.
PREN by family (PREN = %Cr + 3.3x%Mo + 16x%N, typical)
Grade | PREN (typical) | Class |
|---|---|---|
316L | 24 - 26 | Austenitic |
904L | 34 - 36 | High-alloy austenitic |
Duplex 2205 (S32205) | 34 - 38 | Standard duplex |
Super Duplex S32750 | 40 - 43 | Super duplex |
254SMO | 43 - 45 | 6% Mo austenitic |
Hastelloy C276 | 63 - 70 | Nickel alloy |
Annealed S32750 delivers a minimum yield strength of 550 MPa (80 ksi) and minimum tensile strength of 795 MPa (115 ksi) - roughly three times the yield strength of 316L - with good ductility and toughness down to cryogenic temperatures.
Those minima come from ASTM A790 (pipe and tube) and A240 (plate). The high strength means thinner walls and lighter structures for the same pressure, which is a major reason offshore and desalination projects choose it. The table lists the headline values next to the grades it is most often compared with; always confirm the exact figures against the current specification and product form.
Typical annealed mechanical minima
Grade | Yield MPa (ksi) | Tensile MPa (ksi) | Elong. % | PREN |
|---|---|---|---|---|
316L | 170 (24.6) | 485 (70) | 40 | 25 |
Duplex 2205 | 450 (65) | 655 (95) | 25 | 35 |
Super Duplex S32750 | 550 (80) | 795 (115) | 15 (typ. 25) | 41 |
Super Duplex S32760 | 550 (80) | 750 (109) | 25 | 41 |
S32750 is about three times the yield strength of 316L and roughly 20% stronger in yield than Duplex 2205, while keeping corrosion resistance well above both.
The strength gap matters most in pressure equipment: a S32750 pipe carries the same pressure at a thinner wall than 316L or 2205, cutting weight and cost in long subsea or platform runs. The trade-off is fabrication care (see welding below) and a higher material price, which is why 316L and 2205 stay the default until the environment demands more.
S32750 resists pitting, crevice corrosion and chloride stress-corrosion cracking far better than 316L or 2205, and its high PREN lets it shrug off seawater, brines and many acidic process streams.
The high chromium plus molybdenum plus nitrogen combination is what protects against localized attack, while the balanced two-phase structure resists chloride stress-corrosion cracking (SCC) that plagues single-phase austenitic steels in hot chlorides. In practice this means S32750 is the grade of choice for seawater-cooled systems, desalination, and sour oil-and-gas service where 316L would fail quickly. It should not be used in strongly reducing acids at temperature (where nickel alloys such as Hastelloy C276 win) or in long-term service above about 250-300 degC.
The exact corrosion rate always depends on temperature, chloride level, pH, oxygen and crevice geometry. Use the PREN bands above for screening, then confirm with the applicable standard or a corrosion test before final design.
PREN (Pitting Resistance Equivalent Number) is a simple index - %Cr + 3.3x%Mo + 16x%N - that predicts pitting resistance; S32750's PREN above 40 is the single number that explains its seawater performance.
PREN is not a standard requirement, but it is the fastest way to compare stainless grades for pitting. Higher PREN means better resistance. S32750 lands at roughly 41 because its 25% chromium, 4% molybdenum and 0.27% nitrogen add up past the 40 line. Treat PREN as a screening tool, not a design value: real performance still depends on the service environment and on keeping the ferrite-austenite balance correct.
S32750 is specified wherever chlorides, pressure and weight savings meet: offshore topsides and subsea, seawater desalination, oil and gas, heat exchangers, pulp and paper, and chemical process equipment.
Offshore and marine - platform piping, risers and topside systems exposed to seawater (S32750 product forms).
Seawater desalination - RO trains, brine heaters and pump shafts, covered in our desalination technical guide.
Oil and gas - subsea manifolds, flowlines and chemical-injection lines qualified to NACE MR0175.
Heat exchangers - tube and shell exposed to cooling water, described in the S32750 heat-exchanger note.
Pulp and paper - bleach washers and digester lines where chloride and acidity coexist.
Chemical process - reactors, columns and piping in moderately acidic, chlorinated service.
Real shipped examples include F53 weld-neck flanges to Argentina, S32750 butt-welding fittings to Saudi Arabia and ASTM A815 S32750 fittings to Brazil.
Choose S32750 over 316L when the service is chloride-rich, under pressure, or weight-sensitive: it gives roughly 3x the strength and far better pitting and SCC resistance, at a higher material cost.
316L vs Super Duplex S32750 at a glance
Aspect | 316L | S32750 |
|---|---|---|
PREN | 24 - 26 | 40 - 43 |
Yield strength | 170 MPa (24.6 ksi) | 550 MPa (80 ksi) |
Seawater pitting | Poor to fair | Excellent |
Chloride SCC | Good (but limited hot) | Excellent |
Max service temp | Higher (up to ~400 degC in some uses) | About 250-300 degC |
Relative cost | Low | High |
Best when | Mild, non-chloride service | Aggressive chloride / pressure / weight |
S32750 beats 2205 on both pitting resistance (PREN ~41 vs ~35) and strength (550 vs 450 MPa yield), so it is the pick for harsher chlorides; 2205 remains the better value in moderate service.
Both are two-phase duplex grades and both weld and fabricate on similar rules, but S32750's extra chromium, molybdenum and nitrogen widen the safe operating envelope. Our full 2205 vs Super Duplex 2507 comparison works through when each is the right call, including cost and weldability trade-offs.
S32750 (F53) and S32760 (F55) are sister super duplex grades with near-identical PREN; S32760 adds tungsten and a little copper, which nudges strength and localized-corrosion margins slightly higher.
S32760 (W.Nr 1.4501, F55) keeps the same 24-26% Cr and 6-8% Ni but includes 0.5-1.0% tungsten and 0.5-1.0% copper, while S32750 has essentially none of either. Both meet the super duplex PREN threshold, so selection is often about stock, specification and minor differences in acidic service. The detailed F53 vs F55 comparison and the S32760 overview cover the numbers.
S32750 is supplied as plate and sheet, seamless and welded pipe and tube, bar and rod, forgings, flanges and butt-welding fittings - each covered by its own ASTM specification.
Plate and sheet to ASTM A240 for vessels, claddings and structurals.
Pipe and tube to ASTM A789/A790 for the duplex and super duplex piping systems.
Forged pipe fittings described in the forged S32750 fittings guide and the benefits of S32750 fittings.
Flanges and forgings to ASTM A182 F53.
Bar and rod via the round-bars product page for shafts and machined parts.
Sheet and plate also listed under the duplex sheet and plate category.
S32750 is covered by ASTM A789/A790 (pipe and tube), A240 (plate/sheet), A182 F53 (forgings and flanges), A276/A479 (bar), A815 (fittings), with A923 for phase detection and NACE MR0175 for sour service.
Key ASTM and industry specifications for UNS S32750
Product form | ASTM specification | Note |
|---|---|---|
Seamless / welded pipe and tube | A789, A790 | Most common forms |
Plate, sheet, strip | A240 (with A480) | Vessels and cladding |
Forgings and flanges | A182 (F53) | Forge grade F53 |
Bar and rod | A276, A479 | Shafts, machined parts |
Butt-welding fittings | A815 | Elbows, tees, reducers |
Corrosion / phase test | A923, A1084 | Detects sigma/chi phases |
Sour service | NACE MR0175 / ISO 15156 | With hardness limit |
European equivalent | 1.4410 (EN 10088) | W.Nr 1.4410 |
Yes - S32750 qualifies for NACE MR0175 / ISO 15156 sour service when solution-annealed with the required ferrite balance and hardness limit, and it is one of the standard grades for continuous seawater exposure.
In seawater it is a default choice for cooling, desalination and marine structures because of its PREN above 40 and its resistance to chloride SCC. In sour oil-and-gas service it is accepted under NACE MR0175 with a hardness cap (commonly 32 HRC max) and a controlled ferrite fraction; the governing edition also sets temperature and H2S partial-pressure limits, so confirm those for your exact environment. Our desalination guide and the sour-service comparisons in the hub give the practical boundaries.
S32750 welds with matching or overalloyed filler and strict argon purging, but the joint must be kept inside the 30-55% ferrite window and cooled fast enough to avoid brittle sigma/chi phases.
As a duplex grade it is weldable, yet less forgiving than 316L: the heat-affected zone can lose its phase balance and precipitate intermetallic phases if cooled too slowly or overheated, which hurts toughness and corrosion resistance. Use a qualified WPS, argon backing gas, and post-weld ferrite/A923 checks. Because welding is its own deep topic, the hub's dedicated welding and heat-treatment spokes cover procedures and filler selection in full; for now, treat 'qualified procedure plus phase control' as the rule.
S32750's main limits are a ~250-300 degC service ceiling (brittle phases form above it), the need for careful fabrication, and a material cost well above 316L or 2205.
Above roughly 250-300 degC the ferrite can decompose into sigma and chi phases that embrittle the steel, so high-temperature duty should move to a nickel alloy such as Inconel 625 or Hastelloy C276. Fabrication must respect the phase balance (hot forming, heat treatment and welding all matter), and the higher alloy content means a higher price. Within its envelope, though, it is one of the most cost-effective ways to get seawater-grade corrosion resistance plus high strength.
A correct specification names the UNS, the product form and ASTM spec, the required corrosion tests (A923), the sour-service condition if any, and a material test certificate - so the mill delivers exactly the alloy your design assumes.
Name the grade and UNS. Specify Super Duplex S32750 by its UNS number (UNS S32750) and, for forgings and flanges, the forge designation F53. See the S32750 product overview for the full identifier set including W.Nr 1.4410.
Choose the product form and ASTM spec. Match the form to its specification: pipe and tube to ASTM A789/A790, plate and sheet to ASTM A240, bar to A276/A479, fittings to ASTM A815, and forgings or flanges to ASTM A182 F53.
State the corrosion and phase-balance tests. Require ASTM A923 (intermetallic-phase detection) and ferrite measurement so the delivered material stays inside the 30-55% ferrite window and free of brittle sigma/chi phases.
Add the service condition. State whether the part sees sour (H2S) service so the order can be placed against NACE MR0175 / ISO 15156 with the correct hardness and temperature limits, and confirm seawater or chlorinated exposure with the desalination guide.
Request the material test certificate. Ask for an EN 10204 3.1 (or 3.2) MTC showing heat analysis, mechanical properties and the required corrosion test results before shipment.
What is Super Duplex S32750?
Super Duplex S32750 (UNS S32750, F53, 1.4410) is a high-alloy duplex stainless steel with about 25% chromium, 7% nickel, 4% molybdenum and 0.25% nitrogen. Its PREN is above 40, which defines the super duplex class and gives it excellent resistance to pitting, crevice corrosion and chloride stress-corrosion cracking.
What does UNS S32750 stand for?
UNS is the Unified Numbering System; the 'S' means stainless steel and S32750 identifies this exact 25-7-4 chemistry. In forged and flanged product it is also called F53, and in Europe W.Nr 1.4410.
What is the difference between S32750 and 2507?
They are the same alloy. '2507' is the common trade name for Super Duplex, and UNS S32750 is its specification code. You will also see it written as Super Duplex 2507 or F53 for forgings.
Is Super Duplex S32750 magnetic?
Yes, mildly. The roughly 50% ferrite phase makes it ferromagnetic, though less so than fully ferritic steel. It is not as weakly magnetic as 316L, which is mostly austenitic.
What is the yield strength of S32750?
The minimum yield strength is 550 MPa (80 ksi) and the minimum tensile strength is 795 MPa (115 ksi) in the annealed condition per ASTM A790/A240. That is about three times the yield strength of 316L.
What is PREN and why is S32750 above 40?
PREN = %Cr + 3.3x%Mo + 16x%N. With 25% Cr, ~4% Mo and ~0.27% N, S32750 reaches about 41, clearing the 40 line that separates standard duplex from super duplex.
How does S32750 compare with 316L?
S32750 has roughly 3x the yield strength of 316L and far better pitting and chloride stress-corrosion resistance (PREN ~41 vs ~25), but it costs more and needs more careful fabrication. 316L stays the choice for mild, non-chloride service.
How does S32750 compare with Duplex 2205?
S32750 beats 2205 on both PREN (~41 vs ~35) and yield strength (550 vs 450 MPa), so it suits harsher chlorides and higher pressure. 2205 is the better value in moderate service.
What is the difference between S32750 and S32760?
S32760 (F55) adds tungsten and a little copper to the same base chemistry, nudging strength and localized-corrosion margins slightly higher. Both are super duplex with PREN around 41; selection is often about stock and specification.
What temperature can Super Duplex S32750 handle?
Continuous service is generally limited to about 250-300 degC because brittle sigma and chi phases can form above that. For higher temperatures, move to a nickel alloy such as Inconel 625 or Hastelloy C276.
Is S32750 good for seawater?
Yes. With PREN above 40 and strong resistance to chloride stress-corrosion cracking, S32750 is a standard grade for seawater cooling, desalination, marine and offshore service.
Can S32750 be used in sour (H2S) service?
Yes, it qualifies under NACE MR0175 / ISO 15156 when supplied solution-annealed with the required ferrite balance and a hardness limit (commonly 32 HRC max). Confirm the current edition's temperature and H2S limits for your case.
Is Super Duplex S32750 weldable?
It is weldable but less forgiving than 316L. The joint must stay inside the 30-55% ferrite window and cool fast enough to avoid sigma/chi phases; use a qualified procedure, argon backing and post-weld checks.
What ASTM standards cover S32750?
Pipe and tube: A789/A790. Plate and sheet: A240. Forgings and flanges: A182 F53. Bar: A276/A479. Fittings: A815. Phase detection: A923. Sour service: NACE MR0175.
What product forms does S32750 come in?
Plate and sheet, seamless and welded pipe and tube, bar and rod, forgings, flanges and butt-welding fittings - each with its own ASTM specification.
What are the limitations of S32750?
Its main limits are the ~250-300 degC service ceiling, the need for careful fabrication to control the phase balance, and a material cost well above 316L or 2205.
Why is nitrogen added to S32750?
Nitrogen strengthens the austenite, lifts the PREN through the 16x%N term, and helps keep the ferrite-austenite balance - all without adding more expensive molybdenum.
Where can I buy Super Duplex S32750?
JN Alloy supplies S32750 plate, pipe, fittings, flanges and bar with full material test certificates and NACE documentation; see the S32750 product hub and the individual form pages linked from the Super Duplex S32750 guide.
Super duplex stainless steel | A duplex grade with PREN above 40, offering higher corrosion resistance than standard duplex (PREN ~35). S32750 and S32760 are the common members. |
Duplex microstructure | A roughly 50/50 mix of austenite and ferrite phases that gives duplex steels their combination of strength and corrosion resistance. |
PREN | Pitting Resistance Equivalent Number = %Cr + 3.3x%Mo + 16x%N. A screening index for pitting resistance. |
UNS S32750 | The Unified Numbering System code for Super Duplex 2507; F53 is the forge equivalent, 1.4410 the EN number. |
F53 | The ASTM forge-grade designation for UNS S32750, used on forgings and flanges (ASTM A182). |
Ferrite window | The acceptable 30-55% ferrite fraction in duplex steel; outside it, toughness and corrosion resistance drop. |
Sigma / chi phase | Brittle intermetallic phases that can precipitate in duplex steel above about 250-300 degC; avoided by composition control and cooling rate. |
NACE MR0175 / ISO 15156 | The standard that qualifies metals for sour (H2S) oil-and-gas service, with hardness and temperature limits. |
ASTM A923 | Test method for detecting detrimental intermetallic phases in duplex stainless steels. |
MTC | Material Test Certificate (EN 10204 3.1/3.2) recording heat analysis, mechanical properties and tests. |
ASTM A789 / A790 - Standard specifications for seamless and welded ferritic/austenitic stainless steel pipe and tube (UNS S32750).
ASTM A240 / A480 - Specification for chromium and chromium-nickel stainless steel plate, sheet and strip (UNS S32750).
ASTM A182 - Specification for forged or rolled alloy and stainless steel pipe flanges, forged fittings and valves (F53).
ASTM A815 - Specification for wrought ferritic, ferritic/austenitic and martensitic stainless steel piping fittings (UNS S32750).
ASTM A923 - Standard test method for detecting detrimental intermetallic phase in duplex stainless steels.
NACE MR0175 / ISO 15156 - Petroleum and natural gas industries - materials for use in H2S-containing environments.
EN 10088 - Stainless steels - list of grades and technical delivery conditions (W.Nr 1.4410).
JN Alloy, Super Duplex S32750 hub: https://www.jnalloy.com/super-duplex-s32750-guide.html
Need Super Duplex S32750 plate, pipe, fittings or flanges with full MTC and NACE documentation? Contact JN Alloy for a complete quotation covering material, testing and shipping.
