What SAF 2507 is
SAF 2507 is a wrought super duplex stainless steel. Its microstructure holds austenite and ferrite in roughly equal proportion, and the accepted band for wrought duplex structures is 35 to 65 percent ferrite by volume.
Three elements carry the performance. Chromium at 24 to 26 percent builds the passive film. Molybdenum at 3 to 5 percent carries pitting and crevice resistance in chlorides. Nitrogen at 0.24 to 0.32 percent stabilises austenite, raises strength and adds more to the pitting number, weight for weight, than either of the other two. The ferritic half of the structure supplies resistance to chloride stress corrosion cracking, which is the failure mode that limits 300-series austenitics in warm chloride service.
Two consequences follow for anyone buying forgings. Yield strength at 550 MPa minimum is roughly double that of 316L, so wall thicknesses and section sizes come down. Against that, the grade is sensitive to temperature in a way austenitics are not: hold it in the intermediate range and intermetallic phases precipitate, taking toughness and corrosion resistance with them. That sensitivity governs how the material is forged, annealed, welded and used in service, and it is the reason a super duplex forging either comes out right or comes out brittle.
Designations and standards
| System or product form | Designation |
|---|---|
| UNS number | S32750 |
| Werkstoff, DIN and EN | 1.4410 |
| EN name | X2CrNiMoN 25-7-4 |
| Swedish SS | 2328 |
| Forgings, flanges and fittings | ASTM A182 Grade F53, ASME SA-182 F53 |
| Bar and shapes | ASTM A276, ASTM A479 |
| Plate, sheet and strip | ASTM A240 |
| EN flat products for pressure purposes | EN 10028-7 |
| Bar to EN | EN 10088-3 |
| ASME welding classification | P-number 10H, Group number 1 |
| Sour service | NACE MR0175 / ISO 15156 |
| Welding consumables | AWS ER2594 for gas tungsten arc, E2594 for manual metal arc |
SAF and SAF 2507 are trademarks of their proprietor. This works manufactures to the UNS S32750 composition and to the ASTM, ASME and EN specifications listed above. Trade names appear here only to identify the grade.
Chemical composition, weight percent
Limits follow UNS S32750 as written into ASTM A182 Grade F53 and ASTM A479. The aim column gives the target each heat is melted to.
| Element | Min | Max | Aim | Function |
|---|---|---|---|---|
| Cr, chromium | 24.0 | 26.0 | 25.0 | Passive film, general corrosion resistance |
| Ni, nickel | 6.0 | 8.0 | 7.0 | Austenite balance, toughness |
| Mo, molybdenum | 3.0 | 5.0 | 4.0 | Pitting and crevice resistance in chlorides |
| N, nitrogen | 0.24 | 0.32 | 0.30 | Austenite stabiliser, strength, pitting resistance |
| C, carbon | – | 0.030 | 0.020 max | Held low against carbide precipitation |
| Mn, manganese | – | 1.20 | 0.80 max | Deoxidiser, nitrogen solubility |
| Si, silicon | – | 0.80 | 0.40 max | Deoxidiser |
| Cu, copper | – | 0.50 | 0.30 max | Residual, capped |
| P, phosphorus | – | 0.035 | 0.025 max | Impurity |
| S, sulphur | – | 0.020 | 0.010 max | Impurity, affects hot workability |
| Fe, iron | Balance | Matrix | ||
EN 1.4410 caps sulphur at 0.015 percent, tighter than the 0.020 percent allowed by the ASTM range. Orders written to the EN number are melted to the tighter limit. Nitrogen is controlled under vacuum oxygen decarburisation, because the grade only reaches its strength and pitting numbers if nitrogen lands inside the band.
Mechanical properties
Minimum values required by ASTM A182 Grade F53 in the solution annealed and quenched condition, tested at room temperature.
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength, Rm, minimum | 800 MPa | 116 ksi |
| Yield strength, Rp0.2, minimum | 550 MPa | 80 ksi |
| Elongation, minimum | 15 % | 15 % in 2 in |
| Hardness, maximum | 310 HB | about 32 HRC |
| Ferrite content | 35 to 65 % | 35 to 65 % |
Strength in this grade comes from the duplex structure and from nitrogen in solution, not from any transformation. It cannot be raised by heat treatment, and a purchase specification calling for a solution plus age cycle on S32750 should be queried before the order is released.
A182 does not call for impact testing on F53 as standard. Offshore, subsea and sour-service specifications routinely add Charpy V-notch testing at low temperature, together with a maximum hardness tighter than the 310 HB in the base standard. State the test temperature, the energy values and the sampling location on the enquiry, since those requirements drive the forging reduction and the annealing practice rather than being added afterwards.
Physical data and service limits
| Property | Value | Note |
|---|---|---|
| Density | 7.8 g/cm3 | 0.281 lb/in3 |
| Magnetic response | Ferromagnetic | The ferrite phase makes the grade magnetic |
| Hot working range | 1000 to 1200 C | Reheat if the piece falls below 1000 C |
| Solution anneal | 1040 to 1120 C | 1900 to 2050 F, rapid quench |
| Stress relief | Not by subcritical hold | Full solution anneal and quench instead |
| Maximum service temperature | about 315 C | 600 F, set by secondary phase formation |
| Hardening by heat treatment | Not possible | Solid solution and duplex structure only |
Duplex grades carry a lower thermal expansion coefficient and higher thermal conductivity than austenitic stainless steels, which helps in heat exchangers and where a duplex part is bolted to carbon steel. Take exact values for expansion, conductivity, modulus and specific heat from the mill datasheet that applies to your order, because published figures differ between product forms.
Corrosion performance
The pitting resistance equivalent number is calculated as chromium plus 3.3 times molybdenum plus 16 times nitrogen. At the aim composition the result is about 42. Across the full specification range the arithmetic gives roughly 38 at the minima and 48 at the maxima, so the figures of 40 to 42 quoted in trade literature describe normal production material. In this grade the pitting resistance is balanced between the two phases, so neither austenite nor ferrite becomes the weak link.
| Mechanism or medium | Behaviour | Comment |
|---|---|---|
| Chloride stress corrosion cracking | Excellent | The reason the grade replaces 316L in warm chlorides |
| Chloride pitting and crevice | Excellent | Comparable to 6 percent molybdenum superaustenitic alloys. Passes ASTM G48 method A at 50 C minimum |
| Organic acids | Very good | Formic and acetic acid at concentrations and temperatures that attack austenitics quickly |
| Inorganic acids | Good | Broadly comparable to high-alloy austenitic grades |
| Seawater and brine | Very good | Watch crevices and deposits at the upper end of the temperature range |
| Erosion and corrosion fatigue | Very good | High strength works with corrosion resistance rather than against it |
| Sour service | Qualified | Listed under NACE MR0175 / ISO 15156 within the limits of that standard |
| High temperature oxidation | Not applicable | A corrosion resistant grade, not a heat resistant one. Above 315 C look at Inconel 625 or Incoloy 825 |
Corrosion figures are selection guidance drawn from published mill literature for UNS S32750 and are not a warranty for any specific service. Welded and as-forged surfaces behave differently from pickled test coupons, and crevice geometry usually sets the service limit rather than the alloy itself.
SAF 2507 forged products
Every item is forged against a drawing or a dimensional data sheet, solution annealed, machined to the agreed allowance and tested before shipment. Single pieces and prototype quantities are quoted.
Seamless rolled rings
Radial-axial rolled from an upset and pierced blank, so grain flow follows the circumference. Rectangular, contoured and stepped sections to 6,000 mm outside diameter.
Forged flanges
Weld neck, blind, slip-on, socket weld, lap joint, orifice and long weld neck to A182 F53, with ASME B16.5, B16.47 or API 6A dimensions, or to drawing. RF, RTJ and FF faces.
Round bars and shafts
Forged, peeled or rough turned bar for pump and mixer shafts, stems, downhole tooling and fasteners. Turned lengths to 14,000 mm.
Discs, blanks and tube sheets
Upset forged discs, covers, blind flanges and heat exchanger tube sheets, drilled or undrilled, proof machined for volumetric inspection. To 5,000 mm machined diameter.
Sleeves, bushings and hollows
Bored and trepanned hollows for cylinders, liners, nozzles and pump casings, to 1,600 mm diameter by 10,000 mm on the deep-hole drilling machine.
Valve and wellhead parts
Bodies, bonnets, stems, seat rings, blocks, spools and manifolds for ball, gate, globe, check and plug valves. API 6A and NACE MR0175 / ISO 15156 on request.
| Form | Dimensions to give |
|---|---|
| Seamless rolled ring | Outside diameter, inside diameter, height, section profile if not rectangular |
| Flange | Type, nominal size, class, facing, bore, or the drawing |
| Round bar or shaft | Diameter, length, straightness class, surface condition |
| Disc or tube sheet | Diameter, thickness, bore if any, drilling pattern |
| Sleeve or hollow | Outside diameter, inside diameter, length, bored or trepanned |
| All forms | Quantity, delivery condition, NDT class, certification level, impact and ferrite requirements, applicable project specification |
Forging route and heat treatment
Melting
Carbon, alloy, stainless and duplex grades run through the electric arc furnace, are refined in a ladle furnace and are decarburised under vacuum where low carbon and controlled nitrogen are needed. For S32750 that vacuum oxygen decarburisation step is the one that matters, because nitrogen has to finish inside a band 0.08 percent wide. Electroslag remelting is available where a project calls for a tighter inclusion rating or better transverse properties. Each heat is analysed before release and the heat number follows the steel through every later operation.
Open-die forging and ring rolling
Billets are heated slowly to 1000 C, then taken up into the working window and forged or ring rolled to a controlled reduction schedule. Deformation resistance climbs steeply as the temperature falls, and below 1000 C the steel is at risk of sigma phase precipitation, so a piece that cools past that point goes back to the furnace rather than taking another blow. This discipline, not press tonnage, is what separates a sound super duplex forging from a brittle one.
Solution annealing
Finished forgings are solution annealed at 1040 to 1120 C and quenched rapidly in water, immediately after hot or cold forming. Rapid cooling restores the austenite and ferrite balance and takes intermetallic phases back into solution. Section thickness governs how fast the quench has to be, which is why heavy rings and thick tube sheets are planned around the furnace and quench tank from the start. Where maximum corrosion resistance is specified, annealed parts are pickled and rinsed to remove the oxide and any chromium-depleted surface layer.
Machining and welding
Machining
This grade needs its own cutting data. Compared with machinability-improved 2205, cutting speed in turning with coated cemented carbide tooling comes down by about 40 to 50 percent, while feeds are reduced only slightly, in the order of 10 to 15 percent, and with care. Rigid setups, sharp tools, positive rake geometry and generous coolant all pay for themselves, because the material work hardens under a rubbing or dwelling tool.
Welding
Weldability is good. Gas tungsten arc welding is the first choice and manual metal arc is also used. Filler is over-alloyed in nickel to rebuild austenite in the weld metal: ER2594 for gas tungsten arc, E2594 for manual metal arc. Preheat and post-weld heat treatment are not normally required. Keep heat input and interpass temperature under control, since time spent in the intermediate temperature range is what precipitates secondary phases in the heat affected zone. Where a welded assembly is to carry the full corrosion performance of the parent metal, a post-weld solution anneal and quench is the only way to restore it fully.
Testing and certification
Every order is documented back to the melt number. Standard scope and the options that duplex buyers usually add:
Chemical analysis
Ladle analysis on every heat, product analysis on request, positive material identification before shipment.
Mechanical testing
Tensile and hardness to A182 F53. Charpy V-notch at low temperature where the project specification calls for it.
Ferrite content
Point count to ASTM E562, or magnetic measurement, reported against the 35 to 65 percent band.
Intermetallic phases
ASTM A923 screening for sigma and other secondary phases, by the method the specification nominates.
Corrosion testing
ASTM G48 method A pitting test at the agreed temperature, with coupon location stated on the order.
Non-destructive examination
Ultrasonic to EN 10228-3, SEP 1921 or ASTM A388. Dye penetrant to ASTM E165, dimensional and visual inspection.
Certificates are issued to EN 10204 3.1, or EN 10204 3.2 with third party inspection and release by TUV, SGS, BV, DNV, LR or NK. The works holds CCS, BV, DNV, LR and NK approvals.
Plant capability
Most forging suppliers in China buy billet. This works starts one step earlier, at the furnace, and nothing between melting and final machining leaves the site.
| Item | Detail |
|---|---|
| Established | 1997 |
| Employees | 460, including 9 senior engineers, 32 intermediate engineers and 140 technicians |
| Melting | EF, LF, VOD, IF, VIM, IGESR, VAR. Maximum heat 60 t |
| Forging | Open-die presses 6,300 t, 4,000 t and 2,000 t. Hammers 5 t down to 750 kg |
| Ring rolling | Radial-axial mills 6 m, 3 m and 1 m. Maximum outside diameter 6,000 mm |
| Heat treatment | 14 furnaces, car-bottom and well type, deepest well 15,000 mm |
| Machining | Vertical lathes to 5,000 mm swing, horizontal lathes to 14,000 mm, CNC lathes and machining centres, deep-hole drilling to 1,600 mm by 10,000 mm |
| Maximum single piece | 30,000 kg |
| Minimum order | 10 kg, no minimum piece count |
| Lead time | 20 to 60 days depending on size, heat treatment and test scope |
| Approvals | CCS, BV, DNV, LR, NK |
| Export markets | North America, Europe, Middle East, Asia-Pacific |
Where SAF 2507 forgings are used
Oil and gas
Subsea and deepwater production hardware, downhole tooling, wellhead and manifold parts, platform process and service water piping, firewater systems.
Desalination and seawater
High pressure reverse osmosis plant, seawater piping and pumps, ballast and injection water systems, salt evaporation equipment.
Chemical and petrochemical
Heat exchangers, separators, pressure vessels, tube sheets, piping and fittings handling chloride-bearing or organic acid streams.
Pulp and paper
Digesters, liquor tanks, bleach plant equipment and paper machine components.
Power generation
Flue gas desulphurisation plant, condenser and cooling water components, shafts and rings for turbines and compressors.
Mechanical engineering
Gearbox and compressor parts, pump shafts and sleeves, high strength corrosion resistant structural components.
Questions buyers ask
What is SAF 2507 equivalent to?
UNS S32750, Werkstoff 1.4410, EN name X2CrNiMoN 25-7-4 and Swedish SS 2328 all describe the same super duplex grade. Forgings are ordered to ASTM A182 or ASME SA-182 Grade F53. Bar, plate and shapes fall under ASTM A479, A240 and A276.
What are the minimum mechanical properties?
A182 Grade F53 requires 800 MPa, or 116 ksi, minimum tensile strength, 550 MPa, or 80 ksi, minimum 0.2 percent yield strength, 15 percent minimum elongation in two inches and hardness no higher than 310 HB, which is about 32 HRC.
What is the PREN of SAF 2507?
About 42 at the aim composition, using chromium plus 3.3 times molybdenum plus 16 times nitrogen. Across the full specification range the arithmetic gives roughly 38 at the minima and 48 at the maxima, which is why published figures sit between 40 and 42 for normal production material. In practical terms the chloride pitting and crevice resistance is comparable to the 6 percent molybdenum superaustenitic alloys, at roughly double their strength.
Where a project sets a minimum PREN, state it on the enquiry so the melt can be aimed at it rather than at the middle of the range.
At what temperature is the grade forged?
Between about 1000 and 1200 C, with slow heating up to 1000 C. A piece that falls below 1000 C goes back to the furnace, because deforming or holding the steel under that temperature risks sigma phase, which costs both toughness and corrosion resistance.
How is it heat treated after forging?
Solution annealed at 1040 to 1120 C and quenched rapidly in water, immediately after forming. The quench restores the austenite and ferrite balance and dissolves intermetallic phases. There is no hardening treatment for this grade, so an ageing cycle in a specification should be queried before the order is released.
What is the maximum service temperature?
Normally taken as 315 C, or 600 F. Super duplex grades precipitate secondary phases on long exposure above that, and toughness falls before corrosion resistance does. Where the duty is hotter, the usual substitutes are nickel alloys such as Inconel 625 or Incoloy 825.
How does it compare with 2205?
2205 is a standard duplex grade at roughly 22 Cr and 3 Mo, ordered as A182 Grade F51, which requires 620 MPa tensile and 450 MPa yield as minima. SAF 2507 carries 25 Cr, 4 Mo and more nitrogen, lifting those minima to 800 and 550 MPa and raising the pitting number with them. The cost is harder machining, a narrower forging window and tighter control over heat treatment. Where 2205 already passes the corrosion duty, it remains the cheaper choice.
Is SAF 2507 the same as A182 F55?
No. F53 covers UNS S32750, which is this grade. F55 covers UNS S32760, a different super duplex containing tungsten and copper. Both exceed PREN 40, but the chemistries differ and neither can be substituted for the other without the buyer approving the change in writing.
What size forgings can you supply?
Rings to 6,000 mm outside diameter on the radial-axial mill, single pieces to 30,000 kg against a 60 t heat and a 6,300 t press, turned lengths to 14,000 mm and bored hollows to 1,600 mm by 10,000 mm. Minimum order is 10 kg with no minimum piece count. Heavy super duplex sections are governed by quench capability as much as by press size, so send the drawing and the test scope together and the feasible envelope will be confirmed with the quotation.
Who manufactures these forgings?
Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The works has melted and forged on one site since 1997 and holds CCS, BV, DNV, LR and NK approvals. Enquiries go to sales@steelforgepieces.com or +86 189 2135 9659.
Enquiry
Send the drawing or the dimensions, the governing specification, the quantity, the certification level and any impact, ferrite or corrosion test requirement. You will get a price, a lead time and a note on anything that would be better produced as a rolled ring, a hollow or a near-net-shape blank.
Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Email sales@steelforgepieces.com
Telephone and WhatsApp +86 189 2135 9659