Metal Materials
AISI 2507 Super-Duplex Stainless Steel: Properties, Fabrication & Applications Guide
AISI 2507 super-duplex stainless steel is a high-performance alloy that represents the pinnacle of corrosion-resistant materials. It is a super-duplex stainless steel, meaning it has a balanced ferritic-austenitic microstructure (approximately 50% ferrite, 50% austenite) and a very high PREN (Pitting Resistance Equivalent Number) of 41-45.
Key takeaways
- The performance of AISI 2507 is defined by its unique chemical composition and the balanced microstructure achieved through precise processing.
- 2507 is used in the most demanding applications across industries where corrosion and strength are critical.
- The manufacturing process for 2507 is designed to create and maintain the critical 50-50 ferrite-austenite microstructure.
- Comparing 2507 to other materials helps clarify its position as a premium alloy for extreme conditions.
What Are the Key Properties of AISI 2507?
The performance of AISI 2507 is defined by its unique chemical composition and the balanced microstructure achieved through precise processing.
Chemical Composition
The high levels of chromium, molybdenum, and nitrogen are key to its exceptional corrosion resistance and strength.
| Element | Content Range (%) | Its Role in Performance |
|---|---|---|
| Chromium (Cr) | 24 – 26 | Provides outstanding corrosion resistance and forms a stable passive layer. |
| Nickel (Ni) | 6 – 8 | Stabilizes the austenite phase, providing toughness and ductility. |
| Molybdenum (Mo) | 3 – 5 | Critically important for resistance to pitting and crevice corrosion in chlorides. |
| Nitrogen (N) | 0.24 – 0.32 | The key strengthening element. Increases yield strength and pitting resistance. |
| Manganese (Mn) | ≤ 1.2 | Aids in processing. |
| Silicon (Si) | ≤ 0.8 | Acts as a deoxidizer. |
| Carbon (C) | ≤ 0.03 | Kept low to prevent carbide precipitation. |
Mechanical and Physical Properties
2507 provides exceptional strength compared to standard stainless steels.
| Property | Typical Value | Why It Matters |
|---|---|---|
| Yield Strength | ≥ 550 MPa | 3 times higher than 316L (205 MPa), allowing for thinner sections. |
| Tensile Strength | ≥ 800 MPa | Provides a strong safety margin against failure. |
| Hardness | ≤ 310 HB | Provides good wear resistance. |
| Elongation | ≥ 15% | Provides adequate ductility for forming and fabrication. |
| Density | 7.8 g/cm³ | Slightly lower than standard stainless steels. |
| PREN | 41 – 45 | Exceptional resistance to pitting corrosion. |
- Corrosion Resistance: This is the standout feature. 2507 offers excellent resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-rich environments, outperforming standard austenitic and duplex grades. It also meets NACE MR0175 standards for sour service (H₂S).
- Microstructure: The balanced 50-50 ferrite-austenite structure is critical to its properties. This balance must be maintained through proper heat treatment.
- Weldability: It has fair weldability and requires precise control. Low heat input (0.5-1.5 kJ/mm), a low interpass temperature (≤100°C), and matching filler metal (ER2594) are essential.
Where Is AISI 2507 Used in the Real World?
2507 is used in the most demanding applications across industries where corrosion and strength are critical.
Offshore Oil and Gas
2507 is used for subsea pipelines, manifolds, and wellhead components that must withstand high pressure, seawater, and sour gas.
- Case Study: A Brazilian oil company replaced 2205 with 2507 for subsea wellheads. The 2507’s resistance to sulfide stress cracking eliminated wellhead failures, cutting maintenance costs by 90% and extending service life from 7 to 20 years.
Water Treatment and Desalination
2507 is used for high-pressure piping in desalination plants, where it must resist both high pressure and high chloride concentrations.
- Case Study: A Saudi desalination plant tested both 2205 and 2507 tubes. After 5 years, the 2205 tubes showed pitting. The 2507 tubes showed no corrosion and remained operational for over 15 years.
Chemical Processing and Power Generation
2507 is used for heat exchangers, absorber towers, and other equipment that handles corrosive acids and high temperatures.
- Case Study: A U.S. geothermal plant used 2507 for heat exchanger tubes operating at 280°C. After 8 years, there was no corrosion or creep deformation, compared to 2205 tubes which failed every 3 years.
How Is AISI 2507 Manufactured?
The manufacturing process for 2507 is designed to create and maintain the critical 50-50 ferrite-austenite microstructure.
Steelmaking and Forming
- Steelmaking: It is made in an Electric Arc Furnace (EAF) with precise control of the high chromium, molybdenum, and nitrogen content.
- Hot Rolling: The steel is hot rolled into plates, bars, and other shapes. The hot working range is 1150-1000°C.
- Solution Annealing: This is the critical heat treatment. The steel is heated to 1025-1125°C and then rapidly water quenched. This restores the balanced microstructure and prevents the formation of harmful phases like sigma or chi.
Welding and Fabrication
- Welding: Welding requires strict control. Matching filler metal (ER2594), low heat input (0.5-1.5 kJ/mm), and a low interpass temperature (≤100°C) are essential. A root gas purge with nitrogen is used to prevent oxidation.
- Machining: Due to its high strength, 2507 is more difficult to machine than standard stainless steels. Carbide tools and reduced speeds are recommended.
- Post-Weld Cleaning: Passivation with nitric acid is required to restore the corrosion resistance of the weld zone.
AISI 2507 vs. Other Stainless Steels
Comparing 2507 to other materials helps clarify its position as a premium alloy for extreme conditions.
| Material | Yield Strength | PREN | Relative Cost | Best For |
|---|---|---|---|---|
| AISI 2507 | ≥ 550 MPa | 41 – 45 | High | Deep-sea, sour gas, high-chloride environments |
| 2205 Duplex | ≥ 450 MPa | 35 – 40 | Medium | General offshore, marine, chemical applications |
| 316L Stainless | ≥ 205 MPa | 24 – 26 | Low | Mild corrosive environments, general use |
| 904L Austenitic | ≥ 220 MPa | 33 – 38 | Higher | Sulfuric acid, moderate chloride applications |
| Inconel 625 | ≥ 415 MPa | > 50 | Very High | Extreme temperatures, ultra-corrosive environments |
Key Takeaway: AISI 2507 offers the best combination of ultra-high strength and exceptional corrosion resistance for the most demanding environments. It is significantly stronger and more corrosion-resistant than 2205, and while it is more expensive, it is also significantly more cost-effective than nickel-based superalloys for applications where its properties are sufficient. For projects requiring the highest level of corrosion resistance and strength, 2507 is the optimal choice.
AISI 2507 super-duplex stainless steel is a high-performance material engineered for the most extreme corrosive and high-stress environments. Its unique balanced microstructure, high alloy content, and exceptional PREN provide unparalleled resistance to pitting, crevice corrosion, and stress corrosion cracking. Combined with its high yield strength, it enables the design of lighter, more efficient, and more durable equipment. For critical applications in offshore oil and gas, desalination, and chemical processing, 2507 offers the ultimate combination of performance, reliability, and cost-effectiveness.
How to write a spec that gets priced correctly
A drawing is a contract. If it leaves a number open, the shop fills that number in with its own default. The default is rarely the one you had in mind. Put these five lines on every RFQ and most of the back-and-forth disappears before it starts.
- Alloy designation and the standard behind it
- Temper or heat treatment condition
- Mechanical properties you actually need
- Mill certificate and traceability requirement
- Finish and the faces it applies to
The point is not paperwork. Each line removes a decision the shop would otherwise make for you. A complete RFQ comes back priced. An incomplete one comes back guessed.
What actually drives the price
Buyers usually push on material because it is the line they can see. In practice the material is rarely the biggest number on a quote. These five lines decide most of it:
- alloy grade and mill availability
- stock size versus finished size
- heat treatment and testing
- machinability
- certification
Ask for the quote split by line. A supplier who cannot break it down is guessing, and you will pay for the guess. The line you can usually renegotiate is the tolerance band, not the raw material.
Problems you will meet, and the fix
Every process has a failure mode it prefers. The same four show up again and again on this kind of work, and none of them are mysteries once you know what to look for.
- Substituting a similar grade without telling anyone
- Hardness that varies across a single bar
- Corrosion in a weld heat-affected zone
- Distortion after heat treatment on a thin part
Catch the fault on the first part, not the hundredth. A first-article check costs an hour. A bad batch costs the whole order. Write the check into the purchase order so nobody has to remember it.
What to check on the first article
The first article is the cheapest inspection you will ever buy. Use it properly and the rest of the run becomes boring, which is exactly what you want.
- Every dimension on the drawing, with the measured value written beside it.
- The material certificate, matched to the heat or lot number on the parts.
- The finish against the sample you approved, under the same light.
- Fit against the mating part, assembled rather than measured.
- Packaging, because parts that arrive damaged were never in tolerance.
Check in this order: datums, then mating features, then cosmetic faces. If the datums are wrong, every number after them is noise. Keep the report on file. When a problem shows up in month six, that document is the only thing that tells you what changed.
How to compare two quotes fairly
Two numbers are not comparable unless the scope matches. Line them up before you decide, because a low number with three gaps is not a low number.
Same drawing, same material, same finish, same inspection. Anything else is a different job wearing the same part number. Then look at what each quote leaves out. Freight, packaging, certificates and tooling are the usual gaps.
Ask each supplier to state their assumptions in writing. The one who does is usually the one who has run the process before.
Scaling from one part to a batch
The first part teaches you the process. The hundredth teaches you the process cost.
Watch three things as volume grows: setup amortisation, tool wear, and how much hand work the finish still needs. If the unit price barely moves between ten and a hundred, the cost sits in material or in hand work, not in setup. Ask which, because only one of them is negotiable.
Lead time behaves the same way. A one-off is scheduled around other jobs. A repeat order is scheduled around your forecast. Give the shop a forecast and the lead time gets shorter, not longer.
How to read a supplier's quote
A quote is a short document with a long shadow. Four things in it decide whether the job runs smoothly, and only one of them is the price.
- The scope line. It should name the process, the material and the finish, not just the part.
- The tolerance basis. General tolerance or the drawing, and which standard it follows.
- The exclusions. Tooling, freight, certificates and inspection are the usual omissions.
- The validity date. Material prices move, and an open-ended quote is a promise nobody can keep.
Read the exclusions before you read the total. A quote that leaves out tooling is not cheaper. It is a quote for a different job.
What to send with the first order
The first order sets the pattern for every order after it. Send a complete package once and the shop files it, and the second order takes a fraction of the time.
- A STEP or native model plus a PDF drawing carrying the same revision letter.
- The material callout by standard number, not by trade name.
- The finish and the exact faces it applies to.
- Any test the part must pass: fit, seal, drop, salt spray, dielectric.
- A contact who can answer a question inside one working day.
Then write down what was agreed. An email that confirms the material, the finish and the date is worth more than a longer purchase order that leaves them open.
When this is the wrong choice
A good supplier tells you when the process does not fit. These are the cases where we say so.
- The volume is so low that setup costs more than the parts are worth.
- The tolerance is tighter than the process can hold without a second operation.
- The geometry cannot be made without a tool feature that will not pay back.
- The material you need is not available in the form the process requires.
- The schedule is shorter than the tooling or setup time, and nobody has said so yet.
None of these are refusals. They are reasons to look at a different route, and the earlier that conversation happens the cheaper it is. The most expensive mistake in manufacturing is a process chosen before the question was understood.
Planning the ramp from prototype to production
The gap between one good part and a thousand identical ones is a plan, not a machine. Three decisions close it.
First, freeze the design. Every change after tooling starts is a re-cut, and re-cuts are where schedules go. Second, decide the inspection level. A prototype is checked by eye; a production part is checked against a report. Third, agree the change process in writing, including who pays for it.
Write the ramp down as dates and owners, not as intentions. A ramp plan with three names and three dates is worth more than a page of good intentions.
What documentation to expect
Paperwork is not bureaucracy when a part fails at the customer. It is the only record of what was agreed. A normal shipment should carry four documents.
- A dimensional report covering every callout on the drawing.
- A material certificate traceable to the heat or lot number.
- A finish or coating certificate where the specification requires one.
- A packing list that matches the carton labels.
If a supplier cannot produce these on request, they are not running a controlled process. Ask for one sample set before you place the first order and you will know exactly what you are buying.
FAQ About AISI 2507 Super-Duplex Stainless Steel
When should I choose 2507 over 2205?
Choose 2507 when your project involves high chlorides (>10,000 ppm), sour service (H₂S), or high pressure (>300 bar). Its superior PREN (41-45) and sulfide stress cracking resistance make it the better choice for these extreme conditions. Use 2205 for milder conditions, such as low-pressure seawater or less aggressive chemicals, to save cost.
Can 2507 be used at temperatures above 300°C?
Avoid prolonged use above 300°C. At temperatures between 300-500°C, harmful phases such as sigma and alpha-prime can form, which significantly reduce the material’s toughness and corrosion resistance. For applications above 300°C, consider a high-temperature austenitic grade like 347H or a nickel-based superalloy.
What is critical for welding 2507?
Three key steps are essential for successful welding: 1) Use matching filler metal (ER2594). 2) Strictly control heat input (0.5-1.5 kJ/mm) and interpass temperature (≤100°C). 3) Purge the weld root with an inert gas (e.g., nitrogen) to prevent oxidation. Post-weld passivation is also required to restore corrosion resistance.
Our solution for AISI 2507 Super-Duplex Stainless Steel
YiguProto runs metal sourcing and machining in house, from a single prototype to a production batch. We quote the process, the material and the finish as separate lines, so you can see where the money goes instead of arguing with one number.
Send a STEP file or a drawing and you get a DFM report in one to two business days. It flags the features that add cost and the features that will not hold tolerance on the process you picked.
Every order ships with an inspection report on the features you call out. If a part misses, we make it again. Ready to price a part? Start with a free quote and DFM review, or read more about our metal sourcing and machining. You can also talk to an engineer before you commit to a drawing.
FAQ about AISI 2507 Super-Duplex Stainless Steel
Can AISI 2507 Super-Duplex Stainless Steel be made in small quantities?
Yes, and small quantities are where a good supplier earns the next order. Setup dominates the price at low volume, so the cheapest route is usually the one with the fewest operations, not the cheapest material.
How long does a first article take?
Usually a few business days once the drawing is frozen, and longer if tooling is involved. The date we give you is the date we confirm in writing, not the date we hope for.
Is there a minimum order quantity?
No hard minimum. One part is fine. What changes with volume is which costs dominate, so a single unit is priced mostly on setup and a thousand units are priced mostly on cycle time and material.
What should I check before approving the parts?
Datums first, then the features that mate, then the cosmetic faces. Ask for a dimensional report, a material certificate and a finish sample. A part can be inside every tolerance and still not fit, so assemble one before you sign.
What is AISI 2507 Super-Duplex Stainless Steel used for?
AISI 2507 Super-Duplex Stainless Steel turns up wherever the part has to do a real job at a predictable cost: brackets, housings, fixtures, covers and the fittings that hold them together. The honest test is whether the properties match the load and the environment, not whether the material is fashionable.
What files do you need in order to quote?
A STEP file plus a PDF drawing that carries the same revision letter. The model carries the geometry and the drawing carries the intent. When the two disagree, the shop picks one, and it is never the one you meant.
The short version
AISI 2507 Super-Duplex Stainless Steel rewards the buyer who reads the data sheet and the drawing together. Pick the option for the property that matters, not for the price per kilo.
Tighten only what mates. Test a sample before the run. Then let the process do the rest.