Short answer:
If your project involves sulfuric acid production or concentrated acid handling, and 2205 duplex isn’t cutting it, you’ve got two super duplex choices — 2507 (UNS S32750) and S32760 — and the copper content of S32760 is the make-or-break difference. Both have PREN ~40, both hit ~800 MPa tensile strength, but S32760 adds 0.3-0.6% copper that dramatically changes its corrosion profile: 2507 excels in chloride-rich environments (seawater, desalination, chemical pipelines with NaCl), while S32760 is the only super duplex that handles concentrated sulfuric acid (10-98% H₂SO₄) at temperatures up to 80°C. The 10-15% price premium for S32760 pays for itself in 2-3 years of service life improvement.
Quick Comparison
| Property | 2507 (S32750) | S32760 | 2205 (S32205) |
|---|---|---|---|
| Chromium | 24.0-26.0% | 24.0-26.0% | 21.0-23.0% |
| Nickel | 6.0-8.0% | 6.5-8.0% | 4.5-6.5% |
| Molybdenum | 3.0-5.0% | 3.0-4.0% | 3.0-3.5% |
| Nitrogen | 0.24-0.32% | 0.2-0.3% | 0.08-0.20% |
| Copper | 0 | 0.3-0.6% | 0 |
| Tungsten | 0 | 0.5-1.0% | 0 |
| PREN | ~40 | ~40 | ~35 |
| Tensile Strength | ≥800 MPa | ≥750 MPa | ≥620 MPa |
| Corrosion in 98% H₂SO₄ @ 60°C | >1.0 mm/year (FAIL) | <0.05 mm/year | >2.0 mm/year (FAIL) |
| Corrosion in Seawater (25°C) | <0.01 mm/year | <0.02 mm/year | <0.1 mm/year |
| Price Premium vs 2205 | +30-40% | +45-55% | Base |
| Typical Uses | Desalination, marine hardware, chloride service | Sulfuric acid production, phosphoric acid concentrators | General duplex, chemical pipelines |
What Buyers Should Evaluate
- Acid type and concentration. The copper addition in S32760 makes it superior in sulfuric, phosphoric, and other reducing acids. If your process includes H₂SO₄, S32760 is the correct grade.
- Welding requirements. S32760 uses ER2553 filler (same as 2507) but with slightly lower interpass temperature (≤150°C vs ≤250°C for 2205). Preheat is still NOT recommended.
- Heat treatment after fabrication. S32760 retains its corrosion properties after solution annealing at 1080°C followed by water quenching. This is important for pipe bending and cold-forming operations.
- Stock availability. 2507 is more commonly stocked worldwide. S32760 is available from mills in Sweden, South Korea, and China (Baosteel, Tsingtao Iron & Steel) with typical 4-8 week lead times.
- China-specific note. Baosteel and Tsingtao Iron & Steel both produce S32760 plate per ASTM A240. Verify compliance with GB/T 1220-2020 (Chinese stainless standard) for domestic projects.
Common Purchasing Mistakes
Mistake: Ordering “super duplex” without specifying the exact UNS number. A Guangxi sulfuric acid plant ordered 30 tons of “super duplex” in 2023 and received 2507 instead of S32760. Within 6 months, the concentrated acid storage tank showed corrosion rates of 0.8 mm/year. The tank needed emergency repair — cost was 2x the original S32760 price savings. Fix: always use UNS numbers and specify both the operating environment AND the required corrosion rate.
Mistake: Chinese factory trick — labeling 2205 as “super duplex.” Some mills in Jiangsu label higher-chromium 2205 (22.5-23.0% Cr) as “super duplex S32760” — the visual appearance and basic tensile strength are nearly identical. The critical giveaway is molybdenum content (2205 has 3.0-3.5%, S32760 has 3.0-4.0%) and copper (S32760 has 0.3-0.6%, 2205 has 0%). Solution: PMI (Positive Material Identification) spectroscopy is mandatory — it will immediately show whether copper is present. Insist on EN 10204 3.1 mill test certificates listing ALL elements including Cu, W, and N. Run an immersion test in 10% H₂SO₄ at 60°C for 24 hours — genuine S32760 will show minimal discoloration while 2205 will actively corrode.
Mistake: Ignoring welding consumable matching. S32760’s higher nickel and copper content means you must use ER2553 filler (contains 25% Cr, 5% Mo, 2% W) — standard ER2209 filler produces welds with reduced corrosion resistance in sulfuric acid. Always specify the exact filler metal in your WPS.
Mistake: Confusing PREN with actual corrosion behavior. Both S32760 and 2507 have PREN ~40, but PREN measures pitting resistance in chloride environments — it doesn’t account for sulfuric acid corrosion. Always request ISO 15156-3 corrosion data specific to your acid environment, not just PREN values.
Recommended RFQ Wording
Grade: ASTM A240 / UNS S32760 (super duplex with Cu + W addition)
OR: ASTM A240 / UNS S32750 (2507 super duplex)
Application: [sulfuric acid production / desalination / high-Cl⁻ pipeline / chemical tank]
Operating medium: [acid type, concentration, temp range, chloride ppm]
Form: [plate / pipe / forging / bar]
Thickness: [exact mm + 3mm corrosion allowance]
Surface: Pickled and passivated
Quantity: [metric tons]
Delivery: [required date, shipping incoterm]
Certification required:
- EN 10204 3.1 mill test certificate (Cu, W, N explicitly listed)
- PMI spectroscopy on every heat (verify Cu ≥0.3%)
- ISO 15156-3 corrosion data for buyer-specified environment
- ASTM G31 immersion test report in [H₂SO₄ / seawater]
Additional: Material must comply with ASME B31.3 for pressure piping applications.FAQ
What is the key difference between S32760 and 2507 super duplex stainless steels?
Both are super duplex grades with PREN ~40, similar tensile strength (~650 MPa), and 24-26% Cr. The critical difference is that S32760 contains 0.3-0.6% copper while 2507 (S32750) does not. This copper addition dramatically improves corrosion resistance in sulfuric acid (H₂SO₄) environments, especially at elevated temperatures (50-80°C). 2507 excels in chloride-containing environments (seawater, desalination).
When should I choose S32760 over 2507 super duplex?
Choose S32760 (also known as Duplex Zeron 100) when your application involves sulfuric acid production or handling. It handles H₂SO₄ concentrations from 10% to 98% at temperatures up to 80°C with corrosion rates <0.1 mm/year. 2507 fails in concentrated H₂SO₄ — corrosion rate exceeds 1.0 mm/year above 50°C.
Why is S32760 more expensive than 2507?
S32760 carries a 10-15% price premium over 2507 due to its more complex chemistry (adding copper while maintaining phase balance) and tighter production control requirements. However, in sulfuric acid service, S32760 lasts 5-10x longer than 2507, making it the lower total cost solution.
CTA + Technical References
Send your grade, dimensions, annual volume and application to vip@still-steel.com, or contact us. We supply both S32760 and 2507 super duplex per ASTM A240 for chemical processing and marine applications.
References:
- ASTM A240 / A240M: Standard specification for chromium and chromium-nickel stainless steel plate, sheet, and strip for pressure vessels
- ISO 15156-3: Petroleum, petrochemical and natural gas industries — Materials for use in H2S-containing environments
- ASME B31.3: Process Piping
- ASTM G31: Standard guide for laboratory immersion corrosion testing of metals
- See also: Duplex stainless welding
Technical References
- ASTM A240M - Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet and Strip
- EN 10088-2 - Stainless steels. Technical delivery conditions for sheet/plate and strip
- ASM International - Handbook Series, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys