AISI 2507 Super-Duplex Stainless Steel: Properties, Fabrication & Applications Guide

AISI 2507 super-duplex stainless steel is the gold standard for extreme corrosion resistance and high strength. Its unique 2507 ferrite-austenite balance 50-50 microstructure and ultra-high 2507 PREN ≥ 40 make it ideal for the harshest environments—from deep-sea oil rigs to chemical processing plants. This guide breaks down its key specs, performance, and real-world uses to help you select it with confidence.

1. Material Overview & Key Specifications

Understanding 2507’s composition and standards is critical to unlocking its full potential. Below is a clear breakdown of its essential properties.

Chemical Composition & Standards

The 2507 super-duplex composition is engineered for strength and corrosion resistance: 24–26% chromium, 6–8% nickel, 3–5% molybdenum, and 0.24–0.32% nitrogen. These elements create its balanced microstructure and high PREN. It adheres to global standards:

• 2507 UNS S32750 (Unified Numbering System)
• 2507 EN 1.4410 equivalent (European standard for matching performance)
• 2507 ASTM A240 / 2507 ASME SA-240 (for plates, sheets, and strips)

Physical & Mechanical Properties

2507 delivers exceptional strength—far higher than standard duplex or austenitic alloys. Key metrics are organized in the table below:

A Norwegian offshore company uses 2507 ASTM A240 plates for subsea manifolds—they rely on the 550 MPa yield strength to handle 400 bar deep-sea pressure and corrosive seawater.

2. Corrosion Resistance & Environmental Performance

2507’s biggest advantage is its industry-leading corrosion resistance. Its 2507 PREN 41–45 (Pitting Resistance Equivalent Number) is far higher than 2205’s PREN of 35–40, making it nearly immune to pitting, crevice corrosion, and stress cracking in harsh fluids.

Key Corrosion-Resistant Traits

• Pitting & Crevice Corrosion: It has unmatched 2507 pitting corrosion resistance and a high 2507 crevice corrosion threshold—even in tight gaps (e.g., heat exchanger gaskets) exposed to 60 °C seawater.
• Stress Corrosion Cracking: It offers 2507 chloride stress corrosion cracking immunity—critical for desalination plants and offshore pipelines where chloride levels exceed 10,000 ppm.
• Sour Service: It meets 2507 sour service NACE MR0175 / ISO 15156 standards, resisting 2507 sulfide stress cracking in oil wells with high hydrogen sulfide (H₂S) levels.
• Chemical Resistance: It handles 2507 sulfuric acid resistance (resists 30% sulfuric acid up to 50 °C) and has higher 2507 hydrochloric acid limits than 2205 (tolerates dilute HCl up to 30 °C).

2507 vs 2205 corrosion comparison: A Saudi desalination plant tested both alloys—2205 tubes showed pitting after 5 years, while 2507 seawater corrosion rate (≤0.005 mm/year) kept 2507 tubes operational for 15+ years.

3. High-Temperature & Low-Temperature Properties

2507 performs well across a wide temperature range, though it’s optimized for moderate heat and cold environments.

High-Temperature Traits

• Strength & Oxidation: It maintains 2507 high-temperature strength up to 300 °C, with 2507 oxidation resistance up to 300 °C (suitable for warm chemical processes like acid evaporation). The 2507 continuous service temperature is 300 °C—beyond this, avoid prolonged exposure to prevent sigma phase formation.
• Creep Resistance: 2507 creep rupture data shows it can last 10,000+ hours at 250 °C under 150 MPa stress, making it ideal for high-pressure heat exchanger tubes.

Low-Temperature Traits

• Toughness: It has excellent 2507 low-temperature toughness, with 2507 impact energy at -50 °C of ≥45 J (no brittle fracture). Its 2507 cryogenic ductility also makes it suitable for Arctic offshore projects (e.g., subsea pipelines in -40 °C conditions).

A case study: A U.S. geothermal plant used 2507 heat exchanger tubes (operating at 280 °C). After 8 years, no corrosion or creep deformation occurred—unlike the previous 2205 tubes that failed every 3 years.

4. Heat Treatment & Microstructure Balance

Proper heat treatment is critical to maintaining 2507’s 50-50 ferrite-austenite balance and avoiding harmful phases like sigma, chi, or alpha-prime.

Essential Heat Treatment Processes

• Solution Annealing: Heat to 1025–1125 °C, hold for 30–60 minutes, then perform a 2507 rapid water quench (critical to prevent phase formation). This step restores the balanced microstructure and dissolves unwanted carbides.
• Hot Working: Use 1150–1000 °C as the 2507 hot working range for forging or rolling. This keeps the material ductile and preserves the ferrite-austenite balance.
• Residual Stress Relief: Heat to 400–450 °C to reduce stresses from welding or forming. Avoid 475 °C (the 2507 embrittlement at 475 °C temperature) to prevent alpha-prime embrittlement.

Microstructure Control

• Ferrite Content: Maintain 2507 ferrite content 35–55 % (tested via magnetic methods) to ensure strength and corrosion resistance.
• Phase Prevention: Avoid heating to 500–800 °C for long periods—2507 sigma phase formation kinetics and 2507 chi phase precipitation accelerate in this range, making the material brittle.

5. Welding, Fabrication & Machining Guidelines

Welding 2507 requires precise heat control to preserve its microstructure, but it’s workable with the right techniques and consumables.

Welding Tips

• Consumables: Use 2507 welding consumables 2509 / ER2594 (for TIG/MIG welding)—these match 2507’s composition and maintain the ferrite-austenite balance in the weld.
• Heat Input & Interpass Temperature: Strictly control 2507 heat input 0.5–1.5 kJ/mm (lower than 2205’s 0.5–2.5 kJ/mm) and keep 2507 interpass temperature 100 °C max (prevents sigma phase).
• Root Gas Purge: Use 2507 root gas purge 99.99 % N₂ + 5 % H₂ to ensure full austenite formation in the weld root. After welding, perform 2507 post-weld cleaning passivation (pickling with nitric acid) to remove scale and restore corrosion resistance.

Machining & Forming

• Speeds & Feeds: 2507 machining speeds and feeds should be 15–20% lower than 2205. Use 2507 tool life with coated carbide (TiAlN or diamond coatings work best—they resist wear from the alloy’s high strength).
• Formability: 2507 formability limits are moderate—cold bending is possible for thin sections, but avoid excessive strain (anneal after heavy forming to restore toughness). Use 2507 distortion control techniques (e.g., clamping during welding, slow cooling) to keep parts true to size.

6. Product Forms, Sizes & Supply Chain

2507 is available in a wide range of forms to fit nearly any high-corrosion, high-strength project.

Common Product Forms

• Plates & Sheets: 2507 super-duplex plate thickness chart ranges from 3 mm to 200 mm; 2507 sheet gauge sizes (16 gauge to 1/2 inch) are ideal for chemical vessel liners.
• Pipes & Tubes: 2507 seamless pipe ASTM A790 (for high-pressure offshore flowlines) and 2507 welded pipe ASTM A928 (for low-pressure desalination lines).
• Bars & Fittings: 2507 round bar stock (10 mm to 300 mm diameter), 2507 angle iron sizes (20×20 mm to 100×100 mm), and 2507 threaded rod grades (Grade 1 for general use, Grade 2 for high-stress applications).
• Specialty Forms: 2507 coil slit widths (10 mm to 1250 mm), 2507 hollow bar suppliers (for lightweight parts), 2507 custom forgings (e.g., valve bodies), and 2507 clad plate suppliers (for cost-effective large structures like FGD towers).

Supply Chain Tips

Work with global suppliers who stock 2507 seamless pipe ASTM A790 and hold NACE MR0175 certification—these ensure compliance for sour service. For urgent offshore projects, prioritize suppliers with local inventory of common sizes to reduce lead times.

7. Industry Applications & Case Studies

2507’s unbeatable strength and corrosion resistance make it a top choice for industries facing extreme conditions. Here are key use cases:

• Offshore & Marine: 2507 offshore flowlines, 2507 subsea pipelines, and 2507 chemical injection lines (resist seawater, H₂S, and high pressure).
• Water Treatment: 2507 desalination high-pressure piping (handles 80+ bar pressure and high chlorides).
• Power & Industrial: 2507 FGD absorber towers (remove sulfur from power plant exhausts) and 2507 heat exchanger tubes (for acid and geothermal applications).
• Pulp & Paper: 2507 pulp & paper digesters (resist chlorine-based bleaches and high temperatures).

A real example: A Brazilian oil company replaced 2205 with 2507 for subsea wellheads—2507 sulfide stress cracking resistance eliminated wellhead failures, cutting maintenance costs by 90% and extending service life from 7 to 20 years.

Yigu Technology’s Perspective

At Yigu Technology, we recommend 2507 for clients needing extreme corrosion resistance + high strength. We source 2507 ASTM A240 plates and 2507 seamless pipe ASTM A790 from certified mills, ensuring PREN 41–45 and ferrite content 35–55%. For offshore/sour service clients, we provide NACE MR0175 testing and welding support (using 2509/ER2594 consumables). While 2507 costs more than 2205, its 2x longer lifespan and lower maintenance make it cost-effective for the harshest projects.

FAQ

1. When should I choose 2507 over 2205?
   Choose 2507 if your project involves high chlorides (>10,000 ppm), sour service (H₂S), or high pressure (>300 bar). Its PREN 41–45 and sulfide stress cracking resistance outperform 2205. Use 2205 for milder conditions (e.g., low-pressure seawater) to save cost.
2. Can 2507 be used at temperatures above 300 °C?
   Avoid prolonged use above 300 °C (its continuous service temperature). At 300–500 °C, 2507 sigma phase formation and alpha-prime embrittlement occur, reducing toughness. For 300 °C+ applications, choose 347H (high-temperature strength) or 904L (corrosion resistance).
3. What’s critical for welding 2507?
   Three key steps: Use 2507 welding consumables 2509/ER2594, control heat input 0.5–1.5 kJ/mm and interpass temperature 100 °C max, and purge the root with 99.99 % N₂ + 5 % H₂. Post-weld passivation is also required to restore corrosion resistance.