2507 Duplex Stainless Steel: Properties and Key Applications
Share
Table Of Content
Table Of Content
2507 Duplex Stainless Steel is a high-performance alloy known for its unique combination of properties derived from its dual-phase microstructure, which consists of approximately equal parts austenite and ferrite. Classified as a duplex stainless steel, it primarily contains chromium (Cr) and nickel (Ni) as its main alloying elements, along with molybdenum (Mo) and nitrogen (N). This composition significantly enhances its corrosion resistance, strength, and toughness compared to conventional stainless steels.
Comprehensive Overview
The unique microstructure of 2507 Duplex Stainless Steel provides it with exceptional mechanical properties, including high tensile strength and yield strength, making it suitable for demanding applications in various industries. The alloy typically exhibits a yield strength of around 550 MPa (80 ksi) and a tensile strength exceeding 800 MPa (116 ksi), which is significantly higher than that of standard austenitic stainless steels.
Advantages:
- Corrosion Resistance: Excellent resistance to pitting and crevice corrosion, particularly in chloride environments.
- Strength: High strength-to-weight ratio, allowing for thinner sections in applications without compromising structural integrity.
- Weldability: Good weldability with proper techniques and filler materials.
Limitations:
- Cost: Generally more expensive than standard stainless steels due to alloying elements.
- Machinability: More challenging to machine than austenitic grades, requiring specialized tools and techniques.
Historically, 2507 Duplex Stainless Steel has gained prominence in industries such as oil and gas, chemical processing, and marine applications due to its ability to withstand harsh environments while maintaining mechanical integrity.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S32750 | USA | Closest equivalent to EN 1.4410 |
| AISI/SAE | 2507 | USA | Commonly referred to as 2507 |
| ASTM | A240/A240M | USA | Standard specification for stainless steel plates |
| EN | 1.4410 | Europe | Equivalent to UNS S32750 |
| DIN | X2CrNiMoN25-7-4 | Germany | Similar properties with minor compositional differences |
| JIS | SUS32950 | Japan | Equivalent with slight variations in composition |
| ISO | 32750 | International | Standard designation for duplex stainless steel |
The differences between equivalent grades can impact selection based on specific application requirements, such as mechanical properties or corrosion resistance in particular environments.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| Cr (Chromium) | 24.0 - 26.0 |
| Ni (Nickel) | 6.0 - 8.0 |
| Mo (Molybdenum) | 3.0 - 5.0 |
| N (Nitrogen) | 0.24 - 0.30 |
| Fe (Iron) | Balance |
The primary alloying elements in 2507 Duplex Stainless Steel play crucial roles:
- Chromium: Enhances corrosion resistance and contributes to the formation of a protective oxide layer.
- Nickel: Improves toughness and ductility, balancing the strength provided by chromium.
- Molybdenum: Increases resistance to pitting and crevice corrosion, especially in chloride environments.
- Nitrogen: Enhances strength and improves resistance to stress corrosion cracking.
Mechanical Properties
| Property | Condition/Temper | Test Temperature | Typical Value/Range (Metric) | Typical Value/Range (Imperial) | Reference Standard for Test Method |
|---|---|---|---|---|---|
| Tensile Strength | Annealed | Room Temp | 800 - 1000 MPa | 116 - 145 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Annealed | Room Temp | 550 - 750 MPa | 80 - 109 ksi | ASTM E8 |
| Elongation | Annealed | Room Temp | 25 - 40% | 25 - 40% | ASTM E8 |
| Hardness (Rockwell B) | Annealed | Room Temp | 90 - 95 HRB | 90 - 95 HRB | ASTM E18 |
| Impact Strength | Charpy V-notch | -40°C | 50 J | 37 ft-lbf | ASTM E23 |
The combination of high tensile and yield strength makes 2507 Duplex Stainless Steel particularly suitable for applications requiring high mechanical loads, such as pressure vessels and structural components in marine environments.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | Room Temp | 7.8 g/cm³ | 0.282 lb/in³ |
| Melting Point/Range | - | 1350 - 1400 °C | 2462 - 2552 °F |
| Thermal Conductivity | Room Temp | 14 W/m·K | 81.4 BTU·in/(hr·ft²·°F) |
| Specific Heat Capacity | Room Temp | 500 J/kg·K | 0.12 BTU/lb·°F |
| Electrical Resistivity | Room Temp | 0.72 µΩ·m | 0.0000013 Ω·in |
| Coefficient of Thermal Expansion | 20 - 100 °C | 16.0 x 10⁻⁶/K | 8.9 x 10⁻⁶/°F |
Key physical properties such as density and thermal conductivity are significant for applications in heat exchangers and pressure vessels, where efficient thermal management is crucial.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-5% | 20-60 °C (68-140 °F) | Excellent | Risk of pitting at higher concentrations |
| Sulfuric Acid | 10-20% | 20-40 °C (68-104 °F) | Good | Limited resistance at elevated temperatures |
| Sea Water | - | Ambient | Excellent | Highly resistant to seawater corrosion |
| Acetic Acid | 5-10% | 20-60 °C (68-140 °F) | Fair | Susceptible to stress corrosion cracking |
| Ammonium Hydroxide | 10-30% | 20-60 °C (68-140 °F) | Good | Risk of localized corrosion |
2507 Duplex Stainless Steel exhibits excellent resistance to a variety of corrosive environments, particularly in chloride-rich conditions, making it ideal for marine applications. However, it can be susceptible to stress corrosion cracking in certain environments, particularly when exposed to high concentrations of chlorides or in the presence of ammonia.
When compared to other stainless steel grades, such as 316L and 904L, 2507 offers superior resistance to pitting and crevice corrosion, particularly in seawater and other aggressive environments. However, it may not perform as well in reducing environments compared to 904L.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 300 °C | 572 °F | Suitable for continuous use |
| Max Intermittent Service Temp | 400 °C | 752 °F | Short-term exposure |
| Scaling Temperature | 600 °C | 1112 °F | Risk of oxidation above this temperature |
| Creep Strength Considerations | 500 °C | 932 °F | Creep resistance decreases significantly above this temperature |
At elevated temperatures, 2507 Duplex Stainless Steel maintains good mechanical properties but may experience oxidation and scaling. It is essential to consider these factors when designing components for high-temperature applications.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER2594 | Argon | Requires preheating |
| MIG | ER2594 | Argon/CO2 | Good for thin sections |
| SMAW | E2594 | - | Suitable for field applications |
2507 Duplex Stainless Steel is generally considered weldable, but care must be taken to avoid issues such as hot cracking. Preheating and post-weld heat treatment can help mitigate these risks.
Machinability
| Machining Parameter | 2507 Duplex Stainless Steel | Benchmark Steel (AISI 1212) | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 20% | 100% | Requires specialized tooling |
| Typical Cutting Speed (Turning) | 30-50 m/min | 80-100 m/min | Use carbide tools for best results |
Machining 2507 Duplex Stainless Steel can be challenging due to its high strength and work hardening characteristics. It is advisable to use high-speed steel or carbide tools and to maintain optimal cutting speeds to achieve better results.
Formability
2507 Duplex Stainless Steel exhibits moderate formability. Cold forming is feasible, but care must be taken to avoid excessive work hardening. Hot forming is also possible, but temperatures should be controlled to prevent degradation of mechanical properties.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Solution Annealing | 1020 - 1100 °C (1868 - 2012 °F) | 30 minutes | Air or water | Dissolve carbides, improve ductility |
| Stress Relief | 300 - 400 °C (572 - 752 °F) | 1 hour | Air | Reduce residual stresses |
| Hardening | 1000 - 1100 °C (1832 - 2012 °F) | 30 minutes | Air | Increase hardness and strength |
Heat treatment processes such as solution annealing are crucial for optimizing the microstructure of 2507 Duplex Stainless Steel, enhancing its mechanical properties and corrosion resistance.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Oil and Gas | Offshore platforms | High strength, corrosion resistance | Durability in harsh environments |
| Chemical Processing | Heat exchangers | Resistance to pitting and crevice corrosion | Long service life in aggressive media |
| Marine | Shipbuilding | Excellent resistance to seawater corrosion | Longevity and structural integrity |
| Power Generation | Boiler tubes | High strength and heat resistance | Performance under high temperatures |
| Desalination Plants | Pipes and fittings | Corrosion resistance in saline environments | Reliability and safety |
Other applications include:
- Pressure vessels
- Storage tanks
- Valves and fittings
- Structural components in construction
The selection of 2507 Duplex Stainless Steel for these applications is primarily due to its superior mechanical properties and corrosion resistance, which are critical for ensuring safety and longevity in demanding environments.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | 2507 Duplex Stainless Steel | 316L Stainless Steel | 904L Stainless Steel | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High strength | Moderate strength | Moderate strength | 2507 offers superior strength |
| Key Corrosion Aspect | Excellent in chlorides | Good in chlorides | Excellent in reducing environments | 2507 excels in pitting resistance |
| Weldability | Good | Excellent | Good | 2507 requires careful welding |
| Machinability | Moderate | Good | Moderate | 2507 is more challenging to machine |
| Formability | Moderate | Good | Good | 2507 has limitations in forming |
| Approx. Relative Cost | Higher | Moderate | Higher | Cost considerations may affect selection |
| Typical Availability | Moderate | High | Moderate | Availability can vary by region |
When selecting 2507 Duplex Stainless Steel, considerations such as cost-effectiveness, availability, and specific application requirements are crucial. Its unique properties make it an excellent choice for applications where both strength and corrosion resistance are paramount. However, the higher cost and machining challenges may necessitate careful evaluation against alternative materials.
In summary, 2507 Duplex Stainless Steel stands out as a versatile and robust material suitable for a wide range of demanding applications, particularly in corrosive environments. Its unique combination of properties ensures reliability and performance, making it a preferred choice in various industries.