Jade Alloys supplies duplex and super duplex stainless steel products for demanding industrial applications, including fasteners, round bars, sheets, plates, pipes, tubes, gaskets and plugs. The company supports grade selection based on application requirements, applicable standards and service conditions. The distinction between duplex and super duplex stainless steel is not just based on chromium content. Both types of steel combine austenitic and ferritic phases to achieve high strength and corrosion resistance. The true difference lies in the grade specifications, alloying elements, PREN value, mechanical properties, and working conditions.
While technical comparisons often state that duplex contains about 22 percent chromium and super duplex approximately 25 percent chromium, this is useful for general information purposes, but may be misleading when making engineering decisions. Chromium content depends on the grade of the steel. For example, both 2205 and 2507 have certain composition ranges and not just one percentage of chromium.
What Is Duplex Stainless Steel?
Duplex stainless steel is a stainless steel family with a two phase microstructure containing both austenite and ferrite. The balanced structure provides a useful combination of corrosion resistance, strength and resistance to chloride-related stress corrosion cracking.
Grade 2205 is the benchmark duplex grade and is commonly identified with UNS S31803 and S32205. It contains approximately 22 percent chromium, with molybdenum, nickel and nitrogen contributing to its corrosion resistance and strength. The exact composition depends on the applicable specification and grade. For bolting applications, Duplex 2205 fasteners are suitable for demanding industrial environments where the properties of the 2205 grade are required.
What Is Duplex Stainless Steel?
Duplex stainless steel is a stainless steel family with a two phase microstructure containing both austenite and ferrite. The balanced structure provides a useful combination of corrosion resistance, strength and resistance to chloride-related stress corrosion cracking.
Grade 2205 is the benchmark duplex grade and is commonly identified with UNS S31803 and S32205. It contains approximately 22 percent chromium, with molybdenum, nickel and nitrogen contributing to its corrosion resistance and strength. The exact composition depends on the applicable specification and grade. For bolting applications, Duplex 2205 fasteners are suitable for demanding industrial environments where the properties of the 2205 grade are required.
Duplex vs Super Duplex Stainless Steel at a Glance
| Property | Duplex 2205 | Super Duplex 2507 | Super Duplex 2760 |
| UNS Number | S31803 / S32205 | S32750 | S32760 |
| EN Number | 1.4462 | 1.4410 | 1.4501 |
| Chromium | 22.0 to 23.0% | 24.0 to 26.0% | Approximately 25% |
| Nickel | 4.5 to 6.5% | 6.0 to 8.0% | Approximately 7% |
| Molybdenum | 3.0 to 3.5% | 3.0 to 5.0% | Approximately 3.0 to 4.0% |
| Nitrogen | 0.14 to 0.20% | 0.24 to 0.32% | Approximately 0.20 to 0.30% |
| PREN | Approximately 35 to 38 | Approximately 42 to 44 | 42 and above |
| Minimum Yield Strength | About 450 MPa | About 550 MPa | About 550 MPa |
| Minimum Tensile Strength | About 655 MPa | About 795 MPa | 760 MPa or higher depending on specification |
| Relative Cost | Lower | Higher | Higher |
| Typical Service | General industrial and chloride environments | Severe chloride and seawater environments | Highly aggressive corrosion environments |
Common duplex grades
| Duplex Grade | UNS | General Classification | Typical Position |
| LDX 2101 | S32101 | Lean duplex | Lower alloy duplex applications |
| 2304 | S32304 | Lean duplex | Moderate corrosion environments |
| 2205 | S31803 and S32205 | Standard duplex | General purpose duplex grade |
| 255 | S32506 | Higher alloy duplex | More demanding corrosion environments |
Chemical Composition Differences between Duplex and Super Duplex
| Element | Duplex 2205 | Super Duplex 2507 | Main Function |
| Chromium | 22.0 to 23.0 percent | 24.0 to 26.0 percent | Improves corrosion and oxidation resistance |
| Nickel | 4.5 to 6.5 percent | 6.0 to 8.0 percent | Supports austenite formation and toughness |
| Molybdenum | 3.0 to 3.5 percent | 3.0 to 5.0 percent | Improves pitting and crevice corrosion resistance |
| Nitrogen | 0.14 to 0.20 percent | 0.24 to 0.32 percent | Increases strength and supports corrosion resistance |
| Carbon | Low | Low | Limits carbide formation |
| Manganese | Controlled maximum | Controlled maximum | Supports alloy processing |
| Silicon | Controlled maximum | Controlled maximum | Deoxidation and processing |
Duplex vs Super Duplex PREN Comparison
| Grade | Representative Chromium | Representative Molybdenum | Representative Nitrogen | Approximate PREN |
| Duplex 2205 | 22.5% | 3.25% | 0.17% | 36.5 |
| Super Duplex 2507 | 25.0% | 4.0% | 0.28% | 42.6 |
PREN and Corrosion Resistance
PREN Formula:
PREN = Cr + 3.3 × Mo + 16 × N
| Grade | Calculation | Approximate Result |
| 2205 | 22.5 + 3.3 × 3.25 + 16 × 0.17 | 36.5 |
| 2507 | 25.0 + 3.3 × 4.0 + 16 × 0.28 | 42.6 |
A higher PREN generally indicates better resistance to pitting corrosion. However, PREN should be used as a comparison indicator rather than as a complete prediction of corrosion performance.
Need help choosing between Duplex and Super Duplex?
Jade Alloys can help you select the appropriate grade and fastener specification based on corrosion conditions, strength requirements, temperature, pressure and application requirements.
Duplex vs Super Duplex Mechanical Properties
| Mechanical Property | Duplex 2205 | Super Duplex 2507 |
| Minimum Yield Strength | About 450 MPa | About 550 MPa |
| Minimum Tensile Strength | About 655 MPa | About 795 MPa |
| Elongation | About 25% | About 15% |
| Strength Level | High | Very high |
| Impact Toughness | Good when correctly processed | Good when correctly processed |
| Chloride Stress Corrosion Resistance | Very good | Excellent |
| Pitting Resistance | Very good | Excellent |
Lean Duplex, Standard Duplex, Super Duplex and Hyper Duplex Grades
| Duplex Family | Common Grade | UNS | EN Number | General Description |
| Lean Duplex | LDX 2101 | S32101 | 1.4162 | Lower alloy duplex grade |
| Lean Duplex | 2304 | S32304 | 1.4362 | Lean chromium duplex grade |
| Standard Duplex | 2205 | S31803 / S32205 | 1.4462 | Widely used duplex grade |
| Higher Alloy Duplex | 255 | S32506 | Grade specific | Higher corrosion resistance |
| Super Duplex | 2507 | S32750 | 1.4410 | High corrosion resistance |
| Super Duplex | 2760 | S32760 | 1.4501 | High alloy super duplex |
| Hyper Duplex | Grade specific | Grade specific | Grade specific | Higher alloy level than conventional super duplex |
Duplex vs Super Duplex Cost Comparison
| Cost Factor | Duplex 2205 | Super Duplex 2507 |
| Material Cost | Lower | Higher |
| Chromium Content | Lower | Higher |
| Molybdenum Content | Lower | Higher |
| Nickel Content | Lower | Higher |
| Nitrogen Content | Lower | Higher |
| Processing Requirements | Controlled | More demanding |
| Quality Control | High | More stringent |
| Typical Price Position | Baseline | Approximately 20 to 40% higher depending on market and specification |
| Best Cost Advantage | General demanding applications | Severe environments where higher corrosion resistance is required |
Duplex Stainless Steel Applications
Duplex stainless steel is often the practical choice where corrosion resistance and strength are both required without moving to a higher alloy super duplex grade.
Typical applications include:
- Chemical processing equipment
- Water treatment systems
- Oil and gas piping
- Pressure vessels
- Storage tanks
- Pulp and paper equipment
- Chemical tanker components
- Heat exchangers
- Structural components
- Marine equipment
Super Duplex Stainless Steel Applications
Super duplex is generally considered when the operating environment is more aggressive or when the additional corrosion resistance and strength justify the higher material cost.
Typical applications include:
- Offshore platforms
- Subsea equipment
- Desalination plants
- Seawater cooling systems
- Chemical processing equipment
- Oil and gas production systems
- Marine propulsion components
- Flue gas treatment equipment
- High pressure piping
- Heat exchanger components
Frequently Asked Questions
1. What is the main difference between duplex and super duplex stainless steel?
2. Is duplex 2205 better than super duplex 2507?
3. What is the PREN of duplex 2205?
4. What is the PREN of super duplex 2507?
5. Is S31803 the same as S32205?
6. Is S32750 the same as 2507?
7. Is super duplex stainless steel more expensive than duplex?
7. Can duplex stainless steel be used in seawater?
8. Which is stronger, duplex 2205 or super duplex 2507?
About Jade Alloys
Jade Alloys supplies duplex and super duplex products across a range of forms and grades, including duplex stainless steel round bars, super duplex round bars, Duplex 2205 fasteners, Super Duplex 2507 fasteners, sheets, plates, pipes, tubes, RTJ gaskets, header plugs and tube plugs. The duplex range includes grades such as S31803, S32101, S32205, S32304 and S32506, while the super duplex range includes S32750 and S32760.
For sealing applications, see the duplex RTJ gasket and super duplex RTJ gasket ranges.
