Quick Answer
Quick Answer
Duplex 2205 (EN 1.4462) has a mixed austenite-ferrite microstructure with approximately 22 % Cr, 5 % Ni, and 3 % Mo. It delivers roughly twice the yield strength of standard austenitic grades and a PREN of ~35, providing excellent resistance to pitting, crevice corrosion, and chloride stress corrosion cracking.
Overview
Duplex 2205 is the most widely used duplex stainless steel grade worldwide. Its dual-phase microstructure — approximately 50 % austenite and 50 % ferrite — provides a combination of properties unattainable with single-phase austenitic or ferritic grades:
- High yield strength (~450 MPa minimum) enabling thinner wall sections and weight savings
- Good toughness down to approximately −40 °C
- Excellent chloride resistance — PREN ~35 significantly above the austenitic 316L (~24)
- Resistance to chloride stress corrosion cracking (SCC) — a failure mode to which 304 and 316 are susceptible in hot chloride environments
The UNS number is S32205 (formerly S31803). The European designation is 1.4462. In ASME applications the grade appears as SA-790 S32205.
Chemical Composition — Duplex 2205 / 1.4462
| Element | ASTM A790 S32205 | EN 1.4462 |
|---|---|---|
| Carbon (C) | ≤ 0.030 | ≤ 0.030 |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.030 | ≤ 0.035 |
| Sulfur (S) | ≤ 0.020 | ≤ 0.015 |
| Chromium (Cr) | 22.0 – 23.0 | 21.0 – 23.0 |
| Molybdenum (Mo) | 3.0 – 3.5 | 2.50 – 3.50 |
| Nickel (Ni) | 4.5 – 6.5 | 4.5 – 6.5 |
| Nitrogen (N) | 0.14 – 0.20 | 0.10 – 0.22 |
Nitrogen is a critical alloying element in duplex grades — it is an austenite stabilizer, raises yield strength, and significantly improves pitting resistance (each 0.1 % N adds approximately 1.6 to PREN). The MTC must report nitrogen.
PREN Calculation
PREN = %Cr + 3.3×%Mo + 16×%N
For a typical 2205 at mid-composition: PREN ≈ 22.5 + 3.3×3.0 + 16×0.17 ≈ 22.5 + 9.9 + 2.7 ≈ 35.1
This positions 2205 well above austenitic 316L (PREN ~24) and below super duplex 2507 (PREN ~43).
Mechanical Properties — Duplex 2205
| Property | ASTM A790 S32205 | EN 1.4462 (+AT) |
|---|---|---|
| Ultimate Tensile Strength (UTS) | 620 MPa (90 ksi) min | 620 – 880 MPa |
| 0.2 % Proof Strength (YS) | 450 MPa (65 ksi) min | 450 MPa min |
| Elongation in 50 mm | 25 % min | 25 % min |
| Hardness (max) | 290 HBW / 31 HRC | 290 HBW |
| Charpy impact (−40 °C) | — | 100 J (transverse) |
The YS of ~450 MPa minimum is approximately twice that of 316L (170 MPa), enabling significant wall thickness reductions in pressure-containing components.
Physical Properties
| Property | Typical Value |
|---|---|
| Density | 7.82 g/cm³ |
| Thermal conductivity (20 °C) | 19 W/(m·K) |
| Thermal expansion (20–100 °C) | 13.0 × 10⁻⁶ /°C |
| Modulus of elasticity | 200 GPa |
| Magnetic permeability | Ferromagnetic (due to ferrite phase) |
Unlike austenitic grades, duplex steels are ferromagnetic. This must be factored into applications involving magnetic fields or inspection methods relying on permeability.
Standards Coverage
| Standard | Product Form | Designation |
|---|---|---|
| ASTM A790 | Seamless and welded pipe | S32205 / S31803 |
| ASTM A240 | Plate, sheet, strip | S32205 |
| ASTM A182 | Forgings | F51 (S31803) / F60 (S32205) |
| ASTM A276 | Bar | S32205 |
| ASME SA-240 | Pressure vessel plate | S32205 |
| EN 10088-2 | Flat products | 1.4462 |
| NORSOK M-650 | Qualifying materials for offshore | 22Cr duplex |
Applications
Duplex 2205 is the preferred grade when both high strength and chloride resistance are required:
- Oil and gas — subsea umbilicals, wellhead components, topside pipework
- Desalination — brine piping, evaporators, multi-stage flash units
- Chemical processing — vessels and heat exchangers handling chloride-containing process streams
- Pulp and paper — digesters and bleaching equipment
- Marine structures — propeller shafts, deck fittings, structural members in splash zone
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Try TestCert freeFrequently Asked Questions
What is the maximum service temperature for duplex 2205?
Duplex 2205 should generally be limited to a maximum continuous service temperature of 280–300 °C. Above this range, sigma phase and other intermetallic embrittlement phases can form in the ferrite, causing significant toughness loss. For elevated-temperature service above 300 °C, austenitic grades or nickel alloys are more appropriate.
Is duplex 2205 weldable?
Yes, but with more care than austenitic grades. Key requirements include: correct heat input (typically 0.5–2.5 kJ/mm), maximum interpass temperature of 150 °C, and use of over-alloyed filler (ER2209 for GTAW/GMAW) to restore the correct phase balance in the weld. Post-weld solution annealing is sometimes required for thick sections or highly corrosive service.
What is the difference between S31803 and S32205?
S31803 was the original UNS designation for 2205. S32205 is a refined version with a narrower composition range — particularly a tighter minimum nitrogen of 0.14 % (vs 0.08 % in S31803) and minimum Cr of 22.0 % (vs 21.0 %). S32205 is the preferred designation for new construction; many standards now list S32205 as the primary UNS number with S31803 retained for legacy material.
How does TestCert handle nitrogen reporting for duplex MTCs?
TestCert flags duplex 2205 MTCs where nitrogen is absent or not reported, since nitrogen is both a mandatory composition element and essential for PREN calculation. When all elements are present, the platform automatically calculates PREN and compares it against any customer-specified minimum (commonly 35 for 2205 in offshore specifications).