2205 Duplex Stainless Steel
Also: UNS S32205, UNS S31803, 1.4462, X2CrNiMoN22-5-3, duplex 2205, SAF 2205, F51 and F60 (forgings), CD3MN (cast), 22Cr duplex
2205 duplex is half austenite, half ferrite: about twice the yield strength of 316 with far better chloride pitting and stress-corrosion resistance. Values solution annealed.
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At a glance
| Density | 7.8 g/cm³ (0.282 lb/in³) |
|---|---|
| Tensile strength | 655-800 MPa (95-116 ksi); ASTM A240 minimum 655 MPa (95 ksi) |
| Yield strength | 450-550 MPa (65-80 ksi); minimum 450 MPa (65 ksi) |
| Hardness | About 240-260 HB (25 HRC); ASTM A240 maximum 293 HB (31 HRC) |
| Elongation | 25-35% (minimum 25%) |
| Modulus of elasticity | 200 GPa (29 Msi) |
| Thermal | Melts at 1420-1460 °C (2590-2660 °F); thermal conductivity ~15-19 W/m·K; expansion ~13 um/m·K; service range about -50 to 300 °C (-60 to 570 °F) |
| Composition | Fe, 22-23% Cr, 4.5-6.5% Ni, 3-3.5% Mo, 0.14-0.20% N, up to 0.03% C, up to 2% Mn, up to 1% Si |
Typical values, Solution annealed at 1020-1100 °C (1870-2010 °F) and water quenched (the only supplied condition). Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- Tougher than 316: high strength, work hardening and a two-phase chip. Run 20-30% slower than 316 with sharp coated carbide, positive rake, rigid fixtures and steady feed; drilling and tapping want short-flute tools and plenty of coolant.
- WeldabilityGood
- Welds by TIG, MIG, SAW and plasma with 2209 filler (over-alloyed in nickel so the weld solidifies with enough austenite). Heat input 0.5-2.5 kJ/mm, interpass under 150 °C (300 °F), no preheat, argon with 2% nitrogen for TIG roots, and no autogenous welds unless the part is solution annealed afterward. Verify weld ferrite with a ferritescope or ASTM E562.
- FormabilityFair
- Bends and rolls cold with about twice the force of 316 and more springback; use a minimum inside radius of about 2t. Hot forming at 950-1150 °C (1750-2100 °F) must be followed by a full solution anneal.
- Corrosion resistanceExcellent
- Resists chloride pitting and crevice corrosion well beyond 316 (PREN about 35) and is practically immune to chloride stress-corrosion cracking below about 150 °C (300 °F). Handles seawater, brines, sour gas (NACE-listed) and many acids; hot concentrated acids and very hot seawater move to super duplex or nickel alloys.
2205 is the standard duplex stainless: 22% chromium, 5% nickel, 3% molybdenum and 0.17% nitrogen balanced to solidify as roughly half ferrite, half austenite. The ferrite gives it about twice the yield strength of 304 or 316 (450 MPa / 65 ksi minimum) and immunity to the chloride stress-corrosion cracking that fails austenitic grades in warm brines; the austenite keeps toughness and weldability. Its pitting resistance number is about 35, against 24-26 for 316. S32205 is the tighter modern chemistry; S31803 is the older, looser one, and most mill product is certified to both.
It is bought for chemical, pulp and paper, oil and gas, desalination and marine equipment: pressure vessels, heat exchangers, digesters, subsea and process piping, storage tanks, pump shafts and seawater fittings. Because the yield strength doubles, vessels and tanks in 2205 can be thinner than in 316, which often makes the more expensive alloy the cheaper job. It is magnetic, expands less than austenitic grades (about 13 um/m·K), and machines like a tough, work-hardening steel.
The rules are thermal. Prolonged exposure to 300-1000 °C (570-1830 °F) embrittles it (475 °C embrittlement below about 550 °C, sigma and chi phases above it), so there is no stress relief, no post-weld heat treatment other than a full solution anneal, a weld heat-input window, and a maximum service temperature of about 300 °C (570 °F). Below about -50 °C (-60 °F) the ferrite goes brittle. Weld with over-alloyed 2209 filler, never autogenously without a post-weld anneal, and check ferrite in the weld.
Heat treatment
Solution anneal only: 1020-1100 °C (1870-2010 °F) followed by a rapid water quench to lock in the 50/50 phase balance. There is no hardening treatment and no stress relief. Any hold between about 300 and 1000 °C (570-1830 °F) precipitates embrittling phases (alpha-prime around 475 °C, sigma and chi at 600-1000 °C) and destroys toughness and corrosion resistance; if a part is heated into that range by forming or welding beyond the allowed window, re-anneal it fully.
Tempers and conditions
- Solution annealed (the only condition)
Stock forms
- Plate and sheet
- Round and flat bar
- Seamless and welded pipe and tube
- Forgings (F51, F60)
- Fittings and flanges
- Castings as CD3MN (ASTM A890 4A)
Relative cost
Tier 4 of 5. About 1.2-1.5x 316 per pound (less nickel, more chromium and molybdenum, plus the mill premium), but the doubled yield strength lets designers cut wall thickness, so finished vessels and tanks often cost less than 316. Stocked in plate, pipe and bar; sheet and small bar are thinner on the ground.
Typical applications
- Chemical and petrochemical pressure vessels and heat exchangers
- Oil and gas process piping, subsea flowlines and wellhead components
- Desalination and seawater cooling systems
- Pulp and paper digesters and bleach-plant equipment
- Storage tanks and tankers for chemicals
- Pump shafts, impellers and valve bodies in brines
- Bridges, rebar and structures in marine environments
Process compatibility
How 2205 takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | FairFair | Machines like a strong, work-hardening steel: 20-30% slower than 316, sharp coated carbide, rigid setups, steady feed, generous coolant. |
| Laser Cutting | GoodGood | Fiber lasers cut plate with nitrogen assist at slightly lower speeds than 316; the narrow heat-affected zone does not need annealing. |
| Waterjet Cutting | ExcellentExcellent | No heat input at any thickness, so no embrittlement question; the safe choice for thick plate and pressure parts. |
| Plasma Cutting | GoodGood | Fine for plate over 12 mm (1/2"); grind back the heat-affected edge on pressure-retaining welds. |
| Press Brake Forming | FairFair | Twice the force of 316, more springback, 2t minimum inside radius; over-bend and use a wide die. |
| Welding | GoodGood | 2209 filler, heat input 0.5-2.5 kJ/mm, interpass under 150 °C (300 °F), no autogenous welds without an anneal; qualify to ASME IX with a ferrite check. |
| TIG Welding | GoodGood | Roots in pipe and tube with 2209 filler and argon plus 2% nitrogen; back-purge with nitrogen-bearing gas to hold the weld ferrite balance. |
| MIG Welding | GoodGood | Fill and cap passes on plate with 2209 wire; watch heat input and interpass so the heat-affected zone stays within the window. |
| Forging | GoodGood | Forge at 950-1150 °C (1750-2100 °F) and solution anneal and quench afterward; F51 and F60 flanges and fittings are made this way. |
| Passivation | ExcellentExcellent | ASTM A967 citric or nitric after machining and pickling after welding restore the passive film; standard on process equipment. |
| Electropolishing | GoodGood | Polishes evenly across both phases for pump and sanitary parts; a little less bright than 316L. |
| Nondestructive Testing (NDT) | GoodGood | Pressure parts carry radiography or ultrasonic testing of welds plus ferrite measurement; specify the acceptance code on the drawing. |
| Heat Treating | Not recommendedNot recommended | No hardening, no stress relief and no post-weld heat treatment exist for duplex; anything between 300 and 1000 °C embrittles it. Only a full solution anneal and water quench is allowed. |
| Metal 3D Printing | FairFair | Printed 2205 solidifies almost fully ferritic and needs a solution anneal to recover the duplex balance; rare in job shops, so specify wrought or cast instead. |
Compare 2205
Design and sourcing tips
- Specify "2205 per ASTM A240 UNS S32205" (plate) or the matching A276 / A790 / A182 F60 for bar, pipe and forgings; S32205 has the tighter chemistry and is what mills ship today.
- Design to the higher yield strength: a 2205 vessel or tank can be 20-30% thinner than 316 at the same pressure, which is how the alloy pays for itself.
- Put the weld rules on the drawing: 2209 filler, heat input 0.5-2.5 kJ/mm, interpass 150 °C (300 °F) maximum, no autogenous welds, ferrite check on the weld metal.
- Never call for stress relief, post-weld heat treatment or any hold between 300 and 1000 °C; only a full solution anneal and water quench is acceptable.
- Keep service between about -50 and 300 °C (-60 and 570 °F); below that the ferrite embrittles and above it the alloy ages in service.
- Use 2205 where 316 pits or cracks (warm chlorides, brines, sour gas); for hot concentrated acids or seawater above about 40 °C in crevices step up to a super duplex or a nickel alloy.
Frequently asked questions
- Is 2205 duplex stainless magnetic?
- Yes, moderately. Half of its structure is ferrite, so a magnet sticks, less strongly than to carbon steel but unmistakably. It cannot be made non-magnetic; use an austenitic grade if that matters.
- What is the difference between 2205 and 316 stainless?
- 2205 has about twice the yield strength (450 MPa / 65 ksi minimum versus 205 MPa / 30 ksi), much better chloride pitting resistance (PREN about 35 versus 25) and near immunity to chloride stress-corrosion cracking. 316 is non-magnetic, more ductile, easier to form, weld and machine, usable to much higher temperatures and cheaper per pound. 2205 wins in brines and warm chlorides; 316 wins for general fabrication.
- Can 2205 duplex be welded?
- Yes, with discipline. Use 2209 filler, keep heat input between about 0.5 and 2.5 kJ/mm and interpass temperature under 150 °C (300 °F), do not preheat, and never weld it autogenously unless the part will be solution annealed afterward. Too little heat leaves the weld ferritic and brittle; too much precipitates sigma phase. Qualified procedures include a ferrite measurement.
- What temperature can 2205 duplex be used at?
- About -50 to 300 °C (-60 to 570 °F). Pressure codes cap it near 300-315 °C because prolonged exposure above that ages the ferrite (475 °C embrittlement), and below about -50 °C the ferrite loses toughness. For hotter service use an austenitic grade; for cryogenic service, 304L or 316L.
- Is 2205 the same as S31803?
- Nearly. S31803 was the original 2205 chemistry with wider ranges for nitrogen and molybdenum; S32205 tightened them (0.14-0.20% N, 3.0-3.5% Mo) to guarantee the corrosion performance. Mills today produce to S32205 and usually certify to both, so specify S32205 and accept dual certification.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM A240, A276, A790 and A182 (minimums by product form)
- NACE MR0175 / ISO 15156 (sour service limits for duplex)
- IMOA (International Molybdenum Association) Practical Guidelines for the Fabrication of Duplex Stainless Steels
- Producer data sheets (Outokumpu 2205, Sandvik SAF 2205)
