Duplex Stainless Steel Forgings
Duplex stainless combines austenite and ferrite in roughly equal proportion, delivering about twice the yield strength of 304 or 316 alongside outstanding resistance to chloride stress corrosion cracking.
- Chromium
- 21.0 – 23.0%
- Nickel
- 4.5 – 6.5%
- Molybdenum
- 2.5 – 3.5%
- Yield Strength
- 450 MPa min
- Structure
- ~50% ferrite / 50% austenite
- Equivalent
- UNS S31803 / S32205, 1.4462
Duplex Stainless Steel Forgings at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Chromium: 21.0 – 23.0%
- Nickel: 4.5 – 6.5%
- Molybdenum: 2.5 – 3.5%
- Yield Strength: 450 MPa min
- Structure: ~50% ferrite / 50% austenite
- Equivalent: UNS S31803 / S32205, 1.4462
Two Phases, Two Benefits
Ferrite contributes strength and chloride stress corrosion resistance; austenite contributes toughness and general corrosion resistance. Maintaining the phase balance through forging and solution annealing is the whole technical challenge of the grade.
- Twice the yield strength of 316
- Excellent chloride SCC resistance
- Phase balance controlled by heat treatment
- Solution annealed after forging
Tight Processing Window
Duplex must be forged and solution annealed within controlled temperature ranges, or brittle sigma phase forms and toughness collapses. This is not a grade to attempt without proper temperature control and verification.
Applications
Offshore oil and gas hardware, desalination equipment, chemical tankers, pulp and paper process components, and seawater handling systems.
Duplex Stainless Composition and Mechanical Properties
Duplex stainless steel contains roughly equal proportions of ferrite and austenite. The ferrite contributes strength and resistance to chloride stress corrosion cracking; the austenite contributes toughness and general corrosion resistance. Type 2205 (UNS S31803 / S32205, material number 1.4462) is the workhorse grade, forged as F51 under ASTM A182.
| Property | Typical value |
|---|---|
| Chromium | 21.0 – 23.0% |
| Nickel | 4.5 – 6.5% |
| Molybdenum | 2.5 – 3.5% |
| Nitrogen | ≈ 0.14 – 0.20% |
| Carbon | 0.030% maximum |
| Yield strength | 450 MPa minimum — roughly double 316 |
| Structure | ≈ 50% ferrite / 50% austenite |
| Solution annealing | ≈ 1,020 – 1,100 °C, rapid cooling |
Sigma Phase: The Reason Duplex Demands Control
Held in the wrong temperature range, duplex forms sigma phase — a brittle intermetallic that collapses toughness without any visible sign on the part. Avoiding it is a matter of controlled forging temperatures and mandatory solution annealing afterwards, followed by verification. This is not a grade to give to a shop without temperature control and phase-balance verification. Where it is processed correctly, the payoff is real: roughly double the yield strength of 316 allows thinner, lighter sections, which on large offshore assemblies can outweigh the higher price per kilogram.
- Solution annealing after forging is mandatory, not optional
- Sigma phase forms invisibly and destroys toughness
- Phase balance verified after processing
- Used offshore, in desalination and in hot chloride service
People also ask
Why does duplex need solution annealing after forging?
To restore the roughly 50:50 ferrite-austenite phase balance and dissolve any brittle sigma phase formed during processing.
How much stronger is duplex than 316?
Roughly double the yield strength — 450 MPa minimum against 205 MPa — allowing thinner, lighter sections for the same duty.
Topics covered on this page
- duplex stainless forging India
- 2205 duplex forged components
- duplex forging manufacturer
- offshore stainless forging supplier
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
Why is duplex stronger than 316?
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Its ferrite phase roughly doubles yield strength, allowing thinner, lighter sections for the same load.
What is sigma phase and why does it matter?
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A brittle intermetallic that forms if duplex is held in the wrong temperature range. It destroys toughness, so processing temperatures are tightly controlled and verified.
Is solution annealing required?
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Yes, after forging, to restore the correct phase balance and dissolve any harmful precipitates.
Where is duplex specified?
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Offshore, desalination, chemical tankers and seawater systems, where chloride stress corrosion would attack 316.