Duplex 2205 stainless steel

Identity and order requirements

Alleima lists 485 MPa minimum 0.2% proof strength for solution-annealed SAF 2205 seamless tube and pipe at 20°C, for walls through 20 mm. Its guarantee for seamless tubes below 4 mm is 10% higher, or 533.5 MPa by direct calculation at 20°C. Walls above 20 mm may have lower properties. Alleima wall-thickness and proof-strength table

2205 is an austenitic-ferritic duplex stainless-steel family associated with UNS S31803/S32205 and EN 1.4462. SAF 2205 and Forta DX 2205 are producer product names, not evidence of provenance for unidentified stock. Outokumpu lists Forta DX 2205 as S32205, also available in S31803. Preserve the actual designation and certification rather than ordering only “duplex.” Alleima SAF 2205 · Outokumpu Forta data sheet

For a fabricated component, establish structural and corrosion acceptance alongside procurement. A satisfactory material certificate does not establish joint performance, pressure capacity or service life. Review substitutions against the complete drawing and process requirements.

A product-specific strength example

Alleima's current SAF 2205 seamless tube/pipe sheet gives these values at 20°C, for solution-annealed material with wall ≤20 mm. Walls above 20 mm may have lower values; at wall <4 mm, its guaranteed Rp0.2 is 10% higher. Alleima mechanical-property table and applicability

The A value uses L0 = 5.65√S0. Do not apply these tube values to every 2205 form or cold-worked condition. Alleima table and elongation footnote

For acceptance, reconcile the actual ordered standard, dimensions and specimen basis with the certificate. Keep 0.2% and 1.0% proof strength distinct. A tensile upper bound is not a minimum strength, and no tensile entry alone establishes an allowable stress, notch-fatigue life or toughness at a proposed temperature.

Corrosion comparison and its limits

Outokumpu uses PRE = %Cr + 3.3 × %Mo + 16 × %N for rough comparison. Its typical Forta DX 2205 composition includes 22.4% Cr, 3.1% Mo and 0.17% N. Outokumpu composition and PRE discussion

Calculated illustration: 22.4 + 3.3 × 3.1 + 16 × 0.17 = 35.35, consistent with the producer's rounded PRE of 35. This uses typical composition, not a particular heat analysis. PRE is not a corrosion rate, critical service temperature or warranty of resistance in a given liquid.

The producer distinguishes electrochemical critical-pitting-temperature tests from PRE and notes that delivered surface condition can change results. Do not treat a laboratory ranking as a finished-component exposure limit. Outokumpu localized-corrosion guidance

For a compatibility assessment, record chloride and other species, concentration, contaminants, temperature, aeration, deposits, crevices and stress. Include cleaning, shutdown and upset conditions. A pitting comparison does not qualify every crevice or dissimilar-metal interface. Obtain evidence for the actual exposure and final fabrication condition before releasing the material choice.

Define the acceptable general-corrosion rate and localized-attack criteria. Where published data do not match the duty, use producer advice and representative testing rather than inventing a universal chloride limit.

Thermal history and microstructure

Outokumpu warns that duplex steels can lose toughness and corrosion resistance through precipitation. Its guide identifies intermetallic formation in 600–1000°C and ferrite decomposition in 350–500°C, with time and cooling history important. Those ranges describe metallurgical risks, not a complete time–temperature operating envelope. Outokumpu heat-treatment discussion

A fabrication plan should record incoming condition, forming, welding, straightening and any thermal treatment. Do not add an unspecified stress-relief cycle borrowed from another steel. Obtain the correct procedure for the form, thickness and required final properties.

A hardness reading alone cannot reconstruct the thermal history or establish phase balance and corrosion performance. Where the application needs microstructure, impact or corrosion verification, define the test and sampling requirements explicitly. Evaluate weld and heat-affected regions separately from unaffected incoming stock.

Welding and forming controls

For its SAF 2205 product, Alleima recommends welding without preheat, heat input 0.5–2.5 kJ/mm, and interpass temperature <150°C. It lists ER2209 for GTAW/GMAW. These are manufacturer recommendations, not qualification of an arbitrary joint. Alleima welding section

Use a qualified procedure that resolves the actual base materials, joint, thickness, filler, shielding, heat input, temperature measurement and inspection. A maximum interpass number is one control within that procedure; it does not establish acceptable phase balance or toughness by itself. Review repairs and dissimilar-metal joints separately.

For forming and machining, qualify tooling, force, springback and cutting parameters on the actual supplied condition. Plan allowances and final inspection around the sequence of operations. Keep generic material guidance separate from a workshop instruction or the finished-part acceptance plan.

Dimensions, mass and release

Outokumpu lists a nominal density of 7.8 kg/dm³ for Forta DX 2205. For an ideal solid 100 × 100 × 10 mm blank, volume is 0.1 dm³ and estimated mass is 0.78 kg. This original calculation excludes dimensional tolerance, holes, coatings and hardware. Outokumpu physical-property table

Use actual finished geometry for a final mass model. For fitted or pressure-containing components, establish dimensional, surface, leak and proof-test requirements separately. Catalog density or proof strength does not establish the component's pressure rating.

At release, connect the exact designation, heat/lot, certificate, condition, drawing, qualified fabrication route and final inspection. Retain repair and thermal history where relevant. Confirm that any corrosion or mechanical evidence applies to the final form and condition rather than merely to the alloy family.

Source versions

Alleima's live seamless-tube/pipe data sheet prints an update of 2026-02-11. The Outokumpu PDF's actual footer reads 1008EN:13, June 2022, despite later modification timestamps in some download URLs; the PDF was checked directly. Sources reviewed 2026-11-01, America/Los_Angeles. Obtain current controlled documentation for the actual order.

See grades, tempers and conditions.