Duplex 2205: UNS S31803, S32205 and EN 1.4462

“2205” is the most familiar commercial name for the standard duplex stainless-steel family built around roughly 22% chromium and 5% nickel with molybdenum and nitrogen additions.

In enquiries and MTCs you will commonly see:

• UNS S31803;
• UNS S32205;
• EN 1.4462;
• X2CrNiMoN22-5-3;
• the commercial shorthand 2205.

These designations overlap strongly, but they should not be treated as four spellings of one universal specification.

What is duplex stainless steel?

Duplex stainless steels are designed to have a mixed austenitic-ferritic microstructure.

That gives the family a useful combination of:

• higher strength than standard austenitic grades such as 316L;
• strong resistance to chloride stress-corrosion cracking;
• good resistance to pitting and crevice corrosion;
• good weldability when the correct procedures and heat input are used.

Alleima describes 2205 as having roughly twice the proof strength of standard austenitic stainless steels.

How do S31803 and S32205 relate?

S31803 is the older/common 2205 UNS designation. S32205 is a more tightly controlled 2205 chemistry that is widely used in modern specifications.

In practical supply, many producers offer material that can satisfy both S31803 and S32205 and may therefore be dual-certified.

That does not mean the buyer should ignore the requested designation. If the PO requires S32205, the MTC must demonstrate compliance with S32205 requirements under the applicable product standard.

Where does EN 1.4462 fit?

EN material number 1.4462, commonly designated X2CrNiMoN22-5-3, is the familiar European 2205 duplex grade.

Major producers such as Outokumpu and Alleima map 1.4462 to the 2205 family and list both UNS S31803 and S32205 for relevant products.

However, the exact acceptance basis still depends on the product standard:

• plate/sheet/strip;
• bar/forging stock;
• seamless or welded tube/pipe;
• fittings/flanges;
• project-specific offshore or sour-service requirements.

Dual certification is common but should be checked

A certificate may state, for example:

1.4462 / S31803 / S32205

That can be legitimate when the heat chemistry, mechanical properties and product-standard requirements satisfy all of the declared designations.

The practical checks are:

1. does the MTC state the actual product standard?
2. does the heat chemistry satisfy the claimed designations?
3. are the required mechanical properties met for the product form and thickness/size?
4. is the required heat-treatment condition recorded?
5. are project-specific corrosion/NDT tests present where required?

PREN is useful, but it is not the grade definition

2205 typically has a substantially higher pitting-resistance index than 316L because of its Cr, Mo and N content.

But PREN is a screening calculation, not the legal definition of 2205 and not a substitute for the chemistry limits of the governing standard.

See PREN explained for stainless and duplex steels.

Solution annealing is critical for duplex

Duplex properties depend not only on bulk chemistry but also on the microstructure produced by heat treatment and fabrication.

Incorrect thermal exposure can create detrimental intermetallic phases or an unsuitable ferrite/austenite balance.

See Solution annealing of stainless and duplex steel.

Sour service is not automatic

A material being “2205” does not automatically mean it is acceptable for every H2S-containing oil-and-gas environment.

ISO 15156/NACE MR0175 qualification depends on the alloy, product condition, hardness/strength, environment and other restrictions.

See NACE MR0175 / ISO 15156 applicability.

2205 vs super duplex 2507

2507/1.4410 is a more highly alloyed super-duplex family with higher localized-corrosion resistance and generally higher strength.

It should not be treated as a drop-in upgrade without checking fabrication, welding, availability, code and design requirements.

See Super duplex 2507.

MetalMate takeaway

2205 is a family name; S31803, S32205 and 1.4462 are specification designations that overlap but still have to be checked against the actual product standard and MTC. Dual certification is common, but it has to be supported by the heat chemistry, properties, heat treatment and required tests.

Related Knowledge

• Super duplex 2507
• PREN explained
• Solution annealing
• NACE MR0175 / ISO 15156 applicability

References

• Outokumpu, Forta DX 2205 — EN 1.4462, UNS S31803/S32205: https://www.outokumpu.com/de-de/products/flat-products/hot-rolled-coil-strip-and-plate
• Alleima, SAF 2205 tube and pipe — S31803/S32205, EN 1.4462: https://test.alleima.com/jp/technical-center/material-datasheets/tube-and-pipe-seamless/saf-2205/
• Alleima, Sanmac 2205+ — designation and product-standard examples: https://www.alleima.com/en/technical-center/material-datasheets/bar-and-hollow-bar/bar/sanmac-22052/