UNS S31803 vs UNS S32205 Duplex Stainless Steel: Chemistry and Certification

Written by: Emma, Technical Sales Engineer  |  Reviewed by: Ethan, Materials Engineer  |  Updated: August 2026

UNS S31803 and UNS S32205 are both “2205” duplex stainless steel, and both correspond to the European designation EN 1.4462. They are not two completely different alloys, but two UNS chemistry definitions within the same 2205 family — and S32205 carries tighter minimum requirements for chromium, molybdenum, and nitrogen. This article explains the chemistry difference, why modern 2205 is often dual-certified, and how to check an MTC properly.

1. Direct Answer: S31803 vs S32205

Both designations describe 2205 duplex stainless steel. The difference is that S32205 has higher minimum chromium, molybdenum, and nitrogen requirements than S31803, which makes its chemistry control tighter. Because modern 2205 production routinely meets the higher limits, much of the material on the market is dual-certified to both S31803 and S32205. In critical projects, buyers increasingly specify S32205 or the dual certification rather than a loose “2205.”

The reason this matters in practice is that many material test certificates today show dual certification — S31803/S32205 — because a single heat meets both chemistry ranges. A buyer who understands this can specify 2205 confidently without ambiguity, and can verify that the delivered material actually meets the tighter S32205 limits where required.

2. Quick Chemistry Comparison

The table below shows the typical chemistry ranges. The exact ranges must be taken from the applicable ASTM product standard and its edition, not from a summary table.

Notice that nickel and carbon are essentially the same in both designations, while chromium, molybdenum, and nitrogen are where S32205 tightens the requirements. That pattern reflects the elements that drive duplex corrosion resistance and phase balance, which is why those three matter most.

3. Why S32205 Has Tighter Chemistry

S32205 raises the minimum chromium, molybdenum, and nitrogen. Chromium and molybdenum strengthen pitting and crevice resistance, while nitrogen contributes to strength and helps maintain the balanced austenite-ferrite phase balance that duplex stainless steels depend on. The tighter minimums make the alloy’s corrosion resistance and phase balance more consistent from heat to heat.

This is not a “new 2205 alloy” — it is the same 2205 family with a narrower, more demanding chemistry specification that reflects modern production capability and stricter project requirements.

Phase balance is central to duplex stainless steel performance. The desired structure is a roughly balanced mixture of austenite and ferrite, and nitrogen is the key element that stabilizes and strengthens the austenite. If the phase balance drifts, the corrosion resistance, toughness, and strength can all suffer, which is why the tighter nitrogen minimum in S32205 is meaningful rather than cosmetic.

4. Are S31803 and S32205 the Same Grade?

They share the common name 2205 and the EN designation 1.4462, but the UNS specification requirements are not identical. This is why it matters to distinguish three things: the common name (2205), the UNS designation (S31803 or S32205), and the product standard (which sets the actual chemistry and mechanical requirements for the specific product form). Writing only “2205” can leave the chemistry requirements ambiguous in a strict project.

The practical risk of writing only “2205” is that it leaves open which UNS chemistry applies. For routine use this may be acceptable, but for a code-governed vessel or a corrosive service, the project specification will normally name a UNS designation or a dual-certification requirement precisely to avoid that ambiguity.

5. Corrosion and Mechanical Property Implications

S32205’s tighter chemistry generally supports stable, repeatable 2205 performance in pitting and crevice corrosion resistance, chloride SCC resistance, yield strength, tensile strength, and weldability. The higher minimums help ensure consistent phase balance and corrosion resistance, but the actual properties still depend on product form, heat treatment, and the specific material test certificate.

It would be an overstatement to say S32205 is dramatically better than S31803 in every environment. The difference is best understood as tighter chemistry control and greater consistency, which matters most in demanding or code-governed applications.

Solution annealing is essential to duplex stainless steel, because it develops the balanced microstructure and dissolves undesirable phases. The MTC should confirm that the material was solution annealed as required. A duplex product that has not been properly heat treated can lose corrosion resistance and toughness even if its chemistry is correct, so heat treatment status is part of acceptance.

For buyers, the key takeaway is that S32205’s tighter chemistry is primarily about consistency and confidence — ensuring that every heat delivers the corrosion resistance and phase balance the 2205 family is known for, rather than a large step change in performance.

6. What Does Dual Certification Mean?

Dual certification means a single heat simultaneously satisfies the chemistry and applicable mechanical requirements of both S31803 and S32205. It does not mean two steels are blended together. Instead, one heat — with one heat number, one actual chemistry, and one set of mechanical test results — is documented on the material test certificate as meeting both designations.

The MTC is the evidence: it records the actual chemistry and test results that demonstrate the heat falls within both sets of limits. Dual certification is therefore a property of a specific heat and its test record, not a commercial label that can be assumed without verification.

Dual certification is commercially convenient because it allows one inventory item to serve projects that call for either S31803 or S32205. Instead of stocking two separate grades, a supplier can stock dual-certified material that satisfies both. This is legitimate only because the single heat genuinely meets both sets of requirements — it is verified through chemistry and testing, not through a label.

7. How to Check an S31803/S32205 MTC

Do not simply read “2205” on a certificate and stop there. Confirm the UNS designation, the actual chemistry, the heat number against the marking, and the applicable product standard — these are what prove the material is what the project requires.

When reviewing the certificate, also check the heat treatment statement. For duplex 2205, solution annealing is a requirement, and the certificate should state it. A certificate that lists the correct chemistry but omits or misstates the heat treatment should be questioned, because duplex properties depend on it.

8. ASTM Product Standards and Procurement

The applicable standard depends on product form. Common examples include ASTM A240 for plate, sheet, and strip; A790 for pipe; A789 for tube; A182 for forgings and flanges; and A815 for fittings. No single standard covers every 2205 product, so the correct specification must be matched to the product form and confirmed against its edition.

In pressure equipment and sour-service applications, the applicable code or standard may impose additional requirements beyond the basic ASTM product specification — such as specific test requirements, hardness limits, or supplementary tests. Buyers in oil, gas, and chemical service should therefore check the project specification and any applicable code alongside the product standard, not just the ASTM number.

9. Which Should Buyers Specify?

• General 2205 requirement → specify the applicable UNS and product standard.
• Project requires tighter chemistry → specify S32205.
• Need broad 2205 compatibility → consider S31803/S32205 dual certification.
• Strict corrosion or pressure-equipment project → follow the project specification and applicable code.
• Never specify only “2205” when certification requirements are critical.

Once the correct designation is chosen, the RFQ should pair it with the product form, the applicable ASTM standard, and any supplementary requirements such as solution annealing, testing, and heat-number traceability. This is what turns a vague “2205” into a specification that a supplier and inspector can both verify.

10. Common Purchasing Mistakes

• Writing only “2205 stainless steel.”
• Assuming S31803 and S32205 are identical.
• Ignoring the UNS designation.
• Not checking chromium, molybdenum, and nitrogen.
• Not confirming the heat number.
• Treating EN 1.4462 as exactly the same as UNS S32205.
• Not confirming the product standard.
• Reading only the grade name on the MTC without the actual chemistry.
• Understanding dual certification as a mixture of two materials.

The common thread in these mistakes is treating 2205 as a single, self-explanatory product. In reality it is a family of UNS designations and product standards, and the details are what determine whether the material is fit for the project.

11. FAQ

Q1: What is the difference between UNS S31803 and S32205?
S32205 has higher minimum chromium, molybdenum, and nitrogen than S31803, giving it tighter chemistry control within the same 2205 family.

Q2: Are S31803 and S32205 both 2205 duplex stainless steel?
Yes. Both are 2205 duplex stainless steel and both correspond to EN 1.4462.

Q3: Is S32205 stronger than S31803?
Not inherently — the tighter chemistry supports more consistent properties, but actual strength depends on product form, heat treatment, and the MTC.

Q4: Why does S32205 have higher minimum chromium, molybdenum and nitrogen?
To improve corrosion resistance and ensure a consistent austenite-ferrite phase balance from heat to heat.

Q5: Are S31803 and S32205 the same as EN 1.4462?
Both correspond to EN 1.4462, but EN 1.4462 is a European designation, not identical to either UNS designation in its requirements.

Q6: What does S31803/S32205 dual certification mean?
A single heat, with one heat number and one set of test results, meets the chemistry and mechanical requirements of both designations.

Q7: How can I verify dual certification on an MTC?
Check that the certificate lists both designations, the actual chemistry meets both sets of limits, and the heat number matches the material marking.

Q8: Can S31803 be replaced by S32205?
Usually yes, since S32205 is the tighter chemistry, but substitution must still be confirmed against the project specification and code.

Q9: What ASTM standards cover S31803/S32205 products?
It depends on form — for example A240 for plate, A790 for pipe, A789 for tube, A182 for forgings, and A815 for fittings.

Q10: Should I specify S32205 or dual-certified 2205 in an RFQ?
For general use, dual-certified S31803/S32205 is common; for tighter chemistry or strict projects, specify S32205 explicitly and follow the project code.