S31803 and S32205 Sheets are the two types of duplex stainless steel often considered identical. Duplex Steel UNS S31803 Sheets and UNS S32205 Sheets share the same base chemistry and phase balance, but S32205 is manufactured to tighten the compositional window around chromium, molybdenum and nitrogen. For projects specifying Duplex Steel UNS S31803 Sheets, recognizing this distinction affects procurement decisions and long-term corrosion performance.
What Are Duplex Steel UNS S31803 Sheets?
S31803 Sheets combine austenitic and ferritic microstructures in equal proportions. This dual-phase structure offers the grade its defining traits: a tensile strength double that of the standard austenitic grades like 316L and resistance to chloride stress corrosion cracking. Duplex S31803 Sheets hold up in seawater systems, chemical processing lines and pulp and paper equipment, where pitting and crevice corrosion are enduring risks. The balanced microstructure is caused by precision dropping that keeps austenite and ferrite in a workable ratio across the sheet thickness.
How Is UNS S32205 Different From S31803?
UNS S32205 Sheets are adapted from the S31803 specification and refined to reduce compositional variations between production batches. S31803 allows a chromium range of 21.0 to 23.0%, molybdenum of 2.5 to 3.5%, and nitrogen of 0.08 to 0.20%. S32205 narrows chromium to 22.0 to 23.0%, molybdenum to 3.0 to 3.5% and nitrogen to 0.14 to 0.20%. Chromium, molybdenum and nitrogen drive the Pitting Resistance Equivalent Number (PREN), which is crucial for maintaining a tighter compositional range.
S31803 vs S32205: Key Differences
| Comparison Factor | UNS S31803 | UNS S32205 |
| Duplex family | Duplex stainless steel | Duplex stainless steel |
| Relationship | Original/earlier 2205 duplex specification | Tighter version of the 2205 duplex chemistry |
| Chromium control | Wider allowable range | Tighter/higher controlled range |
| Molybdenum control | Wider allowable range | Tighter/higher controlled range |
| Nitrogen control | Wider allowable range | Tighter controlled range |
| Corrosion resistance | Excellent | More consistent corrosion performance |
| Strength | High | Very similar, depending on applicable product specification |
| Certification relationship | Does not automatically satisfy S32205 | Can satisfy S31803 requirements if allowed |
| Typical selection consideration | Suitable when project specification allows S31803 | Preferred where tighter S32205 requirements are specified |
This table is the core reference point for procurement teams comparing S31803 vs. S32205. Buyers evaluating S32205 vs S31803 for a specific project should consider the compositional ranges as the starting point.
Why Does S32205 Usually Offer More Consistent Corrosion Resistance?
PREN estimates a duplex grade’s resistance to pitting in chloride environments, calculated from chromium, molybdenum and nitrogen content. As S32205 restricts these three elements to narrower bands, its PREN value stays closer to the high end across every production heat. S31803’s wider range allows a batch to land near the bottom of its chemistry window and still pass mill certification. That batch will still perform well, but its margin against localized corrosion is thinner than a heat produced to S32205 limits. For Duplex 2205 Sheets destined for aggressive chloride service, that tighter margin translates into more predictable field performance over the life of the installation.
Can S32205 Sheets Be Used Where S31803 Is Specified?
Yes, in most cases this procedural link connects the two grades. S32205’s chemistry falls inside S31803’s broader range, so mills frequently dual-certify sheets to both specifications. A sheet certified to S32205 will generally meet S31803 requirements as well, when the governing specification allows substitution. A sheet certified only to S31803 goes beyond S32205’s tighter chromium, molybdenum, or nitrogen limits.
Which Duplex Grade Should You Choose?
Selection is based on the project specifications. If the governing standard permits S31803 and the service environment doesn’t demand PREN consistency, S31803 sheets meet the requirement with better availability and lead time. If the specification requires S32205, or if the application involves aggressive chloride exposure where the corrosion margin is most critical, S32205 is the appropriate choice. The right answer depends on the applicable code, the service conditions and what certification the end user requires on the mill test report.
Choosing Between S31803 and S32205 Sheets
S31803 and S32205 share a common duplex structure but differ in how their chemistry is controlled, and that difference shapes corrosion consistency and certification flexibility. Reviewing the applicable project specification, the expected service environment, and the required mill certification before ordering will determine which grade is actually required.