S31803 and S32205 both belong to the duplex 2205 family, close enough in composition that buyers sometimes treat them as interchangeable. They aren’t quite. Understanding where these two grades diverge matters directly when selecting duplex steel S31803 sheets for a specific industrial application, since the difference in chemistry, however small it looks on paper, can shape real performance in service. Buyers who treat the two as identical sometimes discover the gap only after a sheet is already installed, which is exactly the kind of mismatch a closer look at the specification avoids.
What Are S31803 and S32205 Sheets?
Both grades share the same duplex ferritic-austenitic structure, roughly equal parts ferrite and austenite, which is what gives duplex stainless steel its combined strength and corrosion resistance advantage over standard austenitic grades. S31803 and S32205 sit within the same 2205 family and share overlapping UNS designations in practice, though S32205 reflects a tightened version of the chemistry originally covered under S31803. Both fall under ASTM A240/ASME SA240 for plate, sheet, and strip product forms, the governing specification buyers should reference when confirming material compliance. Because the two designations trace back to the same base alloy family, spec sheets and mill certificates sometimes reference them together, which is part of why the distinction gets lost in day-to-day procurement.
S31803 vs S32205: Chemical Composition
The practical difference between the two grades comes down to minimum chromium, molybdenum, and nitrogen content. S32205 was introduced with tighter minimum requirements on these elements compared to the original S31803 specification, closing gaps that occasionally allowed S31803 material to test toward the lower end of acceptable duplex performance. That tighter chemistry matters because chromium, molybdenum, and nitrogen are exactly the elements responsible for duplex steel’s corrosion resistance and phase stability, so a tighter minimum gives buyers a narrower, more predictable performance band.
Corrosion Resistance
Both grades resist general and localized corrosion well, a defining trait of the duplex family as a whole. Where performance can diverge is in demanding service environments, particularly those involving chloride exposure, since the tighter chromium, molybdenum, and nitrogen minimums in S32205 support more consistent resistance to pitting and crevice corrosion across a production run. That doesn’t mean S31803 fails in chloride service; it means the performance margin runs tighter, which matters more as chloride concentration or temperature climbs.
Mechanical Performance
Both grades deliver strength and durability well above standard austenitic stainless steel, a direct result of the duplex microstructure itself. Exact mechanical property requirements, yield strength, tensile strength, and elongation, should always get confirmed against the applicable product specification for the specific grade and product form rather than assumed from general duplex steel reputation, since values vary by thickness and processing condition.
Which Grade Is Suitable for Your Application?
Selection depends on the actual service conditions a sheet will face: chloride exposure level, chemical environment, temperature range, and mechanical load all factor in. At Calico Metal, we look at these service requirements alongside the project specification before recommending S31803 or S32205, rather than treating the two grades as interchangeable. Fabrication requirements matter too, since welding procedures and heat input need to preserve the phase balance in either grade. Project specifications often settle the question directly, calling out one grade explicitly, and required material certification should confirm whichever grade gets specified actually meets its stated chemistry and mechanical requirements before it enters fabrication.
S31803 vs S32205: Which Sheet Should You Choose?
Selecting between S31803 and S32205 duplex stainless steel sheets depends on matching the material’s chemistry to the specific demands of your operating environment, particularly chloride levels and required performance consistency.
| Selection Factor | S31803 Sheet | S32205 Sheet |
| Chloride Exposure | Best for moderate exposure | Best for higher exposure |
| Chemical Composition | Standard duplex chemistry limits | Tighter minimums for chromium, molybdenum, and nitrogen |
| Performance Band | Standard operational predictability | Narrower, highly predictable performance band |
| Ideal Service Environment | Standard duplex-grade applications | Harsh, high-chloride, and severe operational environments |
Conclusion
The choice of S31803 or S32205 sheets depends on the service environment, corrosion requirements, and the responsible material specification for the project. Both grades provide true duplex performance, and the difference between them is one of degree, not of kind. We check the real service circumstances, necessary certification, and procurement documents before settling a grade to avoid the mismatch that is only discovered once the material is in service.