S31803 and S32205 are almost identical in composition, physical and tensile properties. S32205 is simply S31803 produced with chromium, nickel and molybdenum controlled to the upper end of their allowable range. Because these three elements drive resistance to pitting corrosion, S32205 has slightly improved and more consistent corrosion resistance. In every other respect the two can be treated as the same grade.
Why the second designation exists
S31803 was developed in the 1930s for paper and pulp manufacture. A number of the leading duplex producers were consistently making the grade to the upper end of the allowable specification, seeking to maximise corrosion performance. This was aided by the AOD steelmaking process, which allowed tighter control of composition and also let producers influence nitrogen additions rather than leaving nitrogen as a background element. Controlling nitrogen, chromium and molybdenum to the top of the S31803 range gives better and more consistent corrosion resistance.
To distinguish this top-of-range material, the further specification UNS S32205 was introduced, though it still meets the DIN 1.4462 caption. Material made to S32205 (F60) fully meets S31803 (F51), but the reverse is not true, so S32205 can be dual-certified as S31803.
What we stock
We stock S32205 (2205) duplex stainless steel as round bar from 5/8" to 20" diameter (15.87-508mm), plate up to 3" (76.2mm) thick, plus pipes in scheduled sizes, flanges and fittings.