UNS S31803 is a duplex stainless steel based on a 22% chromium content, while SS316 is an austenitic stainless steel based on an 18% chromium content. Their different composition and microstructure give them significantly different physical and tensile properties: S31803 has better corrosion resistance and higher strength, though SS316 may still be chosen for other reasons.
What is a duplex stainless steel?
A duplex stainless steel is named for its "duplex" microstructure, a balance of austenitic and ferritic grains. That balance combines the physical and mechanical properties of both, making duplex an attractive and cost-effective proposition.
What is austenitic stainless steel?
Austenitic stainless steels generally offer excellent corrosion resistance, good mechanical properties across a wide temperature range including low-temperature toughness, and are non-magnetic. Ferritic stainless steels are generally lower in corrosion resistance and cost, but resist stress corrosion cracking. Duplex stainless steels combine many of these properties, achieving high strength and excellent corrosion resistance while remaining cost-effective and still resisting stress corrosion cracking.
Difference between UNS S31803 and SS316
Compared with SS316, UNS S31803 has around twice the yield strength. Its PREN is close to 34, against 25 for SS316, so its resistance to pitting corrosion is proportionally greater. However, SS316 is usually lower cost and may be selected on project budget grounds, though that differential narrows or disappears when nickel prices are high. S31803 is also limited in applications requiring low temperature (below -50degC) or high temperature (above 250degC), where SS316 may be preferred.
What we stock
We stock S31803 (S32205, ASTM A182 F51/F60, DIN 1.4462) 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.