Difference between UNS S31803 and SS316
Material Type
- UNS S31803 is a duplex stainless steel based on 22% chromium content.
- SS316 is an austenitic stainless steel based on 18% chromium content.
Physical and Mechanical Properties
- Due to their different chemical compositions and microstructures, they have significant differences in physical and tensile properties.
- S31803 has better corrosion resistance and higher strength, while SS316 may be selected for other reasons.
Microstructure
- Duplex stainless steels are called "duplex" because they have a balance of austenitic and ferrite grains, which means that duplex stainless steels combine the physical and mechanical properties of both.
Corrosion resistance and cost-effectiveness
- Austenitic stainless steels typically offer excellent corrosion resistance, good mechanical properties over a wide range of operating temperatures, including low temperature toughness, and are non-magnetic.
- Ferritic stainless steels are typically less corrosion resistant and less cost effective, but are resistant to stress corrosion cracking.
- Duplex stainless steels combine these attributes to achieve high strength and excellent corrosion resistance, remain cost effective, and also resist stress corrosion cracking.
Strength and corrosion resistance
- UNS S31803 has approximately twice the yield strength compared to SS316.
- The Pitting Equivalent Number (PREN) of UNS S31803 is close to 34 compared to 25 for SS316, implying a relatively low resistance to pitting corrosion.
Cost and application limitations
- SS316 is generally less costly than UNS S31803, so it may be selected for use based on project cost, although the price difference diminishes or disappears when nickel costs are higher.
- UNS S31803 may be limited in low-temperature (below -50°C) or high-temperature (above 250°C) applications, so SS316 may be preferred.
