Duplex (austenitic-ferritic) stainless steels are comprised by austenite and ferrite in proportions from 50:50 to 40:60. Usually, they contain 19-28% Cr, <5% Mo and a bit of Ni (1,5-7% depending on the grade). Thanks to their high content of chromium, nitrogen and molybdenum they show excellent corrosion resistance, enjoying at the same time the advantage of having higher mechanical properties in comparison to the other families.
For instance, the type S32101 has 90% higher mechanical properties than 304, allowing thus the safe reduction of the material’s thickness by 30% (on average).
On top of that, due to their low nickel content they have a more stable price than the austenitic stainless steels. They are distinguished into the following groups.
- Lean Duplex (S32101 /ΕΝ 1.4162, S32304 /ΕΝ 1.4362)
- Standard Duplex with 22% Cr (S32205 /ΕΝ 1.4462)
- Super Duplex is by definition a duplex stainless steel with PRE > 40 (we explain later this term). Their Cr content is usually more than 25% (S32760, S32750, S32550).
- Hyper Duplex refer to duplex grades with a PRE > 48 (S32707, S33207).
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