Duplex Stainless Steel
This refers to standard duplex stainless steel, a stainless steel with 22% chromium , with UNS S31803 and UNS S32205 (both known as Alloy 2205) being the most widely used. Common duplex stainless castings are UNS J92205 (ASTM A890 Grade 4A, CD3MN) and UNS J93372 (ASTM A890 Grade 1B, CD4MCuN).
A 22%Cr duplex stainless steel a minimum 0.2% proof strength of some 450N/mm2
Super Duplex Stainless Steel
A duplex stainless steel with a Pitting Resistance Equivalent Number (PREN) > 35-40, where PREN = % Cr + 3.3 × (% Mo + 0.5 % W) + 16 × % N. Usually, super duplex grades have 25 % chromium , or more. Some common examples are UNS S32760 (Zeron 100), UNS S32750 (Alloy 2507), and UNS S32550 (Ferralium 225). Common super duplex stainless steel castings are UNS J93380 (ASTM A890 Grade 6A, CD3MWCuN) and UNS J93404 (ASTM A890 Grade 5A, CE3MN).
A 25%Cr duplex stainless steel a minimum 0.2% proof strength of some 550N/mm2 .