Super duplex stainless steels resist stress corrosion cracking far better than standard austenitic grades, and copper additions push that resistance further still. Their two-phase austenitic-ferritic microstructure combines high strength with strong corrosion performance.
Duplex alloys were developed around a 22% chromium addition. Super duplex alloys use a higher base composition to raise corrosion resistance further.
They are twice as strong as more standard stainless steel grades, with toughness and ductility that sit between austenitic and ferritic grades.
Corrosion resistance
By combining higher chromium with significant molybdenum and nitrogen, super duplex grades reach a Pitting Resistance Equivalent number that matches or beats all but the most highly alloyed stainless steels, and often rivals some nickel alloys.
The role of copper
Adding copper to these grades brings additional corrosion resistance. Copper can stop or slow the formation of pitting corrosion, and it contributes to exceptional resistance to sulphuric acid.
Resistance to sulphuric, nitric and phosphoric acid makes these grades attractive across many chemical processing applications.
A cost-effective option
Super duplex stainless steels avoid the high nickel additions that are expensive and subject to price volatility, so they offer a cost-effective choice for many demanding applications. That shows up as a direct material cost saving, and can also reduce overall design cost where the application involves suspended loads.