Alloy 20 (UNS N08020) is an austenitic, nickel-iron-chromium based super alloy with additions of Copper and Molybdenum which provide resistance to hostile environments, pitting, and crevice corrosion. It is also stabilized with Columbium to minimize carbide precipitation during welding. Alloy 20 appears to fall between both the stainless and nickel categories as it contains characteristics of both.

It was designed for maximum resistance to acid attack and demonstrates superior resistance to stress-corrosion cracking in boiling 20% to 40% sulfuric acid, and also has excellent general corrosion resistance to sulfuric acid and to chloride stress corrosion cracking. Alloy 20 has good mechanical properties at both ambient and elevated temperatures, up to approximately
930°F (500°C) and is readily fabricated by usual industrial processes.