Glossary

Duplex stainless steel is a type of stainless steel that combines the properties of both austenitic and ferritic stainless steels within a single microstructure. Its name comes from this “dual-phase” composition — roughly 50% austenite and 50% ferrite — which gives it an exceptional balance of strength, toughness, and corrosion resistance. This hybrid structure provides advantages that neither phase can achieve alone, making duplex stainless steels highly valued in demanding industrial environments.

Chemically, duplex stainless steels typically contain 19–28% chromium, 3–10% nickel, and 0.05–0.5% nitrogen, with possible additions of molybdenum, copper, and tungsten to enhance corrosion resistance. The nitrogen and molybdenum are especially important for improving resistance to pitting, crevice corrosion, and chloride-induced stress corrosion cracking, which are major weaknesses of austenitic and ferritic grades when used alone.

Mechanically, duplex stainless steels are about twice as strong as common austenitic grades like 304 or 316, while maintaining good ductility and impact toughness. They have excellent resistance to chloride stress corrosion cracking, a property inherited from their ferritic phase, and superior general and localized corrosion resistance due to their high chromium and molybdenum content. Their reduced nickel content also makes them more cost-stable, as they are less affected by fluctuations in nickel prices.

Common grades include 2205 (UNS S32205/S31803), the most widely used standard duplex stainless steel, and 2507 (UNS S32750), a “super duplex” grade with higher alloy content and even greater corrosion resistance. Duplex stainless steels are widely used in chemical processing, oil and gas production, desalination plants, pulp and paper manufacturing, marine environments, and structural applications where strength and corrosion resistance are critical.

In summary, duplex stainless steels offer a unique combination of high strength, corrosion resistance, and cost efficiency, bridging the gap between austenitic and ferritic grades. Their dual-phase structure gives them the ability to withstand harsh chloride environments, high mechanical loads, and thermal stresses, making them one of the most versatile materials used in modern industrial design.