DuplexStähle

DuplexStähle, or duplex stainless steels, are a family of stainless steels whose microstructure comprises roughly equal proportions of ferrite and austenite. This bimodal structure provides a combination of high strength and good corrosion resistance that is superior to most ferritic or austenitic grades in many environments. Typical compositions include chromium around 20–25%, nickel around 4–7%, with small additions of molybdenum and nitrogen to improve pitting and overall corrosion resistance.

Mechanical properties are characterized by higher yield and tensile strength than conventional austenitic stainless steels, while maintaining good toughness. Duplex steels also offer excellent resistance to stress corrosion cracking in chloride-bearing environments and good crevice corrosion resistance. They can be more sensitive to heat-treatment effects that shift the ferrite–austenite balance, so controlled processing is important.

Welding and fabrication require suitable procedures and filler materials to preserve the balance between phases. For thick sections, post-weld heat treatment or solution annealing may be used to restore optimal microstructure. Proper preheating and heat input control reduce the risk of excessive ferrite or grain growth.

Applications include chemical processing equipment, oil and gas production, seawater piping, desalination plants, pulp and paper equipment, and other environments where high strength and corrosion resistance are valuable.

Common duplex grades include standard duplex such as 2205 and super duplex such as 2507. International standards covering duplex stainless steels include ISO 15156, EN 10088, and various ASTM and API specifications used in industry.