Duplex / Super Duplex Steels
Duplex stainless steels are a family of stainless steels that have a dual-phase microstructure consisting of roughly equal parts austenite and ferrite. This unique structure gives them a combination of properties from both phases: the strength and stress corrosion cracking resistance of ferritic stainless steel, and the toughness and corrosion resistance of austenitic stainless steel.
Typically containing 19–23% chromium, 4–7% nickel, and varying amounts of molybdenum, nitrogen, and sometimes copper or tungsten, duplex steels offer excellent resistance to chloride-induced corrosion and pitting, making them ideal for harsh environments like offshore oil platforms, chemical plants, and desalination equipment. Duplex steels have twice the yield strength of stainless steels and better resistance to localised corrosion.
Super duplex stainless steel castings are an advanced class of duplex stainless steels that offer even higher performance in terms of strength, corrosion resistance, and stress corrosion cracking resistance, especially in aggressive environments. This is generally achieved by increased chromium, molybdenum and nitrogen content which provides an exceptional combination of corrosion resistance, strength, and durability, making them ideal for the most demanding structural and fluid-handling components such as pumps and valves in corrosive, high-pressure environments.
Goodwin produces a specialised grade of 25%Cr super duplex steel called Goodwin 6A-G. This grade provides enhanced low temperature impact, corrosion, and weldability performance over conventional grades such as ASTM A995 5A and 6A, while meeting the chemistry requirements of ASTM A995 6A. The material is particularly suited for production in thick sections up to 350mm, due to its enhanced manufacturability over conventional super duplex grades. (See ASTM A995 6A Supplementary requirement S52).
