Superduplex stainless steels have a very high resistance to localized corrosion in chloride media, combined with a high mechanical strength. The series consists of three grades: 2507 (EN 1.4410), 2507Cu (EN 1.4507) with addition of copper for enhanced resistance in sulfuric acid media, and 2507W (1.4501), with tungsten additions for enhanced localized corrosion resistance. The corrosion resistance of these grades is better than 904 and comparable to 6 Mo austenitics. All these steels have a pitting resistance equivalent number, PREN, above 40, and a minimum guaranteed yield strength of 550 MPa, allowing for leaner design in load bearing applications. The alloy composition, including molybdenum and nitrogen additions, has been optimized to obtain a 50/50 austenoferritic microstructure with outstanding corrosion resistance even for heavy plates. The 2507 series of duplex grades provide cost - efficient alternatives for a wide range of applications, including offshore, phosphoric and sulfuric acid production as well as flue gas cleaning.
