Duplex stainless steel

An ingot of 2507 duplex stainless steel

Duplex stainless steels[1][2][3][4][5] are a family of stainless steels. These are called duplex (or austenitic-ferritic) grades because their metallurgical structure consists of two phases, austenite (face-centered cubic lattice) and ferrite (body centered cubic lattice) in roughly equal proportions. They are designed to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion, and higher strength than standard austenitic stainless steels such as type A2/304 or A4/316. The main differences in composition, when compared with an austenitic stainless steel is that the duplex steels have a higher chromium content, 20–28%; higher molybdenum, up to 5%; lower nickel, up to 9% and 0.05–0.50% nitrogen. Both the low nickel content and the high strength (enabling thinner sections to be used) give significant cost benefits. They are therefore used extensively in the offshore oil and gas industry for pipework systems, manifolds, risers, etc. and in the petrochemical industry in the form of pipelines and pressure vessels. In addition to the improved corrosion resistance compared with the 300 series duplex stainless steels also have higher strength. For example, a Type 304 stainless steel has a 0.2% proof strength in the region of 280 MPa (41 ksi), a 22%Cr duplex stainless steel a minimum 0.2% proof strength of some 450 MPa (65 ksi) and a superduplex grade a minimum of 550 MPa (80 ksi).[6]

  1. ^ Peckner, Donald; Bernstein, I.M. (1977). "chapter 8". Handbook of Stainless Steels. McGraw Hill. ISBN 9780070491472.
  2. ^ Lacombe, P.; Baroux, B.; Beranger, G. (1990). "chapter 18". Les Aciers Inoxydables. Les Editions de Physique. ISBN 2-86883-142-7.
  3. ^ International Molybdenum Association (IMOA) (2014). Practical Guidelines for the fabrication of Duplex Stainless Steels (PDF). ISBN 978-1-907470-09-7 – via www.imoa.info.
  4. ^ Charles, Jacques (2010). Proceedings of the Duplex Stainless Steel Conference, Beaune (2010). EDP Sciences, Paris. pp. 29–82. Archived from the original on 2022-05-06. Retrieved 2019-10-27.
  5. ^ International Stainless Steel Forum (2020). "Duplex Stainless Steels" (PDF).
  6. ^ Dr. James Fritz. "A Practical Guide to Using Duplex Stainless Steels". Nickel Institute.