Outokumpu Details History of Duplex Stainless Steel

Outokumpu Oyj, a major producer of stainless steel, has outlined the nine-decade history of duplex stainless steel, marking the material's 90th anniversary in 2020. The initial development of duplex stainless steel, characterized by a combined ferritic and austenitic microstructure, occurred in 1930 at Avesta Jernverks AB in Sweden, which is now part of Outokumpu.

These early duplex grades were created to address intergranular corrosion issues found in ferritic stainless steels. They were employed in castings, bars, and plates primarily for the pulp and paper industry and for high-temperature applications due to their corrosion resistance and castability. By 1932, duplex steels represented 6.5% of the total global stainless steel market of 5,500 tonnes.

Advancements in the 1950s and 1970s led to improved generations of duplex steels. Increased nitrogen content was introduced to enhance ductility, weldability, and resistance to pitting corrosion. This progression culminated in the development of 'super duplex' grades during the 1970s and 1980s, offering superior corrosion resistance through higher alloy content (chromium, molybdenum, nickel, copper), suitable for demanding sectors like offshore oil and gas.

In the mid-1980s, 'lean duplex' grades, such as Outokumpu's Forta LDX 2101, were developed to reduce raw material costs while maintaining strength and corrosion performance. Recent innovations have also focused on improving the formability of duplex steels, enabling the production of more complex and lightweight components.