What is SDSS?

SDSS is an acronym for Super Duplex Stainless Steel. A duplex stainless steel is a combination of a ferritic and an austenitic microstructure, and combines the most favourable properties of each.  There are a number of different SDSS available, as the family of alloys based upon a 25% chromium (25Cr) content has developed since the 1960’s.

The very first Super Duplex Stainless Steel commercially available was Ferralium 255 (DIN 1.4507, UNS S32550, ASTM F61) developed by Langley Alloys in the late 1960’s. It has been successfully used in a wide variety of demanding applications, including Oil and Gas, chemical processing and subsea. In bar form, it is the only super duplex stainless steel to achieve >85ksi Yield Strength. With it’s increased copper content compared with other super duplex stainless steels, it provides superior performance in a range of acids, such as sulphuric acid. This makes is well-suited for use in fertiliser production.

Subsequently, Zeron 100 was developed by the UK company Mather & Platt (the tradename is now owned by Rolled Alloys Inc.). More commonly known as S32760 (UNS S32760, DIN 1.4501, ASTM F55) this Super Duplex Stainless Steel sacrifices some of the copper content of Ferralium and is replaced by tungsten.

Finally, SAF2507 was developed in the 1980s by Sandvik. More commonly known as S32750 (UNS S32750, DIN 1.4410, ASTM F53) it contains only a modest amount of copper and no tungsten.

A number of so-called ‘lean duplex’ grades have been developed. Primarily supplied as sheet, plate or tube, they sacrifice some of the nickel content in order to reduce their cost slightly. Hyper duplex grades of SDSS have also been developed, where the chromium content has been pushed beyond 25%, up to 32% or even 37%. Increasing the chromium content increases their resistance to pitting corrosion, as well as their strength, but also adds significantly to their cost. As such, availability is limited.

Langley Alloys carries an extensive stock of all these SDSS, with bar up to 16″ (406.4mm) diameter, plate up to 3″ (76.2mm) thickness, and a variety of pipes and fittings.

Got any Questions? Get in Touch

For more information about high-performance stainless steels alloys, as well as Super Duplex Stainless Steels, please don’t hesitate to contact us today. We would be happy to answer any questions that you may have regarding specifications and common applications.