SDSS stands for super duplex stainless steel. A duplex stainless steel combines a ferritic and an austenitic microstructure, drawing on the most favourable properties of each. Several SDSS grades exist, as this family of 25% chromium (25Cr) alloys has developed since the 1960s.
Ferralium® 255
The first commercially available super duplex stainless steel was Ferralium® 255 (DIN 1.4507, UNS S32550, ASTM F61), developed by Langley Alloys in the late 1960s. It has been 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 a yield strength greater than 85ksi. Its increased copper content gives it superior performance in acids such as sulphuric acid, which makes it well suited to fertiliser production.
Zeron 100®
Zeron 100, more commonly known as S32760 (UNS S32760, DIN 1.4501, ASTM F55), was subsequently developed by the UK company Mather & Platt. It sacrifices some of the copper content of Ferralium® in favour of tungsten.
SAF2507
SAF2507, more commonly known as S32750 (UNS S32750, DIN 1.4410, ASTM F53), was developed in the 1980s by Alleima. It contains only a modest amount of copper and no tungsten.
Lean and hyper duplex grades
A number of lean duplex grades have also been developed. Supplied primarily as sheet, plate or tube, they sacrifice some nickel content to reduce cost. Hyper duplex grades push the chromium content beyond 25%, up to 32% or even 37%. Increasing chromium raises resistance to pitting corrosion and strength, but adds significantly to cost, so availability is limited.
We carry an extensive stock of these SDSS grades, with bar up to 16" (406.4mm) diameter, plate up to 3" (76.2mm) thickness, and a range of pipes and fittings.