2205 is a duplex stainless steel, not a super duplex grade. It is the most widely used duplex grade, based on around 22% chromium, and sits below the super duplex grades in both strength and corrosion resistance.
Duplex stainless steels are a family of grades with a mixed microstructure of austenite and ferrite phases. They combine good corrosion resistance with high strength, which suits them to a wide range of applications. Within the family, different compositions deliver increasing levels of both strength and corrosion resistance.
The first duplex grades were based on 22% chromium, giving significantly better corrosion resistance than a standard Alloy 316L austenitic stainless steel, with up to twice the strength. The original S31803 has since been refined into S32205, whose more tightly controlled composition improves corrosion resistance.
How super duplex differs
Super duplex stainless steels carry a higher content of alloying elements such as chromium, nickel and molybdenum, and are based on 25% chromium. This gives them even greater corrosion resistance and higher strength than duplex grades, suiting them to more demanding environments.
The first commercially produced super duplex stainless steel was Ferralium® 255 (S32550, 1.4507), developed by Langley Alloys. It contains up to 2% copper for increased resistance to sulphuric acid, and remains the only super duplex stainless steel to achieve a minimum yield strength of 85ksi (586N/mm2). Other grades include S32750 (1.4410) and S32760 (1.4501).
More recently, hyper duplex stainless steels have been developed. With 27% chromium (S32707) or 32% chromium (S33207), strength and corrosion resistance increase further still, though they are challenging to manufacture and so limited to seamless pipe.
Our duplex range
We carry one of the most complete ranges of duplex and super duplex stainless steels, in up to 40 different sizes and in quantities sufficient for the largest projects.
Ferralium® 255 (S32550) is available only from Langley Alloys, as round bar from 1/2"-14" (12.7-355.6mm), plate up to 3" (76.2mm), pipe, flanges and fittings.
We stock S32205 (2205) as round bar from 5/8"-20" diameter (15.87-508mm) and plate up to 3" (76.2mm) thickness, along with pipe in scheduled sizes, flanges and fittings. S32750 and S32760 are available ex-stock in a similar size range.