Duplex stainless steels combine the best qualities of
austenitic and ferritic stainless steels, including high strength and
toughness, ease of manufacture, and corrosion and stress corrosion cracking
resistance.
The 2205 duplex stainless steel (UNS S31803 / UNS S32205, F51 / F60, 1.4462) has a chromium content of 22 percent and a pitting resistance equivalent number (PREN) of 34. A super duplex stainless steel is one with a PREN value more than 40 and is often made from a chromium alloy containing at least 25% chromium. This ensures excellent corrosion resistance in a variety of environments. Super duplex grades are the industry standard for applications that require long-term performance in seawater, as well as a variety of industrial and chemical process industries that are exposed to certain acids.
Duplex stainless steel has double the strength of normal austenitic stainless steels in the 3xx family, such as Alloy 316L. The minimum yield strength of 2205 duplex stainless steel is 65ksi (450MPa), but the minimum yield strength of Alloy 316L is just 25ksi (170MPa) (UNS S31603, 1.4404). A super duplex grade, such as UNS S32750 (F53, 1.4410) or UNS S32760 (F55, 1.4501), has a yield strength of 80ksi (550MPa). With a minimum yield strength of 85ksi, ferralium 255-SD50 (F61, UNS S32550, 1.4507) is the strongest super duplex stainless steel available (586MPa). Check out Duplex Steel Fasteners
Aside from the obvious benefits of these alloys already mentioned, their strength can be increased through further processing. Work-hardening is a process that increases the yield stress and ultimate tensile strength of duplex stainless steels while lowering the elongation value. When a conventional super duplex stainless steel, such as UNS S32750 (F53, 1.4410), is exposed to a 25% reduction in area, its strength doubles. Cold working, like as drawing or cold forging, can do this, but only for smaller diameter bars. During machining, a little quantity of cold working is also used. This combination of high strength and decreased toughness is acceptable if the component is operating under tension with minimal shock loading. Check out Duplex 2205 Fasteners
Another method for ageing essential components is to use it. Ferralium 255-3AF is a solution annealed form of the product that has been aged. It is possible to raise the yield strength marginally while increasing the tensile strength by at least 5-10% by exposing the forged bar, or even machined components, to a further heat treatment.