Ferralium 255 
What is F255 material?
Ferralium 255 – super duplex 4507 is a super duplex stainless steel supplied in the hot worked and annealed condition. It achieves higher strengths than most stainless steels and alternative corrosion resistant alloys, offering the potential to reduce section size and therefore weight and cost.
As a 25% Cr alloy, with significant additions of copper, Ferralium® 255 offers excellent corrosion resistance in a wide variety of corrosive chemicals including sulphuric, nitric and phosphoric acid. In seawater and other chloride containing environments it also provides outstanding resistance to pitting and crevice corrosion, with Critical Pitting Temperature exceeding 50°C. Excellent ductility and impact strength at both ambient and sub-zero temperatures combine with a high resistance to abrasion, erosion and cavitation erosion.
Listed in NACE MR 01 75 for sour service and having gained ASME Approval for Pressure Vessel applications, Ferralium® 255-SD50 is tested to the highest degree using tests designed to guarantee that the trade-marked product possesses high integrity, a correct phase balance and the absence of sigma and other deleterious phases.

FERRALIUM 255, UNS S32550 chemical composition
Cr 25.5, Ni 5.5, Mo 3.4 C 0.04, Mn 1.5, Si 1.0, Fe Bal, N 0.175, S 0.030, Cu 2.00, P 0.040

Applications s32550, F61
FERRALIUM 255 is a cost-effective alternative to materials such as the nickel alloys, 20 type alloys, brass and bronze. Marine environments have long been the domain of admiralty bronze. Alloy 255 is replacing admiralty bronze, and the nickel alloys, in offshore platforms, deck hardware, rudders and shafting.
Alloy 255 is also making inroads in “borderline” corrosion applications where the nickel alloys and high-performance alloys have been used but may not have been absolutely necessary. In some instances, it has even been used to replace high performance Ni-Cr-Mo-F-Cu alloys in the phosphoric acid industry.
Valves, pumps, shafts, marine environments, Applications in down-hole, waste water, polycarbonate production, and demineralized water production.

What is difference between duplex and super duplex?
Duplex stainless steels are based around a composition of 22% chromium, whereas super duplex stainless steels are based around a composition of 25% chromium. By increasing the chromium content, the level of pitting corrosion resistance is also increased.

Duplex Stainless Steel : 
S31803 Duplex Stainless Steel , 2205 Duplex Stainless Steel Bar
S32750 Duplex Stainless Steel , Stainless Steel Grade Super Duplex 2507 (UNS S32750)
S32760 Duplex Stainless Steel ,SPECIFICATIONS: UNS S32760 | ASTM/ASME A240 / F53 | Werkstoff 1.4501
S31254 Duplex Stainless Steel ,Stainless steel grade 254
S329J4L Duplex Stainless Steel