Alloy F255 (UNS S32550 / W.Nr. 1.4507) is a highly alloyed, superduplex (ferrite-austenite) solid solution strengthened alloy, which provides high strength and wear resistance while offering superior corrosion resistance compared to 316 stainless steel. This combination makes Alloy

F255 ideal for demanding applications in a number of different industries such as Offshore Oil & Gas, Pulp & Paper, Nuclear, Marine, Chemical Processing and Flue Gas Desulfurization.

Operating temperatures should be considered when selecting Alloy 255 as secondary phases could form within higher temperature ranges. If the alloy is allowed to soak between the temperatures of 1000°F and 1800°F, carbides (M23C6), nitrides (M2N) and sigma phase can form. At temperatures approaching 900°F, alpha prime can
form. The maximum continuous operating temperature according to ASME Boiler and Pressure Vessel Code, Section VIII is 500°F.

Resistance to Corrosion

Compared to typical austenitic alloys such as 304, 316 and 317 stainless steels, Alloy F255 displays superior corrosion resistance in most media. Also, Alloy F255 typically out performs duplex alloy 2205. Alloy F255 performs well in sulfuric, phosphoric, nitric and shows excellent resistance to organic acids such as acetic and formic acid. Highly reducing media should be avoided.

Pitting resistance equivalent numbers (PREN) are typically used to compare the pitting resistance of various alloys. This number can be calculated from a number of different equations, which are based on specific alloying elements that contribute to the alloys pitting resistance. For duplex stainless steels the equation typically used to calculate the PREN is as shown below. A word of caution, the PREN is not a guarantee of the corrosion performance of any alloy and should only be used a s guide to help the user select potential alloys for specific use.

PREN = %Cr + 3.3 x %Mo + 16 x N

Fabrication and Heat Treatment

Hot and cold forming can be performed on Alloy F255 via traditional methods keeping in mind that the alloy is higher strength compared to 316 stainless steel. Hot working the alloy should be between the temperatures of 1800°F and 2100°F followed by an annealing heat treatment at 1950°F and water quench. Cold working the alloy to induce more than 10% deformation will require a similar heat treatment. For forming above 20% deformation, intermediate heat treatments should be performed.

Machining Alloy F255 can be performed using the same methods as traditional stainless steels. Carbide tipped tools are preferred. Stress relieving by heating to 675°F briefly, followed by rapid cooling can be performed on heavily machined components.

Welding can be performed by TIG, MIG or SMAW and should be performed on material in the annealed condition. Pre heat treatment is not necessary but it is important to carefully clean the surfaces being welded. If pickling is the desired method for cleaning the surface, a solution with the following composition can be used.

15% HNO3 + 2% HF (volume by volume) at a minimum temperature of 55°F

Post weld heat treatment is not necessary but preferred when welding heavy sections to optimize corrosion resistance.



Common Trade Names

Ferralium® 255

Ferralium® is a registered trademark of Meighs Ltd, Langley Alloys Division

Data Sheet

Chemical Composition:

Element Chromium Nickel Molybdenum Copper Nitrogen Iron
Avg. Nominal % 25.3 6 2 2 0.22 Balance

Standard Products

Alloy 255 Plate

Alloy 255 Fittings

Alloy 255 Tube

Alloy 255 Pipe

Alloy 255 Bar

Alloy 255 Sheet

Alloy 255 Fasteners

Alloy 255 Flanges

Nickel Alloy Flanges

Alloy 255 Welding Product

Alloy 255 Coil

Alloy 255 Plate Shapes

Alloy 255 Custom Profiles

Alloy 255 Forgings

Alloy 255 Machined Parts

Alloy 255 Welded Components