Ferralium 255

Chemical Analysis
C Carbon
0.04 max
Mn Manganese
1.50 max
P Phosphorus
0.04 max
S Sulfur
0.03 max
Si Silicon
1.00 max
Cr Chromium
24.0 – 27.0
Mo Molybdenum
2.9 – 3.9
Nio Nitrogen
4.5 – .5
Cu Copper
1.50 – 2.50
N Nitrogen
0.10 – 0.25

General characteristics of Ferralium 255

This is a high-strength super duplex stainless steel with very good resistance to sulphuric acid and to sea water. The alloy shows excellent ductility and impact strength at both ambient and sub-zero temperatures.


This alloy is particularly applicable to use as large forgings as formation of the sigma phase is much less prevalent than in other super duplex alloys. The alloy’s strength, ductility and corrosion resistance make it particularly suitable for use in the pulp and paper, chemical processing and copper smelting industries.


The alloy may be forged in the range 2100/1830ºF (1150/1000ºC) and forging must be followed by a solution anneal. Forging below 1830ºF(1000ºC) – particularly in the rane 1740/1470ºF (950/800ºC) – will result in the formation of brittle intermetallic compounds, sigma being most notable, but as mentioned above Ferralium 255’s chemistry is less conducive to sigma formation than are those of other super duplex alloys. Solution annealing after forging is carried out at 1960ºF (1070ºC) followed by arapid water quench.

Heat treatment

The alloy is solution annealed at 1960ºF (1070ºC) followed by rapid water quenching. It is important to ensure uniform heating of parts and a soak at annealing temperature. Stress relief, if at all required say during machining operations, may be carried out at around 650ºF (350ºC) for 2 hours.


The alloy may be readily machined and its machinability is reputed to be better than that of other super duplexes.

Carbide tooling is recommended, and as with austenitic stainless steels, so are positive feeds and slow speeds.


The alloy may be welded by all the usual methods, but oxyacetylene welding is not recommended due to the danger of carbon pickup.

Although light-section and repair welds require bo [postweld heat treatment, heavy section welds should be given a subsequent solution treatment to ensure maximum corrosion resistance and ductility.

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