Nitronic 50 is a high-performance austenitic stainless steel with roughly twice the yield strength of standard 3xx grades and better corrosion resistance. It is widely used in marine and industrial applications, and we supply it as Fermonic® 50.

Corrosion resistance

Compared with Alloy 316L, Nitronic 50 has higher chromium and molybdenum, which improve corrosion resistance. Where 316L has a Pitting Resistance Equivalent Number (PREN) of 25, Nitronic 50 reaches 34. Super duplex stainless steels attain a PREN above 40, but with different mechanical properties - which is the main reason Nitronic 50 is chosen instead of super duplex in some cases. It is listed in NACE MR0175 for sour service, given its resistance to sulphide stress cracking.

Strength without losing toughness

To keep the favourable properties of an austenitic stainless steel - ductility and toughness at both elevated and cryogenic temperatures, plus easy welding and fabrication - the grade needs a significant nickel addition. Without it, the microstructure would tend towards a duplex product, with even higher strength but lower ductility and toughness. This does make Nitronic 50 more expensive than duplex and super duplex stainless steels.

Like some super duplex stainless steels, it uses increased nitrogen to raise strength, so it is sometimes called a nitrogen-strengthened alloy. Manganese additions further increase strength through solid-solution strengthening.

Designations and conditions

Nitronic 50 is also widely known as XM19, the generic designation in ASTM A276 and ASTM A479, as well as UNS S20910 or DIN 1.3964.

It is available in two conditions. The first is simply solution annealed, which is the easier form to machine. Most of our customers, however, specify the higher-strength version, supplied in the hot-rolled or strain-hardened condition depending on diameter. Larger diameters reach the higher strength while staying below the maximum hardness (HRC below 35) required by NACE, by hot rolling at lower than normal temperatures to influence the microstructure. For smaller diameters, the strain-hardened condition gives more consistent properties and lower through-bar hardness.

Our Fermonic® 50 is not just an alternative trademark. For the smaller diameters, our manufacturing route is unique to us and ensures we can achieve the High Strength properties across the widest possible range of bar diameters.

Common applications for Fermonic® 50

  • Valve fittings, particularly stems, thanks to the alloy's toughness
  • Marine applications, including rod rigging using cold-drawn lengths, tie-downs and fittings
  • Pump shafts
  • Sucker rods for oil rigs
  • Fasteners
Grade PREN
Alloy 316L 25
Nitronic 50 (Fermonic® 50) 34
Super duplex stainless steel >40