XM-19 is a high-performance austenitic stainless steel best known for valve stems. It offers roughly twice the strength and much better corrosion resistance than standard 316L, while keeping the toughness and weldability of an austenitic grade. We supply it as Fermonic® 50.
The grade is most often specified against the US ASTM reference XM-19, the European 1.3964 number, or the UNS S20910 designation. It is also widely known by the trademark Nitronic® 50.
An austenitic grade with more strength and corrosion resistance
As an austenitic stainless steel, XM-19 sits in the same family as standard grades such as 304L and 316L. It shares their ease of fabrication and welding, is non-magnetic, and holds its mechanical properties across a wide temperature range. It was developed to add significantly better corrosion resistance and strength.
Corrosion resistance
The corrosion resistance of XM-19 comes from higher chromium and nitrogen contents, which improve the quality of the passive film that forms on all stainless steels. The Pitting Resistance Equivalent Number (PREN) is a useful theoretical way to compare the pitting resistance of different grades from their compositions. It is helpful for comparison but cannot predict absolute performance in a specific application.
The most widely accepted PREN formula is PREN = %Cr + 3.3 x %Mo + 16 x %N. Whereas 316L has a typical PREN of 25, XM-19 reaches 34 - comparable with a duplex stainless steel such as 2205.
Strength and toughness
Nitrogen also strengthens the alloy. In the standard solution-annealed condition, XM-19 has a yield strength twice that of 316L. Supplied in the hot-rolled condition, its yield strength is up to four times greater than 316L.
It is also tough. Toughness is measured by impact strength - the energy absorbed when a sample is broken by a weighted pendulum. A higher value means the metal is more likely to resist a shock load. For XM-19, impact strength is retained down to cryogenic temperatures of -196degC.
This matters for a valve stem. A valve may only be actuated occasionally, and if it sticks, considerable force is needed to open or close it. The strength and toughness of XM-19 across a wide temperature range are central to its continued specification.
What we stock
We stock an extensive range of XM-19 in both solution-annealed and hot-worked condition, from 3/4" to 10" diameter. We can supply long lengths for bar-fed machining, or more typically precisely cut billets from our modern, CNC-controlled Kasto saws.
We also stock Fermonic® 60 (Nitronic 60, UNS S21800). This alloy has a quite different composition, with silicon and manganese additions that give superior wear, galling and fretting resistance, so it is used almost exclusively in couplings subject to repeated sliding or frequent assembly and disassembly.