Nitronic 40 Stainless Steel is a nitrogen strengthened austenitic stainless steel with great versatility, combining high yield strength with good corrosion resistance.
AMS 5656, ASTM A276, ASTM A479/A479M, ASTM A484/484M are the applicable specs.
There are two different version of Nitronic 40: UNS S21904 (XM11) and UNS S21900 (XM10).
The difference between the two UNS designations is the maximum allowable carbon content.
For UNS S21900, the maximum allowable content of carbon is 0.08%.
For UNS S21904, the maximum allowable content of carbon is 0.04%.
Therefore, UNS 21904 qualifies for UNS S21900.
The AMS 5656 spec specifically references UNS S21904.
We carry the low carbon UNS 21904 version of Nitronic 40 here at High Performance Alloys.