1.3964 is the Werkstoff number for the more highly alloyed austenitic stainless steel most commonly known as Nitronic® 50. Werkstoff numbers were developed by the German standards body DIN; the word translates roughly as "material". It is also known as XM19, as used in ASTM A182, ASTM A276 and ASTM A479, alongside the unified numbering system caption UNS S20910.
Nitronic 50 is a higher-performance austenitic stainless steel that provides roughly twice the yield strength of regular 3xx-series stainless steels, with improved corrosion performance. Like some super duplex stainless steels, it uses increased nitrogen content to raise strength, so is sometimes called a nitrogen-strengthened alloy. Manganese additions add further strength through solid-solution strengthening.
It is widely used across marine and industrial applications. Compared with Alloy 316L it has increased chromium and molybdenum, which support its improved corrosion resistance: where Alloy 316L has a pitting resistance equivalent number (PREN) of 25, Nitronic 50 has a PREN of 34. It is listed in NACE MR0175 for sour-service applications thanks to its resistance to sulphide stress cracking.