S21800 is the Unified Numbering System (UNS) designation for a more highly alloyed stainless steel most commonly known as Nitronic 60. The UNS system was created by a number of trade groups working together in the 1970’s, to reduce confusion from the same alloy being called different things or vice-versa. Each metal is indicated by a letter followed by five numbers, where the letter indicates the family of metals i.e. S for stainless steels.
Nitronic 60 (Fermonic 60, UNS S21800) is a fully austenitic stainless steel supplied in the hot worked and annealed condition (Nitronic® is a trademark owned by AK Steel Corporation). The general corrosion resistance is between that of Alloy 304 and Alloy 316 stainless steel, whereby is it generally better than Alloy 304 in most environments but superior to Alloy 316 with respect to chloride pitting resistance. More significantly, additions of Silicon and Manganese provide superior wear, galling and fretting resistance than many other corrosion resistant alloys making it preferable for applications where there is repeated movement/sliding or frequent assembly/disassembly. Applications such as connectors and couplings make use of this resistance to galling, allowing them to operate with confidence even if left for extended periods.
These compositional additions also provide almost double the yield strength of Alloys 304/316, and higher strength can be achieved through cold working. Importantly, it remains fully austenitic – and therefore, fully non-magnetic – even after severe cold-working, although there is no improvement in galling performance from this operation.
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