Does austenitic stainless steel rust?

Under the wrong circumstances, all forms of stainless steel will corrode or rust. Aggressive environments containing acids or chlorides i.e. seawater, will increase the likelihood or extent of corrosion, along with contamination of the working fluid, damage to the surface, poor surface preparation or welding. As such, stainless steel is a more appropriate caption than stain-free steel.

There are a wide variety of austenitic stainless steels. The more common grades of 304 and 316 have a pitting resistance equivalent number (PREN) of between 20-25. Higher-performance grades such as Fermonic 50 (XM-19, UNS S20910, 1.3964) possess a PREN of around 34, so provide a significant uplift in resistance to pitting corrosion. There are a number of so-called super austenitic grades, with higher levels of molybdenum and nickel, such as Alloy 254 (6Mo, 254SMO, F44, UNS S31254, 1.4547) which achieves a PREN of 43, so just above that of super duplex stainless steels.

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