In the 1980s and 1990s, more highly alloyed
grades of austenitic, ferritic, and duplex stainless
steel were developed. These grades provide
improved corrosion resistance and higher
strength levels compared to commodity grades
such as type 304 and 316 stainless steels.
Although the terms superaustenitic, superferritic,
and superduplex are often used to describe
these alloys, there is no universally accepted
definition for a “super” stainless steel.
The relative resistance of a stainless steel to
chloride pitting and crevice corrosion can be
related to an alloy composition by an empirical
formula called the pitting resistance equivalent
number (PREN).