Stainless steel with improved mechanical properties and/or resistance to particular corrosive media is necessary in the chemícal industry and in other special applications.
Types 304LN and 316LN, which can be produced on request, thanks to a nitrogen addition, exhibit higher yield strength, while corrosion resistance remains unaltered.
When stress corrosion is the problem, higher molybdenum grades are used, as 329A, having a two-phase strutture, i.e. ferrite plus austenite.
Such strutture resists better than 316 to pitting and to interstitial corrosion by medium chloride concentrations.
High nickel grades, with a full austenitic strutture,as 904L are used in contact with high chlorine ions concentrations at temperatures somewhat higher than room temperatures, such as in condensers, heat exchangers and, when standard austenitic grades cannot resist stress, intergranular or pitting corrosion.