Current status of AISI types 304 LN and 316 LN austenitic stainless steels

High nitrogen steels and stainless steels are considered as promising materials in many conventional and strategic applications in power, chemical, petrochemical, refinery, pulp & paper, and marine sectors owing to their excellent combination of mechanical and corrosion resistance properties. AISI types 304 LN and 316 LN austenitic stainless steels are the current materials of choice for components that have been conventionally made of types 304 L and 316 L austenitic stainless steels. Types 304 LN and 316 LN stainless steel containing nitrogen between 0.06-0.08% are selected for the construction of various vessels, piping and structural components of the Prototype Fast Breeder Reactor of 500 MWe to be built at Kalpakkam. Extensive investigations have been carried out on the various metallurgical aspects of these alloys such as microstructural evolution during high temperature ageing, mechanical properties including tensile, creep, fatigue and creep-fatigue interactions, corrosion properties including pitting, crevice, intergranular and stress corrosion cracking behaviour and weldability including welding electrode development and weld metal characteristics. In this paper, an overview of the metallurgical characteristics and properties of nitrogen-bearing austenitic stainless steels are discussed.