Microstructure evolution in nano/submicron grained AISI 301LN stainless steel

The phase and microstructure evolution of a heavily cold-rolled AISI 301LN stainless steel (SS), before and after annealing is discussed. AISI 301LN SS has been cold-rolled to 63% rolling reduction and subsequently annealed from 600 to 1000 °C for short annealing durations (1–100 s). Phase analysis indicates that the cold-rolled sheet comprises almost 100% martensite, while transmission electron microscopy examination reveals its morphology to be of dislocation cell- and heavily deformed lath-type martensite. The martensite → austenite reversion upon annealing at 600 °C for 1 and 10 s is negligible, but nanoscale austenite grains are formed in the martensitic matrix. Partial reversion to nano/submicron austenite grains is observed for samples annealed at 600 °C for 100 s, and 700 °C for 1 s. Samples annealed at higher temperatures exhibit a complete reversion to submicron/nano-austenite grains with a large grain size variation, as well as secondary phase chromium nitride precipitates.