Precipitation transformation pathway and mechanical behavior of nanoprecipitation strengthened Fe-Mn-Al-C-Ni austenitic low-density steel

Precipitation strengthening has been widely adopted in austenitic low-density steel owing to excellent hardened effects. This approach generally employs the coherent kappa' -carbides and non-coherent B2 particles. Revealing the precipitation transformation pathway is decisive for further optimizing the microstructures under specific engineering applications. Herein, the detailed precipitation sequence of Fe-28Mn-11Al-1C-5Ni (wt%) austenitic low-density steel as well as its influence on mechanical properties during aging process is systematically investigated. Our results reveal that nano-sized kappa' -carbides domains (2 nm) exist in the solution-treated specimen. During aging at 500 degree celsius for 1 h, the cuboidal kappa' -carbides (15-20 nm) uniformly disperse in austenite matrix. However, after aging at 700 degree celsius for 15 min, the coarsen kappa' -carbides (30-35 nm) inhomogeneously distribute and align preferentially along the ( 1 0 0 ) directions. Further, extending the aging time to 60 min, the needle-type B2 particles replace the kappa' -carbides due to the enrichment of Ni elements at the phase boundaries among the austenite and kappa' carbides. After aging at 900 degree celsius, kappa' -carbides entirely dissolve into the austenite matrix, and the intragranular B2 particles are the sole precipitates in the austenite matrix and follow the K-S orientation relationship with austenite. The work hardening capability seriously deteriorates due to the shearing of kappa' -carbides by gliding dislocations. While the intragranular B2 particles preserve excellent work hardening rate by dislocations bow-out mechanism. The present work is meaningful for guiding the design of new generation dual-nano precipitation austenitic lightweight steel.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.