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 κ′-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 κ′-carbides domains (2 nm) exist in the solution-treated specimen. During aging at 500 °C for 1 h, the cuboidal κ′-carbides (15–20 nm) uniformly disperse in austenite matrix. However, after aging at 700 °C for 15 min, the coarsen κ′-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 κ′-carbides due to the enrichment of Ni elements at the phase boundaries among the austenite and κ′-carbides. After aging at 900 °C, κ′-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 κ′-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.