Abstract
Strength-ductility trade-off is usually an inevitable scenario in κ'-carbides strengthened austenitic lightweight steel.The reduction of ductility is primarily attributed to the shearing of coherent κ'-carbides by dislocations,resulting in strain localization and ultimately leading to a low work hardening rate.Semi-coherent B2 particles,on the other hand,effectively enhance the work hardening capability due to the non-shearable feature.However,achieving a large volume fraction and uniform distribution of B2 par-ticles within the austenite matrix,as well as optimizing their morphology as fine particles,remains a challenge for austenitic lightweight steel.In this study,we have addressed the above challenges by im-plementing the two-step aging process combined with pre-cold rolling process.The pre-cold rolling treat-ment,performed prior to the initial aging treatment at 900 ℃,effectively promotes the heterogeneous nucleation of B2 particles by introducing dislocations,resulting in a more uniform distribution of B2 par-ticles and a refinement in size(with an average length of 200-500 nm and a width of 50-80 nm).Fur-thermore,these intragranular B2 particles exhibit the typical K-S and N-W orientation relationships with the austenite matrix.Subsequently,after the second-step aging process at 450 ℃,spherical nano-sizedκ'-carbides(5 nm)are homogeneously dispersed within the austenite matrix.The above dual nanoparti-cles provide an approximate precipitation hardening effect of 400 MPa.Concurrently,the nanoscale"pla-nar slip and dislocation bow-out"multiple deformation mechanisms contribute to an efficient source of work hardening capability,leading to a beneficial synergy of strength-ductility.This promising strategy is expected to expand the applications of dual-nanoprecipitation austenitic low-density steel in various lightweight structural materials.
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