Precipitation strengthening has been widely adopted in austenitic low-density steel owing to excellent hardened effects.This approach generally employs the coherentκ′carbides and non-coherent B2 particles.Revealing ...Precipitation strengthening has been widely adopted in austenitic low-density steel owing to excellent hardened effects.This approach generally employs the coherentκ′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 prop-erties during aging process is systematically investigated.Our results reveal that nano-sizedκ′carbides domains(2 nm)exist in the solution-treated specimen.During aging at 500℃for 1 h,the cuboidalκ′carbides(15-20 nm)uniformly disperse in austenite matrix.However,after aging at 700℃for 15 min,the coarsenκ′carbides(30-35 nm)inhomogeneously distribute and align preferentially along the〈100〉directions.Further,extending the aging time to 60 min,the needle-type B2 particles replace theκ′carbides due to the enrichment of Ni elements at the phase boundaries among the austenite andκ′carbides.After aging at 900℃,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 ofκ′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.展开更多
Strength-ductility trade-off is usually an inevitable scenario inκ′-carbides strengthened austenitic lightweight steel.The reduction of ductility is primarily attributed to the shearing of coherentκ′-carbides by d...Strength-ductility trade-off is usually an inevitable scenario inκ′-carbides strengthened austenitic lightweight steel.The reduction of ductility is primarily attributed to the shearing of coherentκ′-carbides by dislocations,resulting in strain localization and ultimately leading to a low work hardening rate.Semicoherent 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 particles 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 implementing the two-step aging process combined with pre-cold rolling process.The pre-cold rolling treatment,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 particles and a refinement in size(with an average length of 200–500 nm and a width of 50–80 nm).Furthermore,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 nanoparticles provide an approximate precipitation hardening effect of 400 MPa.Concurrently,the nanoscale“planar 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.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52171105 and 51871062).
文摘Precipitation strengthening has been widely adopted in austenitic low-density steel owing to excellent hardened effects.This approach generally employs the coherentκ′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 prop-erties during aging process is systematically investigated.Our results reveal that nano-sizedκ′carbides domains(2 nm)exist in the solution-treated specimen.During aging at 500℃for 1 h,the cuboidalκ′carbides(15-20 nm)uniformly disperse in austenite matrix.However,after aging at 700℃for 15 min,the coarsenκ′carbides(30-35 nm)inhomogeneously distribute and align preferentially along the〈100〉directions.Further,extending the aging time to 60 min,the needle-type B2 particles replace theκ′carbides due to the enrichment of Ni elements at the phase boundaries among the austenite andκ′carbides.After aging at 900℃,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 ofκ′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.
基金supported by the National Natural Science Foundation of China(Nos.52171105 and 51871062).
文摘Strength-ductility trade-off is usually an inevitable scenario inκ′-carbides strengthened austenitic lightweight steel.The reduction of ductility is primarily attributed to the shearing of coherentκ′-carbides by dislocations,resulting in strain localization and ultimately leading to a low work hardening rate.Semicoherent 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 particles 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 implementing the two-step aging process combined with pre-cold rolling process.The pre-cold rolling treatment,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 particles and a refinement in size(with an average length of 200–500 nm and a width of 50–80 nm).Furthermore,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 nanoparticles provide an approximate precipitation hardening effect of 400 MPa.Concurrently,the nanoscale“planar 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.
