This paper focuses on the relationship between the microstructure and tensile properties of Fe-Mn-Al-C low-density high-strength steel processes by hot-rolling and air-cooling process. The microstructure analysis reve...This paper focuses on the relationship between the microstructure and tensile properties of Fe-Mn-Al-C low-density high-strength steel processes by hot-rolling and air-cooling process. The microstructure analysis reveals that the combination of hot-rolling and air-cooling results in the formation of heterogeneous structures comprising different-sized γ and B_(2) phases in the low-density steel with the addition of nickel (Ni). The addition of Ni promotes the formation of the B_(2) phase and induces the pinning of B_(2) phase particles at the γ grain boundaries. This pinning effect effectively hinders the growth of the γ grains, leading to grain refinement. The tensile test results demonstrate that LDS-5Ni (low-density steel, LDS) exhibits excellent high strength and ductility combination, e.g., a tensile strength of 1535 MPa, yield strength of 1482 MPa, and elongation of 23.3%. These remarkable mechanical properties are primarily attributed to the combined strengthening contributions of grain refinement and duplex nano-sized second-phase precipitation hardening.展开更多
In low-density steel,κ-carbides primarily precipitate in the form of nanoscale particles within austenite grains.However,their precipitation within ferrite matrix grains has not been comprehensively explored,and the ...In low-density steel,κ-carbides primarily precipitate in the form of nanoscale particles within austenite grains.However,their precipitation within ferrite matrix grains has not been comprehensively explored,and the second-phase evolution mechanism during aging remains unclear.In this study,the crystallographic characteristics and morphological evolution ofκ-carbides in Fe-28Mn-10Al-0.8C(wt%)low-density steel at different aging temperatures and times and the impacts of these changes on the steels’microhardness and properties were comprehensively analyzed.Under different heat treatment conditions,intragranularκ-carbides exhibited various morpho-logical and crystallographic characteristics,such as acicular,spherical,and short rod-like shapes.At the initial stage of aging,acicularκ-carbides primarily precipitated,accompanied by a few spherical carbides.κ-Carbides grew and coarsened with aging time,the spherical carbides were considerably reduced,and rod-like carbides coarsened.Vickers hardness testing demonstrated that the material’s hardness was affected by the volume fraction,morphology,and size ofκ-carbides.Extended aging at higher temperatures led to an increase in carbide size and volume fraction,resulting in a gradual rise in hardness.During deformation,the primary mechanisms for strengthening were dislocation strengthening and second-phase strengthening.Based on these findings,potential strategies for improving material strength are proposed.展开更多
The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM...The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and thermodynamic calculation（TC）.It was shown that the ferrite-based lightweight steels with 5wt.%or 8wt.%Al were basically composed of ferrite,austenite andκ-carbide.As the annealing temperature increased,the content of the austenite in the steel gradually increased,while theκ-carbide gradually decomposed and finally disappeared.The mechanical properties of the steel with 5wt.%Al and 2wt.%Cr,composed of ferrite and Cr7C3carbide at different annealing temperatures,were significantly inferior to those of others.The steel containing 5wt.%Al,annealed at 820°C for 50sthen rapidly cooled to 400°C and held for 180s,can obtain the best product of strength and elongation（PSE）of 31242MPa·%.The austenite stability of the steel is better,and its PSE is higher.In addition,the steel with higher PSE has a more stable instantaneous strain hardening exponent（n value）,which is mainly caused by the effect of transformation induced plasticity（TRIP）.When theκ-carbide or Cr7C3carbide existed in the microstructure of the steel,there was an obvious yield plateau in the tensile curve,while its PSE decreased significantly.展开更多
Novel strengthening of Fe-29.1Mn-12.5Al-1.35C-4.95Cr steel achieved by warm rolling was investi-gated.The solution-treated steel consisted of aγ-matrix containing nano-sizedκ-carbide((Fe,Mn)_(3) AlC)and elongated pr...Novel strengthening of Fe-29.1Mn-12.5Al-1.35C-4.95Cr steel achieved by warm rolling was investi-gated.The solution-treated steel consisted of aγ-matrix containing nano-sizedκ-carbide((Fe,Mn)_(3) AlC)and elongated prior ferrite,which was transformed into FeAl-type B2 and Fe_(3) Al-type D0_(3) phases.The solution-treated steel exhibited poor strain hardening owing to glide softening associated withκ-carbide shearing by dislocations.However,after warm rolling with a reduction ratio of 30%at 300℃,the yield and tensile strengths significantly increased from 917 to 1300 MPa and 1025 to 1419 MPa,respectively.The tensile test conducted at 300℃to simulate warm rolling exhibited serrated flows,indicating dy-namic strain aging(DSA).Atom probe tomography exhibited that the C atoms inκ-carbide were swept away along the slip direction by disruptive shear during rolling at 300℃.The swept C atoms along the slip direction interacted strongly with dislocations at 300℃,with repeated pinning and breakaway of dislocations from the C atoms.This contributed to significant strengthening owing to the formation of a solute-rich atmosphere after warm rolling.The results of the tensile tests at 300℃indicated that the de-gree of strengthening was proportional to the pre-strain level.Tensile strength of 1.4 GPa can be achieved with good ductility(17%elongation)by warm rolling.This novel warm-rolling strengthening method ex-pedites the potential application of Fe-29.1Mn-12.5Al-1.35C-4.95Cr as a 1.4 GPa class ultra-lightweight steel.展开更多
基金funding from the National Key Technologies Research and Development Program of China(No.2021YFB3703500)the National Natural Science Foundation of China(No.51771014).
文摘This paper focuses on the relationship between the microstructure and tensile properties of Fe-Mn-Al-C low-density high-strength steel processes by hot-rolling and air-cooling process. The microstructure analysis reveals that the combination of hot-rolling and air-cooling results in the formation of heterogeneous structures comprising different-sized γ and B_(2) phases in the low-density steel with the addition of nickel (Ni). The addition of Ni promotes the formation of the B_(2) phase and induces the pinning of B_(2) phase particles at the γ grain boundaries. This pinning effect effectively hinders the growth of the γ grains, leading to grain refinement. The tensile test results demonstrate that LDS-5Ni (low-density steel, LDS) exhibits excellent high strength and ductility combination, e.g., a tensile strength of 1535 MPa, yield strength of 1482 MPa, and elongation of 23.3%. These remarkable mechanical properties are primarily attributed to the combined strengthening contributions of grain refinement and duplex nano-sized second-phase precipitation hardening.
基金supported by the National Key Research and Development Program of China(No.2023YFB3711702).
文摘In low-density steel,κ-carbides primarily precipitate in the form of nanoscale particles within austenite grains.However,their precipitation within ferrite matrix grains has not been comprehensively explored,and the second-phase evolution mechanism during aging remains unclear.In this study,the crystallographic characteristics and morphological evolution ofκ-carbides in Fe-28Mn-10Al-0.8C(wt%)low-density steel at different aging temperatures and times and the impacts of these changes on the steels’microhardness and properties were comprehensively analyzed.Under different heat treatment conditions,intragranularκ-carbides exhibited various morpho-logical and crystallographic characteristics,such as acicular,spherical,and short rod-like shapes.At the initial stage of aging,acicularκ-carbides primarily precipitated,accompanied by a few spherical carbides.κ-Carbides grew and coarsened with aging time,the spherical carbides were considerably reduced,and rod-like carbides coarsened.Vickers hardness testing demonstrated that the material’s hardness was affected by the volume fraction,morphology,and size ofκ-carbides.Extended aging at higher temperatures led to an increase in carbide size and volume fraction,resulting in a gradual rise in hardness.During deformation,the primary mechanisms for strengthening were dislocation strengthening and second-phase strengthening.Based on these findings,potential strategies for improving material strength are proposed.
基金supported by the Shanghai Municipal Natural Science Foundation(Grant No.17ZR1410400)the Shanghai Municipal Science and Technology Commission(Grant Nos.15DZ2260300,15DZ2260301)
文摘The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and thermodynamic calculation（TC）.It was shown that the ferrite-based lightweight steels with 5wt.%or 8wt.%Al were basically composed of ferrite,austenite andκ-carbide.As the annealing temperature increased,the content of the austenite in the steel gradually increased,while theκ-carbide gradually decomposed and finally disappeared.The mechanical properties of the steel with 5wt.%Al and 2wt.%Cr,composed of ferrite and Cr7C3carbide at different annealing temperatures,were significantly inferior to those of others.The steel containing 5wt.%Al,annealed at 820°C for 50sthen rapidly cooled to 400°C and held for 180s,can obtain the best product of strength and elongation（PSE）of 31242MPa·%.The austenite stability of the steel is better,and its PSE is higher.In addition,the steel with higher PSE has a more stable instantaneous strain hardening exponent（n value）,which is mainly caused by the effect of transformation induced plasticity（TRIP）.When theκ-carbide or Cr7C3carbide existed in the microstructure of the steel,there was an obvious yield plateau in the tensile curve,while its PSE decreased significantly.
基金the financial support of the Na-tional Research Foundation of Korea(NRF)grant funded by the Korean government(Ministry of Science and ICT/MSIT,No.RS-2023-00208509)funded by the Ko-rean government(Ministry of Trade,Industry and Energy/MOTIE,20010748).
文摘Novel strengthening of Fe-29.1Mn-12.5Al-1.35C-4.95Cr steel achieved by warm rolling was investi-gated.The solution-treated steel consisted of aγ-matrix containing nano-sizedκ-carbide((Fe,Mn)_(3) AlC)and elongated prior ferrite,which was transformed into FeAl-type B2 and Fe_(3) Al-type D0_(3) phases.The solution-treated steel exhibited poor strain hardening owing to glide softening associated withκ-carbide shearing by dislocations.However,after warm rolling with a reduction ratio of 30%at 300℃,the yield and tensile strengths significantly increased from 917 to 1300 MPa and 1025 to 1419 MPa,respectively.The tensile test conducted at 300℃to simulate warm rolling exhibited serrated flows,indicating dy-namic strain aging(DSA).Atom probe tomography exhibited that the C atoms inκ-carbide were swept away along the slip direction by disruptive shear during rolling at 300℃.The swept C atoms along the slip direction interacted strongly with dislocations at 300℃,with repeated pinning and breakaway of dislocations from the C atoms.This contributed to significant strengthening owing to the formation of a solute-rich atmosphere after warm rolling.The results of the tensile tests at 300℃indicated that the de-gree of strengthening was proportional to the pre-strain level.Tensile strength of 1.4 GPa can be achieved with good ductility(17%elongation)by warm rolling.This novel warm-rolling strengthening method ex-pedites the potential application of Fe-29.1Mn-12.5Al-1.35C-4.95Cr as a 1.4 GPa class ultra-lightweight steel.
