The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood t...The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excellent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,ε_(hcp)-martensite andα'_(bcc)-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate thatε_(hcp)-martensite becomes more stable thanα'_(bcc)-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80℃,ε_(hcp)-martensite transformation,α'_(bcc)-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.展开更多
The crystallography of phase transformation is an important issue for studying metallic alloys.Here,we demonstrate an abnormal orientation relation between face-centered cubic(fcc) and hexagonal closepacked(hcp) phase...The crystallography of phase transformation is an important issue for studying metallic alloys.Here,we demonstrate an abnormal orientation relation between face-centered cubic(fcc) and hexagonal closepacked(hcp) phases due to the intersection of two ε_(hcp)-martensite variants in a high manganese steel.The corresponding crystallogra phic cha racteristics,including invariant line,habit plane and atomic steps,have been characterized by transmission electron micro scopy and the quasi-O-line model.In addition,the models of phase transfo rmation about the intersection are proposed based on transmission mechanisms of dislocations.Our findings enrich the theories of phase transformation and implicate the possibility to fabricate stro nger and tougher steel.展开更多
The Fe-29 Mn-3 Al-3 Si twin-induced plasticity(TWIP)steel is used to conduct quasi-static compression and dynamic impact deformation with strain rates ranging from 8.3×10^(-4) to 3800 s^(-1).The microstructures a...The Fe-29 Mn-3 Al-3 Si twin-induced plasticity(TWIP)steel is used to conduct quasi-static compression and dynamic impact deformation with strain rates ranging from 8.3×10^(-4) to 3800 s^(-1).The microstructures and properties of deformed samples under different strain rates were investigated comparatively.These results show that positive strain rate sensitivity was observed with the increase in strain rates and that there was a significant difference in strain rate sensitivity factor(m)between quasi-static compression(m=0.029)and dynamic impact deformation(m=0.190).Compared to the quasi-static compression,the dynamic impact deformation exhibited higher yield strength.Microstructural examination reveals that the primary twins were frequently found during the quasi-static compression process,and the secondary twins were rarely observed.However,the secondary and multi-fold deformation twins were florescent in the dynamic impact samples.At the initial stage of dynamic impact deformation,partial dislocations and staking faults on multiple conjugate{111}planes were simultaneously activated and produced a large number of Lomer-Cottrell dislocations,resulting in a large increase in yield strength during dynamic impact.展开更多
基金supported by the National Natural Science Foundation of China[Grant Nos.5180106051831004+6 种基金1142780651671082]the China Postdoctoral Science Foundation(grant number 2019M652756)the National Key Research and Development Program of China(grant number 2016YFB0300801)the China Scholarship Council(grant number 201606130008)the financial support from Austrain Science Fund(FWF)(grant number P 32378-N37)BMBWF(grant number KR 06/2020)。
文摘The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excellent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,ε_(hcp)-martensite andα'_(bcc)-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate thatε_(hcp)-martensite becomes more stable thanα'_(bcc)-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80℃,ε_(hcp)-martensite transformation,α'_(bcc)-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.
基金supported financially by the National Natural Science Foundation of China(Nos.51801060,51831004,11427806 and 51671082)the China Postdoctoral Science Foundation(No.2019M652756)+1 种基金the National Key Research and Development Program of China(No.2016YFB0300801)the China Scholarship Council(No.201606130008)。
文摘The crystallography of phase transformation is an important issue for studying metallic alloys.Here,we demonstrate an abnormal orientation relation between face-centered cubic(fcc) and hexagonal closepacked(hcp) phases due to the intersection of two ε_(hcp)-martensite variants in a high manganese steel.The corresponding crystallogra phic cha racteristics,including invariant line,habit plane and atomic steps,have been characterized by transmission electron micro scopy and the quasi-O-line model.In addition,the models of phase transfo rmation about the intersection are proposed based on transmission mechanisms of dislocations.Our findings enrich the theories of phase transformation and implicate the possibility to fabricate stro nger and tougher steel.
基金financially supported by the National Natural Science Foundation of China(Nos.51801060,51831004 and 52171006)。
文摘The Fe-29 Mn-3 Al-3 Si twin-induced plasticity(TWIP)steel is used to conduct quasi-static compression and dynamic impact deformation with strain rates ranging from 8.3×10^(-4) to 3800 s^(-1).The microstructures and properties of deformed samples under different strain rates were investigated comparatively.These results show that positive strain rate sensitivity was observed with the increase in strain rates and that there was a significant difference in strain rate sensitivity factor(m)between quasi-static compression(m=0.029)and dynamic impact deformation(m=0.190).Compared to the quasi-static compression,the dynamic impact deformation exhibited higher yield strength.Microstructural examination reveals that the primary twins were frequently found during the quasi-static compression process,and the secondary twins were rarely observed.However,the secondary and multi-fold deformation twins were florescent in the dynamic impact samples.At the initial stage of dynamic impact deformation,partial dislocations and staking faults on multiple conjugate{111}planes were simultaneously activated and produced a large number of Lomer-Cottrell dislocations,resulting in a large increase in yield strength during dynamic impact.