A duplex ultrafine microstructure in a medium manganese steel (0.2C-5Mn) was produced by austenite re- verted transformation annealing (ART-annealing). The microstructural evolution during annealing was examined b...A duplex ultrafine microstructure in a medium manganese steel (0.2C-5Mn) was produced by austenite re- verted transformation annealing (ART-annealing). The microstructural evolution during annealing was examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on the microstructure examination, it was found that some M3C type carbides appeared in the martensitic matrix at the beginning of the ART-annealing. But with further increasing annealing time, these carbides would be dissolved and finally disappeared. Meanwhile, the austenite lath was developed in the ART-annealing process and the volume fraction of austenite increosed with the increase of the annealing time, which resulted in a duplex microstructure con- sisting of ultrafine-grained ferrite and large fraction of reverted austenite after long time annealing. The mechanical property examinations by uniaxial tensile tests showed that ART-annealing (6 h, 650 ℃) resulted in a superhigh product of strength to elongation up to 42 GPa ·%.展开更多
A hot-rolled medium Mn(0.2C5Mn)steel is annealed at 650℃ to produce an ultrafine-grained duplex microstructure with different austenite volume fractions by austenite reverted transformation(ART)annealing,and the orie...A hot-rolled medium Mn(0.2C5Mn)steel is annealed at 650℃ to produce an ultrafine-grained duplex microstructure with different austenite volume fractions by austenite reverted transformation(ART)annealing,and the orientation relationship strictly obeys K-S orientation relationship before deformation.Tensile tests are carried out in a temperature range from-196 to 400℃ to examine the effects of the austenite volume fraction and the deformation temperature on the tensile properties and the austenite stability.Microstructural observations reveal that the metastable austenite gradually transformed into a-martensite,which is controlled by the deformation strain,the temperature and the austenite volume fraction.Both strain hardening behavior and ductility of the studied steel are dependent on austenite volume fraction and deformation temperature significantly.The stress-strain curves of ART-annealed 0.2C5Mn steel assume an S shape and a very large work hardening rate of about 10 GPa is obtained at liquid nitrogen deformation temperature.Based on the experimental data,a quantitative relation is proposed to describe the ductility dependence on both the austenite volume fraction and its mechanical stability.展开更多
By combining cryo-rolling and post-annealing treatments,the nanostructured NiTi alloy is produced.A diff erential scanning calorimetry measurement was used to test the eff ect of the preparation process on phase trans...By combining cryo-rolling and post-annealing treatments,the nanostructured NiTi alloy is produced.A diff erential scanning calorimetry measurement was used to test the eff ect of the preparation process on phase transformation.The cryo-rolling changes the tensile fracture of NiTi alloy to a ductile manner.Interestingly,the recovered structure exhibits signifi cant strength improvement,while the tensile plasticity is still comparable to that of the coarse-grained structure.This optimized mechanical performance is due to the strengthening eff ect of refi ned microstructure and the high work hardening capability rendered by moderate dislocation density.Ball-on-plate reciprocating dry-sliding wear test reveals that the nanostructured NiTi alloy also has enhanced wear resistance,which is primarily ascribed to the high content of residue martensite formed during cryo-rolling.These results provide an eff ective route to optimize the mechanical and wear properties of NiTi alloys.展开更多
Ultra-strong joints of pure Cu and Cu–30Zn alloy were obtained by friction stir welding under flowing water. The effects of heat inputting condition and material characteristics on the morphologies, microstructures a...Ultra-strong joints of pure Cu and Cu–30Zn alloy were obtained by friction stir welding under flowing water. The effects of heat inputting condition and material characteristics on the morphologies, microstructures and mechanical properties of welding joints were studied. Defect-free stirring zones of pure Cu and Cu–30Zn were characterized by onion-ringed structure and plastic flowing bands, respectively. Both low stacking fault energy and fast cooling condition contributed to the formation of small recrystallized grains less than 1 μm in stirring zones. The welding joints in both materials exhibited enhanced mechanical performances due to ultrafine-grained microstructure in stirring zones and disappearance of soft heataffected-zone. The technique of digital image correlation was used to study the tensile deformation behaviors of welding joints and verify the improved tensile properties.展开更多
基金Sponsored by National Natural Science Foundation of China(51371057,11172187)National Basic Research Program(973 Program)of China(2010CB630803)Program for New Century Excellent Talents in University of China(NCET-12-0372)
文摘A duplex ultrafine microstructure in a medium manganese steel (0.2C-5Mn) was produced by austenite re- verted transformation annealing (ART-annealing). The microstructural evolution during annealing was examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on the microstructure examination, it was found that some M3C type carbides appeared in the martensitic matrix at the beginning of the ART-annealing. But with further increasing annealing time, these carbides would be dissolved and finally disappeared. Meanwhile, the austenite lath was developed in the ART-annealing process and the volume fraction of austenite increosed with the increase of the annealing time, which resulted in a duplex microstructure con- sisting of ultrafine-grained ferrite and large fraction of reverted austenite after long time annealing. The mechanical property examinations by uniaxial tensile tests showed that ART-annealing (6 h, 650 ℃) resulted in a superhigh product of strength to elongation up to 42 GPa ·%.
基金This research was supported by both National Natural Science Foundation of China(NSFC,Nos.51871062,51371057 and 11672195)MNSF of Beijing(No.2182088)Chong-xiang Huang acknowledged Sichuan Youth Science and Technology Foundation(No.2016JQ0047).
文摘A hot-rolled medium Mn(0.2C5Mn)steel is annealed at 650℃ to produce an ultrafine-grained duplex microstructure with different austenite volume fractions by austenite reverted transformation(ART)annealing,and the orientation relationship strictly obeys K-S orientation relationship before deformation.Tensile tests are carried out in a temperature range from-196 to 400℃ to examine the effects of the austenite volume fraction and the deformation temperature on the tensile properties and the austenite stability.Microstructural observations reveal that the metastable austenite gradually transformed into a-martensite,which is controlled by the deformation strain,the temperature and the austenite volume fraction.Both strain hardening behavior and ductility of the studied steel are dependent on austenite volume fraction and deformation temperature significantly.The stress-strain curves of ART-annealed 0.2C5Mn steel assume an S shape and a very large work hardening rate of about 10 GPa is obtained at liquid nitrogen deformation temperature.Based on the experimental data,a quantitative relation is proposed to describe the ductility dependence on both the austenite volume fraction and its mechanical stability.
基金financially supported by the National Natural Science Foundation of China(No.51931003)the China Postdoctoral Science Foundation(No.2020M680223)。
文摘By combining cryo-rolling and post-annealing treatments,the nanostructured NiTi alloy is produced.A diff erential scanning calorimetry measurement was used to test the eff ect of the preparation process on phase transformation.The cryo-rolling changes the tensile fracture of NiTi alloy to a ductile manner.Interestingly,the recovered structure exhibits signifi cant strength improvement,while the tensile plasticity is still comparable to that of the coarse-grained structure.This optimized mechanical performance is due to the strengthening eff ect of refi ned microstructure and the high work hardening capability rendered by moderate dislocation density.Ball-on-plate reciprocating dry-sliding wear test reveals that the nanostructured NiTi alloy also has enhanced wear resistance,which is primarily ascribed to the high content of residue martensite formed during cryo-rolling.These results provide an eff ective route to optimize the mechanical and wear properties of NiTi alloys.
基金supported financially by the National Natural Science Foundation of China (Nos. 11672195 and 51301092)Sichuan Youth Science and Technology Foundation (No. 2016JQ0047)
文摘Ultra-strong joints of pure Cu and Cu–30Zn alloy were obtained by friction stir welding under flowing water. The effects of heat inputting condition and material characteristics on the morphologies, microstructures and mechanical properties of welding joints were studied. Defect-free stirring zones of pure Cu and Cu–30Zn were characterized by onion-ringed structure and plastic flowing bands, respectively. Both low stacking fault energy and fast cooling condition contributed to the formation of small recrystallized grains less than 1 μm in stirring zones. The welding joints in both materials exhibited enhanced mechanical performances due to ultrafine-grained microstructure in stirring zones and disappearance of soft heataffected-zone. The technique of digital image correlation was used to study the tensile deformation behaviors of welding joints and verify the improved tensile properties.