The microstructural evolution and precipitation behaviour of Nb–V–Mo and single V containing transformation induced plasticity assisted steels were investigated during thermomechanical processing. A plane strain com...The microstructural evolution and precipitation behaviour of Nb–V–Mo and single V containing transformation induced plasticity assisted steels were investigated during thermomechanical processing. A plane strain compression testing machine was used to simulate the thermomechanical processing. Microstructures were characterised by optical microscopy, scanning-transmission electron microscopy and microanalysis, and X-ray diffraction analysis, and Vickers hardness was obtained from the deformed specimens. The resulting microstructure of both Nb–V–Mo and V steels at room temperature primarily consisted of an acicular/bainitic ferrite, retained austenite and martensite surrounded by allotriomorphic ferrite.The TEM analysis showed that a significant number of Nb（V,Mo）（C,N） precipitates were formed in the microstructure down to the finishing stage in Nb–V–Mo steel（i.e. 830℃）. It was also found that the V（C,N）precipitation primarily occurred in both ferrite and deformed austenite below the finishing stage. The results suggested that Nb–Mo additions considerably increased the temperature stability of microalloy precipitates and controlled the microstructural evolution of austenite. However, the microalloy precipitation did not cause a significant precipitation strengthening in both Nb–V–Mo and V steels at room temperature.展开更多
The complex producing procedures and high energy-consuming limit the large-scale production and application of advanced high-strength steels(AHSSs).In this study,the direct strip casting(DSC)technology with unique sub...The complex producing procedures and high energy-consuming limit the large-scale production and application of advanced high-strength steels(AHSSs).In this study,the direct strip casting(DSC)technology with unique sub-rapid solidification characteristics and cost advantages was applied to the production of low-alloy Si-Mn steel with the help of quenching&partitioning(Q&P)concept to address these issues.Compared this method with the conventional compact strip production(CSP)process,the initial microstructure formed under different solidification conditions and the influence of heat treatment processes on the final mechanical properties were in-vestigated.The results show that the initial structure of the DSC sample is a dual-phase structure composed of fine lath martensite and bainite,while the initial structure of the CSP sample consists of pearlite and ferrite.The volume fraction and carbon content of retained austenite(RA)in DSC samples are usually higher than those in CSP samples after the same Q&P treatment.DSC samples typically demonstrate better comprehensive mechanical properties than the CSP sample.The DSC sample partitioned at 300℃ for 300 s(DSC-Pt300)achieves the best comprehensive mechanical properties,with yield strength(YS)of 1282 MPa,ultimate tensile strength(UTS)of 1501 MPa,total elongation(TE)of 21.5%,and product of strength and elongation(PSE)as high as 32.3 GPa·%.These results indicate that the excellent mechanical properties in low-alloy Si-Mn steel can be obtained through a simple process(DSC-Q&P),which also demonstrates the superiority of DSC technology in manufacturing AHSSs.展开更多
Nb-Tihot-rolled TRIP-assisted steel with high plasticity and appropriate volume percentage of retained austenite based on fine ferrite grain have been developed in the experiment. The test results showed that niobium ...Nb-Tihot-rolled TRIP-assisted steel with high plasticity and appropriate volume percentage of retained austenite based on fine ferrite grain have been developed in the experiment. The test results showed that niobium tend to exist in solution state in matrix with less precipitation, and niobium-titanium could be precipitated in form of （Nb, Ti）C or （Nb, Ti） （C, N）, which play an important role in increasing yield strength （from 495 MPa to 610 MPa）. Besides, the retained austenite had a positive effect on improving the plasticity by transformation into martensite during tensile deformation.展开更多
The variant selection of martensites（ε-M and α＇-M） and ε-M reversion in dynamic tensile high-manganese TRIP steel were investigated. α＇-M variant pairs with a zigzag morphology frequently formed, and the pairs...The variant selection of martensites（ε-M and α＇-M） and ε-M reversion in dynamic tensile high-manganese TRIP steel were investigated. α＇-M variant pairs with a zigzag morphology frequently formed, and the pairs of neighboring α＇-M variants were examined in terms of mechanical work and strain energy reduction. The occurrence of a primary α＇-M variant is determined by mechanical work, but high products of mechanical work and strain energy reduction are essential for secondary variant selection. In contrast to α＇-M variant pair selection, ε-M variant selection can be attributed to the highest mechanical work. During ε-M→α＇-M transformation, the mechanical work of ε-M reversion is higher than that of α＇-M variant, thereby implying that ε-M reversion in h110 icgrain is possible. e-M plate distribution also affects the feasibility of ε-M reversion.展开更多
文摘The microstructural evolution and precipitation behaviour of Nb–V–Mo and single V containing transformation induced plasticity assisted steels were investigated during thermomechanical processing. A plane strain compression testing machine was used to simulate the thermomechanical processing. Microstructures were characterised by optical microscopy, scanning-transmission electron microscopy and microanalysis, and X-ray diffraction analysis, and Vickers hardness was obtained from the deformed specimens. The resulting microstructure of both Nb–V–Mo and V steels at room temperature primarily consisted of an acicular/bainitic ferrite, retained austenite and martensite surrounded by allotriomorphic ferrite.The TEM analysis showed that a significant number of Nb（V,Mo）（C,N） precipitates were formed in the microstructure down to the finishing stage in Nb–V–Mo steel（i.e. 830℃）. It was also found that the V（C,N）precipitation primarily occurred in both ferrite and deformed austenite below the finishing stage. The results suggested that Nb–Mo additions considerably increased the temperature stability of microalloy precipitates and controlled the microstructural evolution of austenite. However, the microalloy precipitation did not cause a significant precipitation strengthening in both Nb–V–Mo and V steels at room temperature.
基金supported by the National Natural Science Foundation of China(No.52130408)the Natural Science Foundation of Hunan Province,China(No.2022JJ10081).
文摘The complex producing procedures and high energy-consuming limit the large-scale production and application of advanced high-strength steels(AHSSs).In this study,the direct strip casting(DSC)technology with unique sub-rapid solidification characteristics and cost advantages was applied to the production of low-alloy Si-Mn steel with the help of quenching&partitioning(Q&P)concept to address these issues.Compared this method with the conventional compact strip production(CSP)process,the initial microstructure formed under different solidification conditions and the influence of heat treatment processes on the final mechanical properties were in-vestigated.The results show that the initial structure of the DSC sample is a dual-phase structure composed of fine lath martensite and bainite,while the initial structure of the CSP sample consists of pearlite and ferrite.The volume fraction and carbon content of retained austenite(RA)in DSC samples are usually higher than those in CSP samples after the same Q&P treatment.DSC samples typically demonstrate better comprehensive mechanical properties than the CSP sample.The DSC sample partitioned at 300℃ for 300 s(DSC-Pt300)achieves the best comprehensive mechanical properties,with yield strength(YS)of 1282 MPa,ultimate tensile strength(UTS)of 1501 MPa,total elongation(TE)of 21.5%,and product of strength and elongation(PSE)as high as 32.3 GPa·%.These results indicate that the excellent mechanical properties in low-alloy Si-Mn steel can be obtained through a simple process(DSC-Q&P),which also demonstrates the superiority of DSC technology in manufacturing AHSSs.
文摘Nb-Tihot-rolled TRIP-assisted steel with high plasticity and appropriate volume percentage of retained austenite based on fine ferrite grain have been developed in the experiment. The test results showed that niobium tend to exist in solution state in matrix with less precipitation, and niobium-titanium could be precipitated in form of （Nb, Ti）C or （Nb, Ti） （C, N）, which play an important role in increasing yield strength （from 495 MPa to 610 MPa）. Besides, the retained austenite had a positive effect on improving the plasticity by transformation into martensite during tensile deformation.
基金financially supported by the National Natural Science Foundation of China (No. 51271028)
文摘The variant selection of martensites（ε-M and α＇-M） and ε-M reversion in dynamic tensile high-manganese TRIP steel were investigated. α＇-M variant pairs with a zigzag morphology frequently formed, and the pairs of neighboring α＇-M variants were examined in terms of mechanical work and strain energy reduction. The occurrence of a primary α＇-M variant is determined by mechanical work, but high products of mechanical work and strain energy reduction are essential for secondary variant selection. In contrast to α＇-M variant pair selection, ε-M variant selection can be attributed to the highest mechanical work. During ε-M→α＇-M transformation, the mechanical work of ε-M reversion is higher than that of α＇-M variant, thereby implying that ε-M reversion in h110 icgrain is possible. e-M plate distribution also affects the feasibility of ε-M reversion.
