The effect of multiphase microstructure in the center segregation zones(CSZ)of high-strength steel thick plates on work hardening characteristics and crack initiation/propagation were studied.Microstructure was correl...The effect of multiphase microstructure in the center segregation zones(CSZ)of high-strength steel thick plates on work hardening characteristics and crack initiation/propagation were studied.Microstructure was correlated with deformation damage behavior by using Taylor factor(TF)gradients,kernel average misorientation(KAM),and geometric necessary dislocation(GND)density.The results show that the segregation leads to a mixed structure of ferrite(soft phase)and martensite/bainite(hard phase)in the center of the thick plate.Compared to the 1/4 thickness(1/4 T)region,grain refinement occurred in the CSZ,with KAM values increasing from 0.24 to 0.49 and a decrease in the proportion of high-angle grain boundaries(>15°)from 77.4 to 51.8%.In the process of deformation,due to the influence of grain refinement and adjacent martensite/bainite,ferrite grains were divided into structural units with different TF values.The higher KAM value and GND density at the interface between soft/hard phases resulted in severe work hardening.In addition,the presence of micron-sized inclusions in the CSZ caused local strain concentration and non-continuous deformation of the matrix,which induced crack initiation.The fracture surface showed a mixed mode of brittle cleavage fracture and ductile fracture.展开更多
The cold rolling deformation textural evolution of an interstitial-free （IF） steel sheet is investigated by experiment and simulation. The microstructure of the IF steel is observed by transmission electron microsco...The cold rolling deformation textural evolution of an interstitial-free （IF） steel sheet is investigated by experiment and simulation. The microstructure of the IF steel is observed by transmission electron microscopy （TEM）. The relationship between the deformation behavior of individual grain and the grain orientation are connected by Taylor factor M. The results show that the grains with higher Taylor factor are deformed slighter than those with lower ones. By considering the heterogeneous deformation, the texture simulation result can be greatly improved.展开更多
A Cr-Ni type of low transformation temperature（LTT）welding filler was devised in the present study.The LTT weld microstructures of the tungsten inert gas（TIG）and metal active gas（MAG）weldings were investigated b...A Cr-Ni type of low transformation temperature（LTT）welding filler was devised in the present study.The LTT weld microstructures of the tungsten inert gas（TIG）and metal active gas（MAG）weldings were investigated by using electron-backscattered diffraction and orientation imaging microscopy.The results showed that the LTT weld microstructures prepared by TIG and MAG weldings were primarily martensite with 17.5% and 8.0% retained austenite,respectively.The LTT weld metal using TIG welding had larger grain size than using MAG.In addition,based on the Taylor factor calculation,the weld metal using MAG welding was more competent in repressing fatigue crack initiation.Meanwhile,the high angle and coincidence site lattice grain boundaries were dominant in the LTT weld metal using MAG welding.Moreover,the hardness of the LTT weld metal using MAG welding was higher than that of using TIG.Based on heat input and phase transformation,finite element method was applied to analyzing the tensile residual stress（RS）reduction in welded joints prepared by both conventional and LTT welding fillers,respectively.The corresponding outcome confirmed that the LTT weld metal using MAG welding was more beneficial to tensile RS reduction.展开更多
基金The authors are grateful for the financial support from the National Natural Science Foundation of China(No.U20A20279)the technical support provided by Analysis and Test Center of Wuhan University of Science and Technology,China.
文摘The effect of multiphase microstructure in the center segregation zones(CSZ)of high-strength steel thick plates on work hardening characteristics and crack initiation/propagation were studied.Microstructure was correlated with deformation damage behavior by using Taylor factor(TF)gradients,kernel average misorientation(KAM),and geometric necessary dislocation(GND)density.The results show that the segregation leads to a mixed structure of ferrite(soft phase)and martensite/bainite(hard phase)in the center of the thick plate.Compared to the 1/4 thickness(1/4 T)region,grain refinement occurred in the CSZ,with KAM values increasing from 0.24 to 0.49 and a decrease in the proportion of high-angle grain boundaries(>15°)from 77.4 to 51.8%.In the process of deformation,due to the influence of grain refinement and adjacent martensite/bainite,ferrite grains were divided into structural units with different TF values.The higher KAM value and GND density at the interface between soft/hard phases resulted in severe work hardening.In addition,the presence of micron-sized inclusions in the CSZ caused local strain concentration and non-continuous deformation of the matrix,which induced crack initiation.The fracture surface showed a mixed mode of brittle cleavage fracture and ductile fracture.
基金the National Natural Science Foundation of China （Grant No. 50671021） Program for New Century Excellent Talents in University （Grant No. NCET-06-0287）.
文摘The cold rolling deformation textural evolution of an interstitial-free （IF） steel sheet is investigated by experiment and simulation. The microstructure of the IF steel is observed by transmission electron microscopy （TEM）. The relationship between the deformation behavior of individual grain and the grain orientation are connected by Taylor factor M. The results show that the grains with higher Taylor factor are deformed slighter than those with lower ones. By considering the heterogeneous deformation, the texture simulation result can be greatly improved.
基金supported by National Natural Science Foundation of China(Grant No.51774213)
文摘A Cr-Ni type of low transformation temperature（LTT）welding filler was devised in the present study.The LTT weld microstructures of the tungsten inert gas（TIG）and metal active gas（MAG）weldings were investigated by using electron-backscattered diffraction and orientation imaging microscopy.The results showed that the LTT weld microstructures prepared by TIG and MAG weldings were primarily martensite with 17.5% and 8.0% retained austenite,respectively.The LTT weld metal using TIG welding had larger grain size than using MAG.In addition,based on the Taylor factor calculation,the weld metal using MAG welding was more competent in repressing fatigue crack initiation.Meanwhile,the high angle and coincidence site lattice grain boundaries were dominant in the LTT weld metal using MAG welding.Moreover,the hardness of the LTT weld metal using MAG welding was higher than that of using TIG.Based on heat input and phase transformation,finite element method was applied to analyzing the tensile residual stress（RS）reduction in welded joints prepared by both conventional and LTT welding fillers,respectively.The corresponding outcome confirmed that the LTT weld metal using MAG welding was more beneficial to tensile RS reduction.
