The microstructures of pearlitic steel wire rods and steel wires are commonly characterized by secondary electron imaging (SEI)technique using scanning electron microscopy(SEM).In this work,a back-scattered electron i...The microstructures of pearlitic steel wire rods and steel wires are commonly characterized by secondary electron imaging (SEI)technique using scanning electron microscopy(SEM).In this work,a back-scattered electron imaging(BSEI)method is proposed to determine the microstructures of undeformed and deformed pearlitic steels with nanometer scale pearlite lamellae.The results indicate that BSEI technique can characterize the pearlite lamellas veritably and is effective in quantitative measurement of the mean size of pearlite interlamellar spacing.To some extent,BSEI method is more suitable than SEI technique for studying undeformed and not severely deformed pearlitic steels.展开更多
The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel.The ferrite-bain...The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel.The ferrite-bainite dual-phase steel was obtained by intermediate heat treatment conducted on ferrite-pearlite low carbon steel.This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy(SEM),electron backscattering diffraction(EBSD) and fatigue fractography analysis.Microscopic images arrested by in-situ SEM showed that the second hard bainite phase distributed in the soft ferrite matrix had a significant effect on preventing the cracks opening compared with pearlite,and that the cracks in ferrite-bainite steel were "locked" in the second hard bainite phase while the crack propagation path in ferrite-pearlite steel was more tortuous.Moreover,the fatigue fracture surface analysis and the coincidence site lattice(CSL) obtained by EBSD indicated that low-CSL grain boundaries in ferrite-bainite steel distributed more uniformly,which has a more significant effect on the resistance of crack propagation.It was revealed that ferrite-bainite dual-phase microstructures could inhibit the fatigue crack propagation more effectively than ferrite-pearlite microstructures.展开更多
The evolution of morphology of pearlite and crystallographic texture of ferrite matrix in fully pearlitic steels during wire drawing were quantitatively investigated. The study revealed that a fiber structure of the p...The evolution of morphology of pearlite and crystallographic texture of ferrite matrix in fully pearlitic steels during wire drawing were quantitatively investigated. The study revealed that a fiber structure of the pearlite morphology and a 〈110〉 fi- ber texture of the ferrite matrix begin to take shape and develop gradually with increasing strain. The growth rates of the fiber structure and the 〈110〉 texture are different in different regions within the wires with increasing drawing strain. There is a close relationship between the pearlite morphology and the crystalline texture during wire drawing. The pearlite interlamellar spacing （ILS） and thickness of cementite lamellae （To） decrease gradually both in longitudinal and transverse sections. The definition of pearlite colony should be reconsidered for describing microstructure of the wire drawing deformed pearlitic steels.展开更多
基金supported by the National Key Technology R&D Program of China(Grant No.2007BAE15B01)the Major Program of the National Natural Science Foundation of China(Grant No.50890170)
文摘The microstructures of pearlitic steel wire rods and steel wires are commonly characterized by secondary electron imaging (SEI)technique using scanning electron microscopy(SEM).In this work,a back-scattered electron imaging(BSEI)method is proposed to determine the microstructures of undeformed and deformed pearlitic steels with nanometer scale pearlite lamellae.The results indicate that BSEI technique can characterize the pearlite lamellas veritably and is effective in quantitative measurement of the mean size of pearlite interlamellar spacing.To some extent,BSEI method is more suitable than SEI technique for studying undeformed and not severely deformed pearlitic steels.
文摘The purpose of this study was to describe the roles of microstructure types and grain boundary characteristics in fatigue crack propagation behavior in ferrite-pearlite steel and ferrite-bainite steel.The ferrite-bainite dual-phase steel was obtained by intermediate heat treatment conducted on ferrite-pearlite low carbon steel.This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy(SEM),electron backscattering diffraction(EBSD) and fatigue fractography analysis.Microscopic images arrested by in-situ SEM showed that the second hard bainite phase distributed in the soft ferrite matrix had a significant effect on preventing the cracks opening compared with pearlite,and that the cracks in ferrite-bainite steel were "locked" in the second hard bainite phase while the crack propagation path in ferrite-pearlite steel was more tortuous.Moreover,the fatigue fracture surface analysis and the coincidence site lattice(CSL) obtained by EBSD indicated that low-CSL grain boundaries in ferrite-bainite steel distributed more uniformly,which has a more significant effect on the resistance of crack propagation.It was revealed that ferrite-bainite dual-phase microstructures could inhibit the fatigue crack propagation more effectively than ferrite-pearlite microstructures.
基金supported by the Major Program of the National Natural Science Foundation of China(Grant No.50890170)the Scientific Research Foundation for Doctoral Scholars of Southwest University,China(Grant No.SWU112043)
文摘The evolution of morphology of pearlite and crystallographic texture of ferrite matrix in fully pearlitic steels during wire drawing were quantitatively investigated. The study revealed that a fiber structure of the pearlite morphology and a 〈110〉 fi- ber texture of the ferrite matrix begin to take shape and develop gradually with increasing strain. The growth rates of the fiber structure and the 〈110〉 texture are different in different regions within the wires with increasing drawing strain. There is a close relationship between the pearlite morphology and the crystalline texture during wire drawing. The pearlite interlamellar spacing （ILS） and thickness of cementite lamellae （To） decrease gradually both in longitudinal and transverse sections. The definition of pearlite colony should be reconsidered for describing microstructure of the wire drawing deformed pearlitic steels.
