Research On Microstructure And Dislocation Configuration Of Heavily Cold-Drawn Pearlitic Steel Wire

In order to investigate microstructure and dislocation configuration in heavily cold-drawn pearlitic steel wire, mechanical properties have been tested by universal testing machine and micro hardness tester. The evolution of pearlite structure and texture in ferrite lamellae has been studied by scanning electron microscope (SEM) and supporting electron backscatter diffraction (EBSD) system. The evolution of dislocation configuration has been researched by transmission electron microscope (TEM). The broadening of diffraction peaks has been analyzed by X-ray diffraction analysis (XRD) system and dislocation density has been quantitatively calculated based on WH formula improved by Voigt function. The relationships between dislocation configuration and ferrite lamellar thickness have been explored and the critical thickness of ferrite lamellae has been calculated.The results of research on microstructure and mechanical properties in cold-drawn pearlitic steel show that:the tensile strength and micro-hardness of cold-drawn pearlite steel continue to increase, with the increase of strain; pearlites, equiaxed in wire rod, adjust to the drawing direction, then stretch and become thinner, finally become fibrosis. With strain increasing, intensity of<110> texture in ferrite lamellae increases, and tends to saturation.The results of research on evolution of dislocation configuration and calculation of dislocation density in pearlitic steel wire show that:there are few dislocations in wire rod and dislocations are straight. Dislocation density is 1013m-2. When undergoing little deformation, dislocation density increases slowly. Dislocations parallel to each other, become "dislocation array" and are in single slip phase. With strain increasing, dislocation density increases quickly to 1015 m-2. Dislocations interact with each other, become "dislocation tangle" and evolve into "dislocation wall". Dislocations transit to multi-slip phase. Dislocation density decreases after strain reaching to 2.52. When strain reaches to 3.25, dislocations present "bow out" structure.The critical thickness of ferrite lamellae with different strains has been calculated based on F-R formula, improved according to the actual situation of heavily cold-drawn pearlitic steel wire. The relationships between dislocation configuration and ferrite lamellar thickness have been explored. The results show that:1) when lamellar thickness is greater than the critical value, dislocations propagate quickly. Dislocations are easy to pileup and develop into dislocation tangles and "dislocation wall" structure.2) When lamellar thickness equals to the critical value, dislocation propagation slows down. Dislocations are prone to present "bow out" structure.3) When lamellar thickness is less than critical value, dislocation propagation is blocked. It is impossible to pin dislocations and dislocations will slip out of crystal quickly.