Carbide evolution behavior of cold-drawn 82B-V pearlitic steel
The evolution of microstructure and cementite in the process of cold-drawing pearlitic steel wire has an important effect on the properties of the completed steel wire.The SEM,TEM,physicochemical phase analysis and APT were used to study the organization evolution and carbide evolution behavior of 82B-V pearlitic wire rods during the drawing to produce steel wires and strands.The microstructure results show that after the cold drawing process,the pearlitic lamellae gradually turns to drawing direction,and the lamellae spacing decreases from 140 nm to 80 nm,showing good deformation ability.During drawing process,a large number of dislocated cellular struc-tures are generated within the ferrite in the steel wire.As a result,the ferrite lamellae becomes partitioned by disloca-tion walls,exhibiting a distinctive"bamboo"morphology.The cementite rotates and part of cementite phases between the regions of neighboring ferrite lamellae dissolve and disappear.The results of physicochemical phase analysis show that after drawing of wire rod into steel wire,element C in the alloy cementite diffused into the ferrite and a part of cementite dissolves,resulting in a reduction of the mass fraction from 7.99%to 6.67%.The content of alloy cementite in the stabilized strand is slightly recovered and increased to 7.00%;and the results of APT show that,compared with the wire rod,the average concentration of C atoms in the cementite of steel strand is only 13.5%,reduced by 7.5 percent point.The average concentration of Cr,Mn and V atoms in the strand cementite is 0.51%,1.59%and 0.23%,which decreases by 0.246,0.785 and 0.170 percent point,respectively,which fur-ther confirms that the dissolution of alloy cementite occurred in the process of large deformation and drawing and the diffusion of C,Cr,Mn and V into the ferrite.Through the tensile experiments and fracture morphology analysis,steel wire in the tensile process without necking produced,the fracture shows shot and crystalline,there is a tear prism through the entire cross-section.While the steel strand produced necking,the fracture is a gray lusterless fibrous,the heart of the tear prism is shallower,and the crystalline morphology is significantly reduced the strand showed better overall mechanical properties,showing a better overall mechanical properties,its tensile strength and section shrinkage reaches 2 045 MPa and 35.2%,respectively.
pearlitic steel wiredrawingmicrostructurealloy cementitethree-dimensional atom probe
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