Cold Drawing Of The Microstructure And Mechanical Properties Of Pearlite Steel Wire

Along with the fast development of manufacture technique, severe cold drawing wasapplied to high strength product, simultaneity the drawing speed was faster. So themanufacture of steel wires was mostly a high speed severe plastic deformation. Because oflacking systemic investigation of this problem, technique advancement in steel wireindustry was almost experiential.Therefore, the process of drawing pearlite steel wires was investigated in detail by thetensile testing machine, the torsion testing machine, the light microscope, the scanelectronic microscope (SEM) and the micro-hardness testing machine in this thesis. Themicrostructure evolution and properties transform of drawing pearlite steel wires werestudied with the methods of morphological analysis, mechanics analysis, statistical analysisand synthetic analysis. The main research results were as following:The evolvement of microstructure and mechanical properties of drawing pearlite steelwires (70 steel) had been studied, which was drawn fromφ5.5mm toφ1.8mm. the resultsshow that the strength and micro-hardness of steel wires are improved with the increase ofdeformation. The relationship of tensile strength, micro-hardness and deformation arelinear. The deformation microstructure of steel wires is researched by SEM. In thedeformation process, grains were refined in transverse section and fibrous shaped inlongitudinal section after drawing, and pearlite colony rotated and became progressivelyaligned to the drawing axis. Cementite plates are broken and refined after deformations ofcut, bend and draw, and the dissolution of cementite occurs heavily with the severedeformation. Interlamellar spacing of pearlite decreased progressively during the colddrawing process. And it was proportional with exp (-ε/2) when total strain was over 1.5.Severe cold drawn steel wire held high strength as the aging temperature was below300℃. When the temperature was over 300℃, the fine-scale multilayer structure wasdestroyed and the strength of steel wire debased remarkably.The form of crack on steel strand surface, as well as the depth of the crack, affects thetorsion capability critically. Transverse crack is worse than the other two types of crack...