The Microstructure And Mechanical Performance Of High Speed Severe Cold Drawn Steel Wire

As applied to the modern industry, high performance steel wire with a low cost were demanded. Along with the fast development manufacture technique, severe cold drawing was used for high strength, simultaneity the drawing speed was faster. So the manufacture of steel wire was mostly a high speed severe plastic deformation. Because of lacking systemic investigation of this problem, technique advancement in steel wire industry was almost experiential.Therefore, the process of drawing pearlite steel was investigated in detail in this thesis. The reason that caused high strength of high carbon steel wire was studied with the methods of morphological analysis, mechanics analysis, statistical analysis and synthetic analysis. And the production technics of high strength medium carbon steel wire was established on this theory. The main research results were as following:The evolvement of microstructure and mechanics performance of SWRH72A steel wire had been studied,which was drawn fromΦ5.5mm toΦ1.5mm. Grains were refined in transverse section and fibrous shaped in longitudinal section after eight steps drawing. The tensile strength of wire was increased rapidly. With the increasing of drawing strain, cement lamellae that initially have random orientation became progressively aligned along the drawing axis. Interlamellar spacing of pearlite decreased progressively during the cold drawing process, and it was proportional with exp (-ε/2) when total strain was over 1.5. Tensile strength increases with increasing drawing strain. In the initial stages of drawing, the strengthen of peatlite steel was accorded with Hall-Petch relationship. There was a deviation from the Hall–Petch behaviour when the interlamellar spacing of pearlite decreased to less than 100nm.The microstructure characteristic of severe cold drawn SWRH72A steel wire were analysed by XPS, VSM, XRD. It was found that 20 percent cementite dissoluted after drawn. And ferrite became supersaturation because partial carbon atom came into it. Severe cold drawn steel wire held high strength as the aging temperature was below 300℃. When the temperature rised over 300℃, the fine-scale multilayer structure was destroyed and the strength of steel wire droped remarkablely.A model accounting for the cementite dissolution is proposed. It relies on the Gibbs-Thomson effect and diffusion-controlled dissolution. The increase in the cementite molar free energy, as an indirect consequence of the thinning of the cementite lamellae, appears to be the driving force and...