Research On The Microstructure Evolution And Mechenicalpropertites Of Middle-carbon Steel Wire During Cold Drawing

Wire rope, twisted by steel wires, has been widely used in industrial production, with its high strength and light weight. Since the development of the industry, steel wires with higher strength and lower cost are needed. Recently cold drawing is used to produce steel wires. Therefore the manufacture of steel wire has changed into a high speed severe plastic deformation. Since the strengthening mechanism of high strength steel wire has not clear yet, the process development of manufacturing high strength steel wire is always based on experience. The Ingredient of most of the high quality steel wires is high-carbon steel, which has a more complicated microstructure evolution during the deformation as well as a high cost than the wires made by medium carbon steel. Th us the research of the possibility to produce wires with medium carbon steel instead of the high-carbon ones became important. This study was about the microstructure evolution of medium carbon steel wire during deformation. The main research results were as following:The metallographic observation, SEM and TEM test were done to research the evolvement of the microstructure of SWRCH35K steel wire. Grain of the wire was refined and cold drawing texture was found. Shape of pearlite became slim and it tended to have a same direction with the drawing force. The relationship between the thick of the pearlite layer and the strain value meet the Hall-petch formula when the strain is lower than1.5. The change of the mechanics performances of SWRCH35K steel wire had been studied too. And during the deformation, the tensile strength of the wire became higher and higher, this mainly because deformation had caused an increasing number of dislocation. Annealing experiments were also taken to study annealing’s influences to the microstructure and mechanics performance of the wire. Metallographic observation showed that the size of the grain became bigger after annealing and the tensile strength, microhardness and resistivity of the wire became lower. According to the results of the EBSD tests, annealing had due to a decrease of small-angle grain boundaries and a increase of large-angle grain boundaries. Recrystallization had taken place and the some texture disappeared.