| High-carbon steel wire strand mainly applies to super-large public buildings such as cable-stayed bridges,suspension bridges,gymnasiums etc.people have more and more demands on High strength steel strand with the development building trades.higher strength high carbon steel wire rod has been concerned by researchers as raw materials for making pre-stressed steel strand.Micro alloying strengthening research for high carbon steel wire rods are becoming a focus on the field of product development in current studying.Selecting 82 B high carbon steel wire rod as the research object in this paper, enhance the material integrated mechanical properties by the microalloying, focused on Strengthening and toughening mechanism of vanadium microalloying 82 B steel and studied the influence mechanism of vanadium elements on the continuous cooling transformation of 82 B steel. In order to study Strengthening and toughening mechanism of vanadium microalloyed 82 B steels, three kinds of 82 B steel wire coil with different vanadium content as test subjects,this Paper conducted a pilot study by the following three areas:Mechanical tensile experiment results indicated that the effects of vanadium on the strength of the 82 B steel,it had the following characteristics: when the content of vanadium in the range of 0~0.02%,the tensile strength increased 16 MPa for a1% increase in the content of vanadium; when the content in the range of0.02%~0.03%,the results showed that had little effect on the tensile strength with the increase of vanadium content;when the content in the range of 0.03%~0.05%,the tensile strength increased 13 MPa for a 1% increase in the content of vanadium.Judging from the results of the analysis,tensile strength continuously enhance with the increase of content of vanadium. Based on analysis of area reduction of Φ10 mm 82 B steel with different content of vanadium, when the content of vanadium in the range of 0~0.02%,the reduction of area of 82 B steel wire rods showed increasing trend with vanadium contents increasing.When the vanadium content is bigger than 0.03%,contraction of cross sectional area of wire rod decreased continuously with increasing vanadium content,this indicated that vanadium elements added improve plasticity of 82 B with in a range, but once vanadium content crossed thisthreshold value,the ductility declined sharply.Morphology of precipitates and microstructures of 82 B steel with three different vanadium contents were analyzed under SEM and TEM, Most of precipitates gathered in the centre of ferrite. The results showed that the precipitation was vanadium carbide by indexing the diffraction spots of precipitation.The number of precipitation increased with the increase of vanadium content.The average size of precipitation was dozens of nanometers. Microstructure were mainly sorbite,sorbite content can reach 85%. After detail mesurement analysis, sorbite interlamellar spacing had following features: lamellar spacing was decreased with the vanadium content was increased from 0.02% to 0.03%;increasing the content of vanadium from 0.03% to 0.05% makes lamellar distance in pearlite phase transformation macrostructure increased. This behavior occurred because precipitate slowdown migration rate of carbon atoms, reduce the temperature of phase transformation point and postpones the transformation of pearlite,so sorbite thickness reduction.When content of vanadium was higher,precipitate promote ferrite formation, Carbon-poor area forms lead to ferrite encircle the precipitate(That was the reason that precipitation distributed on ferrite),so sorbite thickness increase.The continuous cooling transformation, with the increasing of vanadium content,the results of thermal simulation experiment by Gleeble-1500 showed that pregnant period of pearlite transformation was extended and the progress of pearlite transformation was hindered,this lead to initial transition temperature of pearlite drop and phase change region of pearlite move down. A little pearlite occur along the prior austenite grain boundary at high cooling rate with the increase of vanadium. CCT curve slightly shift to the left because precipitation promote pearlite growing up. |
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