The Distribution Of Alloy Elements And Its Influence On Microstructure During Prarlite Transformation In High Carbon Steel

As a very important product in modern industry,high strength steel wire is widely used in bridge cables,tire cord and cutting steel wire.High carbon hot rolled rod is the raw material of high strength steel wire products.The microstructure of the pearlite determines the mechanical properties and the ultimate performance of steel wires.In this paper,high carbon hot rolled rod is studied to explore the effect of austenitizing conditions as well as alloy elements Mn and Si on eutectoid-transformation process and the microstructure of wire rod,which provide certain theoretical support for component design and heat treatment process of high-performance hot rolled wire rod.The following main results are obtained in this experiment:The higher the austenitizing temperature and the longer the holding time were,the larger the pearlite colony size was.With the same austenitizing temperature,the longer the holding time was,the smaller the effect on the nasal tip temperature of the TTT curve and the starting and ending time of the pearlite transition of the high Si steels were,while the interlamellar spacing of the pearlite was basically the same.In contrast,if austenitizing time is prolonged,the TTT curve of low Si steel will be significantly shifted to the right,leading to the increase of the actual undercooling and the decrease of interlamellar spacing of the pearlite.Also the increase of austenitizing temperature will cause the right shift of TTT curve and the decrease of interlamellar spacing.When austenitized at 900?and isothermal transformed at 580?,both high and low Si steels could completely accomplish the pearlite transformation within 32s,the high Si steel growth rate reached 2.96 x 10^-7 m/s which is higher than that?8.98 x 10^-8m/s?of low Si steel.During rapid transformation process,the conditions of steady-state growth of local equilibrium were difficult to meet on account of the belated diffusion of Mn near the?/?/M₃C three-phase interface,The growth process is not completely in line with the steady-state growth of two phase area which showed the non-steady-state growth feature like the increasing pearlite interlamellar spacing.The diffusion velocity of Si was fast and it strongly accumulated to ferrite.In the early stage of reaction,the distribution process can be completed,and Si atoms in bcc?-Fe structure tend to accelerate Mn atoms diffuse into cementite phase.When the salt bath temperature rises,Si diffusion is so fast that the Si atoms separated from the cementite can rapidly diffuse into the ferrite core,and the Si enrichment phenomenon in the ferrite near the interface disappeared.due to the diffusion rate of Mn is far lower than Si which resulted that Mn cannot diffused to the cementite core and the Mn accumulation phenomenon near the interface was presented.