| Hypereutectoid rail steel is widely used in rails due to its high strength,high wear resistance and high hardness.With the development of the railway,higher requirements are put forward for the performance of the rail.Improving the heat treatment process and microalloying the rail are important ways to strengthen the hypereutectoid rail.In this paper,four components of supereutectoid rail steel smelted in the laboratory are studied,develop a thermal simulation experiment plan by simulating the calendering process on site.Double deformation of experimental steel on a Gleeble 1500 D laboratory desk,cooling to room temperature at various cooling rates(0.5?/s?1?/s?3?/s).Different alloying elements and heat treatment processes to experiment with the effects of steel microstructure,strengthening mechanism and mechanical performance were analyzed.The experimental results showed that,the lamella of the whole pearlite structure obtained at the cooling rate of 1?/s was finer.After adding Ni,rare earth Ce and Ce-Cu composite addition,the interlayer spacing could be refined to 95 nm,86nm,93 nm,and the grain size could be refined to 42?m,36?m,40?m,the strengthening effect of fine grains of rare earth elements is the most significant.According to the calculation results of Thermo-cacl and EDS energy spectrum analysis,the rare earth Ce element could promote the precipitation of Nb C.Analyzing the characteristics of forged steel inclusions,3# steel with the addition of 0.011% rare-earth Ce could improve the morphology of inclusions,and the original Mn S inclusions were replaced by rare-earth oxides and sulfides.At the same time,4#steel with the 0.004% rare earth Ce could reduce the size of inclusions,and when added with Cu,it could induce the generation of Cu element nucleation particles,make Cu element dispersed and distributedUnder the conditions of 1?/s continuous cooling and 80% deformation,the thickness of cementite lamella decreased with the refinement of pearlite lamella and the content of cementite per unit volume increased with the decrease of lamellar thickness.The cementite spheroidization was the most obvious after the addition of rare earth Ce in the experimental steel,and the locally carburized body is most prominently pelletized and dispersed in the ferrite matrix in the form of granules,which played a role of dispersion strengthening.Transmission electron microscopy and XRD were utilized to observe and analyze the dislocation configuration and dislocation density,it was concluded that the dislocation density of the four experimental steels of the control group,Ni,rare earth Ce,and Ce/Cu composite addition to the alloy strength were 42 MPa,45 MPa,52 MPa and 62 MPa.Therefore,when Ce/cu compound was added,the dislocation strengthening effect was the most significant.The mechanical properties of hypereutectoid steels were affected by the cooling rate and alloying elements.By experimenting with the forged and heat-treated states and analyzing the microscopic structure of the steel,the spacing between the layers of the pearlite sheet after the heat treatment was reduced.The chip pitch after adding the CeCu composite was reduced to 87 nm.As a result of mechanical performance test,after the heat treatment,the hardness and tensile strength of the four types of test steel were improved.Among them,after the addition of Ce-Cu composite,the hardness of the experimental steel could increase form 310 HB to380 HB,the tensile strength could from 1159 MPa reach 1378 MPa,the section shrinkage and elongation were 23.95% and11.82% respectively,and the tensile fracture morphology was ductile fracture,and the mechanical properties were greatly improved.Therefore,microalloying and heat treatment processes could improve the microstructure and mechanical properties of hypereutectoid steel. |
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