Microstructure And Mechanical Properties Of Ti And Ce Microalloyed 35MnVs Non-quenched And Tempered Steel

Non-quenched and tempered steel is widely used in automobile crankshaft and other parts due to its advantages of energy saving and cost reduction.In recent years,with the soaring price of vanadium and other micro-alloyed elements,non-quenched and tempered steels are also faced with the problems of further reducing the cost and improving the stability of processing properties.Low cost alloyed element Ti has the effect of fine grain strengthening and precipitation strengthening.Rare earth element Ce can improve the machinability of steel by improving the inclusion of sulfide.However,there are few reports on Ti and Ce microalloyed non-quenched and tempered steels.Therefore,several Ti and Ce micro-alloyed non-quenched and tempered steels have been designed in this paper,and the thermal deformation and precipitation behavior of Ti micro-alloyed steels,as well as the modification mechanism of rare earth Ce on sulfide inclusions and the mechanism of refining the microstructure have been studied,providing basic data for obtaining a low-cost non-quenched and tempered steels with easy cutting.The dynamic recrystallization behavior of austenite in Ti microalloyed non-quenched and tempered steel with deformation temperature ranging from 850℃to1200℃and strain rate ranging from 0.1 s^-1 was studied by Gleeble-3800 thermal simulation machine.The effects of deformation temperature,deformation rate,precipitation behavior of carbonitride and Ti₄C₂S₂ on the dynamic recrystallization of austenite were analyzed.The activation energy of dynamic recrystallization was calculated.The thermal deformation equation and thermal processing diagram were obtained.The results show that the non-quenched and tempered steel with 0.042%Ti content has the highest activation energy and the best comprehensive mechanical properties.The thermal processing diagram was obtained by superposition of power dissipation diagram and plastic instability diagram.The optimal thermal processing process range of Ti microalloyed non-quenched and tempered steel is the deformation temperature of 900～1050℃,the deformation rate of 0.1～0.2s^-1 and the deformation temperature of 1100～1200℃,the deformation rate of 0.1～4s^-1.SEM,EDS and ASPEX were used to characterize the morphology,quantity and size of inclusions in non-quenched and tempered steel with different Ce content,as well as the metallographic structure of the test steel.The formation process of Ce-containing sulfide inclusions was analyzed by Thermo-Calc thermodynamic software.The element distribution at the grain boundary and phase interface was characterized by three dimensional atomic probe（3DAP）.The results show that Ce combines with S at 1800℃to form Ce₃S₄ inclusion,which is transformed into Ce₂S₃ inclusion at1480℃.The composite inclusion with Ti₄C₂S₂ and Mn S is formed below 1480℃.The aspect ratio of more than 90%inclusions in the test steel with Ce element is less than2.5.When the content of Ce is 0.019%,the microstructure of the test steel is the smallest,and the average grain size is 4.58μm.The results of 3DAP show that there is obvious segregation of Ce at the grain boundary and phase boundary,which inhibits the diffusion of C and inhibits the grain growth.In addition,the fine and dispersed Ce inclusions formed in the high temperature zone provide nucleation particles,which together refined the microstructure of the non-tempered steel.