Hot Deformation Behavior And Microstructure Evolution Law Of 24Si2Ni2Mn Bainitic Steel

24Si2Ni2Mn bainitic steel has the characteristics of high strength,good toughness and good welding performance,so it is widely used in the fields of vehicles,aviation components,bridges and shaft components.At present,the construction of high-speed railway in China is in a period of rapid development.More strict requirements are put forward for the quality and reliability of high-speed train axles.Hot working at high temperature is one of the main forming methods of 24Si2Ni2Mn bainitic steel,so the hot working process parameters are the key to control its microstructure and properties.The high temperature deformation behavior and microstructure evolution of 24Si2Ni2Mn bainitic steel at 950?-1250?and strain rate of 0.001s^-1-1s^-1 were studied.The flow stress softening of 24Si2Ni2Mn bainitic steel was studied and the dynamic recrystallization model was established.The microstructure evolution mechanism of the alloy under different process parameters was clarified,and the hot forming process parameters were optimized to achieve the prediction of microstructure and control of overall mechanical properties of24Si2Ni2Mn bainitic steel.The single pass hot compression and multi pass hot compression of 24Si2Ni2Mn bainitic steel were carried out by Gleeble-3800 dynamic thermal simulator.The rheological properties of the alloy under different deformation conditions were studied.The constitutive model of 24Si2Ni2Mn bainitic steel was established based on strain compensated Arrhenius model and modified Johnson cook model.The results show that the Arrhenius model can describe the deformation behavior of the alloy more accurately.Based on the above,the microstructure evolution of 24Si2Ni2Mn bainitic steel during high temperature deformation was studied.The experimental results show that the main softening mechanisms of 24Si2Ni2Mn bainitic steel during high temperature deformation are dynamic recovery(DRV)and dynamic recrystallization(DRX).Strain rate,temperature,number of passes and holding time all have great influence on the softening effect.The dynamic recrystallization critical model and dynamic recrystallization volume fraction model were established based on the experimental data of dynamic thermal simulation compression.The results show that the dynamic recrystallization volume fraction is positively correlated with deformation temperature and strain,and negatively correlated with strain rate.The refinement of dynamic recrystallization grain is helpful to improve the mechanical properties of the whole material.Based on the dynamic material model and Prasad instability criterion,the 3D power dissipation diagram and hot working diagram of 24Si2Ni2Mn bainitic steel were established.The microstructure of different hot working areas was analyzed.The results show that 24Si2Ni2Mn bainitic steel has complete dynamic recrystallization in the deformation parameter range of 1000?-1150?/0.01s^-1-1s^-1,and the microstructure is uniform with excellent comprehensive properties.Therefore,1000?-1150?/0.01s^-1-1s^-1 is the optimal process parameters for hot working of24Si2Ni2Mn bainitic steel.