As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical ...As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical processing.However,little research has been conducted on the phase transformation and microstructure evolution mechanism of EA4T steel under thermal–mechanical load,resulting in a lack of theoretical guidance.The hot deformation behavior and phase transformation mechanism of EA4T steel were investigated under different conditions of strain rates(0.01–10 s^(−1))and temperatures(850–1200℃).A relation of deformation stresses with Zener–Hollomon parameter was established to characterize the mechanical response and dynamic softening effect of EA4T steel during hot compression.The evolution of grain boundaries with different misorientations has been analyzed to evaluate the influence of strain rates and temperatures on the dynamic recrystallization.It was found that the grain refinement mechanisms of EA4T steel by dynamic recrystallization including twin-assisted boundary bulging,sub-grain rotation,and sub-grain growth.Transmission electron microscopy observations confirmed that dynamic recrystallization nuclei and small recrystallized grains impeded martensite phase nucleation during hot deformation,while the ongoing dynamic recrystallization consumed deformation stored energy and reduced dislocation density,which mitigated the stress concentration in the parent phase of martensite,thereby facilitating the uniform growth of martensite lath with a mixing structure of nanotwins and dislocations during quenching.展开更多
基金support was received from National Key Research and Development Plan from China:Demonstration and application of special steel for typical components of high-end equipment(2017YFB0703004).
文摘As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical processing.However,little research has been conducted on the phase transformation and microstructure evolution mechanism of EA4T steel under thermal–mechanical load,resulting in a lack of theoretical guidance.The hot deformation behavior and phase transformation mechanism of EA4T steel were investigated under different conditions of strain rates(0.01–10 s^(−1))and temperatures(850–1200℃).A relation of deformation stresses with Zener–Hollomon parameter was established to characterize the mechanical response and dynamic softening effect of EA4T steel during hot compression.The evolution of grain boundaries with different misorientations has been analyzed to evaluate the influence of strain rates and temperatures on the dynamic recrystallization.It was found that the grain refinement mechanisms of EA4T steel by dynamic recrystallization including twin-assisted boundary bulging,sub-grain rotation,and sub-grain growth.Transmission electron microscopy observations confirmed that dynamic recrystallization nuclei and small recrystallized grains impeded martensite phase nucleation during hot deformation,while the ongoing dynamic recrystallization consumed deformation stored energy and reduced dislocation density,which mitigated the stress concentration in the parent phase of martensite,thereby facilitating the uniform growth of martensite lath with a mixing structure of nanotwins and dislocations during quenching.
