Study on dynamic softening model and grain evolution of EA4T axle steel at high temperature
To optimize subsequent hot working processes,the thermal deformation behavior and microstructural evolution of EA4T steel were studied.The single-pass isothermal constant strain rate hot compression experiments were carried out with a thermal simulation testing machine.The true stress-true strain curves were obtained with the deformation temperature of 850-1 200℃ and strain rate of 0.01-10s-1,achieving a true strain of 0.9.The results show that the low strain rate(0.01,0.1 s1)under all deformation temperatures show typical dynamic recrystallization characteristics.With the increase of strain rate,dynamic recrystallization occurred after hot compression deformation at high temperature and high strain rate(950-1 200 ℃,1s-1)and(1 050-1 200 ℃,10s-1).Recrystallization is important for steel processing because it modifies microstructure along the process route and thus determines the final properties of steel products.Then a dynamic softening model of EA4T steel at high temperature was established by combining Z parameter as hot deformation condition with microstructure evolution.The model can accurately regulate the behavior of dynamic recovery,incomplete dynamic recrystallization,complete dynamic recrystallization,and grain growth phenomena during hot deformation.EA4T steel has multi-level microstructure characteristics of dynamic recrystallization grains,martensite blocks and martensite laths under varying deformation conditions.The grain evolution of EA4T steel was clarified by means of electron backscattering diffraction(EBSD)and transmission electron microscopy(TEM).The relationship model of dynamic recrystallization grains martensite blocks and Z parameters of EA4T steel was established.The results can provide theoretical guidance for hot working process of EA4T steel.
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