| With heightened nationwide emphasis energy conservation and environmental protection,coupled with steady increase in automobile ownership,lightweight automobile manufacturing has emerged as a prominent trend.Twin induced plasticity(TWIP)steel,with its exceptional strength and energy absorption capabilities,presents a new solution to achieve automotive lightweight and bolster crash safety.Therefore,gaining insight into TWIP steel’s mechanical properties and structural changes under external deformation conditions holds tremendous industrial significance for automotive steel production and safety improvements.In this study,I investigated the mechanical properties,microstructure,and fracture morphology of Fe-Mn-C-A1 TWIP steel under different deformation rates and temperatures.Specifically,XRD,OM,and SEM were employed to examine the mechanical properties of annealed TWIP steel.Our findings reveal that yield strength and flexural ratio of TWIP steel gradually increase with an increased strain rate,while tensile strength and elongation decrease.At a strain rate between 3.33×10-4～3.33×10-1 s-1,the strain hardening rate of TWIP steel experiences a sharp decline during the initial stages of deformation,followed by a plateau phase,and finally,rapid reduction.Electron microscopy was utilized to explain observed change in mechanical properties and work-hardening behavior,revealing that recrystallization occurred in TWIP steel due to single austenitic phase before and after tensile testing.The amount of recrystallization decreased with an increase in strain rate.At lower strain rates,the test steel’s twinning time is sufficient during deformation,but at higher strain rates,acceleration of the deformation rate hinders complete twinning.Consequently,the number of deformation twins decreases with the increasing strain rate,leading to changes in the mechanical properties and work hardening behavior,as discussed above.The present study investigates the impact of deformation temperature on the microstructure,mechanical properties and work-hardening behavior of TWIP steel.XRD,OM and SEM techniques were employed to carry out this investigation.The results reveal that the sawtooth rheological phenomenon is present at both room temperature and 100℃,while it is absent at 400℃ and 800℃,As the deformation temperature increases,there is a gradual decline in the yield strength,tensile strength,elongation,and strong plastic product.This indicates that the material’s forming ability weakens with an increase in deformation temperature,leading to a deterioration of its mechanical properties.The strain hardening rate of TWIP steel at 25℃ and 100℃ can be divided into three stages,while at 400℃ and 800℃,it can be divided into two stages.During the first stage,the decline in strain hardening rate is similar to that of TWIP steel at normal temperature.However,no platform appears in the subsequent deformation process,and the decline is more gradual than in the first stage.Throughout the deformation process,the austenitic structure of TWIP steel remains stable.Deformation twins are observed abundantly in the microstructure at 25℃ and 100℃,but their presence is almost negligible at 400℃ and 800℃.After stretching the specimen at low strain rate(3.33×10-4～3.33×10-3 s-1),the fracture of TWIP steel exhibits large and small dimples with dense distribution,and the fracture surface appears relatively flat.This suggests that TWIP steel demonstrates a robust energy absorption ability during low strain rate deformation,effectively impeding crack propagation.However,at high strain rates(3.33×10-2 s1～3.33×10-1 s-1),the fiber zone of the specimen appears visibly reduced and the morphology of the specimen is greatly fluctuated,indicating more prominent brittle fracture characteristics.At high temperatures of 100℃,400℃,and 800℃,the fracture topography of TWIP steel becomes progressively more fluctuating with increasing deformation temperature.Consequently,the energy absorption capacity of the material weakens,hastening the fracture process. |
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