Study On Deformation Mechanism During Static Deformation Of TWIP Steel

According to the domestic and foreign research findings, the present study of TWIP steelsaims to examine the influence of the detailed microstructure changes in its organizationalperformance. And actually，the microstructure morphology of material is the specificperformance of deformation mechanism. So it is an urgent need to find out the question whichto study the competition law of deformation mechanism by analyzing the microstructuremorphology of TWIP steels during plastic deformation.In this paper, the deformation mechanisms and associated microstructure changes duringcompression and tensile deformation of TWIP steel were systematically investigated.Secondly it analyzes the influence of temperature range of Hot Strip Rolling on themechanical properties of TWIP steel, combining with the performance requirements of theautomotive steel, and finally determines the optimum temperature range of Hot Strip Rolling.(a)Under static compression at room temperature conditions, dislocation glidingthroughout the deformation process. In the early deformation, dislocation reaction promptedstacking fault formation and growth, thus completing the nucleation of deformation twins; Asdeformation continues, stacking faults were replaced a lot of deformation twins. In the grain,due to the mutual settlement between twins, so the grain is divided into many small plaid likesub-grain. And with the amount of deformation continues to increase, sub-grain producedistortions; In the final deformation, because the grain is divided small enough to suppress thegeneration of deformation twins, so weakened TWIP effect. Under severe deformation,fracture will occur in the sub-grain boundaries, which resulted in micro-cracks in the graininterior. With the expansion of micro-cracks, the specimen will appear macroscopic crack.The formation of deformation twins of TWIP steel during compression deformation isdifferent from its during tension deformation. During tension deformation, single twinning system preferentially formed, but multiple twinning system generates together duringcompression deformation. Twins formation rate is significantly faster than it during tensiondeformation, which may be related to the formation mechanism of deformation twins.(b)Under static tensile deformation at room temperature conditions, in the earlydeformation, the main deformation mechanism is dislocation interactions, and interactionsamong phase boundaries and grain boundaries; With the increasing amount of deformation,deformation twins formed at the grain boundaries, twinning mechanism is activated. The maindeformation mechanism of TWIP steel is not dislocation gliding but TWIP effect; In the latedeformation, twinning and slip interaction induced the de-twinning mechanisms, layeredorganization appears, and weakened twinning feature, thus resulted the local deformation andfailure of the sample.(c) With the rolling temperature decreases, yield strength, tensile strength and yield ratioof TWIP steel raise, but Elongation, Strain hardening exponent and Strong plastic productreduce. In the late deformation, hot Strip rolling temperature is higher, which is conducive tosustained hardening, thereby enhancing uniform deformation capacity of the material.According to the actual use of TWIP steel in the automotive vehicle body and requirementsfor the use of Car parts steel, we obtain the optimum temperature range of Hot Strip Rollingwhich is1100℃~900℃.