Microstructure Of Fe-Mn-Si-Al TWIP Steel During Deformation At Different Strain Rates And Performance Studies

With the continuous development of automobile industry and the popularity of new energy vehicles,a series of problems such as environmental pollution,energy consumption and safety performance appear when people use automobiles.Lightweight cars have become inevitable.High strength steel,represented by high manganese TWIP steel,is becoming a new generation of automotive steel with great potential because of its low density,high work hardening ability and unique plastic deformation mechanism.In this paper,Fe-25Mn-3Si-3Al TWIP steel is taken as the research object,and compression deformation experiments of high and low strain rates are carried out.Optical microscopy(OM),X-ray diffractometer(XRD),scanning electron microscopy(SEM),backscattered electron diffraction(EBSD)and transmission electron microscopy(TEM)were used to characterize the steel.The microstructure evolution of the experimental steel under different deformation conditions was studied,and the mechanical properties of the experimental steel were studied by combining hardness measurement and tensile test.The deformation mechanism of Fe-25Mn-3Si-3Al high manganese TWIP steel during plastic deformation was analyzed.In order to promote the application of TWIP steel in industrial production and life,the interaction of dislocation,slip band,deformation twins and other substructures in the process of compression was clarified,and the deformation behavior of TWIP steel was comprehensively understood.The main conclusions of the experiment are as follows:Compression deformation of TWIP steel under the action of applied stress.At the initial stage of deformation,dislocations generated by dislocation sources begin to slip in austenia.Dislocation slip will be hindered by precipitates or grain boundaries,and single slip will occur in the most favorable slip systems,resulting in unidirectional and parallel slip lines.As the deformation gradually increases,the hindered dislocations proliferate and intertwine through initiation.As the stress increases,the multisystem slip is initiated,and the cross-slip continues to slip on another slip plane.At this time,the deformation mechanism is mainly dislocation slip.When the stress generated by the material during compression deformation reaches the critical stress of TWIP,the deformation twin will be formed.If the grain size is small,deformation twins will be inhibited,resulting in detwinning phenomenon,thus affecting the mechanical properties of the material.The slip bands and deformation twins generated in the deformation process also play a similar role to grain boundaries,which can refine grains and prevent dislocation movement,so the deformation twins generated will not increase when they reach a certain number.The deformation mechanism under small strain is mainly slip band and deformation twin.The plastic deformation mechanism of large deformation is mainly grain breakage,which makes the hardness and strength of materials can be further improved.The impact compression is favorable to the nucleation of twins,and the twins generated are smaller than those generated at lower strain rates.It is more favorable for twin growth at lower strain rate.