Evolution Of Microstructure Of Fe-24Mn-0.05C-2Al-1Si TWIP Steel During High Pressure Torsion Process

With the rapid development of economy and society,there is a growing demand for material properties in various industries.Comparing to traditional high manganese austenitic steel with excellent mechanical properties,the new generation TWIP steels by adding alloying elements such as C,Al and Si,have higher strength and better formability.In the process of plastic deformation,a large number of deformation twins are produced in TWIP steels,which makes the material obtain high strain hardening rate,large uniform elongation and high ultimate tensile strength.Because twin crystals in steels have a significant impact on the properties of materials,it is of great practical significance to explore the microstructure evolution of TWIP Steel under extreme strain for its material processing.In this paper,the microstructure evolution of Fe-24Mn-0.05C-2Al-1Si TWIP steel during high pressure torsional(HPT)deformation was investigated by using Vickers hardness tester,metallographic microscope(OM),X-ray diffraction(XRD)and transmission electron microscopy(TEM).The effects of severe deformation on grain size,deformation twins,recrystallization and the formation of uniform nanocrystals were studied.This study obtained nanometallic materials by high-pressure torsion treatment of TWIP steel,with an average grain size of 45 nm under steady-state conditions.The results of performance testing and structural characterization indicate that under the condition of equivalent strain less than 10,the strength of TWIP steel increases rapidly with the increase of equivalent strain,and the corresponding microstructure is characterized by grain refinement and a sharp increase in dislocation density;When the equivalent strain ranges from 10 to 55,the strength continues to increase with the increase of the equivalent strain,but the amplitude of the increase gradually weakens.The microstructure exhibits the generation of strain twins,and the number of twins also increases with the increase of equivalent strain;After the equivalent strain exceeds 55,the strength begins to decrease and tends to stabilize after 110.The microstructure at this stage mainly manifests as the reduction of strain twins to disappearance,and recrystallization appears and gradually reaches dynamic equilibrium.