Experimental And Simulation Research On PLC Plastic Instability And TRIP Effect Of Medium Manganese High-strength Steel

The medium Mn steel is a third-generation high-strength steel with wide application prospects in the automotive engineering field.It has a ultimate tensile strength of more than 1GPa and a uniform elongation of more than 30%.The application of medium Mn steel to the car bodies can greatly reduce the weight of cars and improve the safety performance.However,there are two effects(PLC plastic instability effect and TRIP effect)which have a huge influence on the material properties during tensile deformations.The PLC effect leads to a strain localization phenomenon of the material,which causes the roughness in the material surface.The TRIP effect is that the metastable austenite phases transform into the martensite phases.And it greatly improves the strength and ductility of the material.In order to have a deeper study to the mechanism of PLC effect and TRIP effect in medium Mn steel,this paper studies the material from the perspective of experiment and numerical simulation.The main work of this article includes following aspects:1.Based on the digital image correlation method and infrared thermal imaging method,quasi-static tensile experiments of medium Mn steel under different strain rates are carried out.The different behaviors of the PLC effect under different strain rates are compared and discussed.Then the local deformation phenomenon caused by the PLC effect is analyzed,by comparing the local strain field and temperature field of the material.2.TEM,XRD are used to experimental research and analysis on the TRIP effect of medium Mn steel,and to calibrate the element content and phase transform process of each phase of the material.The strain of each phase in the process of tensile deformation of the material is distinguished through the microscopic digital image correlation experiment based on in-situ SEM tensile experiment.3.The constitutive model of PLC effect based on the dynamic strain aging is established,and the local deformation phenomenon of the material is considered to handle with the model.The numerical simulation method is used to simulate the PLC effect under different strain rates.By comparing with the local strain field and temperature field of the experimental results,the local deformation mechanism of PLC effect is analyzed.4.The TRIP effect constitutive model of medium-manganese multiphase steel based on solid solution strengthening and dislocation strengthening theory is established,and the strength contribution of ferrite,austenite and martensite as well as the microscopic mechanism during deformation are discussed.Based on the experimental results of strain distribution,the strain of each phase is distributed and compared with the theoretical strain distribution results of iso-work theory.