Research On The Bauschinger Effect Of The Third-generation Automotive Medium-Mn Steel

The third generation of medium and high strength steel for automobile is characterized by high strength and high plasticity.It can ensure collision safety and have good stamping properties.In the actual production stamping forming,medium manganese steel will be locally in the tension-compression cycle loading state.During the process of deformation,the reverse yield strength of this part will be lower than its positive yield strength.This phenomenon is called the Bauschinger effect,which is widespread found in the metal materials,and was found by the German scholar Johann Bauschinger in the mechanical properties test of metal in 1881.In order to study the stress state and mechanical properties of medium manganese steel during stamping,it is necessary to study the Bauschinger effect of medium manganese steel.The material used in this paper is a medium manganese steel cold rolled steel plate.Before testing the Bauschinger effect of the steel plate,heat treatment is required.It is found that medium manganese at a temperature of 620 ? can achieve excellent performance of 29GPa% of product of strength and elongation(PSE).In the plate metal Bauschinger test,it is necessary to overcome the difficulty of buckling in the reverse loading.The die used in this paper is a tensile and compression mould specially designed by Mr.Chang Ying's team of Dalian University of Technology,which can overcome the phenomenon of reverse yield instability and its test can provide real time force deformation curve in material deformation.The Bauschinger effect of medium manganese steel under the conditions of different strains,strain modes and strain rates was tested and characterized by different characterization methods.It is found that the Bauschinger effect will occur in the medium manganese steel after the pre-deformation and then the reverse loading,and the medium manganese steel RKI can show the hardening tendency in the process of deformation.The RKI values of the medium manganese steel are greater than 1,which means the mechanism of motion hardening is more obvious;The Bauschinger effect of middle manganese ladle is more significant when strain mode is pre-stretched;when the predeformation is compression,the greater the strain,the greater the Bauschinger effect in the middle manganese ladle;the greater the pre-deformation is,the more the strain is,the smaller the Bauschinger effect of the medium manganese steel;In the comparison of the different rates conditions.It is found that the Bauschinger effect of the medium manganese steel is insensitive to the strain rate.