Research On Deformed Microstructure And Texture Of TWIP Steel

Among the wide variety of recently developed steels,high manganese austenitic steels with low stacking fault energy（SFE）are particularly promising in the lightweight design of vehicle,especially when the twin induced plasticity（TWIP）effect occurs.Outstanding mechanical properties combining a high ductility and high strength are then obtained.The influence of TWIP effect on the microstructure and properties of TWIP steel under high strain rate and deep drawing conditions was discussed by studying the microstructure evolution of TWIP steel after dynamic tensile and deep drawing.The evolution law of microstructure and texture of TWIP steel under high strain rate and different stress states was obtained,which could be used for reference in the passive safety design of automobile and the application of sheet metal forming.The main contents of this paper include two parts:The first part is the high strain rate tensile test of TWIP steel by split Hopkinson tension bar,and the performance of TWIP steel under high strain rate deformation condition was obtained.The texture evolution of the deformed specimen was analyzed by XRD technique,and the evolution law under different strain rates was obtained.The second part is the numerical simulation of the deep drawing process of the TWIP steel sheet.The stress states of the main parts of the sheet were obtained,and then the microstructure and texture evolution of each part were tested according to the test results.The relationship between the stress states and texture evolution was analyzed.The results show that:（1）The deformed 24^#TWIP steel mainly contained Goss{011}<100>,Brass{011}<211>,CuT（copper twins）{552}<115>,RG（rot Goss）{011}<011>and S{123}<634>.With the increase of strain rate,the intensity of Goss and CuT was obviously weakened.（2）The tensile strength and the elongation increased of TWIP steel under dynamic tensile conditions increased with the increase of strain rate.When the strain rate increased from 664 s^-1 to 1480 s^-1,the tensile strength raised from 1758 MPa to 1886 MPa and the elongation added from 9.1%to 20.27%.（3）When the depth of drawing was 5mm,the intensity of the copper texture Cu{112}<111>of the cylinder wall and the die fillet was 1.0,and the intensity of Cu texture of punch fillet was down to 0.5.（4）As the depth of drawing increased from 5mm to 15mm,the intensity of Cu{112}<111>was gradually raising at the corresponding position.With the increase of the drawing depth,the cylindrical part was ruptured,and the texture intensity did not change much.