| To meet the needs of vehicles such as safety, efficiency, environmental, responsibility and good surface quality, the steel industry is constantly make progress. By the 21st century, most projects of automobile steels have been focused on developing new kinds of UHSS and new style steels to meet the needs of the plan of ultra light steel auto body (ULSAB). These steels include dual-phase steel, (TRIP) steel, transformation induced plasticity (TWIP) steel and Boron steel.Transformation Induced Plasticity (TRIP) steels exhibit a superior combination of strength and ductility compared to precipitation hardened steels and solution hardened steels. TRIP steels meet these requirements that the weight decrease for fuel efficiency as well as the safety is continuing to be major concerns in automobile manufacturing. The large scale production of TRIP steel sheets has become a fact with production technology improvement and development, and the application prospect will be wider.TWIP steel is mainly manganese steel with Mn mass contents of 15%～30%, TWIP is twinning induced plasticity effect, and it can induce unusal plasticity because of the mechanical twinning in ultra high manganese austenitic steel. TWIP steels exhibit some special mechanical properties, such as high work-hardening, large elongation and high tensile strength. The improvement and application will be wider in the vehicle industry in the future.In this article, two different content high manganese austenite steels(18.8Mn and 23.8Mn) are studied. The relation between Mn contents and deformation microstructure and mechanical properties of samples have been studied, the microstructure and mechanical properties of the hot rolling steel and the tensile strain hardening behaviours of the steel have been studied. These are many conclusions can offer gist of theory and experiment for commercial run.The contents of this article include following items: (1) By the optical microscope, transmission electron microscopy (TEM) and X ray diffraction, the steel of the relationship between deforming amount and microstructure have been studied of the steel that take tensile strain experiment of room-temperature with the strain rate of 10-3/s. The microstructures of the samples at different deforming amount were analyzed, the result indicates that when there exist both TRIP effect and TWIP effect in steel during tensile strain experiment, the dislocation and TRIP happens earlier;the TWIP happens in the medium-term;the TRIP happens in the last. The 23.8 Mn experimental steel exist both TRIP effect. And TWIP effect, but the TWIP effect becomes the main deformation mechanism of the steel.(2) The induration stage of the tensile strain curve have been studied by the true stress and true strain curves.of the two kinds of steels and the optical microscope, transmission electron microscopy (TEM) and X ray analysis discussed, and analysis what law have followed. The 18.8Mn experimental steel deformation could be divided into four different stages:1) elastic deformation phase;2) the linear plastic deformation stage;3) the nonlinear of deformation of the plasticity stage.4) the beginning of the martensite yield stage. And the 23.8% deformation could be divided into three different stages:1) elastic deformation phase;2) the linear plastic deformation stage;3) the nonlinear of deformation of the plasticity stage.(3) The hot rolling process of the 18.8Mn experimental steel, and the microstructures and the mechanical property of the samples have been studied. the ultimate tensile strength is 930MPa, the elongation of the steels is 41%.And the strengthening effect of the Mn among the austenitic steel have been studied. The studied indicated that the solution strengthening is not the main mechanism in the high Mn austenitic steel, and the twinning induced plasticity effect is the important mechanism.
|
PDF Full Text Request