| Iron and steel industry is an important section in the national economy. To meet the needs of automotive industry, such as lightweight, safety, environmental, fuel efficiency and so on, there is still much process to be done in the steel industry. Now, more and more high-strength steel(High Strength Steel-HSS)and ultra high-strength steel(Ultra High Strength Steel-UHSS)were substitued for traditional low carbon steel. Because of twinning induced plasticity effect, TWIP steel exhibits 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.The hot deformation behavior of metal is the theoretical basis for thermal processing technology, sush as extrusion, rolling, reverse, etc. But there are few reports on the hot compression of TWIP steel. In the study, hot compression tests of the TWIP steel after solution treatment were performed on Gleeble-3800 at deformation temperatures from 973K to 1373K, and strain rates from 0.01s-1 to 20s-1. Microstructure characteristic and deformation mechanism of TWIP steel were investigated. In addition, the dynamic tensile test of TWIP steel was carried out by the technology of split Hopkinson compression bar at various high strain rates, To serve the auto industry lightweight development and anti-collision design. The main conclusions are drawn as follows:1. The flow stress of TWIP steel is strongly influenced by deformation temperature and strain rate during hot compression, and decreases with the increase of deformation temperature and decrease of strain rate. The curves exhibit obvious characters of dynamic recrystaIlization between 1073K and 1373K. The hot deformation process is controlled by heat activation,and the relationship among flow stress (σ), deformation temperature (T) and strain rate (ε? ) is satisfied by hyperbolic sine equation. In another words, the flow stress behavior of the steel during hot deformation can be expressed by Zener-Hollomon parameter (Z parameter for short). The expressions of the parameter Z and the flow stress equation for the steel are listed as follows respectively, which is derived from the experiment data through regression analysis:2. Deformation temperature plays an important role in the hot compression deformation of TWIP steel. With the increase of deformation temperature, the recrystallization degree increases gradually. When deformation temperature reaches 1373K, the microstructure of the steel is primarily composed of recrystallized grains, which exhibits obvious growing tendency. When deformation temperature less than 1073K, work-harding plays an important role in the hot compression deformation of TWIP steel. Strain rate also plays an important role in the hot compression deformation of TWIP steel, the higher strain rate, the smaller the size of the recrystallized grains. According to the change of the flow stress, microstructure and hardness, the proper processing parameters of TWIP steel are approximately deformation temperature from 1223K to 1323K and strain rate from 1s-1 to 10s-1.3. The dynamic tensile test of TWIP steel was carried out by the technology of split Hopkinson compression bar at various high strain rates. The results show that, under dynamic condition, the respond time and stress fluctuating appear on the stress-strain curves, there is single austenitic phase before and after deformation. The amount and density of the twins during dynamic deformation are higher than that of the static deformation, besides, two or more twin systems are activated in most grains. The twin-twin interaction, the twin-dislocation interaction, especially more twin systems play an important role during dynamic deformation.
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