Study On Hot Rolling Simulation And Microstructure Of 20 Steel

(α+γ) two-phase region warm rolling in low carbon steel has more advantages when compared with traditional austentite region hot rolling, such as: saving energy and shortening the production cycle. However, the problem of cracking and rolling bad should be taken into account when rolled in two-phase region. Therefore, it has theoretical and practical importance to study the rolling mechanism in the two-phase region of low carbon steel.Isothermal compression tests of 20 steel in(α+γ) two-phase region were performed on a Gleeble-3500 system in the temperature range between 750°C and 850°C at strain rates between 1s-1 and 10s-1.The true stress-true strain curves under different deformation conditions showed that dynamic softening more obviously occurred in the sample with a lower strain rate(ε?) or a higher deformation temperature(T). The results showed that the flow stress level increases at a higher strain rate or a lower deformation temperature, but it increases at the deformation temperature of 850℃.The flow behavior of 20 steel in(α + γ) two-phase region was described by a hyperbolic sine constitutive equation:The microstructure and deformation mechanism of samples were observed by optical microscopy(OM), scanning electron microscopy(SEM) and electron back scattering diffraction(EBSD) techniques. Dynamic recovery and dynamic recrystallization both occurred during hot compression of 20 steel under all deformation conditions. Microstructure observation showed a distinct degree of recrystallization at different deformation conditions. When the deformation temperature was constant, the microstructure consisted of fine grain and coarse grain at a low strain rate, and fine equiaxial recrystallization grain occurred at a high strain rate. Overall, the size of recrystallization grain reduced with the strain rate increasing. When the strain rate was constant, the softening degree and the size of recrystallization grain increased with increasing temperature. The Zener-Hollomon(Z parameters) of deformed specimens under various deformation conditions were used to represent the co-effect of deformation temperature and strain rate in thermal deformation behavior of 20 steel. It was showed that the softening mechanism changed from dynamic recovery to dynamic recrystallization with lower Z. It can be concluded that decreasing of Z value leaded to a higher degree of dynamic recrystallization.The <100>//ND and <111>//ND fiber texture were both obtained during hot compression tests of 20 steel under all deformation conditions. The <100>//ND and <111>//ND fiber texture gradually changed to random distribution with increasing temperature and increasing strain rate.The orientations of recrystallization grain and substructure were close to the orientations of deformation grain during hot compression of 20 steel. When the strain rate was low, the deformation grain in <100> had preference to dynamic recrystallization; The nucleation mechanisms of 20 steel was bow out of the grain boundary nucleation and the mode of dynamic recrystallization was continuous dynamic recrystallization.