Researches On Strengthening And Toughening Mechanism Of Pearlite X70 Steel

Low-alloy and high-strength steels are widely used in most of national construction projects. The toughness is required to be higher and higher considering the structural security. At present, the thickness of the billet and product is mostly determined, the influence of refinement strengthening, dislocation strengthening, solid solution strengthening, dispersion strengthening and residual stress on the material toughness becomes stable. So, the type, content, size of phases become the important factors which affect its toughness. In this paper, the characteristics of its phase transformation under different deformation were studied, typical phase was quantitatively analyzed, then the preparation technologies of the typical multiphase microstructure with different phase content, grain size were obtained. The relationship between the polyphase structure parameters, material mechanical properties and fracture toughness was studied by using experiments and finite element simulation, therefore, the effect and mechanism of phase parameters on the toughening of the F-P complex phase steel were determined.The CCT curves of test steel under different deformation conditions was obtained by using a series of experiments. The characteristics of phase transformation of testing steel were observed systematically by using metallographic tests and the effect of deformation on test steel CCT curve was analyzed. The results showed that phase curves move toward the top left corner with increasing deformation strain in this work. Two stable cooling rate ranges of multiphase microstructure exit in each CCT curves with different deformation.The stress-strain curves of different processes were obtained by using tensile experiment and the influence of typical single phase on the mechanical properties was analyzed. F-P unit cell model of multiphase steel was built by using finite element software ANSYS, which was revised by comparing with experimental data. The stress-strain curves of ferrite-pearlite multiphase steel with different phase parameters was simulated and the influence of the phase parameters of hard phase pearlite on mechanical properties was analyzed.Basing on the mechanical parameters from unit cell model simulation, the fracture model of F-P multiphase steel was built and the JIc values of the testing steel with different phase parameters were simulated. Then, the corresponding stress intensity factor KIc values were calculated. By analyzing the simulation results, the relationship between material fracture toughness JIc and the charpy impact toughness CVN was studied and the effect and mechanism of phase parameters on the toughening of the F-P complex phase steel were determined.