Study on elastic-plastic behavior of X80 high-strength steel

To improve the forming accuracy of high-strength high-strength steel, it is essential to thoroughly understand its elastoplastic behavior. The key is to study the quantitative relationship between the microstructure and mechanical properties of high-strength steel and to gain a deep understanding of the evolution of its elastoplastic mechanical properties under different stress conditions. Based on this, this paper focuses on dual-phase (B + PF) X80 high-strength steel and relies on the micromechanical phase dislocation constitutive theory. By comprehensively utilizing multi-scale experimental data, a 3D Representative Volume Element (RVE) finite element model based on the actual microstructure was established. The varying elastic modulus was embedded into the finite element model through a user-defined field subroutine. A total of 9 different stress states were experimentally tested and 15 types of numerical simulations were conducted to investigate the evolution of the yield behavior and nonlinear elastic behavior of high-strength steel, providing further guidance for the manufacturing and forming processes of high-strength steel. Ultimately, dual-phase (B + PF) X80 high-strength steel exhibited anisotropic yield surfaces under different stress states, and the subsequent yield surfaces demonstrated an evolution law of distortional hardening. The finite element model developed in this study achieved an average subsequent yield point error rate of only 5.79 %. Differences were observed in the nonlinear transition points under different stress states and pre-strains, with the nonlinear elastic points always lying within the corresponding yield surfaces for each stress state and pre-strain, showing softening phenomena. The nonlinear elastic surfaces also followed the evolution law of distortion. These findings aim to further guide the manufacturing and forming processes of high-strength steel.