The genetic evolution mechanism of microstructure and mechanical property of 9310 steel during cold multi-DoF forming and heat treatment

9310 steel has promising applications in aerospace field due to its excellent mechanical properties, but the difficult integral forming greatly limits its industrial application. Cold multi-degrees of freedom forming (CMDFF) is a local forming process that has significant advantages in forming high-strength steel. However, CMDFF formed 9310 steel usually undergoes complex microstructure and mechanical property evolution during subsequent heat treatment (HT). This study investigates genetic evolution of microstructure and mechanical properties of 9310 steel during CMDFF and HT. The results show that with increasing deformation amount, grain size after HT linearly decreases from 7.79 μm to 4.54 μm in surface region, while increases from 12.35 μm to 13.59 μm and then decreases to 9.23 μm in core region. The abnormal grain growth in 20% deformation amount condition is due to the uneven deformation gradients in grains during CMDFF process, low-strain grains would absorb adjacent large-strain grains with higher dislocation energy during subsequent HT. Texture inheritance in surface region is more obvious, the CMDFF textures in surface region experience lattice rotation with 10°∼62° crystallographic angle during HT, leading to more diverse texture distribution. With increasing deformation amount, tensile strength decreases from initial 1200 MPa to 1130 MPa and then increases to 1293 MPa, elongation increases linearly from 8.67% to 10.5% after HT. The strength-plasticity cooperative improvement in 50% deformation amount condition is mainly because that the combined effects of fine grain inheritance, high dislocation density and diverse lattice orientations could effectively delay stress concentration and crack initiation during tensile deformation.