Softening mechanisms and microstructure evolution of 42CrMo steel during hot compressive deformation

Abstract

Hot compression experiments were conducted on 42CrMo steel under different conditions using a Gleeble-3500 thermomechanical simulator. Systematic studies on the microstructure evolution and flow behavior under different deformation conditions were conducted. The results demonstrate that the flow curves exhibit significant peaks at low strain rates and high temperatures, and that the peak stress increases with decreasing deformation temperature and increasing strain rate. The dynamic recrystallization (DRX) critical points under various deformation conditions were derived from the work-hardening curves. The relationship between the peak (εp) and critical (εc) strains satisfies εc = 0.65εp. The value of εc decreased as the strain rate decreased and deformation temperature increased. The softening mechanism under different deformation conditions was determined in conjunction with the high-temperature microstructure and critical strains. When deformed at low temperature, the softening mechanism was a combination of dynamic recovery (DRV) and DRX; when deformed at high temperature, the softening mechanism was mainly DRX, and at low strain rates, the deformed DRX grains coarsened. Analysis of the room-temperature microstructure revealed that the substructure introduced during hot compression can affect the phase transition. Electron backscatter diffraction results show that room-temperature microstructure have a higher proportion of medium orientation angle boundaries and greater average local strain when DRX is incomplete. The higher dislocation density in the tissue with incomplete DRX disrupts the martensitic multilevel structure, whereas with complete DRX, it tends to form a typical martensitic multilevel structure.