Experimental study and crystal plasticity simulation of low-cycle fatigue behavior for bake-hardening high-strength steels

Abstract

Bake hardening is a widely adopted technique for enhancing the strength and surface durability of structural components, particularly in applications within the automotive and aerospace industries. However, the mechanisms by which bake hardening influences the low cycle fatigue (LCF) behaviour of high-strength steels remain insufficiently understood. This study systematically investigates the effects of pre-strain and bake hardening on the LCF behaviour of hot-rolled high-strength steel HR420. Fatigue tests were performed across a strain amplitude range of 0.2 % to 0.8 % to assess the influence of bake hardening on cyclic softening behaviour and microstructural evolution. The fatigue fracture morphology and microstructural evolution were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Furthermore, a crystal plasticity finite element model incorporating the bake-hardening effect was established using EBSD-derived data to simulate microstructural evolution and predict fatigue life. The results show that at low strain amplitude (0.2 %), bake hardening significantly prolongs fatigue life by suppressing crack initiation, with a maximum increase of 90 % observed under 4 % pre-strained + bake hardening. In contrast, at higher strain amplitudes (0.4 % and 0.6 %), bake hardening accelerates crack propagation due to intensified stress localization, leading to a fatigue life reduction of up to 40 %. The simulation results are in good agreement with experimental observations, confirming the model’s predictive capability. This study provides new insights into the fatigue mechanisms associated with bake hardening and presents a reliable numerical framework for fatigue life prediction in high-strength steels.