Theoretical modelling of yield stress in cold-rolled and annealed AISI 420 steel: Dependence on rolling pre-strain

With increasing demands for high-quality metal products, manufacturing processes have become more complex, generally involving both forming and heat treatment stages. During these stages, the developed flow stress after forming evolves throughout heat treatment, leading to residual stress redistribution, which can cause undesirable and unpredictable shape changes. To better understand the evolution of yield stress through these stages, uniaxial tensile tests were conducted on samples taken from cold-rolled and cold-rolled-and-annealed AISI 420 steel strips. Additionally, microstructural changes after annealing were characterized using electron backscattered diffraction (EBSD). The study examined various thickness reductions during cold rolling, while the annealing process was standardized to 760°C for 15 minutes. A two-step theoretical model was developed to correlate rolling pre-strain with the resulting yield stress after annealing, taking into account the combined effects of residual work hardening and the Hall-Petch relationship.