Cellular Automaton Modeling of Nonisothermal Austenite Grain Evolution in 22MnB5 Hot Stamping Steel and Its Constitutive Correlation

The evolution of prior austenite grains in 22MnB5 hot stamping steel under nonisothermal conditions brings challenges in establishing a quantitative linkage between thermal history, microstructure, and mechanical properties. In this study, an experimental–numerical framework is adopted to investigate austenite grain evolution and its constitutive relationship. Based on measured grain size under different austenitization temperatures and holding times, an Arrhenius‐type grain growth model is established with a prediction accuracy of AARE = 2.27%. A cellular automaton (CA) model incorporating equivalent time is further developed to realize visualized simulation of austenite grain evolution under nonisothermal hot stamping conditions, and the predicted grain sizes agree well with experimental results with an average relative error of 4.32%. The effects of prior austenite grain size and cooling rate on the competition between martensite, bainite, and ferrite are analyzed. Finally, a microstructure‐dependent constitutive model is constructed by combining the Hall–Petch relationship, multiphase mixture rule and Swift model. The predicted stress–strain curves are consistent with experimental data, supporting the engineering applicability of the model. This work provides a computationally efficient framework connecting nonisothermal grain evolution, phase transformation, and mechanical response for hot stamping steels.