Many applications in the energy sector such as gas, steam and wind power plants rely on large turbines. The turbine shafts are manufactured by casting, forging and a complex heat treatment sequence with a high material and energy consumption. Furthermore, the alloys used for such applications include critical raw materials, such as Mo, Nb, and Ni, with limited availability and a high supply risk. For optimizing the manufacturing process and designing alloys with improved performance and reduced content of critical elements, advanced simulation models are highly needed. The Horizon Europe project AID4GREENEST aims at developing new simulation tools to support the steel sector. As a contribution to process and alloy design, a mean-field model for the microstructure evolution and the mutual coupling with the thermo-mechanical material behaviour is presented. Derived from a comprehensive thermodynamic framework, it describes a variety of phenomena such as work hardening, recovery, recrystallization, and grain growth, as well as numerous coupling phenomena using a physics-based approach. Using thermo-mechanical experiments and metallographic analyses, the material model is calibrated for a steel used for turbine shafts. In order to predict the final microstructure of the shaft, the model is applied to simulate the microstructure evolution throughout the entire forging process.