<p>Hot isostatic pressing (HIP) is an effective post-processing technique for eliminating internal porosity in metal injection molded (MIM) components; however, the optimization of process parameters still largely relies on empirical approaches, which limits process reliability and efficiency. In this study, a mechanism-oriented numerical framework is developed to investigate stress-assisted pore closure behavior in FD-0205 steel during HIP. Realistic pore morphologies extracted from metallographic images are reconstructed using image-based processing to establish representative two-dimensional microstructural models. A fully coupled transient finite element model incorporating temperature-dependent elastoplastic deformation and high-temperature creep is then implemented to simulate the evolution of pore closure throughout the complete HIP thermal cycle. The results show that densification is governed by the coupled interaction between plastic collapse and creep deformation, which is strongly dependent on pore size, morphology, and local stress redistribution. Larger pores tend to undergo earlier stress-driven collapse due to higher stress concentration, whereas smaller pores exhibit more gradual closure dominated by time-dependent creep deformation. The evolution of equivalent stress, plastic strain, and creep strain exhibits a non-monotonic behavior during heating, holding, and cooling stages, reflecting transitions in the dominant deformation mechanisms. Experimental HIP results validate the simulation predictions, achieving a maximum relative density of 97.82%, with good agreement between numerical and experimental densification trends. Overall, the proposed image-based coupled elastoplastic–creep model provides a reliable framework for predicting pore evolution during HIP and offers a physics-based approach for process parameter optimization of MIM components.</p>