<p>Fe₃C plays a crucial role in both structural and functional materials, particularly in the realms of steel manufacturing and carbon nanomaterial synthesis. This research focuses on investigating the thermal structure evolution of highly crystalline meso/microscaled pure phase Fe₃C obtained by employing the electrochemical etching method. Various characterization techniques such as x-ray diffraction, micro-Raman spectroscopy system, synchronous thermal analyzer, Scanning Electron Microscope, and Transmission Electron Microscope were utilized to analyze the impact of annealing temperature and atmosphere on the thermal stability of Fe₃C. The results show that: The decomposition of Fe₃C into Fe and C occurs from the outside to the interior at 600&#xa0;°C under oxygen-free conditions. A multi-chamber composite structure with a 20-30&#xa0;nm amorphous carbon shell encapsulated Fe is formed. In such shell-core structures, residual Fe₃C always persists, the compressive stress from the overall volume expansion, confined by the thick carbon shell, is responsible for that. Under oxygen-poor conditions, the meso-microscaled Fe₃C can undergo the globally decomposition which results in the formation of a shell-core structure only at 500&#xa0;°C. The introduction of oxygen etched the carbon shell with a more disordered structure. This structural disturbance releases internal stresses within the compound, facilitating the continuous decomposition of Fe₃C, ultimately leading to the formation of nanoscaled particles comprising carbon-encapsulated iron and iron oxide.</p>