Abstract: Low carbon steel plays an important role in many applications due to its high strength. Its high strength comes from the strengthening effect of nano-Cu-rich phase precipitates. In order to effectively adjust the microstructure of Cu-rich phase precipitates and obtain the best properties of Fe-Cu-based steel by adding different alloying elements (Mn, Al), it is necessary to understand the precipitation process of Cu particles. In this paper, based on the Ginzburg-Landau theory, the previous phase field model was modified, and the continuous phase field method was used to simulate the nanometer Cu rich precipitation process and Al content effect of Fe-15%Cu-3% Mn- x AL (x=1%, 3%, 5% mass fraction) alloy at 873K isothermal aging. The morphology, particle density, average particle radius, growth and coarsening kinetics of Cu rich precipitates phase were studied by calculating the component field variables and structural order parameters. The free energy was derived from CALPHAD and the microstructure evolution corresponds to the real alloy system. The results showed that in the early stage of aging, the nano-Cu-rich phase precipitates through a destabilizing decomposition mechanism. Due to the difference in atomic diffusion rate, a core-shell structure with Cu-rich phase as the core is formed. With the extension of aging time, the structure of Cu-rich phase precipitates changed from BCC to FCC. Among them, Al and Mn atoms segregate outside the Cu-rich phase precipitates to form Al/Mn clusters, which can be regarded as a buffer layer that hinders the formation of Cu-rich precipitates; during the precipitation process, as the Al concentration increases, the Al/Mn intermetallic phase of growth of the buffer layer and hinder the growth and coarsening of the Cu-rich precipitate phase.

Keywords: 
• Phase-field method /
• Fe-Cu alloy /
• Cu-rich precipitation phase /
• Coarsening kinetics