Monte Carlo simulation of grain growth in heat-affected zone during welding process of cast steel joint and optimization of welding process

The final microstructure and mechanical properties of a welded joint are determined by the evolution and crystallization process of grain structure during welding. This study aims to improve the mechanical properties of the weak weld root zone in a G20Mn5 cast steel—Q345 low-alloy steel circular butt weld. The microstructure changes of the weld during the welding process were investigated using metallographic testing combined with Monte Carlo simulation, and suggestions for optimizing the welding process were provided. Firstly, the microstructural assessment of welded cast steel joints was conducted using metallographic and hardness tests. It was clarified that the heat-affected zone at the weld root on the Q345 steel side was the weak zone. Additionally, the relationship between grain size and mechanical properties of the joints was established. A Monte Carlo model was then used to simulate the dynamic recrystallization process and determine the final distribution of grain structure in the heat-affected zone. Finally, the calibrated model was utilized to analyze the impact of different welding processes on grain structure and mechanical properties. The findings indicate that employing a three-pass welding process, incorporating a V-shaped groove on the cast steel side, and dispersing the welding start and stop positions can effectively inhibit grain growth in the heat-affected zone, which provides valuable insights for optimizing the welding process of cast steel welded joints.