A coupled computational fluid dynamics approach as a viable tool for thermal history assessment of UNS 532205 duplex stainless steels friction stir welded joints

Friction stir welding is a manufacturing process with several positive outputs for duplex stainless steel joints, such as improved mechanical resistance and the maintenance of optimal phase fraction. Duplex steels are vastly used in naval and petrochemical operations, being commonly manufactured and joined via welding processes. Thus, there is a high demand for straightforward methods of thermal evaluation of friction stir welded joints. In this sense, numerical models are a practical tool for assessing the joints' welding condition. However, the vast majority of works concerning numerical modeling of FSW of duplex steels are limited, by some considerations regarding the heat source modeling, by neglecting the material's flow convective influence, and by omitting the thermomechanical properties of individual phases. This work focused on the development and application of a more complete coupled numerical model for friction stir welding of UNS S32205 plates in order to correlate processing conditions with microstructure evolution. A peak temperature of 1213 degrees C at the joint's central line was observed. Distributions of temperature and material flow through the joint cross-section indicate that a more intense material flow at the retreating side favors coarser grain size. Simulation results indicated that the strain rate plays a more intense effect in microstructure development compared to the welding peak temperatures. The coupled numerical model was additionally used to obtain the temperature profile of the tool, which was thermally stable even after standing temperature values greater than 1200 degrees C. Even after 18 cm of welding procedure, thermal damage of the tool was not observed, leading to sound welded joints.

Automated summary

Friction stir welding improves mechanical resistance and maintains optimal phase fraction for duplex stainless steel joints. Numerical models are practical tools for assessing the welding condition of these joints. This study developed a complete coupled numerical model for friction stir welding of UNS S32205 plates and found that strain rate has a greater effect on microstructure development compared to welding peak temperatures.