Microstructure and mechanical properties of friction stir welded 0.2%C Si-Mn steel
By Zexi Wu (Osaka University), Tomoya Nagira (Osaka University), Kohsaku Ushioda (Osaka University), Hidetoshi Fujii (Osaka University), Goro Miyamoto (Tohoku University)

In recent years, the demand for high-strength and high-ductility steels has significantly increased. However, most of the structural steels are strengthened by the addition of expensive elements such as Ni and Mo, which is not preferable on account of cost issues and natural resource limits. The addition of cheaper elements such as C, Si, Mn and Cr is expected to improve strength and ductility, however, it causes a crucial problem of poor weldability by fusion welding due to the high carbon equivalent value. On the other hand, it has been reported that friction stir welding (FSW), which is a solid-state welding process, has successfully welded the high carbon steels. In this study, Si and Mn were added to 0.2C (wt%) steel in order to enhance the strength and ductility balance, and the weldability of the FSW joint was examined. The microstructures and mechanical properties such as strength, ductility and toughness of the base material and FSW joint were investigated and discussed.