Effect of Notch Position on Impact Toughness of Friction Stir Processed Low Carbon Steel

The effect of single-pass friction stir processing (FSP) on the room temperature impact toughness of a low carbon steel was investigated via Charpy impact test. A fine-grained (FG) microstructure was achieved into the processed zone by large deformation and simultaneous dynamic recrystallization during FSP. The average grain size decreased from 25 μm down to 3.0 μm after FSP. Grain refinement by FSP increased the impact energies as a result of refined grains separated mostly by high-angle of misorientation. Toughness of steel before FSP was about 8.7 J, and it increased up to 11.2 J after processing depending on the notch positions of the samples. The peak impact toughness value of 11.2 J was achieved with the notch position located at top of the surface of processed steel plate.