Fatigue performance of friction stir welded marine grade steel

• An evaluation of the fatigue performance of steel friction stir welds is reported.
• Friction stir welds of marine grade steel exceed the relevant rules for fusion welding.
• New S–N curve parameters for butt friction stir welds are proposed.
• Surface generated process features dictate the fatigue failure mechanism.

An extensive study on the fatigue performance of friction stir welded DH36 steel was carried out. The main focus of this experimental testing programme was fatigue testing accompanied by tensile tests, geometry measurements, hardness and residual stress measurements, and fracture surface examination. The S–N curve for friction stir butt welded joints was generated and compared with the International Institute of Welding recommendations for conventional fusion butt welds. Friction stir welds of marine grade steel exceeded the relevant rules for fusion welding. This newly developed S–N curve is being proposed for use in the relevant fatigue assessment guidelines for friction stir welding of low alloy steel. Fracture surfaces were examined to investigate the fatigue failure mechanism, which was found to be affected by the processing features generated by the friction stir welding tool.