Microstructural evolution of ultrahigh carbon steel during friction stir welding

This study applied friction stir welding to an ultrahigh carbon steel consisting of a (ferrite + cementite) duplex structure using polycrystalline cubic boron nitride tool and successfully produced a defect-free weld. The microstructure and the hardness profile of the weld were examined, and the microstructural evolution during friction stir welding was systematically discussed.