Friction stir joining of dissimilar ferritic ODS steels

Application of the latest developments in materials technology may greatly aid in the successful pursuit of next generation reactor and transmutation technologies. Oxide dispersion strengthened (ODS) ferritic steels are expected to be used as a long life cladding in the future advanced fast reactor. Comparing to the other steels, ODS steels have excellent resistance to creep and swelling as well as superior mechanical strength. Applications of ODS steels grow faster in nuclear engineering society; however, not so many studies have been made for improving weld properties. In ODS steels, it is well known that uniform nano oxide depressed act as pinning points to obstruct dislocation and grain boundary motion, however, those advantages will be disappeared while the material is subjected to the high temperature of conventional fusion welding. Rotary friction welding, also referred to as friction stir welding (FSW), has shown great promise as a method for joining traditionally difficult to join materials such as aluminum alloys. This relatively new technology, first developed in 1991, has more recently been applied to higher melting temperature alloys such as steels, nickel-based and titanium alloys. In this study, FSW is used as a substitutive welding process for ferritic ODS steels, solid state microstructure modification is performed. During the FSW, dynamic recrystallized grains are developed; the uniform oxides dispersion is preserved in the metal matrix. The microstructure and micro texture of the material near the stir zone was found to be influenced by the rotational behavior of the tool. The response of material for different process variables have been discussed in terms of plastic deformation amount and heat input