Steam generators for liquid-metal fast breeder reactors may be subject both to fretting wear as a result of flow-induced vibrations and to wear from larger amplitude sliding movements caused by thermal changes. Wear under these conditions is strongly adhesive so that in tests simulating the larger amplitude sliding of tubing through support plates, mechanical interaction of the wear scars results in high pseudo-friction forces for ferritic steels at the extremities of movement. With austenitic steel combinations in such tests, less wear is found but at temperatures above 500°C static adhesion after a period of dwell can give increased axial forces to initiate sliding, for example, up to three times the contact force at 560°C. A number of test mechanisms have been developed to evaluate the impact, impact-slide, and rubbing fretting behavior of these materials in sodium. With hemisphere-on-flat geometry, specific wear rates for austenitic steel combinations in impact-slide increase with temperature and decrease with time, while specific wear rates for ferritic steel combinations are approximately an order of magnitude greater (10−14 to 10−13 m3/Nm). In rubbing fretting, wear rates are broadly similar for austenitic and ferritic steel combinations. Specific wear rates decrease with slip amplitude and are of the order of 3 × 10−16 m3/Nm at 10 µm and 3 × 10−15 m3/Nm in excess of 100 µm.