Low Cycle Fatigue of Cast Austenitic Steel

Cast austenitic stainless steel 1.4848 is used to manufacture automotive exhaust system components. Low cycle fatigue (LCF) of 1.4848 austenitic steel was investigated through strain-controlled fatigue testing at strain rates of 0.02/s, 0.002/s, and 0.0002/s in the temperature range from room temperature (RT) to 900 degrees C. Its cyclic behavior was characterized in relation to deformation mechanisms. At RT, the material behavior was rate-independent and cyclically stable, which occurred by plasticity. The material exhibited significant cyclic hardening at intermediate temperatures, 400 degrees C to 600 degrees C, with negative strain rate sensitivity. In this temperature range, dynamic strain aging (DSA) presumably occurred due to slip dragging solute atoms. At high temperatures, 800 degrees C and 900 degrees C, the material exhibited positive rate-dependence in the hysteresis behavior, and the cyclic stress response tended to stabilize with increasing cycles. The high-temperature behavior was presumably controlled by a combination of plasticity and dislocation-glide creep. The integrated creep fatigue theory (ICFT) was used to describe the deformation and life behaviors based on the identified mechanisms, which were corroborated by fractographic observations.