Cyclic fatigue loading and characterization of dislocation evolution in the ferritic steel X22CrMoV121

Isothermal cyclic deformation tests have been performed with the steel X22CrMoV121 in the temperature range 20 degrees C less than or equal to T less than or equal to 600 degrees C. The fatigue behaviour was related to microstructural changes in the bulk material. The dislocation density was determined for selected fatigue states by means of transmission electron microscopy. The material is characterized by cyclic softening in the investigated temperature range. Increasing temperatures and increasing stress amplitudes lead to an increase of the plastic strain amplitudes and a corresponding reduction of the number of cycles to failure. In the temperature range 250 degrees C less than or equal to T less than or equal to 350 degrees C dynamic strain ageing processes occur and maximum dislocation densities are observed. Generally the dislocation density decreases with increasing number of cycles and temperatures. (C) 1998 Elsevier Science Ltd.