Study on dislocation cell structure, dislocation density-fatigue property relationship of a structural steel

In this study, the evolution of the dislocation cell structure and variation of mechanical properties of structural steel under low-cycle fatigue were studied using the indentation experiment, optical microscope, and transmission electron microscope examinations. The results indicated that the dislocation cell structure was well-formed under cyclic loading. When the strain amplitude increased, the original grains were broken more, leading to the dislocation cell size tended to decrease, while dislocation density showed an increase with the further increase of strain amplitude from 0.4% to 1.0%, respectively. Both indentation hardness and yield stress tend to increase when the cyclic loading increases. The change in the dislocation structure was responsible for the strengthening of fatigue mechanical properties, meaning that the dislocation density tended to increase, while the dislocation cell size showed a decrease with the further increase of fatigue condition, leading to the increase of both hardness and yield strength since mechanical properties were inversely proportional to the mean cell size. The results of this study can be used for the practical designs as well as to understand the microstructure changes in structural steel subjected to cyclic loading.