Dislocation evolution in interstitial-free steel during fatigue near the endurance limit

Abstract

In order to clear the relationship between dislocation development and endurance limit in fatigued body-centered cubic (BCC) metals, the automotive grade interstitial-free steel (IF steel) was fatigued near the endurance limit in this study. When cycling just below the endurance limit, the dislocation structures are mainly composed of loop patches, moreover, a few large dislocation cells and dislocation walls can also be found, and thus these structures have no significant effect on fatigue failure. However, once cyclic strain slightly exceeds the endurance limit, the small dislocation cells tend to develop near grain boundaries and triple junction of the grains, and which provide a more appropriate structure for crack growth than do large dislocation cells.