The relationship between cyclic stress-strain curve and dislocation structures in cyclically deformed IF steel

The cyclic stress-strain curve (CSSC) of cyclically deformed polycrystalline interstitial-free steels (IF steel), divided into regions A, B and C, have been correlated with the fatigue test conditions. No dislocation arrangement can be found when plastic strain amplitude is controlled in region A. For region B as revealed as a plateau, the plastic strain amplitude is located in the range between ɛpl = 7.5 × 10−5 (Δɛ/2 = 0.05%) and ɛpl = 5 × 10−4 (Δɛ/2 = 0.1%). Loop patches prevail in region B. If the strain amplitude is close to the upper limit of the region B, the loop-patch structure is also predominant in the dislocation structures despite the existence of dislocation walls and a few dislocation cells larger than 2 μm. However, these structures have no significant effect on fatigue failure. The dislocation cells rapidly developed once the plastic strain amplitude is elevated into region C.