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

The Relationship between Cyclic Stress–Strain Curve and Dislocation Structures in Cyclically Deformed IF Steel. C.C.Shih, N.J.Ho, H.L.Huang: Materials Science and Engineering A, 2009, 517[1-2], 235-8