The study of crack-propagation behaviors and dislocation structures in cyclically deformed polycrystalline IF steel

Strain controlled fatigue experiments were employed to evaluate automotive-grade interstitial-free ferrite steels (IF steels). This study demonstrates that the loop-patch structure, dislocation walls and dislocation cells larger than 2 μm have no significant effect on fatigue failure. The cracks prefer to grow near grain boundaries while dislocation cells smaller than 2 μm tend to develop along the grain boundaries and triple junction of the grains. Once the dislocation cells smaller than 2 μm develop from grain boundaries to grain interior, the cracks will propagate near the grain boundaries and through the grain interior simultaneously.

► We established the failure mechanisms in IF steels.
► Fatigue failure only affected by the dislocation cells smaller than 2 μm.
► Crack propagation was accompanied by the formation of dislocation cells smaller than 2 μm.