Cyclic plasticity mechanism of the M330-35A steel

The low cycle fatigue behaviour of a 3%Si polycrystalline ferritic steel has been investigated at room temperature. Measurements of internal and effective stresses with the Handfield and Dickson's method pointed out two regimes of cyclic plasticity accommodation. The transition between these two regimes has been confirmed from SEM, cECCI and TEM analysis. Low strain cycling resulted in high effective stresses, planar slip and transgranular crack initiation. At high strain, internal stresses predominated and channels, veins and walls were observed but walls were located near grain boundaries while veins appeared in grain interiors. Crack initiation was intergranular. It is suspected that a modification by cyclic plasticity of an expected initial short range order between Fe and Si atoms in the as received material occurred and is at the origin of the two observed regimes.