The stability of microstructure in the iron-carbon system during cyclic deformation

The response of various carbide dispersions to cyclic deformation has been examined for quench aged low carbon iron using fatigue tests at constant strain amplitude. In addition, the response of quenched, deformed and aged specimens has been investigated to determine the role of carbides in stabilising the dislocation microstructure against fatigue softening. The differences in dislocation arrangement after cyclic deformation and unidirectional deformation are rationalised in terms of the dissipation of localised strain gradients on reversed deformation. The rates of fatigue softening are considered to reflect the magnitude of the retaining forces exerted on the dislocation substructure by the dispersion of the second phase particles.