strongly impeded dislocation multiplication below Aept -5 × 10 -4, appreciable secondary slip at higher Aepl leading to a cell structure (persistent slip bands do not form), shape changes due to asymmetric slip of screw dislocations and a relatively high effective stress level.The reduction of ~p~ and the presence of solute carbon atoms modify this behaviour significantly, making it more similar to that of f.c.c, metals. In all cases it was found that only the athermal component of the peak (saturation) stress but not the latter itself represents a suitable measure of the properties of the dislocation substructure.On the basis of the cyclic deformation behaviour and of observations of trans-and intergranular fatigue crack initiation it was concluded that the fatigue limit of a-iron is an intrinsic property of the b.c.c. structure whose characteristics, however, are affected sensitively by interstitial impurity content and by the strain rate of the fatigue test.

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