The development of fatigue cracks in armco iron at low temperatures

1. At 77°K the fatigue crack develops along shear planes in individual parts of the propagated crack front. 2. The more developed substructure of iron specimens previously fatigue-tested at 293°K promotes the formation of a more ductile fatigue fracture. 3. In both the testing regimes investigated, the propagation of the fatigue crack in the stable growth stage takes up only an insignificant part (0.25%) of the total life of iron specimens at 77°K.