Substructural development during strain cycling of alpha-iron

Abstract

Substructural developments during reversed axial strain cycling of alpha-iron have been studied at room temperature. The nature of the structure varied considerably at different stages of fatigue life. A distinct cell structure developed gradually during cycling, and the average cell size decreased with an increase in applied strain range. A large number of dislocation loops was observed near the regions of the cell walls, and their density was higher in specimens cycled at a small strain range. Two-step tests in which the specimens were cycled at an initial high strain range for a specified number of cycles, followed by cycles of a lower strain range, showed that although the flow stress decreased rapidly, the modification in the substructure was very slow.

It is shown that the dependence of cell size on flow stress is not always unique.