Cyclic Plastic Behaviour of a Pure Iron, Fe-Ni Alloys and an Fe-Ni-Cu Alloy

Abstract

The relationships between microstructures and fatigue properties in a pure iron, Fe-Ni alloys and an Fe-Ni-Cu alloy have been investigated by mechanical testing and optical or electron microscopy. Results obtained are as follows:
(1) The degree of fatigue damage is affected by the existent states of interstitial elements and ferrite grain size in a pure iron.
(2) Solid solution hardening by Ni or Cu restricts the softening during cycling and increases the fatigue life. The aged structures in an Fe-Ni-Cu alloy harden the alloy during cycling, which is thought to be due to the interaction between dislocations and precipitates.
(3) Fatigue crack propagation property reflects the fatigue damage process in low ΔK level, and is affected by the grain size in a pure iron. In an Fe-Ni-Cu alloy it is improved by precipitation hardening of the Cu-rich zone.