Low cycle fatigue behaviour of low carbon microalloyed steel: microstructural evolution and life assessment

Abstract

In this paper the cyclic stress-strain response, low cycle fatigue (LCF) behaviour, and evolution of dislocation structures under LCF loading in the case of a low carbon microalloyed steel are discussed. The cyclic stress response revealed cyclic softening resulting from the propagation of Luders bands. The experimental LCF life was compared with the life predicted using Tomkins' model and the modified universal slopes (MUS) equation. While the life predicted by Tomkins' model showed good correlation with the experimental results, the life predicted using the MUS equation grossly overestimated the life. Inclusion induced delaminations under cyclic loading were thought to be responsible for the overestimation by the MUS equation. Low energy dislocation structures, i.e. cells, were observed near the fracture surfaces. Interrupted tests revealed cell formation after 10 cycles at a total strain amplitude of 0·3%.