Investigation of fretting fatigue behavior and micro-structure evolution in LZ50 steel subjected to torsional load

Abstract

In this paper, torsional fretting fatigue in LZ50 steel was investigated experimentally using a multiaxial fatigue testing machine. After subjecting the samples to fatigue, they were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The details of the fretting damage and the evolution of the samples’ microstructures in the contact zone were studied under different torsional loads. The results showed how the combined action of fretting and fatigue led to the failure of the specimen. Fretting wear in the contact zone produced a fretting scar and cracks in the specimens initiated in the fretting contact zone. These were caused by the local stress concentrations, and the cracks then propagated due to cyclical torsional fatigue stresses. The modes of microstructural evolution occurring during torsional fretting fatigue were dislocation angling and climbing, and these formed dislocation cells in the structure of the material. Within the LZ50 steel, this pattern of behavior began in the ferrite areas of the structure. For the harder phases, the evolution started later, and in the pearlite structures. The microstructural evolution in the pearlite was accompanied by bending, torsion, and even cracking of the cementite lamellae. The evolution of the microstructures showed that the micro-cracking nucleation mechanism was the deformation of dislocation cells.