Abstract
Eutectoid steel is one of the most important industrial materials. In addition, these materials are usually pre-strained before use during production or machining process. In this study, fatigue test has been performed to research the effect of pre-strain on fatigue properties of eutectoid steel with different plastic pre-strain ratio at εp=0, 2%, 4% and 6%, respectively. At the same time, microscopic behavior of the crack initiation and propagation are also investigated by the successively taken replica method during the pre-strain and fatigue test. The results of the research indicate pre-strain directly affect the fatigue strength and crack initiation and propagation behavior. All fatigue limits of specimens with different pre-strain ratio are lower than that of specimens without pre-strain (εp=0) and the fatigue limits of pre-strained specimens have no obvious change from εp=2% to 6%. Fatigue cracks initiate from slip lines or micro-cracks that are generated in the process of plastic pre-strain. However, for non-pre-strained one, fatigue cracks initiate from boundary or inter-lamellar of the pearlite. The mechanism for this difference is discussed in this paper.
