New insight into the fatigue-atmospheric corrosion process of A1N steel for railway axles

In this paper a detailed investigation about the early phases of the corrosion fatigue process of this material is presented. The corrosion pits appears in the early stage of the corrosion fatigue life and a preferential site of pit nucleation has been observed at the ferrite-ferrite grain boundary. At the bottom of these primary pits has been observed the formation, due to electrochemical action of a secondary pit that works as a trigger for the pit-to-crack transition. The growth of micro-cracks has, also, been analyzed and results dependent on the stress level and strongly affect by the coalescence phenomena with other growing cracks. Key points for the development of a new model for the corrosion-fatigue life prediction of railway axles are defined.