From atmospheric corrosive attack to crack propagation for A1N railway axles steel under fatigue: Damage process and detection

Abstract

In this paper a detailed investigation about the evolution of the corrosion fatigue process of this material is presented. The corrosion pits appear 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, the formation, due to electrochemical action, of a secondary pit that triggers for the pit-to-crack transition has been observed. The growth of micro-cracks has also been analyzed and it is characterized by the development of a surface pattern of coalescing cracks.An original optical detection method has been proposed to inspect the exposed surfaces of the corroded railway axles and to detect the in situ crack pattern associated to the corrosion–fatigue damage. It is shown that the optical detection method is able to identify the damage observed and it has been successfully applied in field observations.