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

• This paper reports results about corrosion–fatigue of railway axles (www.wolaxim.eu).
• We have investigated the corrosion–fatigue process for A1N steel under rainwater environment.
• Pit-to-crack is controlled by formation of a secondary pit when the primary has a size of 30 microns.
• Subsequent damage is characterized by a diffuse cracking and coalescence of microcracks.
• An optical method has been proposed to detect in-situ the corrosion–fatigue damage pattern.

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.

Atmospheric corrosion has a significant influence on the A1N fatigue life. The morphology and the time-evolution of the damage has been deeply investigated and are shown in the following table.Figure optionsDownload as PowerPoint slide