Failure mode analysis of a damaged shackle part used for container transportation

Failure analysis on a shackle part broken during service of container transportation was carried out. Fractured surface around crack initiation site was a little oxidized and there were dendritic structure and intergranularly fractured surface around crack initiation site. Mixture of pearlite and bainite in dendritic region was observed and martensitic structure was observed in adjacent area. On the other hand, microstructure of core region was mixture of pearlite and ferrite. It was considered that the dendritic structure was generated due to repair-welding process and catastrophic failure occurred due to the lack of ductility caused by improper post-heat treatment after repair welding.