Hydrogen induced premature failure of massive cast medium carbon steel anchor fluke

摘要

A 17 tons cast medium carbon steel anchor fluke of an ocean going container ship suffered catastrophic premature failure during demooring from anchorage made after maiden voyage of one month duration. It was evident upon recovery that the fluke simply fractured into halves. Microstructural analysis showed ferritic-pearlitic microstructure and decarburized ferritic surface with massive twinning around the crack initiation zone. Fractography showed brittle (intergranular mode dominating at the crack initiation zone at surface followed by cleavage mode towards the core) crack propagation suggesting embrittle-ment plausibly induced by hydrogen and grain boundary impurities. Casting process apparently incorporated the hydrogen and could not eliminate completely during the post-casting annealing considering the massive size. Embrittlement of decarburized surface was caused by trapping of diffusing out hydrogen in annealing process.