Steve Coryell, 3rd Place - Optical and Scanning Electron Microscopy

This image shows a mounted fracture surface (bottom edge) cross-section of a ductile iron (SAE J434) axle tube. This axle tube was made using an experimental lost foam process to manufacture a one-piece axle tube assembly. This particular axle tube fractured under beaming fatigue. The section was removed and prepared for metallographic evaluation in accordance with ASTM E3. A light 2% nital etch was applied. The image shows a transition (left-to-right) from a pearlitic core nodular structure, to a martensitic region with no nodularity, returning to a nodular structure with a pearlitic core, finally transitioning to a nodular structure with a primarily ferritic core. The region with no nodularity was determined to be the primary cause for fracture. This atypical microstructure was determined to be the ground location during the welding process, which overheated and caused a microstructural change, therefore leading to premature failure.
Steve Coryell, 3rd Place - Optical and Scanning Electron Microscopy
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