Grain Flow
The direction the worked metal fibre runs in a finished part, and the main reason to forge rather than machine from bar.
Rolling and forging stretch inclusions and segregation into a directional fibre. A part machined from bar cuts that fibre wherever the profile changes, leaving end grain exposed at the fillet or thread root, which is where fatigue cracks start. A forged part has the fibre bent to follow the shape, so the strongest direction lines up with the load. Macro-etching a sectioned first article is the standard way to prove it.
Related terms
Where this applies
open-die-forgings, closed-die-forgings
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