What is "grain flow"?
Forgings are produced using the open die forging process through the controlled application of compressive stresses while the metal is heated in the plastic regime. The metal, once subjected to the compressive stress, will flow in any unconstrained direction. The expanding metal will stretch the existing grains and, if the temperature is within the forging temperature region, will recrystallize and form new strain-free grains. This results in even better resistance to fatigue and stress corrosion than a forging that does not contour the component. Other contributors to grain flow are the expansion of microsegregated regions and/or inclusions in the direction of the metal flow. The effect of the elongated microsegregated regions and/or inclusions can be controlled through the use of high-quality material and due attention to the forging technique.

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