I'm not saying grain flow doesn't exist. My claim is that I can't find any support for the idea that grain flow results in superior strength characteristics in the grain direction.
Ahh, I see! This is a common problem with things that are "known" to be true -- often people don't rigourously test them.
This paper [1] has some good data in it:
"The experiments in this study were developed to verify the influence of the grain-flow
orientation on fatigue life and its impact on the anisotropic properties of a mechanical
component. To this end, steel specimens were made, and their fiber was oriented by
machining and hot forging. Subsequently, they were subjected to flexo-rotational fatigue
tests in a piece of specific equipment to determine their fatigue life."
(...)
They then describe three parts: A, properly forged, B, improperly forged, and C, machined.
(...)
"The results showed that specimens of configuration A achieved a much longer fatigue life than configurations B and C, actually doubling it. The results indicated a similar fatigue life behavior between configurations B and C. It is important to emphasize that this similar behavior between these two configurations is valid for this case analyzed (...)"
